So we started discussing SAI and other things in the Panhard thread, and I wanted to carry that discussion further.

hellz_wings and SlickTrackGod: You were discussing changes to adjust SAI (which I'm still used to calling Kingpin angle). I have a few questions. I'm hoping for some general answers, but I know for specifics I'd have to check *my* car.

My setup is stock strut plates, Koni Yellows, stock A-Arms with poly bushings, stock ball joints, 89 spindles modded for 1LE brakes, and stock GTA wheels- *rear wheels on front with 1/4" spacers*. The spindle-to-strut bolts are the stock non-cam bolts. Right now, I have the strut plates all the way in, and have about .8* negative on both sides in the front, with me in the car.

Questions:

Is the stock scrub radius positive or negative at typical alignment settings and stock setup wheels?

Given that my brakes should push the wheel mounting surface out 8mm, and I have 6mm spacers, and a rear wheel on the front for -16mm, I should be about 2mm in from the "stock" location. Since I have not manipulated the strut to hub angle, my scrub radius *should* be close to that stock number, correct?

By pushing the strut out at the upper bolt with a cam bolt (more positive camber via that adjustment), you would tend to go more negative on scrub radius, correct?

I assume that by seeking greater SAI, and thereby more negative scrub radius, you're looking for stability, correct?

I typically look for more caster in my race car. Obviously, I sacrifice some high-speed stability, but given that my top speeds are only about 130mph on the road courses I run, I'm not that worried about it. How much caster angle are you looking for?


Thanks in advance for any insight that anyone can provide. I look forward to our discussion.

 

Alignment has nothing to do with SAI. Steering angle inclination in a built in factory thing and is not adjustable. You have to fudge the bolt to spidle holes to alter this. Both sides need to be identical or as close to identical as possible or else the car will pull to the side with the larger scrub upon braking. SAI is an imaginary line. Alignment techs will simply check SAI to make sure nothing is bent.

You need to talk to your alignment tech and learn more about alignment adjustments long before you starrt messing with SAI changes and alter factory enginnered geometry that will mess with your steering geometry also. You stat just above that you seek high Caster settings at the sacrifice of high speed stability? Really Do you actually drive the car that fast becasue if you did you would know caster increases high speed stabilty- exactly opposite of what you just stated. You need to start out with learning fundemental alignment 101 far before you start trying to learn more complex settings.

Dean aka Vetruck

Besides, I don;t like to share info with this crappy website, I just came into here to see something being talked with my name attached which others brought to my attention

 

Here, read this- This will give you enough info to make your own decissions.

http://www.familycar.com/alignment.htm#Scrub

 

Our cars have positive scrub radius and its just gets worse with wider wheels. I don't know what the stock number is off the top of my head (I want to say 3 inches??)

The downside to fudging SAI to decrease scrub is that you reduce your negative camber adjustment range.
I'm not sure if I'm following you but to reduce positive scrub youd have to tilt the top of the strut inboard relative to the stock strut mounting angle. This is why you lose neg. camber adjustment range.

I think the real trick to reducing scrub is figuring out how to tuck your wheels as much as possible (if you have wide wheels that is).

What would be great is if someone developed a spindle that shortened the steering knuckle and placed it as close to in-line with the ball joint as possible. This would allow you to tuck your wheels decently and would also fix the anti ackermann built in. I think if we got to just parallel steering it would be a huge improvement; Something we need since we aren't rolling around on crappy 70 series tires like what was the norm in the 70s when the car was designed. Another thing that would be great is if the ctrl arm was a little longer and the spindle compensated by by moving the strut inboard relative to the ball joint - essentially keeping the same position but reducing scrub radius at the same time. Admittedly, I haven't put too much thought into everything else you'd affect with this change (Seems like you would increase caster induced camber gain or loss.. might be a very good thing.)


The more scrub radius, the more the car is going to want to pull to one side or another because of road irregularities, different amounts of braking force, etc. So it makes the car harder to drive in addition to literally scrubbing the tire surface as you turn.

I think you have your understanding of caster wrong too, the more caster you have, the more stability you have, the wheel will have more self centering force. You want to run a lot of caster because as you turn the wheel there is a lot of negative camber gain on the outside tire and more positive camber on the inside tire as a function of caster

 

First, I do appreciate the response. I was not intending to "attach a name" for any reason other than I saw your responses to other things previously, and I was hoping for knowledgable input.

...

While I agree that increases in caster contribute to a positive center feeling, I've found that going extreme on caster angles (10*) gets back to the point where bumps to one wheel have a real tendency to "grab" the steering. This is why I asked the question that I did. I also noticed the expected affects of decreased turn-in response, and heavier steering "feel" (no power steering). I did check, and bump steer was not the issue in this case, so I traced it back to the caster. Perhaps I was not correct. Would the fact that my race car is front wheel drive cause the effects to be different?

