So In a continuing effort to try to resolve my steering wheel shake with my 19" summer wheels, I had the car on the lift last night and went over the entire suspension. Grabbed the wheels and shook the car to the point of it almost shifting on the lift. I have NO free suspension play...

Now, I was looking at the vehicle spec guide that Jaguar put out for 9/2009 thanks Jag- and I realized something. they recommend at least in my opinion - very low tire pressures.

This is for any speed - Loads of up to 4 people. Apparently pressures jump by 4psi if you squeeze a 5th person into the center of the back seat.

My wheels are 19 x 8.5"

Front tires are currently 245/40/19
Rears are currently 275/35/19

The closest I could come as far as Jaguar spec were the STR Specs:

They specify 245/40/18 on an 18 x 8 wheel in the front set at 28 psi

in the rear 275/35/18 on an 18x9.5 wheel set at 32 psi

On a NON STR with 245/40/18 all around they specify 31 psi in the front, and 31 psi in the rear.

I'm sure my tire pressures are set higher than that, as most low profile tires tend to be set.

Do you think these pressures make sense to transfer over to my 19's?

Do you think elevated tire pressures might lead to the steering wheel shimmy I have? I would have never thought so, but I was reading a thread on the BMW boards about how a guy was going nuts with wheel shimmy until he set the pressures right (according to the mfg) and 95% of it went away.

I guess it can't hurt to try..

George

 

The jag pressures may be more for comfort and ride than anything else. I tried them and kept an eye on wear. Then added some (3psi, IIRC) front and rear. Can't really feel the difference but the wear's looking more even. (2004 STR, stock 18" wheels)

 

At this point I'm trying to systematically eliminate any and all potential sources of my wheel shake. I'm thinking about setting the pressures to the Jag specs and seeing if it has any affect. Thanks again for posting that spec pdf btw.

George

 

Most luxury car manufacturers recommend tire pressures on the low side because they know their customers want a cushy ride. But when the tires are shot at 20,000 miles or less, the customer is furious. There's a price to pay for a soft ride and it's unfortunately greatly-reduced treadwear longevity....

You have nothing to lose at this point by experimenting with your tire pressures. Just keep in mind that the lower you go, the faster your tread will wear. I'm sure you're willing to sacrifice somewhat if you can just get the set-up back to a decent ride....

Our 2005 S-Type 3.0 has the standard 235/50/R17 tires on all four corners. Relatively cheap Hankook Ventus V4 ES H105 tires installed by the dealer a week before I bought the car. The door sticker calls for 32 psi all around with that particular size. I keep them at 34 to 35 psi throughout the year for longer treadwear and better fuel economy. I'd actually run them another 1 or 2 psi higher than that if I could, but at that point my wife starts to complain about feeling every little pebble on the road. The tires are coming up on 25,000 miles, and they may surprise me and do 35,000 to 40,000 miles before I have to replace them. They have a 50,000-mile treadwear warranty but there's no way they'll do that distance before they're shot....

 

Interestingly the Jag Vehicle spec sheet says 31 psi for your 235/50/17, with up to 4 people, yet bumps it up to 38 psi if you put a 5th person in it.

Now I am assuming this may be a function of the 2003 model year suspension redesign, but the older cars pre 2002.5 call for 26 psi front and 28 psi rear under 100 mph, and 32 front and 34 rear on your car for use over 100 mph..

Where did your 32 psi number come from - the door sticker you said?

I understand about tire wear v/s pressure, but like you said, at this point I'm ready to basically throw these tires away, and sell off the wheels. Do you think I could sell my 3 stock 16" wheels with good tires individually as "full size spares". They fit perfectly fine in the tire well.

George

 

The door stickers appear a bit random. Actually, so do the jag figures
I think Jon89 has it right: add some psi for better wear but in your case you may as well experiment. Good luck.

I'm glad you appreciated the Specs - I was really pleased when I stumbled on them and also pleased that Jaguar saw fit to make them freely available! All sorts of good stuff in there.

