Remeber, they are talking race cars, what sort of spring rates do they run? How much rear travel do they have etc. The reverse watts link, works FINE, if you have limited suspension travel. The problems Dean is describing, are a function of when you get larger ammounts of travel (relative). For example. some open wheel cars run a SINGLE shock setup on their front suspension, you can get away with it, if you have very very little suspension movement, it doesn't work at all, if you need several inches of supsension travel like we do on street cars.

A lot of race cars can get away and take advantage of things in the suspension that most other cars can't, because they need a greater range of movement.

 

A mouthfull here.
1) This

 

A mouthfull here.
I don't really have an answer, but I have approached close to the same problem with tie down shocks. That is split valved shocks, with extra rebound. This slows the transition, and the yaw. You must reflect the the change, by some compensation on the opposite corner. If you do not the shocks will just make you go slower.
This is in a small oval track racer- double wish bones in front, 3 link in the rear. How this would translate to your car... ???? I do think this could be a good place for a Watts (witness the Ausssie cars).
Good luck.

 

Wow, you're awesome. Seems like you are getting a little upset, all I did was point out that I will be happy to take the word of the guy who builds these since he seems to know his stuff, and since this is a proven design. You are the one being personal and trying to impress with your job etc. Whatever, if you don't think it will work, don't buy one.

 

Dewey (John) I all due respect, the revese watts in not fine.

The watts should never be used in this form and was not intended to. WHY?
The link arms attach to the axle= BAD. When the one side comes up and th eother side stays level, the only point that can give is the pivot point, it migrates.
So when the pivot point migrates what happens? the chassis is attached to the pivot point= the chassis moves laterally. You people need to get this, I do not know how many times I need to say it. It is the same situation I spoke of above about me using different spring rates on the rear and the only given point that will move is the roll center. It too will move laterally (in this case towards the heavier rate spring)

Watts link= good
this so called reverse engineered watts link= bad

The body of the car rolls equally around the pivot point on the watts. The body does not lift more on one side like when the axle would articulate over road imperfections. It does not work the same, the reverse ddesign leverages differently from the axle and applies forces that the standard way can not.
Why can't anyone see this visually? I know Chris (Madmax does)

Do a popcicle stick model (heck, use cardboard strips and upside down thumbtacks...something- just try it) I wish I could do one of those movement models Strano linked to of the watts link system in motion. I would prove in a heartbeat the revese will not work.

 

..I still have not forgotten about YAW.

Basically, what I mean with that term is the amount of chassis movement off center when the body rolls. This can and generally does very front front to rear roll centers, thus kicking the chassis of the car left of right of the wheels.

This happens with the greater the leverage arm between the RC (roll center) and the CG (center of gravity).this will vary also based on migration points of RC (statically and or dynamically- in other words, whether the car is stagnant, or is under dymanic motion transfer of weight entering or exiting a corner, etc)

ex- track width of the car is lets say 70", so center line is half that of 35" both front and rear. The car rolls right (Left hand circle track car). The front roll center is lets say fixed 10" right of center on front- OR- 45" from left and 25" from right. This fixed point is where the chassis rolls on (statically for now) so when the body roll right, the left has to lift greater than the right squats=.......

(This is where though need to come into play)NOW, jump to the centerline of the body, not the centerline of the track width. The body starts at centerline 35"/35", BUT the leverage arm of the roll laterally moves the centerline IN ROLL towards the outside maybe 1/2" at 3* roll. You are now at 36/34" on front end of chassis in relation to tire track width. The front YAWED 1" to the right.

OK- take the same senerio and just reverse the RC lateral pivot point to the left 10". We are at 25"/45" as the body rolls. This will render the right to drop at a quicker leveraged rate and the geometry of that drop on the right side shortens the lateral roll measurement to the right. The car in the same 3* roll now only yeilds a 1/2" yaw rate. So the body now sits at only 35.5/34.5" YAW off centerline. Its overall polar movement on the front is less by 1/2"

Now comvine this with both front and back RC's and you have overall chassis yaw. This can and does affect driver stability as a tool just like you would use with Roll oversteer and roll understeer. Yaw is a minor tool, but a tool none the less.
The leverage gains also on RC static migration as well as overall dynamic migration will counter act body roll and maximise yaw at that particular end of the vehicle.

I yaw my *** end

All this is of course controlled by shock valving- shock valving is everything when it comes to the drivers control yaw rate in a corner (A completely different "yaw" ya'll - oh gawd, I just sounded like a NASCAR ******* redheaded stepchild from the west)

 

vertruck here are some assumptions for you;

first, yaw is the amount of movement from center (body center/track center) due to body roll? the lower the RC the more yaw you will have? a RC that is equal to or above the axle centerline will be realized less if only checking tire clearances?

heres what ive figured out using models. whether you think of the axle pivoting and the body staying flat, or the body pivoting and the axle staying flat both are exactally the same. the axle rolls on the RC (actually the roll axis, but close since the RC is determined from the RA) and the body rolls on the RC.

so heres what im getting at. BOTH watts will have migration due to yaw. if an axle mounted watts has a 15" RC with a 30" tire this wont really be noticed. But, the same is true for a chassis mounted watts. if it is mounted at a RC of 15", our street cars dont have enough travel to really matter. it would seem that the worst case scenario would be the body under full roll with one side on the bump stop and the other with the shock fully extended. but, this would require the axle to pivot on the 15" RC, since each is at the full but opposite end of its travel (assuming set up for 50/50 rebound compression travel). so, what is the worst case scenario?

its hard to type whats in my head, but here are some numbers.....