I'd also argue that alignment has nothing to do with SAI. On a strut suspension, don't changes in camber affect SAI? Granted, if your point is that- SAI is what it is, and can't easily be changed for a given camber setting- I wouldn't disagree. However, by doing what was postulated in the other thread, kicking the top of the strut inward while changing the strut-to-hub angle with cam bolts, couldn't they be changed independently?

If you'd prefer not to be bothered, that's fine. I did not intend to aggravate anyone or put anyone on the spot. I'm perfectly willing to accept that I was not completely correct in my understanding, which is why I asked the questions in the first place, while trying to explain what I "knew" (correct or incorrect).

I do find this to be a valuable site, as I have gained from my interactions here. I'm sorry if that is not the case for everyone.

 

Pablo,

Thanks for the response. I was obviously writing my previous response when you posted yours.

I'd agree that positive caster increases stability to a point, but I always understood that you can get to a point where that reverses. It actually was my alignment tech that brought up that I might experience some pull from irregularities when I went up to almost 10* on my race car (actually steering effort was his biggest concern, but he mentioned the "pull over bumps" as well). Perhaps I've been mistaken all along on that understanding.

I understand the loss of negative camber adjustment issue, which was why I was asking some of these questions. In this post, hellz_wings began talking about increasing SAI, and I wasn't sure why you'd want to. Prior to this, my only issue with SAI was when I ran adjustable a-arms on my GT4 car. An uneven SAI led me to look into things deeper, and led me to an incorrectly adjusted arm. I only knew to go for equal, and was not sure why the value itself mattered. Once I equated it to kingpin inclination from my formula car experience, I understood it better. Even so, I'm still foggy, thus the questions.

 

Well I've never run that much caster so I couldn't tell you from experience if it would end up working the other way. Intuitively I would think that it wouldn't. I can see steering effort going way up but I'm having a hard time seeing how it would make the car pull over bumps. That's how I would describe a large scrub radius, not a lot of caster.

As far as a thirdgen is concerned, I have my caster maxed out and it feels more stable to me that way. I do have a large scrub radius though and that really grabs my wheel on uneven pavement.

You mentioned that your race car was FWD, was this unstable feeling occurring when you were on the throttle?

 

Yes and no. I noticed it at Pocono on the infield-to-NASCAR transitions, but also under braking. It did really appear under fore/aft load, and I didn't notice it as much under steady state (however, with that car, I'm very rarely not fully on or off the throttle).

 

Just noticed this thread!

Yes for sure more caster in my experience (RWD camaro, not FWD car) keeps the wheel pull back to center more which, if all else things are equal, makes the car not wander as much when driving straight. The max caster I've been able to get my car at for some weird reason is 4.8 on the right side. Not sure why though.. But 4.8 feels fine to me and I've been up to 120ish without vibrations and the car being very stable keeping it straight and changing lanes and such (3.73's with 700R4 can't go much higher than that lol unless revving really high which I don't normally like to do).

The scrub radius, from my understanding, is that imaginary section on the ground in between the centerline of the wheel vertically and where the imaginary line of the strut intersects with the ground. From my understanding, scrub was already positive from the factory because of the suspension being designed for a 15x7 front wheel, so then when they put 16x8 wheels on, they scrubbed more because the centerline was pushed farther OUT. Plus, if you have the 1LE or LS1 or bigger brake package (which most of us do who race) then the wheel is pushed out even more by 0.3" (not sure about other brake packages but this is what 1LE/LS1 brake kits do) which makes for an even more positive scrub radius.

For SAI: It is the angle between the strut and the vertical centerline of the wheel. So, to say that it cannot be adjusted is odd to me, since adjusting the strut affects that angle indirectly, although SAI cannot be adjusted "directly" per se, you can technically change the SAI by moving the strut towards more negative or positive camber. The whole thing about adjusting the strut/spindle bolts is that it pushes the spindle angle outwards more causing more positive camber, without changing the centerline of the wheel or the strut angle. So say you had a -1* camber reading before, and then you adjust the strut/spindle bolts to move the spindle out and you get say 0* camber, then to bring the camber back in, you would move the top strut mount IN to bring the camber back to -1*. This moves the imaginary strut line on the ground more towards the centerline of the wheel while retaining the correct/preferred camber reading, thus reducing positive scrub radius and INCREASING SAI (when you move the strut mounts in increasing negative camber, you're increasing the SAI. For that matter, anytime you move the wheel centerline out you increase SAI and positive scrub radius. Come to think of it, these camber bolts actually are a really good idea for anyone looking to correct the SAI/scrub radius, provided they have all the other adjustable parts like adjustable camber/caster plates to bring the adjustment back in.. I doubt the stock strut mounts would have enough adjustment for this so aftermarket ones I would say are definitely needed.)

