What Tire Pressure do you run?

What tire pressure do you run? Do you change it depending on type/size of tire? or style of driving, i.e. street vs track/autocross? Weight of vehicle?

Asking from a handling perspective more than drag racing, there is a bunch of threads on that already.

Curious to see the responses but I suspect the right answer for each car will vary quite drastically between setups, intended use, driving styles, tire compounds, and tire load ratings.

For me, I run 34 front/ 32 rear, just a spirited street car, no competition.

When I was autocrossing a stock '11 Scion tC, I believe I had 38 psi in the front and 34 psi in the back. It will vary drastically for every car. The best way to know is to set it to like 34 psi on all 4 corners and go up and down from there.

It really depends. If you have some grocery getter with tall side walls upping the tire pressure can help some. But it'll still be a pig and always will.

With short sidewall tires, I tend to use the same method as the drag racers but on all four corners. Drive thru a shallow puddle and note the tracks left. narrow, center stripe lower pressure a bit. no center stripe up the pressure. track width pretty much matches the tread that's where you start. If the rear feels wiggly you're too low, if the front feels mushy your too low.

Get a different set of tire, do it all over again.

Get some shoe polish and stripe it from the sidewall down onto the tread. Adjust pressures until when you run hard you wear it evenly off the tread but not off the sidewall. I've always done it this way on my autoX and track cars and its worked really well. For a generic recommendation I usually end up at about 42psi front and 38psi rear for lower profile tires on heavyish front engine rear wheel drive cars.

Obviously for significant street miles you might want to go with a lower pressure and then just increase it for the track/autoX. This is what I do and I generally run 32 to 36 on the street depending on the car and tire.

-Jon

Results vary, but I start with 34psi cold, with a target of 41psi hot..

..which I verify and tweak each track day by measuring and comparing the temperature of the tire surface at three places across the width the tire: Inside, Center and Outside.
I make a little chart each time for each tire.
You can use an inexpensive IR 'laser' temperature reader, or an expensive needle gauge.
The goal is an even temperature across the width of each tire.
Hotter in center is too high pressure.
Cooler in center is too low pressure.

For the drive home I go with car Mfr's recommendations.

Good stuff, I figured it would vary a lot, I never thought about different psi up front vs. back (other than for drag racing). I typically run 32-34 just based on modern factory recommendations seem to fall in that range. I am currently running 245/forgot/18's on front and 295/35/18's on back of my Challenger. I am running a drag biased suspension right now but am loving the modern wheel /tire improvements.

The temp gun is a great idea.

That's what I used to do when I did some autocross many moons ago. Although I was not watching the tread as much as the sidewall. On a FWD '85 Duster, I'd end up in the 40s up front. Didn't have to go near that high with the B-body.

So many variables... and the final PSI can change with different vehicles, tires/wheels (different tires of same size can run different psi), daytime temperatures, weather conditions ... the main decision is per event... street, highway, pylon autocross, hi-speed lapping (HSAX/HPDE). For performance driving (AX.HSAX, etc)... always increase a little vs daily driving. Where the heavier weight is (front engine)... run 2-4-6 psi higher than rear. Example street/hwy... front 34, rear 32..... AX/HSAX front 40, rear 36.. (some cars/tires etc... f 45, r 40, etc). You can also dial in understeer/oversteer/nuetrality.. experience and multiple events will tell you that.l

Look at TIRE RACK web site as they offer some recommendations.

For competition events, the chalk or shoe polish is a good practice, as well as temp measurements.

NOTE: www.mcscc.org MIDWESTERN COUNCIL OF SPORTS CAR CLUBS will have 5 season HSAX events this year 2019... Blackhawk Farms Raceway (HSAX School April April 27, HSAX race #1 May 27, HSAX race #2 July 5, HSAX race #3 July 6 (that's my club's race weekend!.. www.nsscc.org hope to see you there!). Joliet Autobahn HSAX race #4 July 20. BHF HSAX race #5 August 24. All these events are on www.motorsportreg.com for pre-registration (cost savings to pre-reg!). Also, all these events are HPDE (lapping sessions) morning and competition HSAX afternoon.

depends on the tire but bfg's 32 all day long!!!

Definitely going to try to make what I can

On my road coarse racecar, 255/40-17 tires, I was at 26psi with even temps across the tread. My street cars, 35psi 245/60-15 on 15X7 front, 20psi 275/60-15 on 15X8 rear to get the wear pattern even, and the rears still wear in the middle.

What Mitch and I are saying is, if you are in competition, you can't be satisfied with a "Oh, it's AX day and I'll run 4psi more than Mfr's recommendation... or "it's Track Day so I'll run 6psi more". That's just pure guessing.

For competition - You want as even temperatures as possible because this implies your tires are contacting the pavement with equal traction. Uneven temperatures means the hotter areas of your tires are working harder than the cooler, and you're not getting full grip from the cooler parts of your tires. My temps range from 102F to 125F measured in the 'valley' of each tire's tread (which is a good location to measure because the 'valley' holds a temperature better than the contact surface which is affected by the pavement your car drove over after coming off the track). Either way, map your temp measurements from the same spots consistently each time you come off the track. I'm usually able to get within 5F, and on a good day within a 2F temperature spread, and I know from years of tracking my ideal temps are always near 41psi HOT right off the track, plus or minus 2psi.

So, try a baseline pressure, get out on the track, and AS SOON AS PRACTICAL when you come off the track, make a chart of the tire temperatures across the face of each tire and take your tires pressures. Gather the data first and read it afterwards. You want a "map" of your tires' temperatures and pressures so you can read what the data tells you to do about it.

What do you read?
Something like 105-118-109 = High in the middle = Needs less pressure.
Something like 120-111-122 = Low in the middle = Needs more pressure.
Try 2-3psi increments.

After you're confident mapping and adjusting tire temperatures, you can look at side to side temperatures to read what your alignment needs to be:

Something like 105-109-114 = Clearly hot to one side = Adjust camber to put more weight on the cooler temperature.
With a car aligned perfectly "symmetrically" driving on a left turning track, you'll often find the right side temperatures to be hot on the tires. So reduce camber on the driver's side tires and increase camber on the passenger side.

What you want out of it will dictate how much time and effort you put into tire pressures.

If you are just starting out, I'm guessing you could gain 0.2 - 0.5 seconds per 60 seconds of lap time.
Tweaking alignment will bring gains too, but means scheduling with a shop or bringing dedicated equipment, which is another level.
Cheers,
- Art

For our average enthusiast, the chalk method is probably adequate. If you are actually pushing limits at an autocross or strip, you really want to look at the tire wear to see what it wants. You can immediately see the abrasion that competition puts on a tread and adjust accordingly. If you want to get a bit more serious, then the temp method not only will tell you pressure needs, but how effective your spring rates are from corner to corner, as well as what your weight distribution demands for pressures.

As low as I can get away with on the backs and +4 psig on the front. On BF's it's 32 and 36 for my E-bodies.

The paint/drive through a puddle method are good for starting points at 2 mph, but a tire changes shape when you are doing 50 mph.

Bias ply absolutely change shape at speed and temp. Radials, not so much. They are very stable in their dimensions. Do radials flex around some, sure. This is why they tolerate a wider range of angles before showing abnormal wear but that is compliance, not deformation. Which is why more serious performance will require temp checks to see what do teh tires need.

Old trick in my oval track bias ply days was to pump up a tire to about 60 psi and leave it in the sun for a week. This produced a larger diameter tire that we used on outside positions. When we changed over to radials that trick no longer worked. We could not get the radials to stretch the same way that bias ply did. Flat out didn't work.