Corner Weighting question: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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July 31, 2011 4:55 p.m. sevenracer New Reader

Looking for people's experience on the practical limit to how much you can bring cross weight back to 50% without creating other issues.

Say for instance, if you are starting at 54%, and you don't move weight around in the car, can you get back to 50%? Is that a practical goal?

I am trying to decide where to put a cool suit system (approx 20lb). My choices are in the spare tire well which will help front/rear weight distribution. Or in the front passenger footwell - which should help left weight and cross weight - but have a slight negative effect on F/R balance.

Not sure if

Thanks, Neil
July 31, 2011 4:58 p.m. sevenracer New Reader

In reply to sevenracer:

To complete my thought - Not sure if I should ignore cross weight and try to optimize F/R, assuming I can fix the CW by adjusting each corner height. Or if the CW is too far out and I should try to place the weight to help that.
July 31, 2011 7:11 p.m. SVreX SuperDork

I'm not sure I am understanding your question.

Are you looking for all 4 corners equal? Not necessary.

Do you mean 54% cross corner weight? Or do you mean F/R?

The corner weight shouldn't be too hard, but you HAVE to move weight.

Do you mean just ADDING weight without SUBTRACTING it from somewhere? Hmmm, not sure...
July 31, 2011 7:29 p.m. corytate Reader

are you setting your crossweight with a substitute for driver weight in the left front?
try subtly changing your ride height in the right rear maybe?
the site has a cool article on setting weights if you're interested:
here it is
July 31, 2011 8:33 p.m. CGLockRacer Reader

I'd go for cross weight and left/right balance before Front/rear balance. Putting the cool suit in the rear spare tire well also will increase inertia which could hurt rotation into a turn, On the other hand, if the car is loose, it could help stabilize it.
July 31, 2011 8:47 p.m. sevenracer New Reader

Ok, forget the added weight for now. Assume static weight is set, and unfavorable due to class rules.

How much can you bring cross weight back to 50% just by adjusting coilovers at each corner and not moving weight on the car? I see people talk about bringing in CW from 52% or so back to 50%. But what if you start at 54 or 55% or even more? Anybody ever needed to do this? What was the outcome?

Or maybe a different way to ask the question - What's the furthest out anybody's started with for crossweight and got back to roughly 50%?

Thanks
July 31, 2011 10:34 p.m. SkinnyG HalfDork

I've done a few cars that had cross weights greater than 56% and I was able to get them to 50% cross weight.

I shoot for cross weights at 50/50. If I can't do that (for whatever the reason), I shoot for 50/50 across the front and I don't care about the back.
July 31, 2011 10:55 p.m. Keith SuperDork

You can easily adjust your cross weights to 50:50 without having to move anything. That's what you get by adjusting the perches on each corner, diagonal weight movement.

If you're worried about front/rear or side/side distribution, then you have to move stuff. You can't affect those by adjusting the suspension.

Here's the order to do things in:
- figure out the location of your extra weight based on side/side or f/r balance. I'd concentrate on side/side myself
- set the ride heights on the car, ignoring corner weights. Get it sitting properly on the suspension
- cornerweight the car by adjusting all four corners at the same time by the same amount. Since the corners are basically paired up, this will have the same effect on the cornerweights as adjusting just one...but it will also keep your car sitting level instead of getting it all cockeyed. For example, if your LF/RR diagonal is light, then raise the perches on the LF/RR by turn and lower the perches on the RF/LR by the same. You'll still get the same weight shift as you would by simply cranking up the LF, but the car will stay level. With enough adjustment, I think you could actually get a car to 95% on one diagonal.
- if you have one corner that's simply too light, move weight in the car. You cannot add weight to just one corner with suspension adjustments.
Aug. 1, 2011 11:57 a.m. 44Dwarf Dork

If you have adjustable coil overs you can set the cross just about anywhere with close to any ride height you want. You just need to adjust on all 4 springs at once. Say cross is high after setting ride height and angles on links and a frames etc. so if cross is high you need to decompress the RF and LR springs 1 turn and at same time turn 1 turn to compress the LF and RR springs. Settle the car the same way each time (ie: three pusshes down on both bumpers same order etc) and recheck. Every car is difrent and spring rates that very side to side does change things but it can be done on my Dwarf 1 turn on all 4 is 1.76% cross change and ride height drop is not measureable with a tape.

44
Aug. 1, 2011 1:40 p.m. sevenracer New Reader

Ok, thanks guys.

Sounds like I can bring the cross weight back into line with corner heights.

So, my decision is whether to improve front left/right balance or to improve front to rear balance. My gut says it's better to balance the front left to right, mainly because currently the LF is very heavy (about 130 lbs more than RF), and I can't really move any weight off that corner.