44" wide shock width (shocks have 6" of travel set up for 50/50 bump/rebound)

so at full tilt, there is a 6" difference in sides assuming one is fully compressed and one fully extended. this leaves a maximum axle angle of 7.83* with the center of the axle staying at ride height. if compressed 1", the max angle is 5.21* and 2.6* at 2" compressed.

assuming we start with a 15" roll center for both the axle mounted and chassis mounted watts, here are the numbers.

degrees / axle mounted migration / chassis mounted migration

7.81* / .0" / .0"
5.21* / .0" / .0911"
2.60* / .0" / .0908

so the most migration your going to see on a chassis mounted watts using my same setup is .090. the more you drop the RC the more you will get, but that does not differ for the axle mounted watts!!!!

Vertruck i am just learning, so correct me where needed. again i do agree that you will get migration, but only under compression or rebound coupled with axle roll. plus, once you drop the RC of the axle mounted below the axle centerline, it wont make a difference other than that it will be constant and wont change with travel. now this still differs from those that i have spoken with that design suspensions for a living. im still being told by the experts that there is NO!!!! migration whatsoever with a chassis mounted watts.

 

btw... i think we're on the same page, but rereading what you wrote

that is impossible. there is no way one link can raise in relation to the axle and have the other stay level

 

Widowmaker Big smiles with you, not at you (Just wanted to lead with this so you know I do respect your debate)

I am sorry tht you ran the "yaw" numbers on the watts, My response on Yaw was not pertaining to the watts link in general, I was responding to Cash's (SDIF) question pertaining to my panhard setup on the rear of the circletrack car. It is alot more exagerated when the migration pointis offset. This car not be done with a street or roadrace car nor should it be attempted in any way to produce such results to turn only one way. Sorry about that- too many topics in one post. Cash even suggested I start a new post on that and I should have taken his advice.

As for the watts link part of your posting in both first and second posts just above, I will address rebuttles to those.
1st, the assumptions you have for me. Answer is NO on the yaw being the amount of movement over the RC. Well half yes, half no but with explination. Yes the movement IS greater with the lower RC (or longer lever arm from cg)... BUT...what I call yaw is a combined result of the both front and rear RC's or better known as "roll axis" angle front to rear. Now with that said, both front and rear can have the same chassis movement off center in roll but yeild absolutely no yaw at all becasue the both migrate the RA sideways in a still parallel line to the track widths. (Hope you are following my typing clearly, this crap is so hard to put visuals into words, if not, then my appologises).
2nd assumption- No I do not believe so without ever documenting things myself but, I do believe even tire measurements would still easily yeild noticible results even if the RC is above the axle line. WHY? Because the higher the RC, the more one side of the body lifts and the other side drops. The lower the RC the more side movement where they both drop (the outer one drops faster in distance) If I were sttanding in front of you I could oh so quickly just show you rather than trying to explain. So here goes.

Stand up straight with feet apart at shoulders width. We will be leaning to the right (left hand turn)

1st one- just bend the right knee. Low roll center slightly left of center.
2nd one- lean right with both legs rigid lifting left off the ground. neutral height RC center -to- right of center

The first is good for roadrace style cars, the 2nd is good for circle track cars. Why? Because the first leverages and weights the outside tire (Just like you would weight the outside footpeg on a motocycle on snow ski to turn each way. You use both turns left and right so you only need conering force of outside tire grip for the most part. The 2nd you need to have the leverage of weight on the inside tire to try and get use out of it even when it is only inside and not being weighted. (note to all- in circle track, the guy that can get "proper" heat onto the LF tire is the guy that will win [note I say proper])

I disagree with you still stating both the 'standard' and 'reverse watts' act the same. I mentioned the leverage problem of the link arms being attached to the axleand you state it being impossible, it is not, It IS in fact what the problem is and I will ty and help you get a better visual as to why. I see that in your second post you write an incorrect statement where I can clearly see you have accidently misinterpeted me. that quote is," there is no way one link can raise in relation to the axle and have the other stay level". I never said that "one link can raise in relation to the axle". What I said is one link raises, and the other one stay put. In opther words one side of the axle raises and the other side stays put in relation to the body. When this happens, the pivot point laterally migrates.

Lets explain this further (a solid works model would be so nice right about now)

With the reverse link watts (pivot on the chassis, not the center axle housing) the axle can not articulate without ill affects on the chassis like it does with the pivot on the center of the axle housing. The standard watts allows for RC adjustment via the chassis brackets WHILE the axle centerline hight and width REMAINS constant. The axle articulates in any way, up down, left up right down, right up left down, right up left neutral......at ANY angle to follow road inperfection, the pivot will always remain constant on the center of the axle and not affect the movement travel up and down of the watts link and eliminating lateral movement within the acceptable perameters of travel.

this revese mount watts can not boast the same results. The axle can not articulate with the links arms atached to the outer edges of the axle AWAY from the axle centerpoint. RC adjustments are made for the pivot point on this design, not the link arm hieghts mounting to the chassis. It would be like always moving just one side of both sides of the fixed mount points of the standard watts, it would trow a curve ball to things and off canter its movement= thus causing the lateral movement I speak of.

...I am going to print this so I do not loose this novel already, more to come...

 

Here, I did a little one of my famous cheap sketches I was known for years ago around here.
Top is watts link. Bottom is reverse engineered watts link with also a migration if the axle articulated up on the left and stayed about the same on the right. note the axle moves laterally to the right.

This should be end of discussion on the reverse watts design being bad. But please respond with questions or debates, I am open minded and love to chat and debate.

 

Regardless of whether you want to call me stupid or the statement I made is stupid (one in the same if you ask me), you still dont get it. So a bunch of guys build a car with cubic dollars and multiple letters after their name and you call whatever is there gospel. That's your mistake. Someone always has a better mousetrap. I'll take the guy who built the part in question in this thread, a couple years ago he made the statement that driving without a front sway bar is stupid and would put my car in a ditch. He's an expert with a lot of backup, right? So its been a couple years and my car hasnt even gotten out of shape and I dont baby the car. So AGAIN, just because someone does something, does not make that the right or best way. Did you get that? Do I need to repeat that yet a fourth time? I feel like I'm in a reading comprehension class. Hell even those oh so special V8 supercar guys might change their own design, making the previous one what? Not as good?

