Caution --Reminder

[Zormecteon]

I took my car out on the freeway and it seemed "squirrely". Then I remembered I had the tires rotated a couple of weeks ago and hadn't re-checked the tire pressures. Sure enough, they just swopped the tires front to back but didn't reset the air pressure(s) making them exactly opposite of what they should be.

REMEMBER. to check once a month. That 3# difference front to back is important in making the car handle properly. (A large part of the reason for the Corvair's bad reputation is that people ignored the factory recommendations. 15 front 26 rear, the higher pressure in the rear helping to prevent oversteer while in our cars the higher pressure in the front helps relieve understeer).

 

[FiestaSTdude]

Thanks for the heads up!
I've wondered what the difference in tire pressure was supposed to do.

 

[RaveBell]

There should be a Forum dedicated to these types of things on the main page.

 

[XR650R]

I've never had my tire pressures correct when I got my car back from anyone, including the dealer I got it from.

Keep a pressure gauge in your car and check it often.

If not often, whenever it feels a little off.

 

[Erick_V]

I check my pressures once a month. Weekly now that I have a slow leak (thanks road work). I patched it but I’m waiting till my track day to install new tires. If something doesn’t feel right it’s super simple to check pressures first. A small pressure gauge with the clip attachment fits in the slit on the left side of the glove box. Always have one on me because I forget things like that for autocross

 

[contemplative_shrimp]

Don't forget to keep the spare tire at the right pressure too. I think many people forget that loses air as well.

 

[Sprinkle_Star]

Yeah and don't forget to re-train TPMS

 

[Intuit]

The lower pressure in the rear merely increases traction. There seems to be much less weight on the rear during maneuvering. Front doesn't seem to be as important but my experiences with too much in the rear is, it breaks loose easily; likes to fish-tail.

Yeah and don't forget to re-train TPMS

With tire rotation the TPMS in this car doesn't seem to care which corner the wheels are on. My Dad's GMC Terrain on the other hand displays each corner's pressure on the dash and will let you know which corner is low.

 

[M-Sport fan]

The lower pressure in the rear merely increases traction. There seems to be much less weight on the rear during maneuvering. Front doesn't seem to be as important but my experiences with too much in the rear is, it breaks loose easily; likes to fish-tail.


With tire rotation the TPMS in this car doesn't seem to care which corner the wheels are on. My Dad's GMC Terrain on the other hand displays each corner's pressure on the dash and will let you know which corner is low.

Yes, if our system was like that GM setup, I would have considered adding the sensors to all of my aftermarket wheels.

 

[Dialcaliper]

The lower pressure in the rear merely increases traction. There seems to be much less weight on the rear during maneuvering. Front doesn't seem to be as important but my experiences with too much in the rear is, it breaks loose easily; likes to fish-tail.


With tire rotation the TPMS in this car doesn't seem to care which corner the wheels are on. My Dad's GMC Terrain on the other hand displays each corner's pressure on the dash and will let you know which corner is low.

Basically the truth here. Lower pressure in the rear kills several birds with one stone. First, the car is nose heavy, and higher pressure on the heavier axle is probably a bid to squeeze better fuel economy on the EPA tests.

Second is that higher pressure in the front makes the front tire sidewall feel stiffer and more responsive, but simultaneously decreases front grip, which promotes a bit of understeer, which is how any modern car comes from the factory for so called “safety” reasons, yet they can stiffen the rear torsion axle to make the car “feel” sportier. (Which is always the same as “faster” or “more grip”)

39 psi is very high for a small car. The only cars that run pressure that high are big heavy cars with low profile tires that are trying to maximize fuel economy and range (Like Teslas and other EV or hybrids) or trucks with very high axle weights. Very few other small cars run pressures over 35-36psi unless they are trying to boost fuel economy numbers.

One last point is that if the car’s handling balance is set up to work with the 3psi tire pressure difference, then absolutely, the handling behavior will change - front sidewalls will feel sloppier and car will be slightly more tail happy. You can make the car work with equal/different/lower tire pressures, but to do it right, you also may need to consider your suspension, alignment, damping and tires with physically stiffer sidewalls if you want to have both a firm “feel” and also take advantage of the increased grip from lower pressures with the larger contact patch on the tires.

 

[Dialcaliper]

Just a followup after some digging - apparently factory tire pressures are determined by a whole slew of factors established by industry standards, including axle load, expected driving conditions, handling balance, tire size, width and aspect ratio, speed rating and tire load curves. There’s a bit of a fudge factor too. Long story short, once you deviate from the factory tire size and speed/load rating, the optimum tire pressure should technically change. But there’s a lot of wiggle room, so technically there’s no “right” answer. But there are wrong ones (generally extremely low or extremely high pressures). Anywhere in the middle you’ll probably be okay if it suits your driving style.

https://www.tirereview.com/determining-the-right-psi/