Your post reminded me of a year in the mid 90s when Michael Andretti and Christian Fittipaldi of the Newman/Haas Indycar racing team both had tire blowouts at the Long Beach Grand Prix. The rumor was that they were running extremely low cold tire pressures, something like 10 to 12 psi, and the subsequent temperature rise, was high enough to blow out the tires.
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Over inflate for better milage on road trips?
- Thread starter outdoordawg
- Start date
-
- Tags
- Range Anxiety Road Trip
There are quite a few reasons not to raise the tire pressure for long-distance trips.
- Rolling resistance takes a back seat to air resistance at the higher speeds you are likely to drive on long-distance trips, so you cannot gain much.
- The tires will wear out unevenly, more in the center, less at the edges.
- Reduced grip, longer braking distance, therefore somewhat reduced safety.
- This could even have legal consequences, if it is found to be a contributing factor to an accident. Not very likely, but not entirely impossible.
- Tires will be harder, so less comfort, less protection from road roughness, more wear on the suspension.
- Tire pressure already rises a bit on its own anyway, as the tires warm up from higher-speed, long-distance driving. To increase the pressure even further makes little sense.
Msjulie
Active Member
Don't disagree with what you are saying but might add a note about over inflating vs tending towards a moderate increase over what is listed on the door jam.
Recall that Tesla's initial recommendation was higher than 42 psi but reduced it in an effort to "fix" what some found too harsh a ride.
Again, anecdotal but my car has 33k+ miles and no uneven wear found and the cold pressure I set is 45; higher than the newer suggestion but well under the tire's max cold pressure as well.
A few extra psi beyond the recommended rating will be totally fine in regular conditions yielding better efficiency. However, is that efficiency gain worth the decrease in braking performance if you need to emergency brake? Stopping a couple feet shorter could make a big difference in the outcome. Pros and cons but ultimately you decide whats best for you. Best to stick with Tesla's recommendation trusting their engineers have figured out the best psi for the balance of safety, efficiency, and performance.
Theoretically, there’s slightly less tread in contact with the road. Higher pressure (psi) in tire means fewer square inches of tread needed to support the vehicle’s weight.
On the other hand, with higher pressure, the tread has more friction (traction) on the road. Also better ability to clear water and light snow from the smaller contact patch. Finally, higher pressure improves sidewall stiffness, leading to better traction and control in turns - a definite plus for active safety.
Lower tire pressure is an advantage off pavement - sand, mud and deep snow. In those low traction scenarios, it’s best to have as much tire surface as possible working to propel the car.
Higher tire pressure is NOT like money in the bank - you can have put too much air in the tire.
- Exceed the tire’s sidewall limit when tire is cold, and and there’s a risk the tire could blow off the rim/wheel. Note that manufacturer specifies cold pressure- before tire heats up from driving. Tire is safe when pressure rises due to driving within its load and speed ratings.
- Raise the pressure enough, and handling deteriorates because the contact patch is so small.
- As tire pressure rises, it is becomes less compliant. It absorbs fewer road irregularities. Some enjoy the greater communication of road conditions. You can tell you’ve run over a coin; you can distinguish between a dime and a quarter; you can call “heads” or “tails”...
Not intending to quibble, but I don't believe higher pressure equates with more friction. Friction is going to be a combination of tread compound, road surface, and contact patch size.
And I think you're right in a sense about the smaller contact patch clearing water better, but I doubt it makes much difference for snow of any depth at all. In fact, floatation and increased tread flex can help in deeper snow.
Msjulie
Active Member
@NickFie Yes thanks but I was looking for a specific citation - changing the contact patch of course has implications in braking, handling, acceleration etc but I was curious if there are measurable/noticeable differences in 2-3 psi and braking distance on the road as opposed to off roading or track use.
A softer sidewall will have implications as well and I don't *think* anyone was suggesting pressure increases that materially impacted contact patch. I can surmise from my own tire wear pattern that there is no excessive (or even visually discernible) increase in center line wear on my tires and even though subtle I would suggest that a slightly increased PSI (over the comfort settings of most manufactures) would be both more efficient and provide better handling.