I'd tend to side with Dean anyway, but I drew this up and he's right. If one tire moves (I used 1.5") with a 'normal' watts linkage with the pivot mounted to the axle, look at it this way... the horizontal length of the axle is less, because its forced to travel in an arc itself. With a 'normal' watts, the locating portion of the link is the center of the axle, and it is forced to move a fixed distance up (or down) some amount less (like half since it's centered) than the movement of the tire that moved. With the 'reverse' watts, the movement of the two links is different because their distance from the tire that is moving is different. Those two points will travel in two separate arcs of non equal radius, forcing the fixed chassis side pivot to migrate. It has no other choice. In drawing this up, its easy to see that with a 'normal' watts the angle of the two links to the center bell crank is almost identical, while in a 'reverse' watts the angles are completely different. Thats why it forces migration. How much? I guess that all depends on the actual dimensions, but at the scale I drew it up to its a whole 1/64". Its not much.... but its there. So in practice its likely not going to be noticed, but a factory panhard doesnt allow all that much movement with limited suspension travel either.

 

how do you calculate roll center with a axle mounted watts? is it no longer the bell crank pivot? why do the some axle mounted kits have bell crank height adjustments?

Tim

 

Interesting debate going on.. try to keep it civil folks, I like coming here since most of the time this site doesn't become a crap-slinging contest.. big egos cause big crashes.

 

Dean, I get this, it does the same with a chassis mounted mumford, or anything else mounted that way.

BUT, even a diff mounted watts, you **can** get later movement. if you make the two arms effective length different, no matter where the pivot is, you are going to have this happen. In real world driving scenerio's you will get latteral movement of some sort, in all of them. There is no "perfect" answer. The chassis mounted watts, does have what I would consider...a more ideal roll center migration though. The roll center migration is consistant with chassis movement. the diff mounted watts, the roll center stays a fixed height from the ground, no matter what the chassis does, so your arm leght changes as the chassis moves.

In my mention of it being acceptable in AV8S cars, is that my guess is, being a pure track car, the wheel rates they run are probably very high, and they have very little roll. With little roll, and little suspension movement, you have very little RC migration, and very very little lateral axle movement, because stuff just doesn't move. This is why that can "get away" with running setups like this. It always them have an easily adjustable RC, and that outweights the trade-offs for them.

The other plus, that I can see to the chassis mounted watts, is that you get less unspung weight than with a diff mounted watts. The whole package is sitll going to weight more than a PHB though.

IMHO, the PHB is still the way to go in our cars, considering all the options. I also very much see your point about axle movement. But, you can get the similar movement with a diff mounted bell-crank, and IMHO, a less ideal RC migration. So, even the diff mount, is not the end-all solution.

 

Dewey (John), the chassis mount pivot migrates to the left in the picture I drew. It goes left with articulation of axle and chassis compression travel. It will go right with axle articulation and travel extension. {see attached pic}

The RC of the watts stays contant. So as the body drops, the RC stays the same height off the ground and the leverage arm shortens. The panhard is 1/2 constant. Body drops 1" the PH RC drops 1/2" so the levrage arm shortens by half to the cg.

The RC of the reverse watts is a 1:1 drop. If the body drops 1", the RC drops 1" also to the ground. the leverage arm stays constant- kindof- the roll center migrtes to the left on compression yeilding different lateral leveraging and yaw from left corners in comparison to right corners.

 

If you draw out the two different styles, you'll find that as the center pivot attempts to migrate on the 'normal' watts, it tries to center the chassis side links. It stays relatively centered, that is chassis to axle. The 'reverse' can migrate, probably because the horizontal distance of each arm is not equal, because their angles relative to horizontal are not the same when only one side of the axle moves. It falls back to the premise that in order for a watts to work properly, the bars are parallel to each other and the ground as well... this keeps their horizontal lengths equal. Somewhere here is posted a gif image of a moving watts linkage, you'll note that in order for the center pivot to draw a straight line, the horizontal lengths of each of the links are the same. Its when they are not the same you have an issue.

Only thing I dislike about the part in question is the price. It doesnt look like $700 worth of parts, labor, and R+D to me. I like the fact it bolts in, thats a definite plus.

 

vertruck - how do you adjust the RC of an axle mounted watts? if you move the pt that the bell crank attaches to the axle any lower or higher than axle centerline, you WILL get migration. that means that unless you can some how move where the links mount to the frame in order to adjust the RC, while keeping the bell crank height constant, it really isnt any better. why would you want an unadjustable RC watts?

im still trying to understand.

Tim

 

Sorry I took so long Cash, let me finally respond to this post (It doesn't really pertain to the Watts but I think there has been a following interest in just reading this stuff in this post even though it applies to circletrack.) There is good geometry info on PH (panhard) setup angles.

Yaw- I answered above- Done- but wuld love to hear any rebuttles on this subject if any questions or debates arrise.

RR spring rate- general rule of thumb- If a car is tight on exit and loose on entrance? raise the Right Rear spring rate. It will tighten the car on entry. Most people assume the opposite here- not true. The added spring increases tire grip under slowing or braking when refenced to stagger. just like more stagger on the outside wheel will drive a car loose off the corner, it will do the opposite going in and will tighten the car. This heavier RR spring weighs that wheel more and the effect of stagger slows that rr corner quicker tightening the car bringing the left side around traveling a tad faster (hence puching more going in)

Now to the marraige of rear spring rates and PH geometry- the PH chassis mount is on the outside of the car (right side) When that mount is lower than the axle side the car will laterally want to lift as weight is pulled against the PH riod straighting it from lateral chassis weight= hence, you do not need as heavy of a RR spring to hold the RR in position with desired roll and mechanical grip.
The reverse PH angle forces body weight down on the RR when the reverse happens and the PH rod pulls the rear chassis weigh down on the RR spring- however, the stratigy is to migrate the Roll center over to the right so the left is weighted through leverage and the left side spring being softer compresses- this pushes the RC pivot point to the right (Migrates it) The pivot point is the weak link and is the only point that can give so it does. The LR tire is now weighted.

