Tires: tire pressures, maximum inflation, inflation pressure

Question
Hi Barry:  I'll try to be concise...  In a car's manual, tire inflation specifications are listed.  In my Audi TT, for instance, I believe they are 34 front, 32 rear.  I just replaced original tires with a different brand.  The new tires have a higher maximum inflation listed on the sidewall than the previous ones did.  Does this mean that the suggested pressures should be adjusted upwards also?  If it means anything, I've always put a couple of pounds more pressure in than recommended, because the slightly better response and tire life that results compensates for the slightly harder ride.  Thanks for your feedback...  Jay

Answer
Jay,

If you will look carefully at the stamping on the sidewall, it will usually express the maximum load and maximum inflation pressure this way:  

Maximum Load XXXX,
Maximum Inflation Pressure YY.

This means these two items are probably independent - and they are.

If you will also compare the original tires with the different brand - if you used the same size, the maximum load was the same (or pretty close).

It turns out the if the tire size is the same (meaning all the numbers are the same), then the load carrying characteristics are nearly the same - which means the inflation pressure shouldn't change.  This is a "laws of physics" sort of thing.

BTW, it is a commonly held myth that changing BRANDS of tires requires a different tire pressure.  This is not true for load carrying capacity - but to be fair, the reason many people believe this is that there can be significant differences in handling characteristics between tires, which can be made similar by inflation pressure changes.  However the real reason there are differences in handling has to do with the size and stiffness of a particular component - the "filler" - which has nothing to do with the load carrying properties of a tire.  

I'm going to take a guess that the new tires have a higher speed rating.  Higher speed ratings can utilize higher pressures to mitgate the speed induced heat build up - and the tires are designed to acommodate that.

I could go on for quite a bit more, but I hope this is enough.