I'm not sure what the effects of increasing SAI are when it comes to steering feel or ackerman etc., but the way I see it, if stock SAI was 23.5* (as Dean posted back when he posted his Ultimate Suspension thread), and I'm increasing negative camber to reduce positive scrub radius, I would assume that I would obviously need to achieve a higher SAI than 23.5 to confirm that I have achieved a less positive scrub radius? Otherwise, I would have to literally measure the angle of the strut and where it intersects on the ground, and then measure the distance between that intersection and the vertical centerline of the wheel.

Also, wouldn't a scrub radius where the strut directly intersects with the centerline of the wheel (probably impossible, but let's say for argument's sake and to have that as the goal) be the 'perfect' neutral scrub radius? That way I'm assuming we would not have the annoying steering pull during braking or when driving over ruts of uneven roads.

Much from what I've learned has been on TGO but also just reading other nice articles online and pictures and diagrams. Alot of what Dean says makes sense too and I have applied much of what he has recommended to my vehicle and have had great results.

Let's continue this discussion it's interesting lol.

 

For discussion, this gets comples in ones interpetation. Hard to express in words to get all opinions on the same page but Ill try.

Technically we are changing the IA, Included angle, but thats only if we consider not changing the camber to the initial setting aftet ajusting the spindle to strut bolts. When you conside the adjustment of these bolts to fudge the vertical line setting of the spindle shaft- we speak of SAI, but in terms of using both Vertical settings and then camber it is considered "included angle" or IA
Of course the SAI will change with camber because the entire asembly "leans" as adjusted. What I refer to SAI is the vertical or neutral 0* camber of the tire as measured against the strut angle- from there you can later talk of camber positives or negatives in degrees. Think of this as a golf club angle of the club face (for any of you golfers out there are familiar with club fitment- its the angle of the shaft when the club face is parallel to the ground (aka 0* camber).

Now- as for what is best for scrub radius via SAI? Just slightly positive is always best BECAUSE when you apply the factor of negative camber on a straight line footprint of the tire contact patch, the center line of the tire is slightly inward of the actualy center of the tire width when about standard street performance setting of -0.8* is applied._ makes straight line braking at about neutral scrub- if you are suffering from brake pad runout you are less likely to get a little twitch pull of thed chassis side to side when trying to set up for the next corner.

With all that said, SAI does NOT change that much at all with camber adjustments. It does change, but the measurements are small. If the car is not lowered, you will run out of camber adjustment very quickly as compared to a shorter baljoint-to-strut mount strut assembly at stagnant height

 

As for Ackerman and SAI or better put IA when camber and caster is applied? the actual part of the tire that makes contact at slow speed tight turns alters greatly because of compound angles. Higher speed stuff is not as bad becuase of less angles as well as sidewall rollover, tire rotation, and slip angles all combined to lessen the ackerman need. If its a daily driver in a grocery store parkinglot? the chassis will lift and front wheel tracking will fight eachother side to side even worse that already experience with the wider factory 16" wheels- compared to what was acceptable to engineers when the 15" initial specs and high sidewall series tires were retained.

This is the kind of stuff that will not be a neglegible change if the car lacks all out performance bushings and bracing of the chassis. Flex is transmitted to the weakess link of the chain until there are no weak links- then adjustments become REALLY REALLY important the more the footprint retains rigidness.

I will put a value on this type of setting or adjustment to be in the last 5% of chassis modifications or else it really is pointless to mess with. Its looking for that last little 1/1oth or even 1/100th's of a second.

And yes I can be abrasive. I like to test someone willingness to learn a topic and actually apply it I can sound like a hardass, but I will always help anyone that shows heart to study and grasp a subject.

 

I think correcting the anti-ackerman has a lot of potential to improve autox handling more than the last 5% if that is what you are saying. Now offsetting the strut and changing the camber gain due to caster, that I'm unsure about. That needs to be worked out. One thing seems for sure, if you can reduce the scrub radius at the same time, the jacking effects will also be reduced. That would be the whole point of offsetting the strut (scrub radius).

The anti ackerman was designed for early radials with super tall and loose sidewalls. So the optimum slip angles were probably huge. When you factor that in, the actual effective ackerman was probably just right.
The problem we have is that our tires are way way better than that now. Our slip angles are tiny compared to what the car was designed for.