The tricky part- It is much harder to do this to the LF of the car-SO... the trick here is to simply reduce the rebound rate on the shock, run a slightly higher LF spring (generally only about 10-25lbs higher rate than the RF) and the main key is to get that LF outward as far as you can extend it within rules to gain as much leverage that way since you are more fixed with the front RC being what it is through rules, angles, and adjustment limitations again as a result of rules (ie, no extended ball joints, slotted arms, fixed length control arms, no spindle mods. Our series I can have a 70" front track and a 69" rear track. The rights NEED to stay in line for cornering track when laterally loaded, otherwise you scrb speed and have banaid fixes keeping the car balanced in the corner. So now with the LF outward as much as possible, the tire will catch and turn the car easier due to leverage on the left to right side CG of the car. If you try the same with the RR instead of the LF, it does not work the same because you offset the track and the *** end will drive you around loose ESPECIALLY coming off the corner. I do not care how much x weigh you put into it, it will be so tight a steady state going into snap oversteer after so much wheel is put into it-THEN- you go into a MAJOR loose off condition.

I got off target, sorry- back to stategy. The longer leverge on the LR helps prevent the car rolling over onto the RF. Now all this tightening of the rear tends to make you believe,well how the hell does the car rotate into the turn, it has to be tight as hell going in?" Thats where front stagge comes into play. I do not have the liberty of having a rear sway bar- rules prevent it. SO.. front stagger (even though they are not drive wheels and have no bearing on solid axle driven properties like the rear does) does come into a major tuning tool for the rear end. Chassis rake and front stagger will rotate the car on corner entrance. Front tire stagger ACTS just like a rear swaybar. I can fine tune corner entrace with front stagger, I can fine turn corner exit with front swaybar- walaa

If you have a problem coming off the corner in your car then try a slightly larger front swaybar. On a Roadrace car, I like heavy front springs and medium swaybar (RC on the higher side sp the swaybar is reduced adn the striaght line ride is not compromised by having to run such an extra heavy spring to control body roll angle on front) and I like progressive rate rear springs and a larger bar in the rear.

So in essense, big spring small bar front- small springs big bar rear.

Then we get into shock valving.

 

Everything is controlled by shcok valving. It is why I have always preached on this website to always by very good quality valved shocks. Heck, on my daily driver worktruck I run 8 shocks total. 2 on each corner.

Why 8 people ask. They are not all the same shock. I just happen to know my sh*t and know how to custom taylor shock vavling to what I need.

So what do I need? What I and most others can not afford= $2000.00 each Penske 4way adjustable racing shocks....ouch no way in hell can I afford that on a daily driver or a race car.

So what did I do? I played with fixed valves QA1 roadrace shocks- some digressive valved, some linears valved. I have one digressive, and one linear on each corner of the truck. Why? Because a digressive valve will damper at low piston speeds but not build too harsh at higher piston speeds....AND a linear vavled shock will not damper at low speeds but will at high speeds.
SO USE BOTH, they combined are cheaper than a 4way.

Trying to increase a linear valved shock in damoper rate to control low speed dampering will build waytoo much and makes the car harsh on faster piston rate dampering (faster MPH bumps), and Vica versa for the digressive shocks "kindof".

So heres what you do. Keep a mild valved linear shock as your main shock- (what most people have), and add a low valved digressive rate shock to assit the lack of low speed dampering the linear lack, yet, you do not gain tooo much as it bleeds off the high speed forces and the linear takes most of the work rather than both of them acting too harsh.

A key note- Shock angle is EVERYTHING. Where you mount them will directly affect what rebound valving and what compression valving you need- you need to know alot to tinker with multiple shocks this way.
------------------
Now to circle track and shock valving.

As mentioned before, chassis motion and laterally laoding into and out of a corner is called dynamic loading. Thus, A cars attitude can and will ALWAYS be controlled by shock valving dynamically. Those of you that understand xweighs on a circle track car will understand this more. Basically, best way I can discribe what x weigh does is it counteracts tire stagger- the two pretty much go hand in hand. People will argue other points to X weighs, but I say thats pretty much the basis of it.

If the X is up, the car goes tight. If the X is down the car goes loose.

Lets say the car is loose in, Great at steady state, and great off the corner.
What do we do? Without harming the steadystate, and off? Plain and simple shock valving. Dynamically on corner entrance we can do one of two things or even both. BUt lets break them down with pros and cons.....

What do we do? Dynamically as the car motion shifts and loads over the front wheels, the wheel with the more load will favor the weigh transfer. In a left turn, if the left wheel is loaded the car will rotate, if the right wheel is loaded the car will push. Back to the problem- Car is loose in_ dynamically in those maybe 3 seconds on dynamicweigh transfer going in UNTIL the car settles WE CAN MOMENTARIRLY INCREASE the load onto the RF tire causing the car to balance out to push more getting it to neutral. Then once dynaically set it relaxes at the full roll point and motion settles (you hope) in steady state. (this is known as Corner Yaw Ratio The amount of time it takes to enter, settle, then exit a corner. The faster the speed, the less the entry and exit ratio and the longer the steadystate- driver works too hard, suspension settlings need to be redone to correct Corner Yaw Ratio so the driver can control the car)

To increase that RF weight we can reduce the LR rebound or we can increase the RF compression. By reducing the LR rebound the car will roll over more onto the right front, the better altenative is to increase the RF compression one click.

