Infiniti recommends 18 psi below the max tire pressure?

[nemo]

Originally Posted by niky

I've actually seen center rib wear at high pressures on some extra wide low profile tires, but most ordinary tires will see no extra center wear at 40-45 psi.

A point to note here is be sure the rim width is correct for the tire being used. In the past, it was a fairly common practice for people to use rims which were too narrow. This would contribute to additional tire wear.

[niky]

Good advice, but they were the proper width. These were UHP summer tires, so the extra wear was more evident during the months I stayed away from the track.

[ChazInMT]

Ya know reading this all just made me realize what we're talking about with a tire. At first, I thought, "There's not a solid steel band, so how can steel belts help?" Then I realized, if you had a flat cable in the middle of the tire, and its circumference was exactly 25" with no ability to stretch out, and the circumference of the cables near the sides of the tread on a tire were 25" circumference with no ability to stretch, you'd have no way to make it "Bulge" in the middle and wear out the center first. The tire will hold its cylindrical shape because the steel belts don't stretch.

Sort of reminds me of another thing that has no bulge because of its steel belts.



Same principle, just shorter, smaller, rubberier, and less corny.

[CapriRacer]

A couple of additional thoughts:

First is that the steel belts in tires are indeed cables, but they are at an ANGLE to the circumference. In other words - they are NOT hoops and they can stretch! That means that while they RESTRICT growth in the center of the tread, they don't PREVENT it.

Some tires have cap plies - usually made of nylon - and while those also restrict the growth of the tire in the center of the tread, they ARE (more or less) circumferential. Needless to say, tires with cap plies would be less likely to wear out at the center than those without.

HOWEVER, tire pressure has a small affect on even-ness of wear. There are other things that have more affect. For example, it is known that "spirited driving" tends to wear the shoulders out. So if you go around corners quickly, and use high inflation pressures, there is a cancelling effect on even-ness of wear

So to answer the original question: Why the difference between the vehicle manufacturer's specification and the max on the sidewall?

Well first, the tire manufacturer doesn't know what vehicle the tire is going on, so what is written on the sidewall is an operational limitation. The important thing to remember is that the load carrying capacity of the tire and the shape of the tire's footprint is based on normal load vs inflation pressure usage.

The vehicle manufacturer sets the inflation pressure based on a lot of different parameters - and ride quality is certainly one of them. But ALL the vehicle manufacturers work within a small range of load vs inflation pressure values - ones that are easily characterized so the tire manufacturers set up their tires for those conditions. I am of the opinion that using inflation pressures outside the vehicle manufacturer's specification has inherent risks - and ones that we just don't have a good handle on.

[undata]

Originally Posted by Daox

In short, yes.

31 psi is to give you a nice comfy ride. Autocross racers run more like 45 psi for better handling. We do the same, but because it lowers the rolling resistance of the tire (just like your bike tire). Sorry, your tire guy has no idea what he is talking about and is probably just regurgitating what some sales guy spewed out. The fact is the tire can easily take 51 psi without any issues what-so-ever. You will notice a harsher ride, but IMO its quite livable. I run all my tires around 50 psi.

BTW, no, nitrogen is not necessary at all. No tire requires it. Its just a money making gimmick.

Except, filling up with nitrogen is preferable to filling up with air + water. A lot of places, I test the "air" hose before I put it on. A surprising amount of water comes out.

[TooMuchGlass]

Originally Posted by CapriRacer

. . . the tire manufacturer doesn't know what vehicle the tire is going on, so what is written on the sidewall is an operational limitation. The important thing to remember is that the load carrying capacity of the tire and the shape of the tire's footprint is based on normal load vs inflation pressure usage.

The vehicle manufacturer sets the inflation pressure based on a lot of different parameters - and ride quality is certainly one of them. But ALL the vehicle manufacturers work within a small range of load vs inflation pressure values - ones that are easily characterized so the tire manufacturers set up their tires for those conditions. I am of the opinion that using inflation pressures outside the vehicle manufacturer's specification has inherent risks - and ones that we just don't have a good handle on.

I'm beginning to be swayed. . . I was originally sold on pumping these things up to 51 and riding off into the sun, however, I'm having second thoughts. Given that these are "low profile" tires on a 4,000 lb luxury car, I'm hesitating to pump it up much about 40. It definitely seems like using regular compressed air is preferable to pure nitrogen, but 40 psi is quickly becoming my absolute (and admittedly somewhat arbitrary) max.

Am I just being a chicken?

[serialk11r]

Originally Posted by TooMuchGlass

I'm beginning to be swayed. . . I was originally sold on pumping these things up to 51 and riding off into the sun, however, I'm having second thoughts. Given that these are "low profile" tires on a 4,000 lb luxury car, I'm hesitating to pump it up much about 40. It definitely seems like using regular compressed air is preferable to pure nitrogen, but 40 psi is quickly becoming my absolute (and admittedly somewhat arbitrary) max.

Am I just being a chicken?

If your ride quality sucks then maybe it's worth losing a little fuel economy for a less jarring ride. Afterall, there are diminishing returns with higher pressures.

[ksa8907]

I may have missed it, what size tires are they?

[TooMuchGlass]

Originally Posted by ksa8907

I may have missed it, what size tires are they?

The tires are dunlop 225/55 r18

Killer and others: the issue really isn't a jarring ride. The ride is completely comfortable, I'm just worried about safety. With the car being so heavy and being driven strictly on city streets (some of which are pretty shoddy) I'm starting to become more concerned about a blowout.

[Daox]

Increased tire pressure will help prevent a blowout from bent rim or pinched tire from pot holes and bumpy roads. It does increase the risk of puncture somewhat though. Honestly, neither of these has been a problem for me, and Wisconsin has some pretty crappy roads here and there.

If you don't feel comfortable going to 50 psi try 40 out first, then try 50 later if you want to try it.