Devil is in the details here; these are my results in a number of cars over (too many) years of driving. It would be interesting to see any real studies, in controlled situations, where tire pressure differences were plotted against braking performance.
A softer sidewall will have implications as well and I don't *think* anyone was suggesting pressure increases that materially impacted contact patch. I can surmise from my own tire wear pattern that there is no excessive (or even visually discernible) increase in center line wear on my tires and even though subtle I would suggest that a slightly increased PSI (over the comfort settings of most manufactures) would be both more efficient and provide better handling.
Devil is in the details here; these are my results in a number of cars over (too many) years of driving. It would be interesting to see any real studies, in controlled situations, where tire pressure differences were plotted against braking performance.
From tracking my car and running with both higher and lower than recommended pressures on the Michelin P4S-TO my experience is:
With higher pressures (42-45 cold), your car may feel more precise due to stiffness, but the ultimate grip is reduced due to a smaller contact patch. Mileage is certainly better.
With lower pressures (35-38 cold) You get more ultimate grip with a larger contact patch but the tires will more easily chew up and chunk the edges when overdriven. P4S seem especially vulnerable to this, and do not react as well as some other tires to reduced pressure.
With higher pressures (42-45 cold), your car may feel more precise due to stiffness, but the ultimate grip is reduced due to a smaller contact patch. Mileage is certainly better.
With lower pressures (35-38 cold) You get more ultimate grip with a larger contact patch but the tires will more easily chew up and chunk the edges when overdriven. P4S seem especially vulnerable to this, and do not react as well as some other tires to reduced pressure.
Last edited:
I had a mobile guy work on my car today. He put the tires to 45psi and said that's the sweet spot for not just efficiency but for even tire wear. He said the 45psi recommendation sounds high due to weight of the car but their experience notes that its optimal. Going above or below will wear the sides or center of the tires more. Going back to the OP: Is the minor efficiency gain worth the uneven tire wear?
Excuse the thread necro....
I took delivery of a 2021 M3 LR in April. 19" stock tires were inflated to 42 PSI from the factory, on the road they would heat up to ~45. The ride was too stiff for me as a daily driver even though the roads around here are in great condition.
After experimenting with tire pressures, I found that 40 PSI when cold was the sweet spot for comfort and handling, as they warm up to the "max" of 42, sometimes 43. 38 or 39 was too soft and had a lot of sidewall flex in low speed turns; backing out of the driveway felt like steering a water bed.
I live in a hot environment, so YMMV. For distance driving, going back to 42 cold is the way to go. I don't think I could tolerate 3 hours of 45 PSI cold.
Hopefully this helps others figure out their ideal tire pressure.
I took delivery of a 2021 M3 LR in April. 19" stock tires were inflated to 42 PSI from the factory, on the road they would heat up to ~45. The ride was too stiff for me as a daily driver even though the roads around here are in great condition.
After experimenting with tire pressures, I found that 40 PSI when cold was the sweet spot for comfort and handling, as they warm up to the "max" of 42, sometimes 43. 38 or 39 was too soft and had a lot of sidewall flex in low speed turns; backing out of the driveway felt like steering a water bed.
I live in a hot environment, so YMMV. For distance driving, going back to 42 cold is the way to go. I don't think I could tolerate 3 hours of 45 PSI cold.
Hopefully this helps others figure out their ideal tire pressure.
I set mine at 43-44 so that I don't have to fill them so often (factory setting is 42). We used to jack up the pressure in our Prius to get a bit better gas mileage. I'm sure the ride was worse and one day we broke a belt in the tire when we hit a pot hole. No way to know if it would have broken at the normal factory pressure as well, but it surely didn't help. After that I decided that it wasn't worth any very small marginal gain in efficiency.
At the track we (or I) usually monitor the tire after each run - if there isn't even wear across the tire tread I lower the pressure (e.g the outer edge of the tread isn't getting used). If the wear is starting to reach the sidewall (i.e it's deforming too much) then it's time to raise the pressure. So perhaps it's an optimum tire pressure rather than high/low
Candleflame
Active Member
i find the range benefit minimal above 45psi anyway. I inflate to 45psi cold, but when i do that in the evening during daytime sunny driving it can go up to 50psi.