Too much rebound on the left side of the car will soon make the car skip up the bank turn. Go as high as you can on the left side compression to reduce body roll proprtionally front to rear until you go too much and skip, then back it down.

Lots of genreal rules of thumb- if you waht toi know more anyone, this info is readily availiable all over the internet- they are no secrets.

 

hi Tim, Just as you would have adjustment points on the chassis side of the panhard rod to adjust its RC, the two chassis mounts of the watts link have adjustment increments that you can move both equally up, or down to raise and lower the rear roll center statically. [edit- I reread what I wrote and I wrote this wrong- sorry. The RC itself is fixed on the pivot point. The pivot point has to be moved and then the arms repositioned parallel for proper articulation range though travel.]

Rear RC height is a tool for corner entry balance. Raise it and the car will turn in much quicker (loose), lower it tightens entry. This is for entry to steady state balance. If the car is loose on steady state still, then the rear spring rates are generally too stiff. Lowering the PH (or roll center) would balmce the steady state (SS) of the corner but then tighten the entry. So you would then lessen the rear spring rate and raise the rear RC to see it it works better. It all has an effect on the "roll couple" (The front has direct impact on the back. So what you do up front, will also affect what you do out back)

Ps, call me Dean if you would like

 

dean - thanks for all the info. im not looking for a way to lower, but rather the way to calculate RRCH for the axle watts. my thought would be that it was the center of the bellcrank, but is there another way? does it have to do with the angles of the links?

a phb should be level to start, and therefore at ride height, the phb height is your RRCH. with a reverse watts its the pivot for the bell crank, but im not sure what it is for an axle mounted watts.....

thanks, Tim

 

Tim, The bell crank (pivot) center bolt is the RRCH on the watts is the RC height as to which the rear of the car rotates around. If the pivot is fixed and non adjustable, then the RRCH is non adjustable even if the arm brackets to the chassis are. The arm links merely need to articulate in a range parallel to the ground (mid point of travel is parallel for best range of motoion without breaching the boundaries of 0 lateral movement.)

It is not critical to have the center of the bell crank centered verticaly on the axle, just as long as it is within about 2" up or down of the actual horizonal centerline of the axle. Slight variations of height (ex 2" higher may yeild a very small amount of lateral movement- aprox 1/16")

Dean

 

dean - thats what i thought. it seems to me that it would be VERY important to be able to dial in your RRCH, and the axle mounted allows you to do it, but if you do you get a lot of migration.

ran some simple numbers based on my examples above. the RRCH can either be 2" above or below for these numbers on an AXLE mounted watts.

7.81* .271"
5.21* .181"
2.60* .090"

sin of the angle using (2") as the hypotenuse and solving for (x) which is our migration. worst case scenario (which might only be seen turning into tight driveways with some angle involved) would give me a whopping .271"!!!! and that doesnt get divided by two since the bell crank pivot never leaves center.

am i missing something?

thanks, Tim

 

Tire hieght on these cars is 25.7" (roughly 26") so the centered RRCH would be 13". Lower that 2" to 11" off the ground and get say 6" up on one side into the body with roll or a bump(doesn't matter which) and that will kilter the aprox 70" track width to about a 3* angle. So 3* on a 2 inch radius circle = .105". Shave that for radius lateral circle drop and the end result is about .095" to the right or left. A hard chicane transition would yeild about an 1/8th" mvement laterally of the rear axle.

Like I guessed, aprox 1/16th and inch of lateral movement if 2" off center.

11" roll center is low.

 

unless im missing something thats over my head, using your example i get the following;

sin^-1(6/70)=4.917* (not a 3* angle)

sin(4.917) or 6/70 =.0857

x/2=.0857

x=.0857(2)

x=.1714

so it comes to more like 3/16". still not a whole lot, and an extreme example, but thats just my point. its still more than i calculated for a reverse watts at axle height (.090), so all im saying is that i think the migration of the reverse is more than acceptable for the added benefits.

 

With all this hoorah having been said....Whats wrong with a good old wishbone locator???? Linear movement in the x axis with the ability of the rearend to pivot around the slip yoke and NO lateral movement???? Or am I just stuck at the dragstrip?????

 

its a good device, but your roll center is really high. straight line is ok, but corner carving is not so good.

 

I have seen them used from the bottom of the rear.......but I dont think that would work for us. Then again I have not gotten under the car to see either.

 

Sorry Tim, I saw this the day you posted it but have been very busy (day job work load, personal issues, and a race weekend coming up I am prepping for and getting the car ready). Anyways, I am not that proficiant in Calculus. I received a A in the class back in highschool over 20 yrs ago and have not used it much over the years. I never grasped the concept of all that sin, cosin secant.... mumbo jumbo (I have to admit I kindof cheated my way through it and never really understood it). I work things on grids and geometry measurements. Probably takes a bit longer, but works for me.

With that said, I want to really sit down and work the scale model through motion and get fairly accurate numbers. I had a scale model and a few calculations a few years back and I do not know what I did with that info.

I thought I would have time already to respond with some facts, but not yet. (ps- I happen to be going through a major divorce of 17 years- lots of BS right now, but all is good. Just takes up alot of my free time, that and dating again )

I will try and have some figures by the end of the weekend. That reverse mount has to be figured with axle articulation like I spoke of in many posts already. That is the evil.

 

dean - sorry to hear about the issues. if life could only be simple.....

the numbers im running are in a single plane. there could be other things going on that im missing.

for me, its either a phb or a reverse watts since i have a 12 bolt and the cover isnt strong enough to support the force. i had thought about making a plate that bolted to the housing btwn the housing and cover, but im still not sure its going to be strong enough. plus, id still run a crossbar to keep the frame (working on a 70 chevelle now) from sucking in on either side. either way, i end up with the same amount of weight, and maybe a little more unsprung with the axle mounted watts. my biggest issue is getting the exhaust through any of them with the lowered ride height.

