Question on vibration and or correct tires
 

Hi, I am a new member who just bought a 2006 XK8 Conv. Base. 19 inch wheels. Car has 60K miles. The car has vibration issues at different speeds and sometimes it is more noticable than others. Other points:

1. The two front tires are Firestone FireHawk GT 245/40 R19 98W
2. The left rear tire is also a Firestone FireHawk GT 245/40 R19 98W
3. The right rear tire is a Goodyear Eagle RS-A (dealer claimed they ran over a spike getting it out of storage and this was the only replacement available to them). I didn't notice this until I had it home.

My questions are:
1. Would this tire makeup cause vibration issues?
2. Would replacing the one GoodYear tire with the Firestone Firehawk GT be a suitable correction, if I included an alignment and proper balancing?
3. I also am considering putting on the correct Pirelli tires (Direzionale in front and Asimmetrico in the back) as well as the alighment.

Any thoughts? And yep, I absolutely love this car! It represents a lifelong dream to own one!

First, remember that performance tires need to be warmed up to remove 'spotting' that occurs when hot tires are parked on cool surfaces for several hours or longer.

Second, only the most bizzare mis-alignment (read: almost impossible - maybe a .000001% chance/million) can cause vibration.

While I personally would never own a set of Goodyears or Firestones for more than a couple hours it is difficult to point a finger at one thing without also having other things checked. If you want new tires, by all means, get some and don't waste money having your current tires balanced. However, with that being said, don't be surprised if you're told you have a bent wheel, etc. when those new tires are being balanced.

Maybe at first, but as the tires wear they will get out of balance and that will cause the vibration. So the bad alignment is the root cause.

+1 on checking the wheel isn't bent and having alignment checked before balancing and definitely before replacing tyres.

I may be old fashioned but it was always accepted wisdom not to mix tread pattern (and therefore manufacturer) on an 'axle'. The mixed rears are unlikely to be contributing to the vibration but may give rise to some interesting handling issues. If they lose traction at different rates, the DSC will receive out-of-range inputs. Many 4.2 owners find this system over sensitive already without adding another variable.

Graham

:icon_doh:

NO! NO! NO! do not do it, here in the UK the general opinion is to get rid of the Pirelli tyres at the earliest opportunity.

I replaced all mine (even with plenty of tread) it was the easiest way to obtain an improvement to the car. Money well spent

I have a similar problem and turns out 2 wheels are slightly out of round, both on the left side. Balancing takes out most of it but there is still some noticeable vibration at differnt speeds. My guess is that some speeds work well because the vibration frequency matches up with a harmonic of the suspension.

A decent tire shop should be able to check the balance and tell if they the wheels are a bent.

FWIW, my case is smooth as glass at 80+ so I just have to make sure never to go slower than that. :D

Also, the standard spec for the 19" wheels is a staggered fitment where the rears are wider than the fronts. You mention the rear Firehawk is the same size as the front. Is the Goodyear the same size, or proper size for the rear and you are running two different sizes on the rear?

I agree with Stumpy also, stay far away from the Pirellis. They are overpriced and not that great of a tire.

Point re: alignment not causing vibration is that nearly all alignment wear is smooth and continuous/concentric. Huge amounts of positive caster can cause issues, especially the 'Chevy truck death shake'. When that occurs each front fender heaves and crashes independently as the steering wheel whips back and forth uncontrollably. If you don't crash as a result you'll be lucky to have either thumb remaining - it is impossible to hold the wheel. That sort of thing will affect tire wear and cause a vibration. ;-)

I had problems with two sets of Pirelli's until I switched to Dunlop Sport Maxx's , end of problems ;) ,

All the best ,

Nik

I agree with Stumpy, Keith and Nik Pirelli's are not up to par I have a set and I've shelved them (they're sitting on a shelf in the back of my shop)and replaced with Michelins Pilot Sport They seem to perform better.

thanks to all that offered advice
 

I want to thank everyone for their advice on this subject. After some thought, I decided to try to just replace the tires first (mostly because I did not like what I had). I thought with this approach I would learn or accomplish:
1. Were any of the tires out of round.
2. Would get a new alignment
3. Would get the correct size tires, ie wider in back than on front.

I purchased the Vredestein Ultra Sessanta 245/40ZR19 front and 255/40ZR19 in the back. Had them also do the alignment. Tires were purchased and installed by local Jag Dealer (they were very interested in acquiring the Vredestein, a first for this Dealer).

Problems with vibration are now gone and I do like the look and feel of the Vrederstein. All your email responses gave me things to think about and helped me to this conclusion. Thanks Again.

Major Dan

I replaced the two lousy Pirelli P-Zero Rosso rear tires on my wife's 2006 XK8 with two new Yokohama YK580 tires from Discount Tire back in mid-April. To get them spot-on right, the new Yokohamas had to be Hunter Road Force Balanced the next morning. Discount Tire acknowledged that after listening to my complaint, performed the Hunter Road Force Balance at no charge to me, and the two new Yokohamas were immediately perfect afterwards....

Lesson learned - when putting new rubber on this particular car, I will always ensure that they are Hunter Road Force Balanced before leaving Discount Tire....