How much tire pressure is too much?

[Andre S. Veteran]

I see a lot of conflicting advice on tire pressure online. Lots of people say just put the recommended pressure, lots of people also say put a bit more so you improve fuel economy.

Recommended pressure for my car is 33 psi and I've been using 38-40 PSI this summer. I've seen a great increase in fuel efficiency although I did the 100000km maintenance recently which probably also helped. However yesterday I had a tire failure which I don't know was caused by what, didn't see anything on the road, was in the middle of changing lanes on the highway, heard a loud BANG, suffice it to say it was not a pleasant experience. Fortunately it was a rear wheel so I didn't lose much control. Tire has a large whole on the inner wall (the side opposite to the road) but I did have to drive with it flat for maybe a kilometer which likely aggravated the initial damage.

Anyway, perhaps the failure is simply due to some object I hadn't seen but I'm wondering whether I'm taking risks by running at higher pressure than recommended. Surely a few PSI over is safe? How much is too much?

[fusi0n]

I always do the recommended for normal driving.. My car that I have for drifting and racing, sometimes I'll run it higher pressure or lower depending on the track. If you are doing just normal driving, I would say keep it as close to the specs of the tires as possible..  

[Brian M. Veteran]

It depends on what you're doing, quality of the tyres, how full the car is, the speed you're going, surface of the road, etc.

[Andre S. Veteran]

I'm doing a 20km commute on mostly highway at very conservative speeds, typically well under 100km/h. The car is empty save for me and I'm a slim nerd. Tires are good I think (Continental ContiProcontact I believe), don't seem too worn out, although I got them used when I bought the car.

[Ironman273]

Over-inflating your tires as little as 6psi can lead to excess damage when driving over uneven sections of road and/or potholes. When the tire is overinflated, it cannot compress and spread impact over its entire surface. This will also lead to a rougher ride, as the tire cannot cushion the weight of the car as well.

 

Overinflation will also cause the tire to bulge out along the center of the treads. This will result in a decrease in traction and stopping distance, since less of the tire is contacting the driving surface.

 

When tires are overinflated, they will wear unevenly. This will cause more stress on the tire itself, which can lead to leaks and blowouts.

Read more : http://www.ehow.com/list_6109527_effects-overinflation-tires.html
 

[Jim K Global Moderator]

I see a lot of conflicting advice on tire pressure online. Lots of people say just put the recommended pressure, lots of people also say put a bit more so you improve fuel economy.

Recommended pressure for my car is 33 psi and I've been using 38-40 PSI this summer. I've seen a great increase in fuel efficiency although I did the 100000km maintenance recently which probably also helped. However yesterday I had a tire failure which I don't know was caused by what, didn't see anything on the road, was in the middle of changing lanes on the highway, heard a loud BANG, suffice it to say it was not a pleasant experience. Fortunately it was a rear wheel so I didn't lose much control. Tire has a large whole on the inner wall (the side opposite to the road) but I did have to drive with it flat for maybe a kilometer which likely aggravated the initial damage.

Anyway, perhaps the failure is simply due to some object I hadn't seen but I'm wondering whether I'm taking risks by running at higher pressure than recommended. Surely a few PSI over is safe? How much is too much?

 

The maximum tire pressure listed on the tire is just that...the MAXIMUM (not the recommended pressure).  The right pressure depends on the vehicle and the tire size and should be listed on your door/manual.  If you have the same size/type tires as the ones that came with the car ... those listed pressures are valid.  However, if your load index on the newer tires are lower than you will need to add pressure ... and vice verse.  

 

Anyway, I would just stick with whatever the vehicle manufacture suggests...in your case 33 PSI.

[Andre S. Veteran]

Thanks for the tips. When I change my tires for the winter I'll stick with the recommended pressure. 33 PSI just seemed... low to me. But that's probably irrational.

[sc302 Veteran]

33 psi is fine and is the recommended to get the most life, fuel mileage, and best grip combination.  You can increase fuel mileage or grip by going higher or lower with the air pressure, but you will hurt life and the other attribute (fuel mileage or grip) if you go too high or too low. 

 

Lower pressure can increase grip, but by doing this you will gain more rolling resistance which decreases gas mileage (making the tire softer).  This will also decrease tire life

Higher pressure can increase gas mileage by decreasing rolling resistance but this will decrease surface grip (making the tire harder).  This will also decrease tire life.

 

Shouldn't really play much beyond 5psi, unless you are racing.  Usually drag racing with the right equipped tire, you will see pressures as low as 18psi or lower(remember that whole grip thing that I mentioned before, it comes in play heavily here). Even autox, you will have your tires ~5 psi lower than what the doors say. 

[DirtyLarry Veteran]

While we are on the topic, and please realize I am not a big car guy at all, which PSI do you all go by? The one that is on the inside of the drivers door on a sticker or on the tires themselves? As for me they are two different numbers entirely.

 

Also the tires almost always list max load. So is there some kind of calculation to figure out normal load?

[sc302 Veteran]

The door has manufacturer recommended psi, I usually go 5 above during winter time when using air out of a compressor.  Air molecules like to shrink in cold, so psi drops.  If they are nitrogen filled, I believe they also fill ~5 above.  Nitrogen molecules are closer together so there is less of a psi drop or increase during the cold or hot months.  Besides, I have pressure indicators in my cars...If I don't over inflate slightly those lights come on within a week during the winter months.

[notchinese]

The PSI listed on the tire itself is a maximum PSI, not recommended.

[DirtyLarry Veteran]

The door has manufacturer recommended psi, I usually go 5 above during winter time when using air out of a compressor.  Air molecules like to shrink in cold, so psi drops.  If they are nitrogen filled, I believe they also fill ~5 above.  Nitrogen molecules are closer together so there is less of a psi drop or increase during the cold or hot months.  Besides, I have pressure indicators in my cars...If I don't over inflate slightly those lights come on within a week during the winter months.

Both of my cars will tell me when the pressure is low, just neither unfortunately tell me when it is correct, unless I am missing something.

 

The PSI listed on the tire itself is a maximum PSI, not recommended.

Yep, which is why I asked this...

Also the tires almost always list max load. So is there some kind of calculation to figure out normal load? 

[+Raze Subscriber²]

Yep, which is why I asked this...

 

Here's a very good site to get information about tires and inflation standards. - http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=205

[spacer]

Recommended tire pressure varies per tire and per car. As long as you're sticking with the factory recommended model/size tire for your car, just check the manual for the required pressure. Anything under or over that is bad.