Tim

 

You'd have to get them to tailormake your Watts for your axle tubes. It says on the ad that it only fits stock axle tubes, and by that, I'm assuming 10 bolts, as they're the only rear that went 82-02.

Dean, good to see you posting again. Did you get to keep the Camaro in the divorce? I know you were always saying it was your wife's DD, but I mean, you put so much into that thing....

Also, on this Watt's subject. When you hit a bump (or a pothole) with one wheel while the other stays flat, in this reverse setup, I can understand the body moving. But, given the fact we have 6" of up/down, and the dead center of the Watt's would be 13" off of the ground or about there, it looks like each straight bar on the Watt's is about 1/4 of the total track width on the car, making each of those about 17.5", assuming 70" track width. When you move something up or down 3" at the shock, it's going to get toned down to 1.8-2" of actual movement where the straight bars from the Watt's attached, am I right? What's stopping it from just moving? The Watt's has five pivot points, the center, and at each end of the bars. What's stopping the one bar from just pivoting up 2", pulling the center link a small amount, causing it to push on the other side? I think I need a flash video to understand this. >.<

 

just as you said, the watts will not be mounted to the ends of the axle, but rather somewhere btwn 12-~17". this means that if one tire stays on the ground and lets say the other lifts 4", youre going to get 3" of shock movement on the far side, 2.5" of watts movement on the far side, 1.5" of watts on the near side, and 1" of the shock on the near side. now thats all pulled out of my ****, but id only be making up numbers to calculate, so my accurate calculations wouldnt be any better.

so although you may see a big difference btwn tires, you wont see much btwn the watts. my .090 - .100 came out to be true when i mapped it out in corel draw. i couldnt put motion to it, but i did use different length links and bellcranks and only saw minor (+/- .005) fluctuations.

im assuming that the 10 bolt has 3" tubes just like most housings. ive only seen aftermarket ones with anything bigger.


Tim

 

The S60 has 3" tubes, and that thing's a pig and a half. Never knew that most axles had 3" tubes. Good information.

Well, I guess the verdict is out on this until anyone gets it and starts jumping on their decklid. It'll be interesting to see how this product does in a real-world environment.

 

Looks like there should be a good comparison at our club's (Autocrossers, Inc.) autocross this Sunday at FedEx Field. Two fairly similar fourth gen Camaros prepped for ESP with the main difference one has the new Watts Link and the other one doesn't.

Sam will be there and should be able to mount his data logger in the cars and drive both of them.

Weather looks like it will be good, around 70 degrees and partly cloudy.

Pat

 

There's some discussion on frrax.com about the autocross Sunday:

http://www.frrax.com/rrforum/index.p...c=11943&st=120

There were three ESP F-Bodies there:

- A "Watts Link" ESP LS1 car owned by John Crouse
- A standard ESP LT1 Camaro owned by Brian Burdette, finished 3rd this year in ESP at the Solo Nationals
- A standard ESP LS1 hardtop Formula owned by Karl Bender

Of the three cars, the only real difference in suspensions was the Watts Link on John's car. All were on 17X10s with 315 Hoosiers.

Sam drove the Watts Link car during competition then drove all three during fun runs. Basically turned the same times in all three cars, however, John just put the Watts Link on the car, and Sam felt there could still be some time there through tweaking. Brian's and Karl's cars are pretty "known commodities" and haven't varied the setup in awhile.

I drove the Watts Link car during competition and thought it was really predictable. It really put the power down well and other than one screwup on my last run, it never got out of shape. John's tires weren't the greatest in the world, but I don't recall getty any excessive wheelspin or one-wheel peel. The only thing I didn't like is that it was too stable and pushed big time in slower 2nd gear sections, which is one of the things Sam noted could be tweaked with adjustments. John did do an adjustment on the Watts Link during fun runs, but I didn't get a chance to drive it.

Still like to see some more guinea pigs, but I know John's pretty dedicated to making his car one of the top ESP cars in the country. It would also be interesting to see how it affects a third gen. Oh wait, I have one of those.

Pat

 

Now Pat... there you go trying to interject real world findings into a theoretical pissing match.

I'm highly entertained by all the philosophy that's been spewed in this thread with very little practical use or knowledge of watts equipped car.

FWIW, I was very interested to read that Carroll Smith, who was a very highly esteemed engineer stated in his book Tune to Win that "to be effective, the pivot must be attached to the chassis, not to the axle..." Seems to fly in the face of what some others think.

To be fair, Herb Adams states in his book:
"A Watt's Link eliminates the slight side to side variations that happen with a Panhard bar. Because a Watt's link gives a straight line control of the axle, it is a better system from a design standpoint.

However, it is a more complex system, and because the roll center height is at the main pivot point, it is more difficult to arrange the mechanism at the best height. It is also more difficult to change the rear roll center height because the whole mechanism must be moved. If the Watt's link is located behind the axle, the bracketry must be very strong and stiff to absord the loads without bending. Remember the loads on any rear axle lateral control system can be over 2000 lbs., with peak loads as high as 10,000 lbs."

Now, what you can't see is that he is talking about a differential mounted pivot. With a system like the Fays2, or the sets Steeda makes for late Mustangs the pivot is mounted to the chassis, like Smith feels is better. What's more is you don't have the arrangement issues or pain in adjusting the RC height Adams is getting at. Unlike a differential mounted Watts link this chassis mounted pivot type is more easily adjusted, and you can set the RC height easily to where you see fit.

And to add a few more opinions to the fire from those who've used both PHB's and a Watts link here are some quotes from various people who drive OE PHB equipped cars:

"I have had a regular panhard bar, and adjustable one, and the watts link I felt little diff from regular to adj
from adj to watts was day and night."

