Tires: Downside to 40+ PSI?

JEDI

Lifer
Sep 25, 2001
29,391
2,737
126
higher psi = better gas milage

whats the downside, if any, to going to the car tire manufacturer max (~50psi)?
 

Demo24

Diamond Member
Aug 5, 2004
8,356
9
81
Wears the middle part of your tread down faster, and you can actually get worse grip with higher psi's like that. Since the tires don't wear as evenly/properly you'll need to replace them sooner, not really worth the potential fuel savings.
 

Doppel

Lifer
Feb 5, 2011
13,306
3
0
High pressure is a risk for reasons mentioned but 40 probably doesn't count. A great many hybrid drivers who do it swear it raises their mpg by a couple. It will give a bit of a harsher ride.
 

saratoga172

Golden Member
Nov 10, 2009
1,564
1
81
He simply asked what higher pressure does. No harm in that.

Jedi I would just run it what the inside door panel says or within a few PSI of that.
 

JCH13

Diamond Member
Sep 14, 2010
4,981
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91
Reduced grip.
Reduced tire life.
Poor wear.
Increased chance of blow-out.
 

yh125d

Diamond Member
Dec 23, 2006
6,886
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Makes your car super awesome and able to climb hills at full throttle in top gear


seriously, do it.
 

thomsbrain

Lifer
Dec 4, 2001
18,148
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0
You will definitely notice the reduction in ride quality. Steering response will improve due to reduced sidewall flex, but overall grip will be diminished due to reduced contact patches.

On my Accord, I run my tires high (though not that high), and it actually evens out tire wear for me because my commute is on a very twisty highway and at stock pressure I wear out the edges of my 65-series tires quickly because the sidewalls roll over in the corners.

On the S2000, the challenge is to drive ENOUGH corners to even out tire wear, even at stock pressure. -2.0 degrees of camber FTW. :)
 

Howard

Lifer
Oct 14, 1999
47,982
10
81
You will definitely notice the reduction in ride quality. Steering response will improve due to reduced sidewall flex, but overall grip will be diminished due to reduced contact patches.

On my Accord, I run my tires high (though not that high), and it actually evens out tire wear for me because my commute is on a very twisty highway and at stock pressure I wear out the edges of my 65-series tires quickly because the sidewalls roll over in the corners.

On the S2000, the challenge is to drive ENOUGH corners to even out tire wear, even at stock pressure. -2.0 degrees of camber FTW. :)
I thought camber didn't affect tire wear much?
 

helpme

Diamond Member
Feb 6, 2000
3,090
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I thought camber didn't affect tire wear much?

What he's getting at is that with -2 degrees of camber, unless you corner hard, the outside of the tire will never wear because it won't be carrying any load.

Also, unless you have 0 toe, camber will cause the outside of the tire to not scrub compared to the inside/middle of the tire when going straight (causing less wear on the outside edge).
 

dawp

Lifer
Jul 2, 2005
11,347
2,709
136
Do you like riding on balloons? if the recommended pressure is around 30 psi, it will be like you're rolling on balloons. I tried it just to prove a point to fleabag and the ride quality suffered immensely.
 

JEDI

Lifer
Sep 25, 2001
29,391
2,737
126
Reduced grip.
Reduced tire life.
Poor wear.
Increased chance of blow-out.

Reduced tire life How?
Wears the middle part of your tread down faster like a previous poster said?
 

PlasmaBomb

Lifer
Nov 19, 2004
11,636
2
81
Reduced tire life How?
Wears the middle part of your tread down faster like a previous poster said?

Yes, depending on the car/setup.

It can also increase skipping off bumps which will change the wear characteristics.
 

JCH13

Diamond Member
Sep 14, 2010
4,981
66
91
Reduced tire life How?
Wears the middle part of your tread down faster like a previous poster said?

Yep, it wears down the middle faster. It also concentrates heat in the middle portion of the tire tread, which can potentially weaken the tire a dangerous amount.
 

PlasmaBomb

Lifer
Nov 19, 2004
11,636
2
81
Yep, it wears down the middle faster. It also concentrates heat in the middle portion of the tire tread, which can potentially weaken the tire a dangerous amount.

I would have thought that increasing the PSI would have lead to the tyre running cooler due to less sidewall flex?

I suppose it would depend on tyre composition, tyres using more kevlar won't spread the heat as well as tyres using a higher proportion of steel...

You got any more info JCH? Thanks :)
 

JCH13

Diamond Member
Sep 14, 2010
4,981
66
91
I would have thought that increasing the PSI would have lead to the tyre running cooler due to less sidewall flex?

I suppose it would depend on tyre composition, tyres using more kevlar won't spread the heat as well as tyres using a higher proportion of steel...

You got any more info JCH? Thanks :)

eHow says that either over inflating, or under inflating, can increase blow-out risk.

I think it works like this: when a tire is under-inflated, like you said, the sidewalls deform more and this flexure creates heat. As previously mentioned, the center of the tread is bearing all of the vehicles weight, so the tread around this very narrow band is now flexing instead of remaining flat. This little bit of tread is doing what the entire sidewall used to do. Also the heat of tread wear is being focused into a much smaller part of the tire. These two effects will concentrate the heat into a much smaller part of the tire than if it was properly inflated. Rubber (and steel for that matter) is a terrible conductor of heat, so the heat can build up to dangerously high levels.

As heat builds in the narrow contact patch of an over-inflated tire, guess what? The compound softens, its wears faster, and builds heat faster. As the tire heats up, pressure inside the tire increases, further reducing the contact patch and exacerbating the wear and heat problems. Also, the hotter, softer, compound reduces fuel efficiency. It's a vicious cycle.

In race cars, where tire temperature is a more pressing concern, you'll see setups like this that are used to help dial in tire pressures.

5447174397_0a0d8c5247.jpg


One adjusts tire pressure until the same temperature is seen across all of the sensors.

EDIT: other info.

http://www.retailtire.com/2011/01/t...ion-for-new-tires-and-used-tires-in-tampa-fl/
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1&
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=2
 
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Zap

Elite Member
Oct 13, 1999
22,377
2
81
Can't find the link right now (I think someone at ecomodder.com linked to it) but there have been comparisons done on fuel efficiency and tire pressure. Seems as if going below around 30-35PSI can cause a great hit to gas mileage, but going above only gave tiny gains, at least with two different test configurations. Thus, the gains are minimal. You can probably get as good or better gains by going to a lower rolling resistance tire, or a narrower one.

Besides gas mileage improvements, you lose pretty much everything else such as performance, comfort, etc.
 

brandonb

Diamond Member
Oct 17, 2006
3,731
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Well, here is my experience...

On a hot day, the air expands and pressure is increased. Go on the highway, the pressure is increased... Hit a pot hole, pressure > tire, and you have a blow out.

You never know what threshold is going to cause a blow out. At 30psi, on a hot day on the highway the tire is likely to sit around 40-50 psi anyways after things warm up.

Why play with fire? I learned the hard way. It really sucks having to change a tire on the interstate when people are flying past you 70+ mph with about 3 feet between you.