How much of an increase in mpg can I expect with overinflated tires?

[garyhgaryh]

I would have to disagree.. Both overinflating and underinflating tires will cause premature wear. It's not just underinflating it.

I've seen pictures of over inflate tires and it's wear after 20k miles from tire companies. The middle budges out. Yes, the steel belts are there and the one in the picture was steel belted.

Gary

Originally Posted by skewbe

Overinflating is not really a cause of premature wear, low pressure is the major cause of that.

It may affect wet handling adversely, so practice. Dry handling effects are good, the sidewalls are nice and stiff and do not flex as much in the corners (them guys that drive on two wheels use like 100 psi).

Them steel belts keep things lined up pretty well so there's no appreciable bulging from overinflating.

[bowtieguy]

skewbe,

thank you for the tip. tried it (paint across the tread) and found that 60psi is too much for the rears, but not for the fronts. weight distribution right?

[DarbyWalters]

Low Profile Tires on a larger diameter rim for the same or bigger tire diameter won't hurt mileage ( I know you meant on the same sized rim but it could cause confusion).

There is a point where rolling resistance will increase with tire pressure...if the tire is set so high it stops conforming with the road surface, it can be detrimental.

Tires do grow convex and/or convex with different psi's. This will happen in the middle of a tire and causes different running temps along the inside, middle and outside edges of a tire...you really want pretty even tire temps for best results. No reason to get uneven wear on tires and then all the money you saved on fuel goes to new tires. Agreed that low psi's are much worse, so err on the side of high psi's.

[brucepick]

I've read that on modern steel belted tires additional pressure doesn't cause the center bulge as on non-belted tires.

The proof seems to be in the anectdotal reports of drivers who have run their tires at considerably more than max sidewall pressure for tens of thousands of miles with no uneven wear detected. In fact the additional pressure reduces rubber flexing. Flexing creates the heat that softens rubber and destroys tires, and those runnning higher pressure long term report tire life at least as long as expected if not longer.

[trebuchet03]

I've read that on modern steel belted tires additional pressure doesn't cause the center bulge as on non-belted tires.

Yep -- a few months ago, I remember seeing a picture of someone's tire with a broken belt.... The difference belted vs. no belt is VERY clear.

An easy test would be to roll your tire onto flexible measuring tape, then pump up and measure the diameter change

[skewbe]

One could also paint a stripe across the tread and drive around "normally" for 25 miles or so with them pumped up and see if they wear evenly or not.

[bowtieguy]

Originally Posted by skewbe

One could also paint a stripe across the tread and drive around "normally" for 25 miles or so with them pumped up and see if they wear evenly or not.

brilliant skewbe! just inflated mine to 60psi(from 44) and i'm gonna try that. thank you.

[trebuchet03]

Originally Posted by skewbe

One could also paint a stripe across the tread and drive around "normally" for 25 miles or so with them pumped up and see if they wear evenly or not.

ha, that would totally work too Actually, that's one method to check gear lash on really really big gears -- spray on some paint and then run the machine for awhile... Then check how the gears are meshing.

[skewbe]

Originally Posted by bowtieguy

brilliant skewbe! just inflated mine to 60psi(from 44) and i'm gonna try that. thank you.

Originally Posted by trebuchet03

ha, that would totally work too.

I should qualify this a bit. If you have been driving around with "underinflated" tires, the outsides WILL have worn down and pumping them up can give the impression that there is a bulge in the middle.

I think the chalk test followed by rolling forward a couple tire revolutions would be better than paint for identifying "bulge". The paint might be better for monitoring the effect of alignment changes in "the real world" (i.e. cornering/accelerating/braking).

Originally Posted by trebuchet03

...Actually, that's one method to check gear lash on really really big gears -- spray on some paint and then run the machine for awhile... Then check how the gears are meshing.

Ah yes, reminds me of a little tube of prussian blue I've had for years.

[DarbyWalters]

The difference is not readily discernable to the eye...use a pyrometer and take temps across the tread...you WILL see a difference. The higher temps in the middle show an overinflated tire and uneven wear will result. You just have to weight the cost savings verses the wear factor...you have to assume that the vehicle is properly aligned

Higher pressures are used in Auto-X to keep tire squibb to a minimum...you dont' have time to build up heat on a run

Lower pressures are used in Road Racing...heat builds and psi increases

For the street you are pretty safe unless you run underinflated...BOOM!!!