I think there is a fair amount of evidence pointing to this being a problem. If you look at all of the serious autox guys, they are all having to run a lot of toe out to compensate. IIRC rayar said something like he had to take it up to 1/8" toe out before it started to turn. My own personal experience is that at the center hairpin at adams, I was losing massive time as the front tires struggled for grip. It was way too easy to get on the backside of the slip angle curve. I've made this problem worse by moving the rear axle forward. Running a lot of toe out seems like a poor crutch to me since you are putting more heat into the tires (possibly already on the back side of the slip angle curve just going in a straight line)
Another thing to look at is how other macpherson cars have their ackerman setup.

My 318is has parallel steering at least, and possibly a little more than that to give some ackerman. To compound that, their wheel base is 5 inches longer which is effectively increasing the ackerman % as well.
Considering that the front suspensions are very similar but the one difference is that the cars were designed 10 years apart, I would bet the difference is due to the advancement in tire construction.

Of course, on a road course, with small steering inputs, this stuff doesn't matter that much. Parking lot and autoX I think it would make a big difference. I have severe tire drag in tight turns and that's even with my 17x9s

 

Just to help out the discussion, which is great already, I found a website with some diagrams concerning the topic. Perhaps they will aid in explaining some items:

http://www.familycar.com/alignment.h...on%20%28SAI%29

 

That site is great for diagrams and explanations. That's one of the websites I've been to that helped me learn about alignments. Although it isn't specific for our cars it's very helpful.

Pablo: Getting the scrub radius alot more closer to neutral, but remain positive is now the goal IMO. And by adjusting the camber bolts to move spindle outwards and then move the strut mount back IN will hopefully get the scrub radius just slightly positive from neutral.

 

Sorry that I lost track of this thread, as I've got a bunch flying around my head right now.

Dean (may I call you Dean?)- I too can be a bit abrasive at times. I was just more worried that I offended you, when my point was just the opposite. As I like to tell my students though, sometimes it takes abrasives to get the smooth finish you want

My original point of the thread was two-fold. First, I'm playing with my Camaro, and since I'm still in the building phases, I was trying to learn as much as I could so that I didn't have to go back and make massive changes later. I'm also limited by my ruleset for Time Trials, so what many consider to be the "last 5%" may be the only 5% I have to work with. I'm sure that you and others can appreciate my desire to be thorough and efficient, though I'm self-defeating with that at times. Just in this thread I've learned of a major misconception I had from not doing enough research and trusting one source I thought was "in the know".

Basically, I'm trying to determine if I need more alignment adjustability options up front. Currently, I can get about -1.0 camber on both sides, and even though I want to track the car, I want it to keep tires alive on the street. My previous experience with my driving habits tells me that I can get relatively neutral tire wear at about -1.5 in my other car (Plymouth Neon- not a good analog), and from doing some observations on this car, I think I might be able to go with more than I currently have in this car.

My questions revolved around the issue of camber bolts versus camber plates. Bolts are the cheaper way to go, and my current plates are in decent shape, but I'm at the adjustment limit of them. I didn't want to use camber bolts to crank in more negative (while at the same time moving the wheel centerline away from the kingpin angle, which if I am thinking correctly, would increase an already positive scrub radius?) and run into issues.

To complicate matters, I'm contemplating going to a 17x9.5 ZR1 replica (with 2" spacer) since it's actually easier to find decent 17" street tires than 16"s anymore... That said, my race tires will stay on my GTA wheels for the track. If my calculations are correct though, my wheel CL should be within a few mm on both setups. The 17" is -56mm offset, with a 2" spacer that should bring it to approx. -5mm. My current setup runs -16mm with a 6mm spacer for -10mm. Theoretically, *I think* (please correct me if I'm wrong), that puts my wheel CL more inward for the 16", right?

I'm sure I'm overthinking all of this, but dammit, I'm an engineer at heart, and one that likes overkill at that...

My other thought process involves my racecars. They are a Dodge Shelby Charger and a Neon. Both have camber plates and cam bolts for adjustment. Prior to reading any of these discussions, I would crank the bolts as negative as possible, then use the plates for final settings. That way, adjustment was easier. Now, I'm beginning to think that I should crank the plates in as far as I can that will give me equal angles on both sides (max the one, match the other to it), and then use the bolts for adjustment. Given though at those cars are probably negative scrub radius to begin with, would I have accidentally gotten it right? Should I be tending towards 0 scrub radius as much as I can? Also, is 0 scrub really a bad thing? I think we may have encountered that with our former Showroom Stock Neon, as place with long corners (the NASCAR oval at NHIS for example), we noticed the steering felt very vague at steady-state, and we had a LOT more tire wear overall than with our previous setup... Our laptimes did improve and we could pull those corners very well though, so we chalked it up to a neutral push, and an over-driving issue...

