midnightfirews6

iTrader: (1)

I'm about to pull the trigger on Ground Control weight jacks for the adjustability, because I hate using a spring compressor to do springs, and every aftermarket lowering spring I've seen is too soft. (I'm wanting to go around 1.5" lower and about 850/175 ish)

I've heard Dean and a couple others mention needing to corner balance the car to get the most out of the jacks and because they can throw the car's balance off and was wondering to what extent this is true. My car is mostly a street car that sees a lot of corner carving, a few autoxes and sometimes I'll throw it sideways on exit ramps but it is not an all out track car and it won't be used to break records or go 10/10ths every time it's driven. I can definitely see the benefit on a track car, but on a street car with a full sized tank that may see passengers, would eyeballing the heights get the car close enough to even for the average spirited driver? I want the car to handle better than it does now, but I also don't want to throw $400 out the window on something that I won't really be able to feel & that may be thrown off if I buy lighter parts, don't keep the fuel level constant or start cruising around with the Pawn Stars as passengers

SCCAjunkie

You *can* do it by eye, but all that you'll be doing is setting the height. It is possible that things could be off somewhere, and your corner weights could go screwy, and with that spring setup, it could make the car squirrelly. It's a lot of "could"s though.

Honestly, with a little work, you could make your own corner scales for about $100.



If you're going through the time, effort and expense of jacks, why not set them up correctly?

BMR Tech

You cannot corner balance a car by eye. You're not balancing anything, you're just visually evening the car out. Once you hit the scales you'll find that your car is probably way off.

Find out how much you weigh and put that weight into the driver's seat. If you really want to set the car up for a passenger, throw 160-180 in the passenger seat so you can compensate for that person as well - I do not advise you balance a car for a passenger unless you have an instructor in your car and want the car to be setup with that guy in there.

Using adjustable coil perches you can adjust the weight to spread it as evenly as possible for the particular chassis. Most cars will never achieve the 25% on every corner, so you'll set the vehicle up to be even side-to-side.

3602lb front engine rear wheel drive car may end up looking like this if it's dialed in correctly.
928-928

873-873

That is a 52/48 weight distribution front to rear balanced side to side. There is no way to visually determine this. And, at these settings, the car may sit a little funky, but it will be evenly balanced left-to-right.
- Kevin

SlickTrackGod

Really what BMR (Kevin) stated does hit the nail on the head. (Thumbs up)

Only thing I can suggest if you do not have scales is you are merely going for chasiss height and try to eliminate any rake in the chassis attitude at all.

With that said, chassis is most always not perfect in corner heights. Generally a chassis height is taken off the outside rails just behind the front wheels and just in front of the rear wheels (can be done along the rockers-where SFCs are welded in. NOTE: I would not suggest measuring off SFC's unless you have squared the chassis prior to welding them in, AND you have had the car on flat ground and on scales to make sure they are accurate to use as measurement reference points.

Best thing to do is to ge tthe car on flat ground where you know all 4 tire footprints are on exactly level ground- A laser level from HomeDepot is a good tool for setting 4 different points of level from the laser height down making sure on point is not a 1/8" off in height. Then you mark boxes on the ground and make sure you place the car onto those points each time percisely AND DO NOT ROLL THE CAR BACKWARDS onto them. The car should always be rolled forward with the driver in the seat (or weights as Kevin suggested. If driver used, then driver needs to stay there for measurements)

now lets set corner heights. Lets say if you want the fronts 4" off the ground and the rears 5". You set the two fronts so the chassis is 4" and the rears so they are close to 5" and roll into into position (do not hit the brake pedal either so as not to dive the chassis- just roll gently into position) take measurements and you FOR EXAMPLE find that the fronts arefronts are LF 4" RF 4" LR 5 1/4" RR 5" on flat ground. You then without scales can at best just take any rake out of the chassis by just changing the heights diagonally from the 5 1/4 down to 5 1/8" and bring the front up to 4 1/8" You'll probably be surprised to find out that the chassis may settle at 4 1/16" and 5 1/16" rather than 1/8" readings. Setting chassis heights with weight jacks will do very unexpected changes when adjusting corners- it takes ALOT of experience to fine turn which spring to adjust and how much. keep in mind that a front spring change is alot more sensitive than a rear when putting a full round in or taking a full round out of a chassis. "A full round out" is sometimes what we do for a qualifying setup in NASCAR based on the track. Its to get the car there quicker when we have two qalifying laps only and can bring the car temps up fast enough to get the suspension to come into itself. A full round consists of one full turn of the weight jacks in to raise the RF and LR diagonally to take Xweight out of the chassis and put a full turn into the LF and RR to also take Xweight out of the chassis all at once. It makes the RF and LR not hold as much of the in general 54% X weight we normally run in race setup for going lefts(ALOT more into this that just xweight- but this is for understanding what is done using weight jacks for racing stuff and chassis changes) In doing this change, it will change the rake AND ride heights of each corner of the car even though you would think you are doing things symetrical.

You have to play with them to understand, but balance out any variance in ride heights using fronts first and fine tune with rear adjustments. Ill give another example on which to turn:
Back to that same senerio where yoiu have LF 4 RF 4 LR 5 RR 5 1/4. I would only frist try and move JUST the LF weight jhack about a half a turn to extend (raise the chassis/force that tire onto the ground more) and then run the car around the block and reset it on the pads ro rechack ride heights. SInce the front is heavier spring rate. it will lift the front slightly but will push the rear down slightly too. You will probably end up with both fronts going up 4 1/16" and the RR staying at 5 1/4 but the left rear will also raise from 5 to 5 1/8". Now you are at LF 4 1/16 RF 4 1/16 LR 5 1/8" RR 5 1/4". NOW- move the RR weight jack taking half a turn out and do it all again since that will reduce things not as much affecting the fronts.(Keep in mind that little fronts movementsWILL affect the rear, but little rear movements usually do not affectthe front in height changes since the spring rates are much softer.

