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Ludicrous speed! GO!
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So I recently bought some 5 spokes to put on the Supra. The plan was to reuse the tires that were already on the sawblades cause they still had good tread left, but I decided to go all out and bought brand new tires as well.

Thus began my journey to find the correct tire pressure for them that would give me the best feel for the road. My search began on SM and all I could find was this:

http://www.supramania.com/forums/sho...=tire+pressure

It didn't give me numbers to work with, but told me what to expect when adjusting tire pressures. Since the Supra likes to oversteer somewhat going into a turn, I would want the rear to have a tad bit more pressure to counter it.

Moving on, I found this information on SF, which is actually quite good:

http://www.supraforums.com/forum/sho...d.php?t=164205

The most significant piece of information I could find was post #24 which references BFGoodrich's site here: http://www.bfgoodrichtires.com/bfgap...rget=expe rts

Post #35 also had a tad bit of useful information concerning max load and tire pressures required for that load.

According to the BFGoodrich formula used in post #24:

Stock Mk3 Supra Turbo Targa AT weight: 3640 lbs

3640 lbs / 100 = 36.4 lbs
Add 2 psi to heavier end = 38.4 lbs front/36.4 lbs rear
Add 2 psi all around for stock suspension/alignment = 40.4 lbs front/38.4 lbs rear

So the numbers are:
Modified suspension/alignment: 38.4 lbs front/36.4 lbs rear
Stock suspension/alignment: 40.4 lbs front/38.4 lbs rear

Just as I thought my quest was over I find this piece of information on tirerack (for V-speed rated tires): http://www.tirerack.com/tires/tirete...adj_Vspeed.jsp

It recommends that I should adjust tire pressures according to high speed driving (which is partly what the Supra is built for, and what I'm building it towards). Toyota recommends 32 lbs F/R. Adjusting for high speeds that my Supra is currently capable of I, get 37 lbs F/R. To counter the oversteer I'd probably add 2 lbs to the rear and get 37 lbs front/39 lbs rear.

So the numbers that I am looking at now are:

Toyota recommends stock: 32lbs F/R

BFGoodrich formula (modified suspension/alignment): 38.4 lbs front/36.4 lbs rear

BFGoodrich formula (stock suspension/alignment): 40.4 lbs front/38.4 lbs rear

Tire Rack high speed adjustment: 37 lbs F/R

Tire Rack high speed adjustment + counteract oversteer: 37 lbs front/39 lbs rear

I'm in quite a pickle now. Tire Rack sells tires, and they have some good information backed by engineers and race car drivers. BFGoodrich is the manufacturer of some fucking good tires and they also have engineers and race car drivers. Toyota, the maker of our much beloved Supra (all generations) and some fucking great engines (7m, 1j, 2j, 1uz), also have engineers and race car drivers to back them up.

Who the hell do I listen to? I just want a good tire pressure that will give all around performance. The drive to work is spirited and through some winding roads. I also take it out on the freeway where I will once in a while give it boost.
 

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Formerly Nosechunks
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1,071 Posts
well u would want less pressure in the back to counteract over steer, the more pressure in a tire the less footprint (grip) but better stability (less sidewall flex = less heat generation with is better for highway or high speed driving). just run 32-35, u wont notice anything else.
 

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487 Posts
Nice info. So with this info my civic which weigh around 2200 lbs should have tire pressure at 22psi.
 

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nosechunks said:
well u would want less pressure in the back to counteract over steer, the more pressure in a tire the less footprint (grip) but better stability (less sidewall flex = less heat generation with is better for highway or high speed driving). just run 32-35, u wont notice anything else.
I agree. I generally follow the car manu's guidelines though I usually keep the fronts a couple pnds higher. If I'm going on a long trip, I air them all up a few more pnds to save on gas and if I'm dragging, I overinflate the fronts and underinflate the rears. Remember to try to check your tires pressure when they've been run awhile and are plenty warmed up for obvious reasons. Remember, the sidewall reads the MAXIMUM pressure the tire should be aired up to. Not the normal running pressure.
I've been down this road, too and I haven't found anything definitive on tire pressures, either. So until then, this is how I'll do it. There are so many variables...
 

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Formerly Nosechunks
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1,071 Posts
idk i think u wont notice any diffrence driving around anywhere from 28-38psi. maye if u were REALLY REALLY driving the car ud notice the lower pressure by sluggish steering feedback, or drag racing and launched with 38 then 28 ud notice the traction increase, unless ur on the track anywhere from 30-36 is good.
 
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