"makes the car feel firm in the rear. noticeable when shifting lanes on the highway. around turns. I wouldn't go back for sure
I had one of my friends (non-car guy) drive the car and he instantly felt the difference and knew i had installed something."

"I wanted to let you know how your watts link changed my GT 500. Prior to installation, when I put the car hard into a curve it was difficult to tell when the suspension was going to set and when it did it still wasn't very stable. Probably the worst part was that there wasn't any consistency in what the car was going to do. under steer, over steer, you just never knew what to expect. After I installed the watts link I took it hard through some sharp curves to see if any thing had changed. Wow, I was amazed, Finally the car handled the way it should. The car's suspension set and stayed set. I feel body roll was also minimal. But most importantly the car was predictable and stable. A huge difference. This is a very worth while Mod."

"The Fays2 Watts link completely changed the way the car handles. I was totally amazed. Previously, I struggled with the car in several sections of my "home track", Texas World Speedway. There is a particularly difficult section for me which features a sharp, fast left followed quickly by a right and then another quick left. At the end of the second left, you are up on the long front straight. I was never really able to take this set of corners very good, and it cost me a lot of time. With the Fays2, the car was immediately easier to handle through this transition. The car no longer felt like it was right on the edge of disaster the whole time. I was much smoother and faster through this section. Also, I found myself driving much faster throughout the track. I have to completely re-learn how to drive, as I'm now approaching ALL the turns much faster. I attribute this to exiting the previous turn smoother and faster. Some folks told me the Fays2 made their car handle like it was "on rails". I completely agree. I just didn't believe it would make that much difference. I'm not a test development engineer, so I can't quantify all that is going on. All I know for sure is the only change I made to the suspension was the addition of the Fays2. I ran the exact same tires I ran 6 weeks ago, on the same track with the same car. There has been no engine work at all. I feel much more comfortable on the track now. The car is much easier to drive everywhere. Thanks for the great product and the great after the sale support. I've told all who will listen to me how much of a difference this system made."

"The bottom line, I don't know how I ever got along without the FAYS2 Watts Link. It is well beyond any reasonable expectation of improvement and I cannot wait to install the final production version. The only downside to this experience was driving the car after removal of the pre-production prototype. Now that I know what the car is capable of with the FAYS2 Watts link, the driving experience with a pan-hard rod really bites."

"I installed the watts link on my vert about a month ago.I wanted to try it for a while before making any comments. I have put about 1000 miles on the car so far. I will say now that this setup absolutely rocks. I am on street tires with 585lbs of torque at the tire. I used to have to fight the beast all over the road when it broke loose. When I punch the car now it simply just goes straight. It seems to hook a lot better as well. These kits look bad *** and work even better. Highly recomended mod...."

Just search, find opinions that are based on real-world experience not just what some theorize is best. I've gone rounds with others (including some in this thread) about why this and that won't work. But yet it does, and I've got the real-world results to prove it. We aren't F1 teams. We can't computer simulate things to the Nth degree. Even when they can, did you notice they still actually do setup and testing work? That's because their calculations can't tell them everything, and I'm quite sure the guys @ Honda F1 are as smart as anyone else, but yet their car sucked.....

To each his own. Watts links aren't new tech. They aren't scary, and there are more and more folks with them. The differences are tangible if you are into that sort of thing. If you don't believe, that's fine, but sticking your head in the sane and claiming somehow a PHB is superior is just insane. The only way a PHB is "better" is that they are cheaper...

 

I realize that this is an incredibly old thread but I was researching general guidelines for watts links design and this was googles second result.
This forum is great because of the huge technical knowledge contained in it, but the amount of BS being passed around is astounding.

First, a simple fact:
A watts link DOES NOT PROVIDE FOR ZERO HORIZONTAL MOVEMENT
It can't!
It can be minimized by having a short turnbuckle and links that are close to perpendicular to the turnbuckle, but it MUST gave lateral movement.

Next:
Weather we are referring to a linkage where the pivot is chassis or axle mounted is basically irrelevant.
Both will have the same lateral movement. The chassis mounted pivot has the added advantage of a movable roll center.
The axle mounted pivot design will typically be somewhat more biased to move laterally because of the angles of the links, but the movement can be minimized

The advantage in both designs is that the roll center remains constant and therefore takes a variable out of the equation when trying to get the most from a setup

The main benefit is the elimination of lateral jacking and loading of the suspension in a turn

The wikipedia link posted has some good info and even shows how there will still be lateral movement.
Again, it can be minimized with some clever link placement, but cannot be eliminated

 

You are so unbelievebly wrong. You have no clue in visualizing BOTH the chassis articulation AND THE AXLE ARTICULATION. They are both doing different things.

Do the model WITH BOTH chassis and axle articulation combined in movement. Not just one or the other, THey both need to be studied together because in real wworld movement thats what they do and they DO NOT stay vertical when combined.

 

3 years later, but, let me take another stab at this to explain the trouble with the reverse watts (with the bell crank mounted to the chassis side) as opposed to a normal axle mount bell crank watts.

When the beall crank is on the axle and the chassis mvoves up and down, regardless of axle angle differing from chassis angle the link arms remain symetrical in angle at all times.

When the bell crank is on the chassis side and the chassis and axle angles do not match, the link arms do NOT remain symetrical in angle and the geometry lengths of those individual links now will vary causing lateral movement between the axle and chassis to compensate for the dual link setup.

If you can't understand that then you are over your head. THis is a very simple and easy explination I wish I wrote 3 years ago.

 

Please keep to the topic without the verbal sparring, or I'll lock the thread.

