Cornerweight Questions for the Experts

[David Palmquist]

I'm trying to make sure I have my head around this and have not missed an important nuance before touching the car...

I corner balanced the 911 last week and we achieved very favorable weights at all four corners (50.1% cross and front corners within 25lbs). However, when going back to double check everything we ended up with the passenger side about 1/2" higher than the drivers side. DOH!

So this has been bugging me and I was thinking that I could drop the whole passenger side by 1/4"-3/8" and then sleep at night once again. My thinking is that if the front and rear on one side are adjusted equally, there will be little or no net effect to the corner weights. So, is this right, or am I missing something?


BTW, I know the proper solution is to get it back on the scales and do it right, but I just don't have much time these days. Also, the events I run are not fiercely competitive like SCCA. I have been finishing in the top 3 "PAX" positions all year with cross weights at about 43% and a difference of 150lbs on the front corners! Obviously not ideal.

Thanks.

[John Stimson]

Hi David,

If the motion ratio is the same for the front and rear suspension, then adjusting the front and rear spring seats on the same side down by the same amount should preserve your cross balance. If the motion ratios are different, you need to take that into account. The amount distance you lower should be proportional to the motion ratio, moving the spring seat less on the end with the lower motion ratio.

Example - you want to lower the right side by 1/2". If the front motion ratio is 1.0 and the rear motion ratio is 0.8, then you should lower the front spring seat by 1/2" (1/2" * 1.0) and the rear spring seat by 0.4" (1/2" * 0.8).

[David Palmquist]

Thanks.

I should clarify...

My car uses and old fashioned horse and buggy torsion bar setup, rather than coilovers. So I have simple adjustment screws to change ride height. In my case, motion ratio calcs would be complicated, so my method for re-adjusting would be to measure the chassis height at fixed points and then remeasure after moving the car and "setting" the suspension again.

But, your answer supports my theory that it can be done, even if our methodology is a bit different. Let's see if others agree...

[Marshall Grice]

i'd re-level it. I'd put it back on the scales though too. If you can't put it back on the scales then leave it as is.

Interesting side note, if you start with a car that is level (or really left and right at equal heights across an axle), perfect corner weights are only a turn or so way.

[Toby Larsson]

i'd re-level it. I'd put it back on the scales though too. If you can't put it back on the scales then leave it as is.

Interesting side note, if you start with a car that is level (or really left and right at equal heights across an axle), perfect corner weights are only a turn or so way.

Hmmm, only way I can achieve "perfect" corner weights would be if I lost about 80 lbs, time for weight watchers.

[Mike Simanyi]

i'd re-level it. I'd put it back on the scales though too. If you can't put it back on the scales then leave it as is.

Interesting side note, if you start with a car that is level (or really left and right at equal heights across an axle), perfect corner weights are only a turn or so way.

Hmmm, only way I can achieve "perfect" corner weights would be if I lost about 80 lbs, time for weight watchers.

Hmmm, only way you can achieve 80 lbs weight loss at weight watchers will be by increasing about 79 lbs first.

[Steve Ekstrand]

Its a combo deal....

Weight watchers
5-mile walks
Amputation

[Marshall Grice]

i'd re-level it. I'd put it back on the scales though too. If you can't put it back on the scales then leave it as is.

Interesting side note, if you start with a car that is level (or really left and right at equal heights across an axle), perfect corner weights are only a turn or so way.

Hmmm, only way I can achieve "perfect" corner weights would be if I lost about 80 lbs, time for weight watchers.

LOL, sorry I meant cross weights, which is all you can adjust with spring height adjustments.

[David Palmquist]

i'd re-level it. I'd put it back on the scales though too. If you can't put it back on the scales then leave it as is.

Interesting side note, if you start with a car that is level (or really left and right at equal heights across an axle), perfect corner weights are only a turn or so way.

Marshall -

I realize that YOU would certainly put it back on the scales! You probably would have never taken if off the scales with cross weights off by 0.1%.

However, in the context of my original post, and the fact that my 40 year old car is delightfully unsophisticated, less than perfect corner weights are acceptable as long as the change is negligible. I will of course re-weigh it....some time....down the road....eventually ;)

But, is the theory sound that by lowering the front and rear of the chassis on one side equally, cross weights will be "unaffected"?

