What is Corner Weighting and how important is it?

I am new to the track and I am trying to best prep my 2004 Z-06.

I just lowered the car about an inch in the rear and 1/2" on the front using stock bolts. I have new CC Wheels 18" 335/30 for the rear and 305/30 on the front. I have gotten some recommendations on alignment settings from Subdriver and others I am going to start out with. So before I go ahead with the alignment changes....

What is Corner Weighting and how important is it?

And how do I do it?


Thanks

 

Basically corner weighting adjust the weight so that cornering force has the same front-to-rear ratio when turning left or right. It may not make it possible to corner as hard in both directions, but it'll make the car handle the same in both directions.

 

Yes, the goal is to get all four corner weights as close as possible, but equalization between the front left and right to each other as well as the rear left and right to each other is critical in setting the car up for track duty. Couple that with proper bump steer, shock valving, spring weights and suspension settings and you have your hands full... idea is to get the car as balanced as possible to it will track as flat as possible under acceleration, braking and corner transition for better entry and exit speeds in corners.

One thing I noticed after doing the Z06 swaybar and shock swap was that the car tracked smoother and didn't have such snap oversteer tendancy when the TC was turned off, when compared to the previous stock C5 suspension. When I installed the BAER Eradispeed 14inch rotors on the back of the car, the car changed braking characteristics BIG TIME. The car now brakes flatter with less nose brake dive under hard stops, almost NONE.

To better adjust your car for corner weighting, you really need coil overs and a selection of springs, and while you're at it, get the adjustable tie rod kit sold by Corvette Central and others and install it with the bumpsteer spacers when you have the car corner weight balanced. To do it right, make sure the car will be in track trim with YOU in the car, and with half a tank of gas and on the wheels and tires you'll be at the track with... prepare to be there a while... it is a LONG process when doing the full suspension setup with alignment, bumpsteer measurement/ setup, and cornerweighting.

Mike

 

 

In the late 1950's, I was part of the Pontiac factory team (#9 car). We used four feed scales, one under each wheel. We had a big screw on top of each spring seat (coils in the rear) so that spring pressure over each wheel was adjustable. The anti roll bar system was also adjustable. This was called "Jacking weight", the amount of weight read out on each scale could also be changed by just changing tire air pressure.
Drag racing you want to increase weight or push over the right rear wheel, circle (put your foot in it and turn Left), you want increase the weight reading over the right front. In road racing, the course would dictate car balance. This is the way it used to be done, I don't know what trick thing they use to day, but the principle should be the same.

 

A good illustration/explanation.

http://www.grassrootsmotorsports.com/cornerweight.html

 

Olitho,
I note that you lowered the front less than the rear which can be dangerous at high speeds due to lift. I read one report on the forums about two years ago about a Vette that went airborne on a drag strip in this condition.
Here is how I checked to make sure my nose was lower than the rear. With the car on a level surface, measure ground the frame clearance right behind the front wheel and right in front of the rear wheel (use the actual frame, not the fiberglass). The rear should be about 1/2" higher. 1/2" is a rule of thumb. Precision here isn't key, only that the rear is higher than the front.

Corner weighting is not commonly understood and there is some misinformation above. You can not change the front-rear or left-right weight balance without moving mass in the car from one spot to another, which is something we rarely do in a street car. While it would be nice to have the same weight on the RF as LF tires, that isn't something you can do by merely adjusting ride height at each corner. Corner weighting is generally adjusting ride height at each corner to attain 50% of the weight on the RF+LR (and by definition 50% on the LF+ RR as well).

Think of a car as a table with four perfectly equal length legs on a perfectly flat floor. All four legs have the same weight on them. Now imagine you cut 1/4" off one leg. If you push down very slightly on the table at that leg, what is the table going to do? The opposite corner leg will come off the ground and the table will rock on the other two legs. 100% of the weight is on those two legs, 0% on the other two (give or take a pound or two as you balance the table on those two legs). A car will not handle well in this situation.

