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Tire Temps- pressures (RA1) / Wheel Offset Question

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#1
Justin Baltrucki

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Couple questions about tires/wheels for my 1.6L SSM.

I bought the car this past winter - long term NE region SSM race car with a history of regional podium finishes.
I went to buy another set of wheels for rains, and I noticed all mine are all 15x7 ET 38 offsett. (koseis)
Car has OE studs and no wheel spacers.

I notice many people on here with 25mm offsett wheels.
My math says my track is 26mm narrow compared to everyone else?
Am I missing something, or should I be running some long studs and 13mm monster spacers to get the track wider?


Second question about tires.
I have always set tire pressures by using a pyrometer.
After a hot session I get a crew member to read times immediately.
I look at inside middle outside.
ideal pressure thumb rule says = (outside + inside)/2 = inside temperature.

Following this rule I always come up with a lower "ideal" pressure than I read here on the forum.
My ideal pressure vares from corner to corner depending on the track, but its typically 34 - 35.5 psi.

I have never seen ideal as high as the 38 - 40 people suggest on here.
Even 37 psi will show temps 8 degrees too high in the center of the tire.

Car is SSM with 2.0 front 2.5 rear camber, caster maxed in the front - toe is a smidge ~ 1mm out in the front and zero rear toe.
Front/rear bars max setting.

Can anyone explain why I should be listening to the forums and not my pyrometer??
I have tried higher 27 - 28 psi and didn't notice a huge difference in lap times, if anything I think it understeered more at the higher pressures.
The higher speed the track is the lower the pressures want to be based on the pyrometer temps.

My tire wear has been fantastic with these RA1's - very even wear - I did multiple endurance races on the same set of tires with very little fall off in lap times. Tires are all shaved 3 to 4/32 at beginning of life.


Thanks in advance

#2
Johnny D

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Use the 13 and long studs on your 38 offset unless you want to get a set or 2 or 25's.

YMMV on temps. Keep testing until you hit the sweet spot per track.
Camber seems low in front, but I'm not the 1.6 guy, maybe have bent Lower control arms.
Tire life, not sure if that's good or your just slower than others which gives you long tire life.
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#3
William Bonsell

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Definitely want 25 or 30 offsets with the help of extended studs and spacers. Most racers I know are running either 25 or 30 offset wheels (5 mm spacer allowed on the 30's). I find on most of the tracks I run, that the 35-36 hot pressures are better for me. I have been front cambered challenged for two years. Finally replaced some parts and now have 3.4 in the front. Car handles much better with 3.4 front - 3.4 rear - 3.5 caster - and 0 toe all around. But that's me, with my car. Just find what you are comfortable with and compare lap times. With the minimal front camber you have, you should be wearing the outside shoulders more than the inside, unless you are simply not pushing the car.


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#4
davew

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I would suggest either long studs with spacers or some new wheels. The difference between 25 and 30mm offset is not noticable accept to a very few drivers. 25 to 38 mm is noticable to most people.

Your tire temp theory is wrong. The idea is to have flat temps accross the tire. 130-160-190 will match your formula, but is just way off on allignment. You definately need more camber and soften the bars. I know nothing about you or your driving style except what you wrote above. It sounds like you are not pushing the car at all. Multiple endurance races on 3-4/32 shaves and no fall of in lap times tells me the car is being under utilized.

Trying to interprite tire temps on a tire as narrow as the RA1 is difficult. And different tracks will give drasticly different temps. i.e. Homestead uses the right tires right up to and including the pit entrance. The left tires are along for the ride. Road America has 1/2 of a mile of straightaway between the last turn and the pit lane. And even more distance since the last time the right side tires where used.

Also, tire gauges may vary by 3-4 psi. You should compare yours to several other gauges

Dave
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#5
Jim Drago

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Following this rule I always come up with a lower "ideal" pressure than I read here on the forum.
My ideal pressure vares from corner to corner depending on the track, but its typically 34 - 35.5 psi.


