RKD in OKC

The scales I have access to for corner balancing my GTS require lifting the car and setting it down on the scales. Does the suspension settling issue of the 928 effect corner balancing like it does alignment?

iJeremy

No, the car will weigh the same at the corners whether the suspension has settled or not. You should be perfectly fine.

Lizard928

I would recommend just using a couple 2x4s and driving up onto them.

All the scales I have seen are just steel pads, that with a slight incline you can get onto.

RKD in OKC

These scales are on stands that have rollers to allow the wheels to move around as the car is set down on them. Also allows adjustments to be quickly made as the car is basically up on a lift.

Marine Blue

Wouldn't a lifted front end cause the weight to shift to the rear due to movement in the fluids?

Lizard928

Afshin, not really.
The issue I see is for attaching and removing any preload from the adjustable droplinks for the swaybars.

jon928se

The reason the front (mostly) needs to settle before an alignment is because the suspension bushes are artificially holding up some of the weight of the car rather than all of it being held up by the springs.

If you could guarantee that bushes on each side were doing equal amounts of holding up the car then lifting the car 1st would not be an issue for corner weighing. I don't think you could in theory guarantee this - in practice the differences may be small.

As for then adjusting the ride heights to get the corners balanced you would also need to ensure that the bushes reacted the same. In theory you can't, in practice the differences may be inconsequential.

dr bob

With the known stiction and settling issues with the 928, you'll want to verify the corner weights with the car settled. Potential is that one corner sticks more than another. Even under the best conditions (drive-on scales with no appreciable ramp height) the spring adjustments are 'sticky'. ie: You make an adjustment but see no change on the scales. Bouncing on the car will help some as you adjust, but ultimately, this is the same as a ride height adjustment. It's an iterative process, where you adjust, settle, verify, and repeat until you have the results you are looking for. I can't see a way to get anything close to accurate settings if the car is lifted and placed on the scales.

dr bob

What Jon said...

Ispeed

Just loosen the lower control arm rear bolts when it's up, and re-tighten. I don't think it would make much of a difference anyways, especially as it should affect diagonal weight even less than front to rear.

mark kibort

If all 4 springs and shocks reacted the same to being lifted and let down, i would say there would be no issue, but if there is just .25" of difference, that could be near 50lbs on one corner difference, and this is likely, so why even bother unless you use 2x4s as was suggested to drive up on to the scales.
as far as weight shifting, no, not really. the movement of the fluids really cant count for much, especially with the gas tank being pretty narrow.
Personally, I think cornerbalancing a street car is kind of a waste due to the ways all the weight can change anyway due to passengers and gas. But, you might want to see if it is way out to get the cross weights correct, and thats really should be the goal as it could help tire wear and handling to a certain extent.

RKD in OKC

My mechanic is wanting to check the corner balance to see what is going on. With a hunter alignment rack alignment and double checking with drive over bear alignment checker looks perfect but pulls to the right.

Corner balancing my street 944 Turbo made a 2 second difference in 65 second lap time autocrosses. It got rid of the car rocking like a 4 legged table with one short leg when transitioning in slaloms and esses. And that was with only 1/16 of an inch adjustment to get the cross weights balanced.

Will have to make sure to get it on the scales with the suspension at it's settled height. Used before and after tire to fender gaps and bouncing it down on the alignment rack.

mark kibort

2 second difference? For most, that would take two people sitting in the car. 1/16th of an inch? I would have to say, that would not make more than a tenth or so. Ive got hit in the rear, knocking the alignment 1/2" toe in and it was not fun to drive but could keep lap times within a second or so. anderson saw the same thing when he got tagged and his rear wheel had about 5 degrees of camber. if I put in 100lbs more gas, cornerweights are way off, vs empty, but can turn near my top times, even though it might be more work, most being from the sheer weight.
pulling to the right is not due to a cornerbalancing issue, its an alignment issue. If you do the alignment correctly, it wont pull, and that means no jacking up the car before the checking and adjustments. bouncing on the car, pulling it down, all dont really do much. Ive had mechanics swear up and down that the alignment was to spec, only to have pulling, or other really weird driving characteristics and some really bad tire wear. (before I figured out many years ago, how to do it myself or check others work).

RKD in OKC

You make is sound as if rear alignment is not very important on your courses in a 928. I've always been told a good driver can make a fast car go fast, but a great driver can make a slow car go fast. Still doesn't stop me from wanting my car setup as good as it can be setup.

On our courses cornering is a big part of lap times. We try to set up our courses to balance out the advantages between high horsepower straight line cars and the quick in the corners low powered cars, ie., Vipers versus Miatas.

I've set FTD in my well setup 944 Turbo and then gave a 300 lb guy a fun run ride with the timers still on. We usually don't allow passengers with the timers on for insurance reasons. Anyway, with the 300 lb passenger I matched my previous official FTD time. On that fat lap my top speed at the end of the few straights was 10 to 15 mph lower due to the extra weight, yet the added weight increased corner speeds enough to make up the difference.

At that time with that car I was very adept at very late braking then initiating a 4 wheel drift on turn-in and maintaining that drift through the apex throttle steering and also through the exit until the car was pointed straight again. Being smooth made a huge difference and the rocking of the un-corner balanced setup made it a LOT more difficult to get into the 4 wheel drift consistently on entry. The car would break loose when it rocked on turn in lowering my entry speed to keep from understeering then oversteering as the car settled and rotated causing even more speed to be scrubbed off. I gained quite a bit of corner entry speed after it was balanced just from the added smoothness alone.

I am hoping my mechanic will learn how to align the dern thing so I will have somewhere I can take the car and depend on it being done right. He's had it on the rack 3 times now.

Marine Blue

Thank you for the explanation, this helps.


I'm not an expert but I thought I would throw different ideas out there just in case they haven't been covered. Have you checked all of the suspension components for wear? Maybe one of the components isn't holding under stress? I assume your mechanic would have covered this but just in case he's not familiar.