In an real car, we set up the corner weights so that the RF+LR=LF+RR.
A real world example. I set my car up for a race at Memphis earlier this year with about 5/8 tank of fuel and me in the car. My weights came out as follows:
LF 906 RF 863
LR 819 RR 773

Total 3361
Front 52.7%
Rear 47.3%
Left 51.3%
Right 48.7%
Cross Weight 50.0% (906+773=1679, 863+819=1682 equal within 3 lbs)

To set corner weights, the car/scales must be perfectly level (I use a laser leveling system) and sway bars disconnected. Corner weights can be adjusted by raising or lowering a corner, but that will not change front to rear or side to side. If I raise the LF, the LF and RR will get more weight and the RF and LR will lose weight. For example, if I raise the LF and it gains 10 lbs, the RF must lose 10 lbs as the front of the car didn't change weight. Since the RF lost 10 lbs, the RR must gain 10lbs as the right side of the car didn't change weight. And the LR will lose 10 lbs as the rear didn't gain weight. The final result would be:
LF 916 RF 853
LR 809 RR 783

Total 3361
Front 52.7%
Rear 47.3%
Left 51.3%
Right 48.7%
Cross Weight 49.4% (916+783=1699, 853+809=1662 off by 37 lbs)

A good discussion of corner weighting is here:
http://www.grmotorsports.com/cornerweight.html

So how important is a properly corner weighted car. Well... it is pretty important. Should you worry about it? Maybe, especially since you just changed all your ride heights. How can you tell if it is a problem? Track your car. If it handles differently in each direction (e.g. understeers one way and oversteers the other), you need to fix corner weights to get to 50%.
But not to worry everyone who has lowered their cars, for street driving this isn't something I would worry about. An improperly corner weighted car will only be an issue at the very limits of performance, something I don't encourage anyone to find on the street.

 

Subdriver: Nice write-up!

Mark at MSI just did the corner weighting and alignment on my car after he installed the QA1's and coilovers. (I had to disclose my true weight... )

I have not been to the track yet, but I did get to do some spirited driving and the car feels much better and "tighter".

 

Subdriver's explanation was excellent:

"Think of a car as a table with four perfectly equal length legs on a perfectly flat floor. All four legs have the same weight on them. Now imagine you cut 1/4" off one leg. If you push down very slightly on the table at that leg, what is the table going to do? The opposite corner leg will come off the ground and the table will rock on the other two legs."

Some times I get "Senior moments".

 

Thanks again to Subdriver and all the other contributors to this thread. This information is invaluable.

Do you have a recommendation of who to go to in southern California for this work to be done? I am in Trabuco Canyon/Huntington Beach in Orange County just south of Los Angeles.

Subdriver, I will check my front and rear heights, but I believe they are OK, but better safe than sorry. The fastest track I am driving is Buttonwillow and I am hitting about 140 down the back straight. That does not seem fast enough to be a problem for the changes I made in ride height... or am I kidding myself?


Thanks

 

There's a couple shops in San Diego. Check out www.sdsolo.com to find out more.

 

All, thanks for the kudo's. Glad to have helped.

Olitho,
I really don't have any concrete testing info, so I can't answer your question accurately. But, in the case I mentioned above, it was at a drag strip, so it occurred well below 140...
However, in that case, the guy did have a splitter nose on the car which made it worse (more lift of the nose) and he was driving into a head wind.
His post was enough to open my eyes and make sure my nose was lower than the rear.
Sorry, but can't help you on the tuner shops in socal. Been on the east coast too long...

 

Thanks Leaftye:

I followed your link and found Jae Lee at Mirage Int'l in San Diego. The locals on the San Diego SCCA site spoke very highly of him.

Jae referred me to Darren of:
West End Alignment
(310) 808-9233
18008 S Vermont Ave
Gardena, CA 90247

$110 for the Corner Weighting on a 2004 Z-06, plus $110 for four wheel alignment.

 

Olitho,
That is a decent price for both the corner weighting and the alignment from a good race shop.

 

I've heard VERY good things about Mirage. For parts and even some work, Dave Turner's is decent too. FWIW, I've been to Dave Turner's, but not Mirage.