I don't know that I subscribe to your pyrometer theory, but unlike most, my car is usually as good or better than most on handling and my target numbers are in line with yours, never end up at 38 unless I made a mistake. I shoot for 35 PSI hot on all four tires with the RA1's

As far as the forums.. You can get some of the best and some of the worst information.. You need to sift. :) There are a some that give advice that are super fast, but don't know a darn thing about the car.. There are some who are self proclaimed experts that sound like they know what they are talking about that can't turn a laps within 5 seconds of the leader... Be careful who you listen too and do you own testing regardless of what anyone tells you. Lots try to help and do more harm then good. This does not refer to anyone mentioned above, just general knowledge.
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#6
JP3

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Lots of good advice esp about the forums . Personally never ran frt bar full stiff on front of 1.6 car ,keep taking temps adjust car to your driving style ,dont worry about what the forums say :D
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#7
Justin Baltrucki

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Thanks for the feedback. Looks like 13mm spacers and long studs are in order for 2012
I have 3 sets of wheels now and don't want to change them all out for 25 offset wheels.
Any advice on where to buy 13mm spacers?

In regards to camber - SSM (showroom spec miata) in new england region limits car prep more than SM.
Max camber is set to 2.0 F 2.5 rear so I can't play with alignment.
A bent set of upper arms and fresh LCA's and I can get -3.5 all day long up front but it's not allowed in SSM.

For tire wear I have been rotating through 2 sets of tires to even out the wear at 4 different tracks so the wear has been pretty even.
The fronts do eat the outer edge more, but I am impressed compared to a V710 or a hoosier they have been very consistent with grip and they just wear like iron.

The car tends to oversteer in the lower speed corners and understeer at higher speeds which is faster for me.
so I have left the bars alone except for the rain where I disconnect the rear one completely.

I just wanted to clarify the tire temps because I never seem to hit the 38 - 40 I have seen quoted on here.
With camber fixed at max the only tool to even out the temps is pressures.
The example with 130,160,190 is to me a perfect pressure for the given camber.
I can play with pressure in a matter of seconds but I can't adjust camber on the fly without fixing toe changes.
I was wondering if there is some lower rolling resistance or perceived gearing advantage people are aiming for with the higher pressures.

It seems I am not far off with my 34 - 35.5 hot I typically see with temperature method.


Thanks again.

#8
davew

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JIm, I am only 2 seconds off the fast guys. :spin:

Justin, you do not need bent control arms to get 3 degrees camber.

Understeer in high speed sounds like too stiff a front bar. Also sounds scary, but I am 2 seconds slow :noidea:

Oversteer in low speeds sounds like too stiff a rear bar. Sounds fun but slow.

Dave

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#9
Jim Drago

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JIm, I am only 2 seconds off the fast guys. :spin:

Justin, you do not need bent control arms to get 3 degrees camber.

Understeer in high speed sounds like too stiff a front bar. Also sounds scary, but I am 2 seconds slow :noidea:

Oversteer in low speeds sounds like too stiff a rear bar. Sounds fun but slow.

Dave


You know I wasnt referring to you.. :crying2:

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#10
Justin Baltrucki

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JIm, I am only 2 seconds off the fast guys. :spin:

Justin, you do not need bent control arms to get 3 degrees camber.

I have had NA miatas without bent parts lowered very low and never saw more than 2.5 degrees.
My autocross miata I couldn't get more than -1.8 and -2 degrees up front with the car very low. I put in some $80 delrin eccentric bushings in the upper arms and can get 4+ if desired.
I don't see how you can get -3.5+ without something being bent out of spec, but I have only worked on 3 different NA's so far.


Understeer in high speed sounds like too stiff a front bar. Also sounds scary, but I am 2 seconds slow
:noidea:
Well understeer is safer than oversteer at high speed for me, it's easier to drive at the limit than having the rear end step out.
I would agree - maybe soften the front bar, but since it oversteers at lower speed corners when getting on throttle I figured less front bar would just make the low speed oversteer worse.

Oversteer in low speeds sounds like too stiff a rear bar. Sounds fun but slow.

It's probably all going to change with the hoosiers next year so im not going to get too worried.
I will have to figure out pressures all over again with the hoosiers.
Based on my experience with an ITB car and hoosiers they needed lower pressures than RA1's to have a good temperature distribution.

#11
Glenn

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Has anyone confirmed that 25mm spacing will work with the Hoosiers?

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#12
Keith Novak

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Has anyone confirmed that 25mm spacing will work with the Hoosiers?


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