Well folks, egg in my eye.Last fall I replaced my old Dunlop XXX tires with continental extreme contact d/w summer tires.

Several days later I drove to a small town and had an incident with a deer in route. The car suffered a broken fog light, broken grill mount and some bumper cover damage. The car still drove straight and felt fine. The deer ran off of the road way and may or may not have survived our contact.

The following week while assessing the damage I checked the tire pressures and they were all very high 35~40 psi. I lowered that pressure down to my preferred comfort level of 27 front 30 rear. That weekend I drove the car into the Hill country and noticed that there was something very wrong with the handling at any speed above 65~70. I then took it to an alignment shop and they indicated that one of the upper front bushings was bad

so

I replaced all the upper bushes, the upper ball joints and shimmed the shock mount. Drove the car and everything was much tighter but the car was still not going where I pointed it in and out of turns.

Now

I have a work bench full of bushings, mounts, end links, ball joints etc for the front and rear that I will install sometime soon.

But

just for the heck of it I upped the tire pressure to 30 front and 35 rear and…there it is, the car is 90% better.The turn in is crisper the transition is as expected, life is almost good again. I remember having read that the Continentals were prone to the side walls rolling over but thought the newer Extreme Contacts had eliminated that trait; I guess they did if you fill the tires with enough air.

Bottom line, different car/tire combinations require different air pressure settings.



wj

and for those that wonder about their capabilities , they stick in turns well enough to twist that convertible frame a bit!

 

Glad you found your tire pressure sweet spot. For my wife's 2006 XK8 with 19-inch Yokohama YK580 tires, it has always been 32 to 33 psi in the front and 28 to 29 psi in the rear. Took me several months to finally figure it out way back in 2012....

 

I thought general rule of thumb was a little higher pressure at the front due to the additional weight of the engine and better traction with lower pressure at the rear.

 

WOW, now that is eye opening!
In all of my years as an auto enthusiast I never read or saw mentioned the front tires carrying more air pressure than the rears.
So, I have never even considered it. I do know that on an old Taurus SHO that I drove too fast I kept me tire pressures pretty even front to rear but all of my rear wheel drive vehicles have favored a higher rear pressure. Where have you read this? I want to investigate.

wj

 

well let the internet be your friend.
I guess the reason I never knew @ higher front pressure is due to the fact that I've only had 3 front wheel drive cars in my 71 years!
I will restate: I have never heard of a rear wheel drive vehicle carrying higher front tire pressures...but I guess some do.
wj

 

Couldn't say I've read it anywhere in particular but I have owned a few rear wheel drive cars (2 jags currently and BMWs previously) and book pressures tend to be higher at the front.

I remember hearing about drag cars running low pressures on the driving wheels in order to get better grip so I sort filled in the gaps with these pieces of information. An extreme example I know but the theory must hold some weight.

I could be completely wrong but only logical explanation for higher pressures at the front seemed to be engine weight.

 

Would you please confirm this sometime in the near future?
I pulled up several old service manuals from my past vehicls (928, 500SEC, 911Turbo, F348) they all recommended higher rear pressures. Maybe a USA thing? Even my 2005 xk8 recommended 2 more psi in the rear (from several sources...not the factory manual)
wj

 

dumb me, of course there is a relationship between tire pressure and WEIGHT DISTRIBUTION. ie; 50:50, 45:55 etc.Since most rwd vehicles tend to have a higher weight bias towards the rear many manufacturers recommend higher rear pressures.. Not necessarily higher direct weight over the front or rear wheels but rather higher weight bias toward the front or vise versa the rear.


wj

 

For regular driving, tire pressure is all about getting even wear across the entire tread width. I run 28-29 psi on the rear and 32 up front.

Higher front to rear also helps reduce understeer. You can do a lot to a cars handling by just adjusting tire pressure.

 

My Mercedes 560SL sticker calls for 28 psi front 35 psi rear, in spite of 60/40 front/rear weight distribution. This always mystified me, but the handling is what matters most. The XK8 handles much better with the staggered sizes and recommended pressures. To date I have been unable to squeal the tires cornering on the Jag but do so routinely in the MB.

 

The sticker on the doorjamb of my 2005 XK8 says 32 front, 34 rear.