owners manual recommended normal tire pressure = abnormal tire wear on my rear tires. The vehicle care manual lists normal tire pressure as 32 psi F & 34 psi R for my 18" wheels. Sadly, 34 psi in the rear tires has developed into the classic sign of over-inflation, i.e. more wear in the center / less wear on the outside edges of the tread.

Anyone else experience this when following the manual guidelines ??? Maybe it's happening because I'm not carrying two full adults in the rear seat ???

Z

PS There are lower tire pressures listed for "maximum comfort". However, the price of having "maximum comfort" is having your top speed restricted to 100 mph ???. Sheesh, might as well drive a Yugo if I'm going to have to observe nonsensical limits like that

 

I run 26 rear, 29 front on my 18" wheels to get even wear across the tread, but I also think your tire choice plays into that as well.

 

Z, what are you using to measure pressure?

So many gauges have accuracy of +/- 5 or 10%. Could that possibly be a contributing factor here?

If you're already watching this, never mind. Just dont want to overlook it. God knows it took me years to realize it.

John

 

I don't remember where I got this but I did remember that it showed pressures for the "real world" being much lower and more in line with what some of us have determined over time.

 

I have a pretty good digital gauge, but I never trusted it, so I double check every tire with a mechanical dial gauge, that's always been spot on. Both gauges agree with each other, so I think I'm putting in the amt. of air I think I am, and always careful to measure when the tires are cold,

the chart mirrors my owners manual, but for my tires at least, thats way too high. Maybe the brand of tire has a little to do with this. I'm running BFG Comp 2 A/S, a pretty soft tire.

Z

 

Centre wear is a sure sign of over-inflation and Rothwell's chart for "real world tyre pressures" is cool. Low profile tyres look cool, but it's difficult to visually see what tyre pressure you're running. Try reading the tyre pressure gauge after a long drive. The result might surprise you.

The overall expected tyre life is a factor of many things. Enthusiastic driving habits and high speeds in hot, sunny weather will eat into tyre life quicker. Also heat sources affects working tyre pressure and the front tyres can get very warm with the engine nearby and hard braking, thus again shortening tyre life. I wouldn't trust the Jaguar manual as it wasn't written considering Oklahoma as your location and your usage habits.

I have an extreme situation in Bahrain, where summer temps can reach 50degC (that's 122degF) and that's in the shade. Also, after a period of time, even if I had sufficient tread left, the rubber basically cooks in the hot sun here. So past 3 years, the rubber will be rock hard and hysteresis sets in. Cracking of old tyres between the side wall and tread is common here especially if the car is parked outdoors. I inspect my tyres regularly during summer and play with the tyre pressures between winter (28psi) and summer (26psi) according to ambient conditions. The last thing I want is a high speed blow-out caused by over inflated hot tyres. I've always run with Pirellis as I previously had a 360 blow out spin with another s#$%$y brand.

 

I have always considered recommended pressures to be precisely that. They are recommended, not specified. The optimum pressures (best compromise between grip and wear) are determined by experiment as there are many factors which influence this:

tyre brand and type
ambient temperature
load (passengers/luggage/fuel)
road surface
driving style

The wear on your rear tyres is indicating you should use lower pressures to get the best wear for your particular combination of factors.

I check my tyres monthly when cold, always over inflating by 2 to 4 psi on the inflator gauge (notoriously inaccurate!) and then dropping to the required pressure using a tyre gauge. My recently acquired digital gauge is no more or less accurate than the manual Dunlop gauge I've had for more than thirty years but is more convenient.

Graham

 

This is what happened to my left and right rears at 29psi over the lifetime of the tire, still poor wear pattern. Look at the trend rather than particular values, clearly tread depth can not increase, this is explained by using different positions on the tire each time.

 

that chart numbers for my 18" tires are identical to the numbers in my owners manual, no nothing new there.

after a drive, a tire will always show increased PSI, sometimes a lot more. Not sure what the point is here. It's useless to use that number to tell you anything, unless you are a Formula 1 team and are shooting for an exact number to coincide with the tire compound being used and track conditions. Us mere mortals don't have enough sensors on our cars ( relating to tire temperature, tire psi, relative humidity, ambient air temperature, maximum track speed, and track temperature ), to be able to use hot tire psi to tell us anything

what I'm most concerned with here, is Jaguar's warning not to exceed 100 mph when using the lower tire pressures. Sure, I'd love to get more even wear across the entire tire. But not at the cost of being unsafe at speeds over 100 mph.

Do I go over 100 mph every day ? No, my schedule won't let me get out of town and hit the deserted roads as often as I'd like. But I won't let too many days go by without a trip to my favorite secluded roads where I'm sure to exceed 100 mph at least a dozen times for several seconds at a time.

It's those times that I'm wanting to know my tires have the correct inflation for the driving being done. I want to concentrate on, and enjoy, the driving tasks at hand. Not having a buzz-kill, worrying about having enough / not too much air in the tires.

Z

 

After experimenting with tire pressures during the first year of ownership of my wife's 2006 XK8 with 19-inch staggered wheels, I determined that the sweet spot for tire performance vs. tread life is about 32 psi for the front axle and about 29 psi for the rear axle. I have stuck with those pressures year-round ever since and always get even treadwear as the tires age. The sets of Yokohama YK580 tires that I have stayed with since 2012 typically last about 48,000 to 49,000 miles on the front axle and about 33,000 to 34,000 miles on the rear axle....

 

I think it's sustained speeds over 100 mph rather than exceeding it for a short period and dropping back. It will have been written with the German Autobahns in mind where driver's can and do go at maximum speed for considerable distances.

Graham

 

I guess if Z wants to play he gets to pay.

Going over 100 mph has got to cost you something.

I don't think tires themselves would be unsafe at 100+ speed. Its the maneuvers a driver might try (right after he says "Hey watch this...I saw it done in Fast & Furious") that are the unsafe part.

 

My 97 with the stock 18" wheels had very even wear with 32/34, but I could see that the 06 with staggered 19's was wearing at the center when I bought it. I followed Jon's suggestion when I replaced the rears and I now use 32/30. I have a Airco regulator gauge that I use as a master to check my other gauges.