Tire pressure

[Vinsanity]

Has anyone experimented with raising air pressure in their tires for better mpg? I tried raising the psi from 30 to 36 over the weekend, but I noticed I was using the brakes more due to the preservation of momentum and getting a rougher ride before I noticed an increase in mpg. So I lowered the pressure back to 30 psi, per specs on the door jamb.

Has anyone noticed a worthwhile improvement in mpg from raising the tire pressures?

[Byteme]

Has anyone experimented with raising air pressure in their tires for better mpg? I tried raising the psi from 30 to 36 over the weekend, but I noticed I was using the brakes more due to the preservation of momentum and getting a rougher ride before I noticed an increase in mpg. So I lowered the pressure back to 30 psi, per specs on the door jamb.

Has anyone noticed a worthwhile improvement in mpg from raising the tire pressures?

All else being equal raising tire pressure will reduce fuel consumption because you are reducing rolling resistance, which is why you experienced "preservation of momentum'.

Your trade off is ride and handling and tirewear on the center of the tread.  Diminishing returns also applies here.  if increasing tire pressure 5 pounds gave you a 1 MPG increase in mileage adding another 5 pounds won't give you an additional 1 MPG increase.

Years ago CandD did or reported on a test in which a guy replaced the wheels and tires with 4 60 PSI temporary spares.  IIRC it had a significant impact on mileage, at the expense of road handling and safety of course. 

[Laconian]

Did they determine what percentage one could overfill the tires without severely impacting R&H? Or--let me guess--it depends on the car and the tire. :P

[The Pirate]

Did they determine what percentage one could overfill the tires without severely impacting R&H? Or--let me guess--it depends on the car and the tire. :P

I think it does depend.  I've been running my tires at 35 psi (manual calls for 29 psi) for the last 10K miles.  Ride is a bit stiffer, but not harsh, and I've yet to see any abnormal tire wear.  Handling (and turn in) is definitely better, and I think the car's fuel consumption is a bit less.  I've no way to prove this though.  Fuel economy aside, the improvement in handling response is worth the penalty of a stiff ride alone (and this car didn't ride like a Caddy to begin with).

[Vinsanity]

Funny thing is that the owner's manual says that overinflating the tires may cause the car to have "unusual handling". if by unusual, they mean the steering responds quicker, then correct. I did like the new lively feel of the steering and suspension, and call me spoiled, but I just couldn't get used to the more jittery highway ride.

[GoCougs]

The recommended PSI (on the door jamb) I have to believe is more than arbitrary; there is likely significant engineering behind it. One significant component of proper PSI is contact patch, which is in itself almost entirely due to vehicle weight. Further, I would not be surprised to discover that anything beyond recommended PSI is where improvements in MPG are tiny to nil.

[Soup DeVille]

Did they determine what percentage one could overfill the tires without severely impacting R&H? Or--let me guess--it depends on the car and the tire. :P

The maximum pressure for the tire is listed on the sidewall of the tire. The manufacturer's recommended pressure is listed on the doorjamb.

Anywhere betwen the two is OK for experimentation.

[Cookie Monster]

So do you get better handling with an over inflated tire because of the stiffer sidewalls, or an under inflated tire because of the bigger contact patches?

[Soup DeVille]

So do you get better handling with an over inflated tire because of the stiffer sidewalls, or an under inflated tire because of the bigger contact patches?

I don't think there's one simple answer. Generally, I've found that most cars handle better when they're overinflated by about 5-6 pounds on each tire, but YMMV.

[JYODER240]

Funny thing is that the owner's manual says that overinflating the tires may cause the car to have "unusual handling". if by unusual, they mean the steering responds quicker, then correct. I did like the new lively feel of the steering and suspension, and call me spoiled, but I just couldn't get used to the more jittery highway ride.

You're beginning to sound like Trep.

[Cookie Monster]

You're beginning to sound like Trep.

He became like Trep when he sold the S2000 for the TL.

[AutobahnSHO]

Plus keep in mind any 'increased preservation of momentum' also means you have less braking surface.

Because it's not how well the brakes grip the wheels, but how well the wheels grip the road.. (most of the time..)

[NomisR]

I don't think there's one simple answer. Generally, I've found that most cars handle better when they're overinflated by about 5-6 pounds on each tire, but YMMV.

Yeah, it depends on the car.  My RSX seems to handle better at higher pressure while the Elise gets better lap times with lower tire pressure than the door states. 

But one thing though.  Optimal tire pressure is usually measured at cold tire pressure.  So what about when the tires are warmed up since the pressure is higher? 

[Vinsanity]

You're beginning to sound like Trep.

He became like Trep when he sold the S2000 for the TL.

to both of you

[S204STi]

It's best not to just jack up your tire pressures and hope for the best.  I recall reading something on how to set tire pressures for track work to create the best compromise. It involved rubbing chalk or something like it (maybe temporary paint) on the shoulder blocks overlapping both the tread and sidewalls.  Drive around the track and see how much was rubbed off.  If the sidewalls saw significant rubbing, try a higher pressure and recheck.

Perhaps a more intelligent idea is to use an infrared thermometer to check temps across the tire after a run.  This would be more practical for the daily driver, because he/she could simply check it after their normal commute and see which parts were hottest.

Personally I just observe tire wear over time.  Over the course of just one oil change your tires will have formed definite wear patterns.  Using this method I have found an ideal tire pressure of 38psi front, 33psi rear, roughly 6 and 4 psi higher than spec respectively, though I could probably run the rears a bit lower to be honest.  With these pressures i have little shoulder feathering (some is to be expected due to the effects of caster on camber during a turn) and fairly flat tread wear patterns on the whole.

[S204STi]

Yeah, it depends on the car.  My RSX seems to handle better at higher pressure while the Elise gets better lap times with lower tire pressure than the door states. 

But one thing though.  Optimal tire pressure is usually measured at cold tire pressure.  So what about when the tires are warmed up since the pressure is higher? 

I forget but there is somewhere a nice little guide which says maybe 4psi per every "X" degrees of temp change.

I think it was a Michelin spec, but is should apply universally.