Car Tire Pressure - how high do you go?

[radhak]

Today I had a couple of tires changed for my RAV4 at Family Tires. They seem to be a franchise too, but felt more reasonable than the TirePlus or TireKing (they patched a puncture on my spare for $10!).

But that guy was very categorical about the tire pressure : keep it at 40psi, he says. I was surprised, because my vehicle sticker says 32psi all the wheels. He said, that's the car-manufacturer, while the Tire manufacturer mandate 40psi.

I have always been very careful in following the car sticker, and rarely allowed it to go above 32psi; 40 seems to be vastly over-inflated !

Any comment on how correct he was? Why would he recommend such high pressure? How much do you keep your tire-pressure?

[sweensdv]

When tire manufacturers start engineering and building cars then I'll listen to the recommendations of a tire salesman. Until then, I'll let the car manufacturers tell me what tire pressure works best for the car they built.

[leehljp]

I have been noticing an occasional reference to higher pressures also. And, I notice that some of the tires on my girls cars as well as others - seem to be wearing on the outside/inside shoulders faster than the middle. With 32 PSI, this would seem to say that they DO need to be more pressure.

I bought a used Honda van and the dealership service manager told me the same thing you were told. And, my local tire dealership said the same thing. So, our van stays on about 36 PSI. I keep my old ranger pickup at about 35 PSI front and rear.

[cabinetman]

Your best guideline would be the car manufacturer for the sizes recommended. If the sizes are changed, pressures can be recommended for the load they will carry.

If you check tire pressures, check them when they are cold. Warm or hot tires will pick up several pounds of pressure. Likewise on cold days they may read slightly low.

.

[jking]

I have never run into an instance where the tire mfg & the auto mfg were that much different. Tires have maximum pressure printed on them. I'm curious what is listed on your tires?

Generally, I run my cars at 32 psi. I'd be questioning anyone who told me 40, because I'm used to seeing 36 max on passenger tires. I think you have to be careful when the recommended pressure seems out of the norm. Remember the whole Explorer/Firestone issue?

[RAFlorida]

On our 4Runner,

I keep it at 40 psi. That's what the manual calls for as well as the writing on the tires.

[Relative]

42 psi per my local tire dealer. Pointed out that the full width surface of the tire is in contact with the ground at that inflation for my weight car.

Mike

[jbrain]

On our Honda Odyssey 40psi

[sparkeyjames]

Follow the tire pressure recommendations on the side of the tire. Every inflatable tire
I have ever owned has one. The ones on my car (check) the ones on my riding mower
(check) the ones on my bicycle (check). Check for it it's there use it. Most tires in
my experience give the best road mileage and traction when inflated to a tires max
recommended pressure.

[radhak]

I checked just now, and looks like it has the MAX Inflation Pressure : 44 PSI.

Now the 40 psi does not look at that dangerous, somehow !

[LCHIEN]

Disadvantages of Underinflation

An underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle’s tires are underinflated by only 6 psi it could lead to tire failure. Additionally, the tire’s tread life could be reduced by as much as 25%. Lower inflation pressure will allow the tire to deflect (bend) more as it rolls. This will build up internal heat, increase rolling resistance and cause a reduction in fuel economy of up to 5%. You would experience a significant loss of steering precision and cornering stability. While 6 psi doesn’t seem excessively low, remember, it usually represents about 20% of the tire’s recommended pressure.

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. Higher inflated tires cannot isolate road irregularities well, causing them to ride harsher. However, higher inflation pressures usually provide an improvement in steering response and cornering stability up to a point. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures. The pressure must be checked with a quality air gauge as the inflation pressure cannot be accurately estimated through visual inspection.

the above was from http://www.tirerack.com/tires/tirete...e.jsp?techid=1

I am inclined to agree with the text above.
Overinflating has some minor advantages - it makes the tire have less rolling resistance and get better gas mileage.
But overall the disadvantages I'd be worried about are
Safety-
less rubber in contact with the road (less traction)
Easier to blow out due to impact or debris
possible shortened tire life since the tires will wear in the center more just as underinflated tires wear at the edges.

comfort-
harsher ride


And don't forget if its at 40 PSI and the max pressure rating is 44, when the tire gets hot it will go up by 3-4 PSI so you have no safety margin at all.

Finally who's interest are at stake - who are you going to listen to?
The tire guy who is anxious to sell you new tires
or the car manufacturer who will get sued if your car crashes due to tire problems?

I go with the car manufacturer suggestion.

[LCHIEN]

I have been noticing an occasional reference to higher pressures also. And, I notice that some of the tires on my girls cars as well as others - seem to be wearing on the outside/inside shoulders faster than the middle. With 32 PSI, this would seem to say that they DO need to be more pressure. ....

That's one possibility, but given the manufacturer's suggested pressure is actually 32, I would think more likely the car needs a front end alignment or possibly repairing some front end worn components like bearings or bushings.

[LCHIEN]

I checked just now, and looks like it has the MAX Inflation Pressure : 44 PSI.

Now the 40 psi does not look at that dangerous, somehow !

Don't forget if its at 40 PSI and the max pressure rating is 44, when the tire gets hot from driving highway speeds on hot highways it will go up by 3-4 PSI so you have virtually no safety margin at all. I'd call it dangerous.

[LCHIEN]

I checked just now, and looks like it has the MAX Inflation Pressure : 44 PSI.

Now the 40 psi does not look at that dangerous, somehow !

Don't forget if its at 40 PSI and the max pressure rating is 44, when the tire gets hot it will go up by 3-4 PSI so you have virtually no safety margin at all.

Furthermore the tire rubber gets softer and weaker as the temperature goes up, more likely to burst from maximum pressure. Maximum pressure at maximum operating pressures would be the worst combination.

[Kristofor]

Furthermore the tire rubber gets softer and weaker as the temperature goes up, more likely to burst from maximum pressure. Maximum pressure at maximum operating pressures would be the worst combination.

Is that really true? Or rather do you you think the atmospheric effects of temperature (hot air/road) will have a greater impact via increased pressure than the internal friction of an under inflated tire? I'm not claiming to know the answer, but it seems to me the Explorer/Firestone blow-out roll-overs were largely blamed on under-inflation. I strongly suspect that those max inflation ratings are determined to be safe knowing that when driven they will increase, and that driving a tire is not an unexpected use case...

That said, I've always been told to go by what's on the door/in the manual, not what's printed on the tire itself (which seems counter intuitive but it's what I do).