Tire Pressure

[Jim Wehr]

What tire pressures are you running for street use? I have 17" wheels. 9 front and 10.5 rear.

[rich grsc]

Good rule of thumb is 1# per 100# of weight

[TMartinLVNV]

25 psi works well with mine with the same tires. Any more and the tires will begin to "crown" from too much pressure without a lot of weight.

[J R Jones]

Armed with wheel and tire dimensions, and weight by axle, I would survey: FFR Jim Schenk, your tire manufacturer tech department, and Tire Rack tech support.

[NAZ]

The size and construction of the tire and weight it supports can require a wide variation of proper pressures. My wife's Mercedes lists 39 PSI front and 45 PSI rear. I run 50 PSI front and 18 PSI rear on my hot rod street tires. There is no one size fits all pressures and when you are dealing with a custom installation you have to work up the pressures that are right for your combo.

What I do is pick a reasonable starting point and find a straight section of highway where I can get up to 75 (easy to do here) for a few miles. Get off at a safe place where I can park and quickly take OB/CTR/IB temps across the tread width. Best to do this with a tire temp probe but an IR gun will work too if you hold it very close. I adjust pressure until I get a reasonably close temp across the tread. You have to consider that tow-in and camber can influence the temp readings on the inside edge (negative camber) and outside edge (tow-in) if these adjustments are more extreme. An even temp across the tread shows that you have an even contact patch.

[GoDadGo]

Good rule of thumb is 1# per 100# of weight

I'm with Rich on this one (1-PSI for every 100-LBS) on my MK-4.

#23-Front (245/45-17) with #21-Rear (285/40-17)

[caesarmascetti]

I'm 22psi all around same size wheels as you

[Old Timer]

Type 65 coupe, with 17"
I run 20-21 PSI front, and 18-20 PSI rear.
Nitto NT555r2

[BEAR-AvHistory]

23F/22R. NITTO 555RX17". You need to do some trial & error. Start with 1psi X100lbs weight. I use an old trick of running a white shoe polish stripe across the tire & up the sidewall. When the stripe wears evenly & does not roll up the side wall its pretty well set.

https://cimg2.ibsrv.net/gimg/acurazine.com-vbulletin/850x566/80-front_5bc52dfbc3a1d0a67d65f223fcf67db9ce98c109.jpg

Paint in on & take a hard back road run on twisty roads & adjust as necessary. Middle wears reduce pressure. Outer wear increase pressure. Balance optimum pressure against the tire rolling under by adding a little more air.

[CraigS]

20-22 works for me w/ 275 and 315s on 9 and 10.5 wheels.

[Rdone585]

I've been using 21F / 19R for track and street for many years with different sets of tires. That's a general rule of thumb and seems to do well. These cars are so light compared to production vehicles that you don't need to take the recommended pressure as the right pressure for our cars.

[Avalanche325]

I'm with Rich on this one (1-PSI for every 100-LBS) on my MK-4.

#23-Front (245/45-17) with #21-Rear (285/40-17)

You're nose heavy? That would be pretty unusual.


Based on chalking on autocross and track days, so this is based on sidewall roll-over for Nitto NT05s. I run 23lbs all the way around.

[Lickity-Split]

I've settled on 22 psi all around with 245/45 tires front, and 315/35 rear, on 17" wheels.

[steno]

22 front and back!

[Rivet49]

Wow, what a great question! And here is why, I inflated my Coyote powered Mark IV with BF Goodrich TA's to 32 psi, what I thought was about right, Wrong. While demonstrating the performance and sound of the car in front of my friend and his two teen age sons. I spun the car two complete 360's and finally got stopped about 10 feet from the curbing in the parking lot. I was embarrassed beyond words, by my performance. The tires did not chirp, squeal or give any warning what so ever, before the total loss of control. I asked a good friend, who sets up race cars for a living, SCCA Formula Ford. He suggested 22 psi, After lowering the pressure, the tires now start to chirp and squeal as they approach the limit of traction. I can drive much quicker with confidence now, knowing that the tires will give warning at the limit of traction. So, you guys recommending the one pound per 100 lb chassis weight are right on!!

[Rivet49]

That is a great idea. It's all about the tire patch, what a great way to check chassis set up and tire pressure. Very cool....CE

[AdamIsAdam]

Off-roaders use chalk test. Go to a flat surface like a level parking lot. Make a chalk stripe across the tread as pictured above in the shoe polish post. Then move the car forward a rotation or two of the tire. Now check the chalk for wear. Adjust tire pressure and repeat until chalk wears off evenly.

[GoDadGo]

Off-roaders use chalk test. Go to a flat surface like a level parking lot. Make a chalk stripe across the tread as pictured above in the shoe polish post. Then move the car forward a rotation or two of the tire. Now check the chalk for wear. Adjust tire pressure and repeat until chalk wears off evenly.

After that remember to do a little Burnout on very flat concrete to verify your work.
The entrance to my workshop has now been properly signed.
Just understand that this was a less than safe practice.

[BEAR-AvHistory]

After that remember to do a little Burnout on very flat concrete to verify your work.
The entrance to my workshop has now been properly signed.
Just understand that this was a less than safe practice.

There is a really nice graduation 11 in a near by big box parking lot.

[wareaglescott]

Armed with wheel and tire dimensions, and weight by axle, I would survey: FFR Jim Schenk, your tire manufacturer tech department, and Tire Rack tech support.

I wouldn't feel to good about tire rack tech support in this case. Anything to far away from the standard and they are less equipped to answer than the people here in my opinion.
Would be interesting to hear what Jim at FFR recommends!

[NAZ]

I know many of y'all relate to autocross so here's one of many informative reads on setting tire pressures, this one is from NASA but you should really research other sources as well. Some folks really get into the science of tire air pressure and the affect on traction. Remember, what you're trying to achieve with air pressure and realize that you set your temps "cold" (at ambient temp) and the pressure changes ~.8 PSI for each 10F change in temp (also altitude will have an affect but you can do your own research if interested).

https://nasaspeed.news/tech/wheels-tires/setting-air-pressures-for-hpde/

[Avalanche325]

It's all about the tire patch,......

Well, sort of. Sidewall rollover is also a consideration.