Tire pressures

[AZhitman]

Dennis mentioned something in another thread here that got me thinking...

My 96V tires have a "35psi max press" designation on the sidewall. I understand there is some wiggle room based upon safety and the nitwit attorneys who want to protect the deep pockets of the manufacturer.

That said, is there any benefit to running these at, say, 42 psi (measured after a 30-minute 100mph blast on a hot Phoenix freeway)? After six months of testing, I've settled on keeping all four set at 39 psi, where they feel the best.

Any problems with this?

[greg_atlanta]

I like lower psi, helps handling since tires hug the road better. If the tires are overinflated they may wear faster in the center of the tread.

I've never measured my tires hot, so not sure how much the psi goes up. But I wouldn't inflate beyond 35 psi when cold.

[Q45tech]

There is always more safety factor in overinflation than underinflation BUT generally there is no point in going beyond the max cold inflation pressure.Obviously V rated is stronger than lessor tires BUT DON'T think they are more than 10-15% stronger.35 psi cold for 96V is ~~ 1560 pounds which would be the front load plus you [170#] 1560-[170/4] =1520- [1200 static] leaving 320 extra # for weight shift during cornering or braking!

I would rather see you inflate to 90% of cold max or 32 psi COLD [first thing in morning before car is moved an inch] then take what ever pressure increases come from driving or temperature changes during the day.

What is tire size brand and wheel width [important to develop ideal sidewall shape].

[AZhitman]

Thanks Dennis and Greg - I'm running the 245/50V16 Yoko's on '99 Q alloys.

It seems that these tires like the higher pressure (39 feels ideal) but if this will be detrimental I will return to a lower pressure.

Dennis, at this size, and assuming 32 psi cold, what kind of max PSI increase can I expect (say, at 122 ambient air temp, 100 mph for 30 minutes). I'm sure I could just measure it myself...

[firstq]

Hitman, I thought you were running YK420 - those are H rated tires, did you upgrade recently to a "V" rated tire? Let us know what tire and if you like it so far...

[AZhitman]

No - Check again. The 245/50V16 is indeed V-rated.

How's your Q doing Arshad?

[Chally]

My 96V rated tires recommend a max of 44psi at 1565lbs. I have Dunlop Potenza's & they handle & wear very nicely at 40psi.

I have a sneeky suspicion that the tires in Australia are of higher quality for the same rating of the U.S. (eg. 1}the blowouts on the Explorers in the U.S. hasn't happened here & 2}all Jap imports must have their tires changed to be legal in Australia)

[firstq]

Hitman, I got YK420 in the 225/60/15 size and they are indeed H rated tires. May be in your size they upped it to a "V". I like these Yk420s, they are very quiet.

The Q is dead right now, broke yet another intake collector runner - this time it is number 1 - so may be I will be able to replace it w/o having to remove the plenum. If I keep braking the collectors with this speed, I may end up getting the record for removing the plenum in any given period of time.

These damn all aluminium collector runner threads are as delicate as the car itself...just a little bit of incorrect force trying to get the bolt in and you can kiss the threads goodbye...

[AZhitman]

Sorry to hear about the runner... I gotta come by sometime when you're pulling it apart (I've never had the opportunity to see one apart).

Discount Tire confirmed that the 50-series YK's are V-rated, all others are H. I'm loving mine.

[Q45tech]

Just like the 1% density change for each 11F, there are a few relationships that should be ingrained in memory for tires [in 65-50 aspect ratios] it is roughly 1 psi per 10F change in average carcass temperature.

There is a 3-5 psi cold to highway relationship but this would depend on CAMBER!!!!!!!!!!!!!!!!THE CAMBER is what destroys tires in that a 80F morning may get the inside edge to 150-175-200F after 3 hours of 80 mph expressway at 95F........just going straight. The rubber just melts away at extreme temperatures because the rubber is such a good insulator and [but] the metal cords do conduct some of the heat away to other parts of the tire and heat the interior air volume.

Some tires use more metal than others some nylon, some arimid [kevlar], some all polyester, so their ability to move heat around inside is more limited

Important to measure the diffferential temperature across the tire tread face with IR point and shoot meter.An accurate all electronic tire psi gauge is almost mandantory!

[AZhitman]

Roger that Dennis. I've got 2 gauges (one calibrated digital and one real expensive analog) and access to an IR thermometer, so I'm gonna do some testing...