I typically slightly over inflate my tires for a little better handling and improved fuel economy. The door sticker recommends 32 PSI in my tires, which are on 18" rims. The sidewall of the tires lists 35 PSI as the recommended pressure, so I typically inflate to about 34-35 cold PSI. My car has a TPMS that shows you in real time the pressures of all 4 tires, and it seems pretty accurate when compared with a decent gauge I have.
I never pay that much attention to the pressures while driving except an occasional glance to make sure all is well. I do frequently look at the cold PSI when I first start the car. We had our first 80-degree day this year yesterday and I was on a 90-mile road trip, driving about 70-75 MPH. I was a bit alarmed to see my tire pressures at 40 all around once the tires warmed up. I know that under inflated tires are the main cause for blowouts, and over inflated tires can cause unusual wear patterns. I also know that racers typically over inflate their tires when using street tires on a track, so I’m assuming the tires can take over inflation… for a while anyway.
My question is, how much is too much? I’m assuming that I’m fine as long as I’m not exceeding the cold PSI on the sidewall, as the tires are designed to accommodate the expansion when the tire (and air) warms up. Continual warm pressure of 40 PSI seemed a bit much though, and we typically get temperatures that are much warmer than 80 in the summer. Thoughts?
I think anything over 5 psi cold above the placard pressure is too much. I think you are OK in what you are doing. A 5 psi build up is at the edge of what is acceptable.
You are doing the exact same thing that I’ve been doing for 40 years oblivion. Until the advent of TPMS…I had no idea what was really going on with the tire pressure in my tires. Now…I usually see 28psi on a cool morning and around 38psi when it heats up in the afternoon or on the interstate. I think your 35psi is perfect.
35psi is fine. When your tires get well worn, you’ll want to check the wear. You might have to accept a bit more wear in the tire’s center, depending on the vehicle and your driving style. Max pressure is typically 44psi (it’ll be on your sidewall), so you have plenty of safety margin.
My car is FWD with about a 60/40 weight distribution. I run my fronts at 32psi and my rears at 29. Takes a wee bit of the understeer away.
Perfect. I do the same thing. The sidewall pressure is a cold pressure max, not a recommended. I’m surprised it is that low. 40 psi hot should be OK. I have seen over 40 psi after extended high speed running (within the speed rating of the tires!) on a German Autobahn with the pressures set to the placard recommended 35 psi.
Heck, a BMW 5 series I worked on listed 40 psi cold as the placard pressure for the rears when fully loaded, but at a reduced speed limit - 200 kph! (119 mph), I think. Still pretty fast. It would do 135 or so.
I regularly see 41-43 psi on front tires inflated 2-3 psi below placard recommendations on track days. My target hot pressure is 41 psi front and 38 rear for track days. Any more and the car gets greasy.
Back in the RWD days, I carried a higher pressure in my rear tires than my front tires. It seemed to help the handling even though there was a higher percentage of weight on the front tires. With the front wheel drive cars I have owned it seems to me the manufacturer called for equal pressures all the way around. The 1961 Corvair I owned was very explicit that the rear tires carry more pressure than the front tires
Especially with the motor hanging off the rear and the old bias ply tires.
Come to think of it, I seem to remember that varying pressures as having a greater effect on handling with the old bias ply tires than with radials. Perhaps Capri could shed some light on this?
I check tire pressure every month. I overinflate wrt the car manufacturer’s recommendation by 2 to 3 psi so that if I lose pressure over the month, it isn’t much less than the car company recommendation. I use the recommendation as a midpoint.
That is my approach also.
In order to get slightly improved handling, tread wear, and gas mileage, I inflate my tires to 3 lbs over the mfr’s recommended pressure. The bonus is that, if the tires lose pressure due to a temperature drop, then they aren’t underinflated.
Yes, I also inflate to 2 PSI over spec for the same reasons.
There is a lot of margin on the high side. When I picked up my new Forester last year, I drove 300 miles before the TPMS light came on. It was from overinflation, not under. The dealer had not reduced the pressure from the 46 PSI used for transport.
In the summer, I run cool morning pressure the same as the recomended. Inthe winter, I try to stay 2 to three lbs up. So 32 becomes 35. The only time I increase the pressure is in the truck when towing and the car when my wife’s the chauffer for her friends. I try to vary the pressure then with the anticipated load.
I am with the majority, over-inflate by 2 PSI. I don’t have live pressure reading on any of my cars, just a TPMS light that would go off if one tire was low/flat or something close to that.
In my car the TPMS system can be easily “initialized” once the pressures are set to the desired levels. The instructions are in the owner’s manual. Oddly, they’re in a different place in the manual that the “reset” instructions, which do not establish a new “baseline” from which the system then references. You could conceivably set all four tires to different pressures and the system wouldn’t care as long as those pressures didn’t drift beyond the range that the system detects as abnormal.
An interesting question to which I don’t have an answer is how that would affect my ABS system. I’ll have to check into that.
The people who make the tires know about the pressure increase when tires get warm. The tires can take it and will probably be cooler with 35 PSI cold pressures. To me, the temperature means more than the pressure. Keep them inflated.
Temperature certainly does affect inflation pressure noticeably. I commuted using our Cobalt with TPMS this past winter for a while. It is parked outside and on days when the temperature was less than 10F, the pressure of one or two tires would be low. Within 10 to 15 minutes the pressure would be back in the normal range.