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Old 02-16-2010, 08:49 PM
Epstein Epstein is offline
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Default New S14 bumpsteer graphs

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.
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Old 02-16-2010, 09:21 PM
Def Def is offline
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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.
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Old 02-16-2010, 11:12 PM
Longfellow Longfellow is offline
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He doesn't have any spherical bearings on the entire car.
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Old 02-17-2010, 06:36 AM
Equinox Equinox is offline
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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.
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Old 02-17-2010, 08:23 AM
Epstein Epstein is offline
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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.
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Old 02-17-2010, 08:24 AM
logr logr is offline
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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.
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Old 02-17-2010, 08:32 AM
Epstein Epstein is offline
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Quote:
Originally Posted by Def View Post
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!
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Old 02-17-2010, 08:33 AM
Epstein Epstein is offline
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Quote:
Originally Posted by logr View Post
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"
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Old 02-17-2010, 10:07 AM
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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
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Old 02-17-2010, 02:35 PM
jmauld jmauld is offline
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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!
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