Dean

SlickTrackGod

Also note that if you just changes shocks and struts on the car, AND you are changing spring rates and ride wheights FROM WHAT IT WAS SET PRIOR TO THESE ADDITIONS, you are sitting on top of those 4 tire pads with an imbalanced alignment. THis imbalance of narmal tire to ground contact patch (and angle based on Camber readings) will change the height of a corner of a car. If you have lets say an accidental -2.5* camber in the LF and -1.0* in the right front- then you scale the car, AND THEN you align the car- IT WILL BE WRONG becasue once you decrease that -2.5* downm to say both match at -1.0*, it will release pressure off that corner of the car because the camber angle is no longer lifing that corner of the car as much as it was with the higher negative camber.

Another IMPROTANT NOTE: Make sure your tire pressure is exactly where you want to run them evenly left side to right side. If you think youll run somewhere in the range of 45psi fronts and 41 psi rears. the both fronts need to be exact whether they are both 40 psi, or both 45 psi, and then both rears need to match in a close proximity also within the intended psi range of use

SlickTrackGod

If you can eveer get the car onto scales, you will immediately want to record the ground to rail heights like I described -this will get you the most out of the time on scales so you can make future changes and still ge tthe car back to that xweight (or at least very very close). By using 4 points under the car rails that are FIX position rigid points as rail to ground measurements, you could then take the entire car apart and put it back together with those same shocks and spring rates (assuming the shocks are the same nitrogen pressure, or passive pressure in static form) and you will be able to just seet the chassi back to those measurements and know for the most part the chassis is balanced still within about 0.2-0.3% of what it was initialy referenced at.

I would do this with the Supertruck just for an example. My chassis ride heights with a slight rake were (since I had a 4" minumum rule)
LF 4 1/8" RF 4 5/8"
LR 4 3/8" RR 5 1/4"

With the same spring rates- even if I revalved the shocks (since they are passive under load when it pretains to rebound force unlike a lifting HP nitrogen loading shock) I would then put the car onto scales and it would generally be right on my desired 54.3% Xweight every time within about 0.5% (yes I said 0.5%, not the 0.2-0.3% I said above) WHY the change? becasue we were ALWAYS changing tire carcasses which would make a a difference with every set of tires we ran. I then had to adjust the chassis to that set of tires (But thats a whole different topic we are getting into) you for the most part change tires once every 2 or 3 years.

SlickTrackGod

If you guys are ready for more, Ill take Kevins snerio and take it a little further into reality- I can tell in all due respect to Kevin that he was keeping it simple so people can somewhat understand, but if you want more then here it goes.

Lets say the car is the 3602 (With drivers weight included. Keep in mind that the driver sits to the left side so the left to right weight (which scales will also tell you will probably be about 53% and the right side tires will hold 47% (these are simply aproximations for a real world senerio- all cars differ and all drivers differ in exact weights)

With that said the car is sitting like this if the front to rear bias is 52/48 and the left side bias is 53%


Exact corner weights would be (not a guess, this is exact)-
LF 1008.5 RF 864.5
LR 936.5 RR 792.5

Those figures would be an exactly corner balnced car with 50% X weight and would corner equally well both left and right corners based on everything else being symetrical.

I tell everyone how I figured that later when I have more time- gotta go. But this info is handy to understand how to figure if you are building a car from scratch and can place weight where you need it

Dean

SlickTrackGod

math on this is pretty easy.

Car and driver weight= 3602 lbs

52/48% front/rear weight bias Front 3602 x .52= 1873 front wheels/ so 1729 rear wheels

Same with left side weight bewing 53% you times that toal by .53 and get 1909 left/ 1693 right

Now you have:
* 1873

*1909 1693

* 1729

Next get the difference between the corners:

*****1873
***36****180
*1909*****1693
***180***36
*****1729

Next take the front 1873-36-180= 1657 divided by 2= 828.5 The CROSS OVER the corner differneces from left to right (36), and from right to left (180)and add them to the 828.5....
...so, 828.5+180= 1008.5 LF and 828.5+36= 864.5 RF

Same for rear- except you do not x over the corner differences (we just know the left side of the car has more weight so is the higher of the differences used in the equation, Niote the front and rear have the same differences between corners, just cattycorner form eachother in the first equation. you really do not need to figure the rear corner differences for the sides, but I showed it up top so you better understand the symmetry of the 180 and the 36. Its the same for both axles once you get one axle figured- checking both is a way of cross checking your own math.

1729-180-36= 1513 divied by 2= 756.5

...so, 756.5+180= 936.5 LR and 792.5 RR

Now you take the diagonal weights and add them

1008.5____864.5 = 1801 lbs (936.5+864.5)
*******X****************> 50% cross weight
936.5_____792.5 = 1801 lbs


EDIT- My spacing on my number displays would not keep proper spacing when I submitted the post, I had to add *asteriks to keep the numbers in proper position from each line to the next

Bullydawg

iTrader: (7)

Great info! Subscribed for my future weight jack installation!