I currently have 255/40/ZR18 Michelin Pilot Sports on my '03 XJR. This may sound like an odd question but I have checked the archives and find many posts from owners wanting to go a larger size. I'm looking at the possibility of a SMALLER size. I want to stay with the same 18 in. Asteroids, but these tires are wider than the English Channel. I live way out in the country and with the road imperfections, the car does tramline a great deal. It's perfect on the highway so I don't suspect any mechanical problems and I attribute the tramlining to the width of the tires. Has anyone tried a smaller size, 225-245? Anyone tried a different profile? 45-50? I've used the converter calculator on the Tire Rack website and there are a few options that have little effect on the circumference and height of the tire.

Just wondering if anyone has used a narrower tire or a higher profile tire, and what the results were, or if anyone has recommendations....

Thanks

 

I don't see why people put wider tires on the stock wheels. The stock 255's are too wide as it is. 245's are much better and should be the widest size for the 8 inch wide wheels, especially for the front.

 

I have XJR rims on my Vanden Plas. I currently have 245/45/18 Contiental Contiextreme Contact tires on it. My car USED to not tramline much at all. Now that my bushings are shot, it tramlines terribly. If your bushings are ok, you should be fine with this size. The only concern I initally had was that these tires have a slightly larger diameter, and they are very close to the fenders. However, I have hit many bumps that crashed into the chassis stops with no clearance issues. The close clearance in my opinion looks better than slightly larger gap of the 255/40/18. Unfortantely, I currently have a bent rim due to the rims being 18'' and a huge bubble in my tire's sidewall. I need to get it repaired. I dont think this damage has anything to do with the tire size, and the slightly thicker sidewall probably helped out. Where I am (Boston) the roads are HORRIBLE!

 

Always remember section width is tied to aspect ratios. (example: 245/45/18 245 is section width, 45 is aspect ration) Larger diameter wheels allow shorter sidewall heights to increase cornering performance, but at a cost of a rougher ride.

http://www.dunloptires.com/care/widthRatio.html

 

Thanks Burmaz. And BTW. I likes your Jag.

 

I'd be willing to give up a bit of cornering for a smoother ride and less tramlining!

 

If a smoother ride is the desired outcome, you may want to reconsider rim diameter. Many get caught up in trends of "cool factor" of using larger rim diameters, but if the desired result is the smoothest ride, you have to get away from really low sidewall profiles. Maybe a set of rims from a regular XJ or an XK. (16" or 17") The more sidewall height you add, the more the sidewall will absorb road imperfections, but remember, cornering is not as responsive.

 

My primary desire is less tramlining, which I believe I can conquer with a narrower tire. I'm not willing to switch out my 18" Asteroids. I'm simply looking to determine if I can use a 235 or 245 instead of the 255's that are on it. At the same time, if I can switch to a 45 or 50 aspect tire, the ride would improve. I'm wondering if anyone with an XJR has tried using the alternate smaller size.

 

Fairlane500, you can use another size tire, but a smaller treadwidth/aspect may not have the proper load rating. You could for example go to a 225/40ZR18 which can be mounted on your 18"x8" width, and yeild 1" less treadwidth at the same tire circumference but the load capacity of the tire is less than what you should use. You will have to search carefully the various tire manufacturers to get the proper size/load/aspect/circumference.

Looking at Michelin's specs, the tire you have is actually a little too wide for the 8" rim, and should have been mounted on a 9" wide rim. This will certainly affect how the sidewall performs. When you go looking for a replacement, look at the placard in the door to see what was the original size and more important, load requirements. The correct tire circumference is 26.1". (this affects car ride height, suspension geometry and speedo/milage accuracy) So when you are searching for your new tires, start with a tire designed for an 18x8 rim, with the overall circumference of 26.1. Make sure your choice meets or exceeds load requirements.

 

I guess I should have been clearer. The 255/40ZR18 is the original manufacturers spec tire for the XJR, so they shouldn't be too wide for the rim.

 

Fairlane500, that can actually depend on tire manufacturer. Goodyear may rate a tire's aspect ratio on a different rim size than Pirelli or Michelin, or Firestone than Conti or Dunlop. That's why I say you have to look closely at the specs.

Michelin rates their Pilot 255/40ZR18 on a 9" wheel, who's wheel width range is 8.5" to 10" with a diameter of 26", and if you have 18" Jaguar Asteroid's, then the Michelin is really a little too wide for your 8" rim width. Jaguar's XJR's Milan wheel (18x9) would be a good choice for the Michelin. Goodyear rates their Eagle GT 255/40ZR18 on an 8" rim width, with a recommended wheel of 7.5" to 9" wheel width with a diameter of 25.1". And to be honest, neither of them would be the appropriate choice to give the right wheel size/tire diameter. Again, you have to match the right tire with the right wheel with the right load and right diameter. Not all tires are created equal. There is a lot more to tire technology than a given size.

The Conti's have a couple, (which were also OE) ContiSportContact3 225/45ZR18 which are designed for 8" width and close to 800 rev/mile. Section width is 8.9"...3,042 lbs load/pair. ContiSportContact2 245/45ZR18 (OE Jag) which also is for 8" rim, section width at 9.6" but gets close to being a little tall, and may cause speedo to show a little off at highway speed @ 781 rev/mile (26.7") 3528 lbs load/pair.

 

I apologize - I should have replied sooner and said thanks for the information. I'll be storing the Jag for the winter and I'll revisit this in the spring when I'm shopping for new rubber!

 

Interesting...

I'm running 245/45/18 on my car with zero issues. I typically drive for 3 hour long stretches at a time and do not have any issues with tracking or tramlining.

Ken

 

I have 245-40ZR 18s, and they seem like a factory size... I actually think they may save some fuel. As far as ride is concerned, they ride like a factory size. I have had problems with bent rim though... Maybe the 40 aspect ratio makes the wheels more vulnerable. I actually kind of want the more agressive, sporty look of a wider tyre. Next set will be wider.

 

Like many, I would also like to have everything as it was from the factory. Although I always had 245-45 for my 18" Astroids and for this winter I switched to 255-40 because I still had them lying around, but the handling is noticeably different.
As mentioned above, much more tramlining. So much that after a ride on the highway I already want to go back to the 245-45 (which is a much more commonly available size in the Netherlands).

As far as control arm rubbers are concerned, they still look good and are not torn or rotten. There is a very small amount of play in the right lower ball joint, but I don't think this should affect the driving behavior that drastically. The top ones are good.