Every time I sit and think about this, it starts to hurt. Then I throw in the rear suspension stuff and all but go comatose. My wife keeps asking why I'm filling so many papers with sketches and calculations, when the Camaro is supposed to be "just a toy". I don't have the heart to tell her...

 

Got another alignment today (finally) after the extended ball joints lowered the car about 1/2" or so in front.

Camber:
front driver:-1.2
front passenger: -1.2

Caster:
front driver:4.2
front passenger: 4.8

Toe:
front driver:0.05
front passenger: 0.06

SAI:
front driver:14.2
front passenger: 14.7

Sooooo.. To sum it up.. My SAI seems eternally low compared to most thirdgens out there. I don't get why though. We adjusted the strut bolts on the driver's side to give me 0* camber (from -1.0) and then dialed the top back to -1.2* to bring the SAI pretty much equal on both sides. The car tracks straight, very straight. I replaced a bent tie rod adjuster (SPOHN aluminum bump steer kit was bent on driver's side) and then adjusted toe to slight toe in.. Although again, the steering wheel could not be centered. The shaft moves ever so slightly but the pitman arm does not. Looks like it's in the box (a new Lee Performance 670 box is about 1500 miles, and 2 years old). So that is the best most accurate toe reading I could get.

What puzzles me is that the SAI is so low. A couple of years ago I had it at 24* or something like that and the wheel felt 'heavier' but more accurate. It also lifted when turning and returned to center much quicker (this is what lots of SAI does tho). Atleast the SAI is pretty much equal.. I might try adjusting those strut bolts even more to gain positive camber and then bring the strut mounts even more in to bring the strut angle more negative to see if this will increase SAI more.

Any recommendations?

 

I can answer BOTH questions from hellwings and SCCAjunkie in one answer.

The zero scrub radius or even negative scrub radius is bad because of that very thing hellwings is experiencing- the lack of wheel return and predictable feel.

I have stated before that positive scrub is alot like positve caster.


SCCAJUNKIE- On your Neon was sketchy in those high speed banks because of lack of caster feel with the negative scrub. Combine that with "bank turn suspension compression" and the car will get real squirlly with any dips in the road during bank cornering- a little shake-hop-and bobble that will keep you awake. The car does not roll as much under compression banking so the inside tires will load more that on flat cornering- and of course you are not turning the wheel hardly at all either so it is more of a "all four corners squated-car going straight- something pushing the tires sideways" kind of thing. Overdriving? maybe not. Just pushing the car past its previous capabilities, and causing more flex with everything eelse including tire contact patch. More bank speed is more weight on the tires...is more wear.

Yes, calling me Dean is OK in my book. It beats alot of other names people call me And your name?

 

Last thing I will add is....with anything, moderation is the key. (It applies to just about eveything in life)

Too much of one thing generally is not good. What do I mean by this? Take Caster into point. By decreasing the scrub to zero, you need to bump up caster to keep track with high speed stability or with low speed wheel return. Too much caster will generally cause bumpsteer (when the tierods come up AND back) and well as alot of induced chassis roll at low speed tight cornering when the inside tire lifts the chassis.

With that said. Scrub radius just slightly positive is best for a RWD car. (FWD make my head hurt- but thats a mute point)

 

Dean,

My name is Matt, nice to meet you. I'm a hillclimber and roadracer from the PA portion of the east coast...

Thanks for the insight on my issues. Believe it or not, I was just looking at bumpsteer on my racecar (the Shelby Charger), and was wondering about exactly what you said- if the extreme caster was making any issue I had there much worse as the car travelled through bump. I was also thinking that caster angles that high might change effective wheel rate, since the bump forces are not simply up, but slightly up and back, therefore more efficiently transferring motion through that angle...

Bottom line though- that extreme caster was an experiment- and one that didn't provide positive results, at least not from a feel/driver confidence perspective. Overall, my laptimes that weekend were better, but I believe I can attribute that to other factors. The original intention was to run a test day at Summit Point and try some back to back testing, but I never got that far before the budget ran out last year.

 

Hi Matt, my pleasure also.

You are exactly correct on the wheel rate. The strut angle changes so it does reduce the overall effectiveness of a spring rate and a shock damper(in this case of course its a strut). The positive byproduct of a shorter strut is a reduction of rear jacking effect on the chassis under braking (more food for thought). I lowered car will transmit braking force more so through the wheel spindle as opposed to more over it- that lowering thus is a result usually of a shorter strut length which also makes for a broader range on camber and caster adjustments. The higher caster will induce a little more brake dive, but combined with reduced rear jacking also it settles the chassis into set quicker into a corner under braking. Again though- too much of a good this way can start to cause a bad in other ways.