 

George,

Yes, the 32 psi recommendation came from the drivers side door jamb sticker. I believe it's also printed in the owners manual. But my policy is to always bump up the pressures a bit because the car manufacturers keep their recommendations too low in order to maximize the cushy ride factor. They don't care that the tires wear out in a heartbeat if you run around at 28 to 30 psi. Of course, many people wind up doing that anyway because they check their tire pressures once a year instead of once a week like you should....

I know you don't want to hear this, but if I were in your shoes I would try to sell the aftermarket wheels and tires and go back to my stock set-up. Yes, you'll have to buy one new wheel and tire, but at least you get the vehicle back to proper operating condition. I realize that in this lousy economy, selling aftermarket wheels is a tough job and you may have to take a bit of a beating to unload them. Good luck whichever way you decide to go. I know this experience has been miserable (and costly) for you....

 

I actually have a replacement stock wheel on the way. $129 on ebay. My tire is fine. I need to get replacement washered lug nuts as well. Bytor is actually sending me some stock ones just to mount the original wheels.

I'm still going to get a different set of wheels and tires, I have a line on a set of 18's from an 04+ XJ. Yes, I am persistent... I don't care about the $$ as much as I do about the frustration.

George

 

Well I'll be damned...

First of all NEVER trust a tire shop to do things right.

I took out my tire gauge and decided to check my tire pressures.

Both front 245/40/19 tires were at 41psi cold.

Both rear 275/35/19 tires were at 39psi cold.

So I proceeded to experiment. First I aired them all down to 35 psi. Took the car for a short ride. And the steering shake was MUCH improved. It was still there, but not nearly as bad or as violent especially in the bad indicated 45-50mph range.

So I then proceeded to drop another 3 psi and take the car to 32psi all around. This is the best the car has ever felt on these tires. There is still some vibration and shake, and the effect of dropping from 41 to 35 was more noticeable but its more of annoying pulsation in the wheel rather than the violent shake, especially when you're stuck cruising at that 45-50mph range. before my watch used to rattle... Now you can feel confident with two fingers on the wheel. I only got the car to about 65mph, but that felt almost completely smooth.

I'm going to let the tires cool off and tomorrow perform the next experiment. Setting it as jag recommends you set an STR which uses 245/40/18 front and 275/35/18 rears. 28psi front and 32 psi rear. - And take the car for a ride. I have an air compressor so if the ride worsens I can always come back up to 32psi.

My guess is that the bigger the volume of air in the tire, the more potential change in psi from cold to operating temp... hence potentially lower cold psi's BUT it does have a marked effect.

I don't care if i get 10k miles or less out of these tires as long as the car feels better. I had them pretty much written off as a lost cause. They are basically going to stay on the car until I get a replacement set of wheels / tires and not a day longer.

More to come....

George

 

George, I totally agree with you about 'trusting' the garages. The one I use ALWAYS over-inflates my tires, but about 10 psi...and I keep telling them to calibrate their gauge or get a new one. They all use the one that 'attaches' to the air line, and nobody 'double-checks' using a standard gauge. First thing I do, come home, and let out some air. (shaking my head of course the whole time)

 

Fronts more pressure than the rears in an S-Type

When you find the best setting you can, wait again until they're cold and be fussy with the pressure gauge to get each axle set pair as exactly alike as you can.

Hope it all works out!

 

As far as the tire shops are concerned, whenever I have a nail repair or buy new tires, I tell the manager or the counter guy to inflate to my desired psi for that vehicle and I have him write down that psi on the ticket that goes out to the shop floor. I always take my trusty digital tire gauge with me, but I keep it in my pocket. Once the job is done and the vehicle is outside waiting for me, I ask the manager or the counter guy to come outside with me to check the pressures with my gauge. Invariably, adjustments have to be made. Usually, the tires are slightly overinflated and I adjust them down as necessary right there with the guy watching me. On occasion, the tires are underinflated and I immediately ask for an air hose so I can pump them up to my preferred psi myself while the guy watches me do it.

I've never been refused, treated rudely, or even questioned for doing this. They all seem to understand that I take very good care of our tires and I want them correct from the second I drive out of their parking lot. The manager at one of the local Discount Tire shops that I really like has even said to me "Jon, if all of our customers were as obsessive as you are about your tires, we'd sell a lot less of them due to premature wear!"