New S14 bumpsteer graphs

[Epstein]

I hinted at this in the traction arm thread. Here are my latest findings on rear bumpsteer on the S14. I learned a lot doing my first set of bumpsteer measurements. Carrying that forward, I have 100% confidence in these results.

During the testing it occured to me that the traction rod isn't the only thing that could affect bumpsteer. The RUCA also should have some affect as well. I'm running low rear camber, so I took another set of measurements with the RUCA shortened 1/4" to simulate a setup with more negative camber.

While getting the setup sorted with the Maximum Motorsports gauge, I ran into repeatability issues. Under compression, the car was lifting off the jackstands, and I was having to force the assembly down to measure droop. This was already with the coilover removed and the swaybar disconnected. Loosening all the joints (except alignment adjusters) fixed all of this, and the measurements were repeatable.

Traction rod lengths: 8.00", 8.25", 8.50"
RUCA lengths: 12.25" 12.50"


PM me with your email, and I'll send you the .xls file.

[Def]

Professional BadAss stuff right here.

PM'd for the file since this is all the info of stuff I've wanted to do on my own car.

BTW - you don't have sphericals in the back of your new car do you? Should have another GB coming up for them if you're interested.

[Longfellow]

He doesn't have any spherical bearings on the entire car.

[Equinox]

How much camber were you running with each camber arm length?

Thanks alot for the info. The graphs look very similar to what I measured when I did mine. Shows I was on the right track.

[Epstein]

At a RUCA length of 12.50, I was running 1.75* camber. I'm estimating that a 12.25" RUCA would put you in the 2.25* area. I know that the stock RUCA is 12.00" and at the heights used above, would result in 2.75-3.0* of camber.

I didn't do the tests with a stock RUCA length because I don't know anyone who both: cares about bumpsteer, and runs stock RUCAs.

I'm glad that our numbers are similar!

By the way, numbers that are given in 1/4's of an inch are rough, measured with a tape. Numbers given in thousands are off of a dial caliper.

[logr]

Very cool, thanks for going to the trouble. What is the stock length of the arms?

edit; I see you just posted one and I have the other one somewhere I can measure, thanks.

[Epstein]

Professional BadAss stuff right here.

PM'd for the file since this is all the info of stuff I've wanted to do on my own car.

BTW - you don't have sphericals in the back of your new car do you? Should have another GB coming up for them if you're interested.

hahaha, I haven't heard PBA in a looong time.

Right now I'm running all rubber/poly parts. I kinda want sphericals based on my positive experience last time, but I also kinda want to keep it the way it is, since it drives like a dream. I'll probably just leave it, since this is just a fun street car. I do have SPL tie rod ends, but I don't think that counts!

[Epstein]

Very cool, thanks for going to the trouble. What is the stock length of the arms?

edit; I see you just posted one and I have the other one somewhere I can measure, thanks.

RUCA= 12"
Traction arm = 8 1/4"

[turtl631]

Hm. My take on this is that the back tends to work better with a little less camber, probably around your 12.5" RUCA length measurement. So the 8.5" traction rod length is pretty ideal for that geometry, with a little bit of toe out under compression that actually normalizes as you compress past 1". That should be comfortable hitting midcorner bumps...I like it.

Strong work

[jmauld]

So, you're saying with no spring, you were getting enough binding in the bushings to lift the car?

If so, is there any chance you were able to isolate that to a single bushing? That info would be invaluable!

[Def]

The stock bushings act like an undamped spring with travel. Twisting that little bushing by even a few degrees takes a lot of force. Multiply that by 3 for each side(plus 2 rlca bushings) and it's very significant. They do bind some as well due to their unwillingness to axially deflect as well.

[Epstein]

Yes. With the car on 4 jackstands, the jack under the balljoint, and the coilover/sway removed, the car would start to lift past 2.5" on some configurations. And it's more than teetering, since I've got the front jackstands way way forward by the toe hooks. I've done it before with sphericals. The bind forces are in the directions of the arms. Basically, the traction arm is a lot shorter than the RUCA and toe arms. It starts pulling in sooner, which fights the other arms that aren't at such a radical angle. Once the bushings are fully loaded, the car starts coming up.

But, lets be honest here. 2.5" is a lot of travel under compression. That'd put my fender half way up my sidewall. Not to mention the weight transfer needed to accomplish this with moderate spring rates.

[Epstein]

The stock bushings act like an undamped spring with travel. Twisting that little bushing by even a few degrees takes a lot of force. Multiply that by 3 for each side(plus 2 rlca bushings) and it's very significant. They do bind some as well due to their unwillingness to axially deflect as well.

I actually loosened the bolts to prevent the "twist" bind. There is axial bind, but what was picking up the car was in-out bind. That is, in it's intended direction.

[CodyAce]

Well this is certainly interesting data, but I'd like to verify what Im' thinking, as I could certainly be way off.



Lets assume car has 12.25 RUCA length, and the traction arm at 8.0 inches long, you'd essentially have your innside wheel (under compression) in a 'toe out' situation' and your outside (drooping) in a 'toe in' situation correct? With that assumption made, would this lead to a very 'tail happy/loose' rear, maybe best for drifting? And then when compared to the traction arm at 8.25, you'd have an instance of it acting similarly, but not so dastic correct?



I know this may sound very simple of me asking this question, but I'd rather understand what is prefered.

[SoSideways]

............

Drift cars actually could use as much grip as possible, so the "tail happy" bit is not true for drift cars.

Maybe for your average POS broke ass 240 owners' "drift cars", but not any of the more serious drift cars have a suspension setup that is more closer to an all out grip setup than you might think.