Also, Pablo, What I meant as for the last 5% of tweaking was in reference to peoples degree of modifications. it is kind of pointless to do this on a stock car. It really has to be built about 95% until you start worrying about things like this. Your car is really important as you stated with those wide tires and that tight hairpin at AMP. You were scrubbing and fighting the wheel and the car- now it looks (from viewing your old videos and then later seeing the car in person) that you are getting around that corner much better that at first.

I really wish our ride along went better- sucks you had that fluke vapor lock briefly when I jumped into the passenger seat (major hot day). Now you moved your *** to Italy so I will have to wait someday in the future for a ride along

I am on a friends computer with spell check...what a nice feature. I need to enable it on mine.

 

Am I happy that I stumbled onto this thread. Its a great discussion jam packed with alignment information. I've been searching for a thread that can answer some questions I've had about proper alignment after lowering and adding larger wheels.

My '86 was lowered a long time ago - about 5/8 inch in the front - with the factory 15 x 7 wheels. Factory spces called for a 1° of camber but was set at zero camber due to being lowered. The shop explained very well that ride height affects how a car handles. Lowering a car changes the ride height and camber needs to reflect this change. I can't remember every word but in short the shop tech said lowering is like adding or removing weight. Less weight, higher ride height, puts the top of the tire outward, and more weight, lowered ride height, puts the top of the tire inward. I hope I got this right.

I am trying to picture this in my mind. If factory set up is 1° positive before lowering, then zero after lowering, it must have something to do with less suspension travel after the car has been lowered. I haven't been able to verify or refute this. I have not been able to determine why camber adjustment is necessary after lowering except that negative camber increases steering and handling ability while positive camber has something to with vehicle loading.

Now the car has 17 x 8 wheels - no aligment yet - but I believe the suspension geometry has changed with the new wheels. The tire diameter is roughly the same, about 26 inches (255/45/ZR17's). It has a tight turn feel but seems to float a little at higher speeds. I checked the steering but all seems well there.

I would suspect after reading this thread and others like it, that the scrub radius has changed. And most likely the camber is no longer sitting at 1° from the last time it had an alignment. Caster at the last alignment was 3.3° for both front left and right. Factory specs for caster are 3.0 to 4.0°.

I am fully aware that a visit to the alignment shop is in order with the addition of a wider and larger wheel set up. What if the shop wants to align to factory specs even with this new set up; how do I convince them otherwise and what specs do I ask for? Do larger wheels require neg or pos camber? Thanks.

 

ZZ3 Z28: There are a few things here..

There are many ways to lower our cars (ex: springs, extended ball joints, dropped spindles, lower a-arm spring pockets, etc.) the most common being springs, although there are reasons why it's not the "best" method per se (you can look around on TGO for the explanations as to why, it's kinda long to explain), it's still a decent way to lower it. That being said, if your car is lowered via lowering springs or cut springs, then it will affect your roll center and camber reading (for roll center, it changes the angle of the control arm, the bushings are lower than before in relation to the ball joint, which lowers the roll center much more than it lowers the center of gravity, which means the front will have MORE roll which usually makes it handle worse depending on the setup, even though your car is lower to the ground and is supposed to roll less in theory.)
For the camber part: if the car is lowered 5/8", then the strut angle will change (it is bolted to the spindle down below, and to the strut mount up above.) A general rule is that if you LOWER the car, you will increase NEGATIVE camber and increase POSITIVE caster, this is generally a good thing for handling on our cars considering they have not enough caster and too much positive camber from the factory. If you RAISE the car, you will increase POSITIVE camber and increase NEGATIVE caster, this is a bad thing for handling but I don't see anyone doing this if they want to achieve a good handling car.

Also, factory specs suck badly.. Alignment shops will put your car to the stock GM specs unless you tell them you want custom specs, in which case I hope the guy knows what he's doing.

When you were talking about adding or removing weight, it's true what the shop tech said, "top of the tire outwards" is positive camber, and "top of the tire inwards" is negative camber. When you add or remove weight it raises or lowers the "sprung" weight on the car (ie. the body and weight that sits on the springs, which is also where the top of the strut is bolted to, so when this body goes up or down, it changes the angle of the strut which then changes the camber and caster angles accordingly). The thing is, if you remove or add weight you can re-adjust the camber and caster via the strut mounts at the alignment shop (or at home if you have the necessary equipment and are good at it).