[Toby Larsson]

But, is the theory sound that by lowering the front and rear of the chassis on one side equally, cross weights will be "unaffected"?

It will change the weight between front left and right, on an older 911 with no ABS I would try to keep the front corners as equal as possible.

[John Coffey]

But, is the theory sound that by lowering the front and rear of the chassis on one side equally, cross weights will be "unaffected"?

I don't think so.

[John Stimson]

There's negligible weight shift from left to right due to lowering the right side.

David, it will be tough to preserve the cross weights if you can only measure the ride height.

My intuition is that if you can measure the corner heights (ground to a hard point on the chassis) perfectly, then if you end up with the front and rear heights on the side you are notchanging exactly the same as when you started, then you'll still have correct cross balance. But my intuition also tells me that the correct cross balance is going to be extremely sensitive to errors in the corner height measurements, and you're better off using scales, or trying to figure out the ratio between the amounts that the front and rear adjustment screws change the height of the suspension (with no weight).

[Jason Isley BS RX8]

I'm trying to make sure I have my head around this and have not missed an important nuance before touching the car...

I corner balanced the 911 last week and we achieved very favorable weights at all four corners (50.1% cross and front corners within 25lbs). However, when going back to double check everything we ended up with the passenger side about 1/2" higher than the drivers side. DOH!

So this has been bugging me and I was thinking that I could drop the whole passenger side by 1/4"-3/8" and then sleep at night once again. My thinking is that if the front and rear on one side are adjusted equally, there will be little or no net effect to the corner weights. So, is this right, or am I missing something?


BTW, I know the proper solution is to get it back on the scales and do it right, but I just don't have much time these days. Also, the events I run are not fiercely competitive like SCCA. I have been finishing in the top 3 "PAX" positions all year with cross weights at about 43% and a difference of 150lbs on the front corners! Obviously not ideal.

Thanks.

Don't bother, you are going to get whooped on Sunday anyway. }:)

Why not run it as is to see how it feels? You can always change the ride height at the event.

[David Palmquist]

Don't bother, you are going to get whooped on Sunday anyway. }:)

What? Did you get your little Yaris back together?

[Jason Isley BS RX8]

What? Did you get your little Yaris back together?

You could not handle the competition from that, it would only further embarrass you. Good thing the head and cams are not done yet. :unimpressed:

I am going to drive one of those plastic cars with a V8. They seem to work well for putting P cars in their place.

[Mako Koiwai]

But my intuition also tells me that the correct cross balance is going to be extremely sensitive to errors in the corner height measurements

It's interesting to see how the corner balance changes just by altering tire pressures. Try it next time you have a car up on scales.

[Marshall Grice]

But, is the theory sound that by lowering the front and rear of the chassis on one side equally, cross weights will be "unaffected"?

if you're not that concerned about the cross weights, just go set the LF and RF ride heights the same and set the LR and RR ride heights the same. The cross weights will likely be pretty close if your L/R heights are the same across an axle.

[David Palmquist]

Thanks for the input guys. I think I'll leave it for this weekend and see how it works after the changes.


As for Mr. Isley - Put a new set of batteries in your Barbie car and we'll see you Sunday.

[Jason Isley BS RX8]

Thanks for the input guys. I think I'll leave it for this weekend and see how it works after the changes.


As for Mr. Isley - Put a new set of batteries in your Barbie car and we'll see you Sunday.

Glad to see you are not going to mess with the alignment... You need the time to polish your gold chain.

[David Palmquist]

Glad to see you are not going to mess with the alignment... You need the time to polish your gold chain.

You must have me confused with one of your plastic car brethren. You'll never catch me with gold chains - they add weight and cost money that could be spent on better things like sticky tires and fresh brake pads.

[Steve Abbott]

I don't know if your car has swaybars, but you better have them set with zero preload.

Steve A.

[Jason Isley BS RX8]

I don't know if your car has swaybars, but you better have them set with zero preload.

Steve A.

I think he is ok.

[Steve Ekstrand]

I'd check the toe on that.

[Jason Isley BS RX8]

I'd check the toe on that.

I guess with no weight on the front the turn in better with a little extra toe.

[David Palmquist]

Dang it Isley! You've been snooping around again!


The turn-in on this thing is going to be amazing!