Let's talk tire pressure :)

[oldgeezer]

Interesting. I was a bit concerned about my tire pressure, so I bought a gauge at an auto parts store. I set the pressure at 32 cold per the manual, and checked the dash read-out. Yep, 32! But then I had the car serviced, including a tire rotation, and got it back with 35!

So I am keeping it at 35 for now, and will check the wear when I need new tires. Can't wait to see how the tires look!

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[F0J]

+1 TPMS is relatively accurate (once you've driven a few minutes) as per my Intercomp 360045 - So if you want to know if your 2$ pressure gauge is accurate, measure the pressure after driving a while and compare to the TPMS readout.

But again, "it's much more complicated" than generally thought. Tires don't have an optimal pressure, they have an optimal temperature. The best way, IMO, to get to know your tires is to play with the pressures. I found the non-PP all seasons got slippery when the pressure approached 40PSI. After driving on them hard for a summer I noticed the fronts needed more pressure as the center of the tires had 2/32nds more rubber. Ford's recommendation of 32PSI all around is an oversimplification that assumes you'll rotate your tires (which is generally true).

(The rear-right tire also had 1/32nds more tire on the inside which I haven't figured out yet but it could be an alignment issue - and the outside fronts were used up real hard == our cars don't have enough camber)

Consider too that Ford would have reason to recommend that you over-inflate your tires because at the cost of grip, more pressure usually means better mileage (as there's less surface of the tire gripping to the road). More pressure also means premature wear == buying more tires.

 

[jasonstang]

Personally I run my tires between 32 to 34 psi for just a bit more stiffness when cornering.

 

[jcl78]

I run all PP tires pressure at 32PSI cold, reads 35PSI when hot in the cluster (it has been in the mid 90's here for reference). When I bought the car, the dealership had the rears at 32 and the fronts at 40 COLD. Yikes, I knew something was off as they felt like overfilled balloons on the test drive, steering response was way off.

 

[Norm Peterson]

I can't imagine ever thinking about this stuff if I didn't have the cool gauge that shows the tire pressure on each tire at any given moment.
Crazy right :headbonk:

Anywho, my tires read 30 -31 in the morning at 30-40 degrees.
If I get in my car in the afternoon when it's warmer at 60 degrees the tires might read 31-32

Drive for 20 -25 minutes and the pressure is up to 34-35ish

Any Thoughts ?

Roughly speaking, every 10°F temperature change corresponds to a 1 psi change in inflation pressure - once the air inside the tire has had enough time to reach the same temperature as the ambient air outside it. A two to four psi increase just from normal driving is reasonable. Track driving (road course) causes greater inflation pressure increases.

Wondering if I should lower tire pressure a little more or :shrug:

No. The best you can reasonably do is check/set inflation pressures without driving the car at some "good average temperature" for the time of year, and just let inflation pressures vary between a psi or so under to a similar amount over. Just like we always did when we didn't have near-real-time inflation pressure readouts (and never worried about exact psi's).


Norm

 

[BlackandBlue]

I will add an observation to this conversation.

The PS4s seem very sensitive to pressure. At 33 hot (30 cold) I notice marks on the lower edges of the front sidewalk. I run them at 32 cold and get 35 front and 34 rear hot. This seems to be the sweet spot for me.

I used an expensive rotary gauge and assumed for the longest the Tpms was wrong. It read about 3 psi high and (35 cold 37-38 hot) on the Tpms. The car would feel very unsettle and loved to understeer and oversteer. The regripping was also compromised.

I find the PS4s to be an awesome tire but the hard outer edge and the softer inter tire rubber make pressure extremely important. Also the traction coefficient at 80 degrees vs 120 degree is huge.

 

[Norm Peterson]

The most moisture you'll ever have in compressed air is when you take it directly from the compressor. If you take it from a cool storage tank the %MC will be minuscule.

This ↑↑↑

Even the little "pancake" compressors spit water out when you open the valve when you're done. That would be moisture that didn't make it into your car's tires, moisture that condensed out before the air it came in with was forced into the tires.

One has to believe that the mfrs planned on some amount of inflation pressure increase when dialing in the car's handling and ABS/stability control calibrations. Because that's the actual driving condition.

So for a car driven on the track, cold pressures are basically irrelevant for any more than as a rough guideline of where to start the day out. Which means moisture content is less important once you start bleeding air out at the end of each session as necessary to meet your "hot pressure" target(s). Just don't forget to air the tires back up for whatever street driving follows.


Norm

 

[2017GBGTPP]

I will add an observation to this conversation.

The PS4s seem very sensitive to pressure. At 33 hot (30 cold) I notice marks on the lower edges of the front sidewalk. I run them at 32 cold and get 35 front and 34 rear hot. This seems to be the sweet spot for me.

I used an expensive rotary gauge and assumed for the longest the Tpms was wrong. It read about 3 psi high and (35 cold 37-38 hot) on the Tpms. The car would feel very unsettle and loved to understeer and oversteer. The regripping was also compromised.

I find the PS4s to be an awesome tire but the hard outer edge and the softer inter tire rubber make pressure extremely important. Also the traction coefficient at 80 degrees vs 120 degree is huge.

I have noticed the same. In cold weather I actually ran a higher pressure (34 cold) because the tires felt too squishy at 32. Now that it's summer I have actually dropped pressure to 32 cold to keep them from being overinflated and they feel fine because the heat here quickly pushes the pressure up to 35.

It seems to me that 35-36 is the optimum operating pressure for these tires.

 

[Flyhalf]

using the MEME of Terry...

 

[Notagain]

Anyone else running Nitto NT05s?

I just got a set of 20x10s rear with some 305s debating on playing with the tire pressure. Anyone running 28-30?

 

[Burgo]

I set mine at 32 psi cold at around 20º ambient temp. I have a Michelin digital gauge that is accurate to -/+ 0.1 psi and my tyres according to the TPMS, well 3 of them always are spot on with the Michelin gauge and other one is usually at 1 psi less.

Some mornings when the ambient is around a couple of degrees C then they may read around 28 and in summer when I'm doing a road trip in 44º C ambient temps I've seen them hit 42 psi.

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