Suspension travel is reduced as a result of the strut being more compressed now that the body is lowered. If you lower the car too much the strut may bottom out and cause damage. If you lower the car, say, more than 1", then you could compensate by installing aftermarket strut mounts that mount the actual strut 1" HIGHER than stock, meaning you regain that 1" of lost travel, which will definitely help prevent the strut from bottoming out.

Adding wider wheels will change the suspension geometry. It will change you "scrub radius" in a bad way. Our cars were designed for 15x7 wheels, so even the 16x8 IROCS had crappy scrub radiuses. 17x8 will be the same thing but there's nothing you can really do about it unless you really get into changing things like aftermarket strut mounts, adjustable strut bolts, etc. But then you'll need to spend LOTS of time at the alignment shop just to get it right and yeah it's a pain and alot of money, so don't need to worry too much about that really unless you get into extreme racing or something.

With the new tires/wheel sizes, you will need an alignment, and I would suggest custom specs. 255/45/17 are a good size for our cars and if set up properly will be able to carve corners VERY well. I would recommend between -0.75 and -1.0 degree for CAMBER (anywhere in between there is still good for street but the more negative you go, the more the tire will wear out on the inside edges so it's a compromise between handling and tire life..) For CASTER, I would recommend you put the passenger's side as FAR back towards the firewall as you can get it (mine doesn't go more than 4.8*) and then set the driver's side to 0.5* LESS than the passenger's side, which means my driver's side is at 4.3* caster.. Why do this? This is to compensate for the road crown so the passenger's side will pull SLIGHTLY making the car go straight (also, increasing caster makes the steering feel a bit heavier, BUT makes the steering CENTER better which means greater straight line and high speed stability). For TOE, street handling cars are better when there is "TOE-IN" rather than "TOE-OUT" (this is when the front of the tires are facing inwards towards eachother or outwards away from eachother). Toe in is better for high speed stability, so a slight amount of toe-in will suffice, such as 3/32 or total toe of 0.09 (depending on how the alignment shop's equipment reads). These are the specs that I go by and it handles a ton better than stock. You will definitely notice the difference.

As for floating at higher speeds, it could be (off the top of my head) worn out shocks, bad alignment, badly balanced tires, etc. But it could be related to a few things. Get the alignment first since you need it anyway and then go from there.

I hope this clears it up for you and helps you understand a bit more about our cars suspension design.

 

Hellz_wings,

I appreciate the lengthy and fast feedback. Its a thousand times more than I ever expected.

My car was lowered with Rancho struts and rear springs a long while ago. It was one of the first things I did to it. It certainly isn't slammed but lowered just enough to make the lines look better. Plus with the rear springs not cut, the donuts are still intact, the ride isn't like a bobbing roller coaster. Its stiff but not as much as my new German engineered daily driver with 40 series tires.

I also never really saw any uneven tire wear with this set up. I rotated the tires regularly so tire wear was even. So I can assume that the alignment set up from the last time was adequate and even appropriate. That was part of my questiona and impetus to join this conversation. With the addition of a larger wheel size and width I was looking for the same results. Even tire wear with an improved ride handling characteristics.

I can assume that proper alignment after adding wider/larger wheels and lowering one's vehicle is problematic. Like I said, I've read a lot of posts here and other places, and it seems that some do not take that into consideration when they modify their car. Only after seeing a bald half of a tire do they relaize that something is amiss. Conversations liek this get people thinking and hopefully acting.


The suggested specs you outline are exactly what I was looking for. I figured that factory specs weren't going to cut it and what I had with the 15 x 7's wouldn't be correct any more, so there had to be something more appropriate. At least now I have something to go on and when I go the alignment shop I can suggest/request that they align it to what I want instead of what they/factory require. Or at least I can discuss with them and see if they are on board with such a change. Maybe I'll get lucky and find a gearhead instead of a techie.

Thanks again.


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ZZ3,

I got carried away in the response and didn't even notice how long it was till it was done lol. No prob everything I told you is what I've learned on here, I'm just passing it on

To respond to your other questions: Cutting springs is fine on our cars. I've done it in the rear and it lowered it just right. I did 1/4 coil at a time just to be safe until I got the height I wanted. It did make the rear slightly stiffer but that's a good thing for my particular suspension setup (I have the rear roll center lowered 3.5 inches for additional rear grip and braking).

Whether you have 15x7 or 17x8 wheels, alignments are typically the same thing (except for scrub radius, IA, and SAI, which are not really adjustable). The alignment can be set to, for example, -1* camber and 5* caster and 3/32 toe in regardless of wheel size. What changes is the fact that the wheel is wider which probably changes the centerline of your wheel, which changes scrub radius, IA and SAI. This can change the way your car handles in many different ways. But yes, when you change the wheel width, you should get an alignment, even if the centerline is the same, which in most cases it is not. The wheel is usually pushed farther out depending on wheel offset.

