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PostPosted: December 12, 2015, 10:51 pm 
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Location: White Rock, BC, Canada
Hey guys, a little OT here but may help a Locost.

I autoX my daily driver Toyota Yaris. I run in H-Stock with R-comps (all-seasons when too cold), soft springs and a huge amount of body roll. In corners I often only have 3" of contact on the inside front tire (which is super easy to spin). In an attempt to reduce the roll and increase the contact patch, I tried a stiffer front bar. My question is: Is there any way to know whether you should reduce tire pressures, or negative camber to get more rubber down in corner/braking? I typically run 50psi front to reduce the edge wear, 40 in rear to get the balance right. I was able to drop around 8psi in the front, and keep the same edge wear. Like this, the car's balance/braking/accel is about the same as before the swaybar, but much faster through slaloms etc. I run -2.8° camber, and definitely lose a bit of traction on braking/accel due to it. I didn't notice any loss of traction on braking when I was only -2° so if I could remove a bit of the camber, I might see gains as well.

I can't think of any viable way to test, other than on-track timing/testing. Tire temps would help maximize each choice (less PSI or less neg camber), but not tell you which was overall faster. Any input would be great.

Cheers.
Cory

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PostPosted: December 12, 2015, 10:58 pm 
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Some pics of the car before installing the larger F swaybar. You can see why I wanted to try something to get more rubber on the asphalt.

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PostPosted: December 13, 2015, 8:25 am 
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It sounds like you need to determine the maximum amount of dynamic roll and degree of steering input, then recreate that statically to check the camber and ackermann. Imho, ideally it would be the 75% of the peaks averaged from a data logger.

As an alternative to time-critical tire temps, you could make a baseline tread depth, checking all over for the average, then make runs, let them completely cool, then check tread depth all over again to determine where the tire is getting the most heat based on the average.

I agree on the soft springs and thick bars, but if the suspension has poor camber gain, you may not want it to move much at all, in which case it won't matter so much how you get there.

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PostPosted: December 14, 2015, 3:56 pm 
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I'm kind of in a weird spot with this car. I'm staying in Stock class because then I can't waste money on it... and instead spend it on faster things :mrgreen: . I also get cheap NT01s so I can't run STF where more mods are allowed.

I've basically maxed out what I can do in Stock class now. It just comes down to whether the front bar is faster, and whether I should reduce tire pressure or neg camber. I think it's going to come down to doing on-track testing. Preferably with someone taking video of the tires.

Cheers.

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PostPosted: March 23, 2016, 10:48 pm 
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Just an update:

I dropped camber down a little to -2.5°, and dropped my tire pressures. Car is definitely faster, and probably about as well balanced as it's going to get in Stock Class. For once, ignoring what is "correct" actually paid off! :mrgreen: Cons are I see a bit more understeer at times, but only in non-autoX scenarios (turning w/o trasfering the weight to front).

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PostPosted: March 24, 2016, 3:54 am 
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One small suggestion you might try. Keep a firm but lower pressure in front (35 ish) and go with at least 10 lbs higher in the rear. Although my experience is in STF w/ a civic si, that variation from common wisdom did wonders to tame understeer and increase rotation. :drive: I've never seen a Yaris on the track but it sounds like fun!


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PostPosted: March 24, 2016, 7:54 pm 
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Location: Kamloops, BC, Canada
I used to autocross front wheel drive cars and would run whatever pressure in the front that got me the best traction without rolling the tire over onto the sidewall, then crank the rear pressure higher to get the amount of rotation I wanted. A lot of times I was up around 50 psi in the rears. Had to be careful not to cut throttle mid corner or in a slalom though.
Kristian

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PostPosted: March 24, 2016, 10:06 pm 
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Thanks for the suggestions. The way I do my tire pressures is to mark tires and adjust until I am using all of the tread (with no sidewall) on F&R. Then adjust the rear to get the balance I want (it understeers badly if left there). Because I was running 50psi+ up front to keep from savaging my sidewalls, I couldn't run higher in the rear. I'm currently running 46/36 and probably need to up the fronts 2psi to save the sidewalls.

Currently the tail will come around fairly well, and I can make it more aggressive (to the point of uncontrollable) by dropping the rear pressures. So long as you have the car loaded with the weight transferred to front in sweepers, it will do well. It's biggest problem would be a sweeper where you were unable to get the weight to front.... then it would plow pretty hard.

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