JamesC

 

this is possibly true, but doesnt have to be.
i have done several models of both systems and it is possible to get nearly linear movement with both.
if you mount the arms to the axle, and the bellcrank goes through the centerline of the mounting points of the axle mount points, you have symmetry throughout all range of movement you do end up with, however a slight angle in movement, which can be rectified by rotating the entire assembly by half a degree (or whatever angle your movement is at) and re-aligning everything.

with the axle mounted bellcrank is considered, you realize that most of the time, the other links are chassis mounted, therefore not centered vertically throughout the range of movement. again this can be alleviated by rotation of the entire link, but in this case that would make the thing very asymmetrical.

the top one has the bellcrank chassis mounted and the lower one has it axle mounted.
dont criticize the geometry, i just threw the illustration together real quick, its the concept i am after.
you will notice that in both cases, the links are perfectly symmetrical.





edit:
just re-read your post. the links will only be symmetrical at ONE POINT in travel. again, i have done numerous models of this system and can prove it if you like, but i dont think that should be necessary. simply draw two circles connected by a short line. you will see for yourself what i am talking about.


hopefully this isnt read as a personal attack. it is not meant to be one.
i have been out of the thirdgen world for a 8 mos or so since my car was rear ended and taken from me by the insurance since it was considered totalled.
i was simply researching info on long travel watts links for off road usage and this thread popped up as the second result.
some of the info passed around by many people was blatantly wrong and i was hoping that it could be cleaned up some to help others who may stumble upon this discussion.

 

Axle mount bellcrank watts= red links stay symmetrical (don't confuse symmetrical with parallel) to eachother in angle. They are mirror image of eachother. What one side does, the other side does exactly opposite- they remain symmetrical.

On the graphs A1 and A2 you can imagine the chassis rotaing or leaning around the circle. The red links always remain relative in angle to this lean. The graphs B1 and B2 do not.

 

Also, as your winipeg whatever link shows, any watts in long travel will go off center when the travel is further than the link arms. we would never travel that far and anyone using short link arms is as silly as someone using a PHrod half the length we have. The length geometry needs to be proportioned to the travel and it will remain vertical on the axle mounted watts at all times. It will NOT stay vertical on the "reverse watts" with the bell crank mounted to the chassis side.

 

either way, although the arms are not necessarily parallel, the effect is basically the same.
if the bellcrank is fixed to the chassis, then we can say that it will always roll about that point on the chassis.
if it is fixed to the axle, it will always rotate about that point on the axle.
which is better is up to the driver/chassis designer.

i cannot imagine a case where the axle of a thirdgen camaro would move by more than 2 or 3" in any degree of freedom during hard cornering, and most hard cornering will be steady state.
if the roll axis is fixed to the chassis, then i imagine that you will have a significantly different feel than an axle mounted one.

however to say that one is vastly superior and that the other one is bunk is rediculous.
clearly the aussie v8 supercar series uses this design with great success.

honestly, i am not here to debate weather one is better or worse, but to point out that each has its merits, and that both are valid methods of locating the rear axle.

you simply cannot say that it is a poor design and incorrectly implemented without testing each design on the same car with the same unbiased driver.
even that test will only be valid for that scenario.

my theory is that the chassis mounted bell crank will be superior in conditions with the possibility of lots of wheel travel.
in this scenario you can mount the bellcrank pivot wherever you want and avoid having long brackets on each side of the car and can more easily center the whole apparatus to provide for linear travel.

ymmv

 

a note on your drawing.
in the last drawing B2

look at the angles between the arms and the bellcrank.
they are the same

 

The motion isnt the same, its a physical impossibility. The reason is simple, with a typical watts in a car the bellcrank is attached to the differential and is assumed to be the moving part (one point in space), and the ends of the two links (two points in space) are "fixed" in place. When you reverse this arrangement, you have the ends of each of the two links moving (two points in space) and the bellcrank is is "fixed" in place (one point in space). So put simply, there is no way for one moving point and two fixed points to have the same motion as two moving points and one fixed point. Make sense? Dynamically, sure all kinds of things happen. If you enter that realm, you'd need some pretty intricate modeling to measure what is going where and when.

Go read about your aussie V8 supercar watts setup. You might read something along the lines of the kinematics of the arrangement being different than a watts with the bellcrank mounted to the diff. That means the motion isnt the same, and they know it. Trivial amount of difference, maybe so, but there is only one fact and that is that it IS different.

 

Looking at it, it seems possible to mount Del-Spheres in place of the rod ends for better street characteristics. Also, seems fairly simple to fab up. Sure, most of us wouldn't have that nice sweeping bend in there, but some good 4130 tubing and some gussets could fix that.

 

I think that curve is there for exhaust reasons.

I still like the fact it bolts right in, thats a major plus. Being able to adjust the roll center would probably be a good thing to have as well. Def. a nice piece.

 

I figured as much. And it being bolt on is nice as well. At least if you buy it and try it, you're not stuck with it on the car forever. Just unbolt it and put the old PHB back on.

 

whether one point or two points are moving is irrelevant.
look at it this way.
in both cases, you have exactly one degree of freedom in the vertical direction.
if the bellcrank is axle mounted the two other links move up and down.
if the links are axle mounted the bellcrank moves up and down

http://www.brockeng.com/mechanism/Watt.htm

here you can see exactly what i am talking about.
first imagine that the bellcrank is axle mounted. in this scenario the axle would be moving up and down and the car body would be stationary.

easy enough.

now picture that the bellcrank is chassis mounted and the chassis is moving around while the axle is fixed.

this should be easy to see, although i suppose its the same as the dancer gif.
http://scienceblogs.com/omnibrain/spinning%2Bdancer.gif

you see it one way and its hard to picture the other scenario
for those who have never seen it, the dancer isnt really spinning, but depending on how you look at it, either from above or below, she will appear to be spinning either to the left or the right.

to make her switch directions, first look away, picture an object spinning the way you want to see, then only look at her shadow. it will click in