So, the alignment specs you had before on your 15x7 were the stock settings which are still not the best for handling, regardless if the wheel is 15x7 or 17x8. Although, you may feel the steering pull more in uneven road surfaces due to the wider wheels and a more positive scrub radius from the centerline being pushed farther outwards.

An alignment shop that has a trained tech should definitely be able to adjust a 1986 suspension design, although I've seen some pretty crappy techs so just make sure he knows what he's doing and aligns the strut mounts and tie rod adjusters properly. Sometimes they'll tell you that "it's as far as it goes" which could be the case, but that could also mean that he's being too lazy to try to push it farther (this also happened to me). Just be persistent, but respectful and buy the tech a coffee or something as a good gesture, plus he'll be more awake when adjusting lol.

 

Thanks again for the update. I ordered some new tie rod adjusters to replace the old ones currently on the car. I hope to get these installed soon and get an alignment done. Its not a DD so there is no rush.

I am surprised that no else has chimed in with what they've done after lowering thier Camaros regarding alignments and such. A majority of owners here tend to lower their cars but make no mention of how they compensated for it or if they didn't, what the consequences were. I was at a car show over the past weekend which had a lot of tuners in attendance and I asked a couple of guys who slammed their cars what they did when they did that. Mostly I got shoulder shrugging. But it looks cool doesn't it?

I view my Camaro as as et of sub systems. The engine is one, the suspension is another, brakes, cooling etc. are all pieces that when are tuned to each with other work as a complete smooth running system. If one sub system is lacking the entire system suffers.

Want to go faster? You need better braking. Want higher hp? More cooling is needed. Bigger wheels, wider wheels? Is the suspension up to par. This is what I mean. I've done a lot of things to improve my Camaro but I still have a long way to go to get the whole system to work as one, to gel together. Wider and larger wheels was the latest thing I've done to my car so of course, changes to the alignment and suspension dynamics are in order.

I can't wait to change the specs and see how much better it handles.



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A perfect marriage of components in any car is what will make it truly perform all-around. If you ordered tie rod adjusters, I would recommend a bump steer kit because if you lower the car alot, bump steer could be a problem. I have SPOHN's kit, I'm sure there are other kits out there. It's more expensive though, but you can adjust the height of the outer tie rod's mounting point with the spindle (which can correct bump steer). It's not really necessary unlesss you lower alot but can help when going over bumpy roads and your steering wheel tries to dance in your hands lol (gotta love Montreal roads/pot holes lol)

Yeah, there's not a single soul that I know that knows how to properly lower their car. I get those answers too,

Guy: "yeah bro I installed a lowering kit for my car! It handles like the bomb!"
Me: "what's the spring rate now compared to before?"
Guy: "What's a spring rate?"
Me: "........." (insert cricket sound)

Yeah.. It's bad.. lol

 

With Racecraft 2" drop spindles (also swapped in LS2), I'm running:

Left Front Right Front
-.7 Camber -.7
3.4 Caster 3.8
.04 Toe .05 = total toe-in .09


Had to try multiple attempts with caster as tires kept rubbing on the plastic fender inserts. This set-up has no rub.

Brian

 

Those seem like good specs TEDSgrad. It's interesting that your caster is low and doesn't rub, i was around that and rubbed. now im about 4.3L and 4.8R and rubs alot less. Also, the ls2 must have raised your car about 2 inches because of the weight reduction.. How did that change the angle of your control arms and camber/caster limitations? I would assume the dropped spindles brought the car back down to a low height?

 

Opened hood, turned weight jack bolts, closed hood

Yeah, those afco weight jacks come in handy after all that work is done!

posts 17-22


https://www.thirdgen.org/forums/susp...g-vetruck.html

 

Pardon me. I'm going to hijack this thread somewhat but my question is about my SAI numbers. After reading all these posts, I think there is something seriously wrong with my car. My camber and caster are within factory spec. I just had it aligned. I noticed on my alignment print out my SAI is Left 11.7 Right 29.5 Included angle Left 12.4 Right 30.1
If I'm understanding all this written on this post correctly, I've come to the conclusion a spindle would have to be bent to get number like that. Am I correct or am I visualizing the workings of how the suspension angles move incorrectly?

 

With that much? YES, Something is definately bent. You will have a few degrees of "fudge" room from the mounting slop tightening the two strut to spindle bolts, but no where near that much. You have a bent spindle