I am thinking about downsizing the 19in alloys on my 08 XJ X358 to 18s in order to improve the harsh ride.

Has anyone done this? If so pictures of X358s on 18s would be great.

Thanks in advance.

 

I downsized late last year to 17" Elegant wheels from 19s. "Elegant" wheels were an option on the X350s but not on the X358s for some reason. They take a 235/55R17 tyre. However you can't fit them if you have the larger brakes of the XJR. My last X350 had 18s. Again on these I had downsized from 20" Sepangs. Best thing I ever did ! Why people love their teeth fillings being knocked out is beyond me, as is the obsession with enormous wheels and very low profile tyres in general. The manufacturers pander to this "Sport, sport, sport" obsession as if we're all going the track days ever weeken. We need to get back to comfortor at least the option for it.

 

I’ve ran 17’s, 18’s, and 20’s on our x350’s, and 19’s on the x100. The more sidewall you have, the more comfortable of a ride it will give.

On the x350 I don’t think you can go wrong with 17’s or 18’s. The 17’s we run with are more of a balloon like ride, whereas the 18’s feel a bit firmer and sportier. Take into consideration the tire manufacturer and the type of tire they are, as that can play into how they feel, too. Once you are up to 19’s and 20’s the ride is very stiff and jarring, comparatively.

I’ve run previous cars on 18’s and the ride was horrendous, because the sidewall was so small. The x350 doesn’t have as much of a problem on 18’s because it has enough sidewall. Here is a picture of our blue XJ with Coventry Whitley 17’s, and our topaz XJ with stock 18’s (the car looks lowered as ride height had not been reset).

 

Actually, when I checked the difference in diameter between the 19" and the 17" tyres it was about 2-3mm, so I didn't have to reset the ride height, or the speedometer. The wheel diameter can be reset on these cars as when I swapped the last car from 20" to 18" the dealer entered the new wheel diameter. Its not a big job, just an entry onto a laptop with it plugged into the diagnostics port.

Use this site to check out what your have and what you want to put on: -

https://tiresize.com/tyre-size-calculator/

 

Sorry Fraser, I didn’t mean to sound like the ride height needed adjusted after a wheel change. I was only pointing out that the topaz XJ suspension was in jacking mode and needed to be started and driven for the airbags to pressurize. I haven’t messed with the ride height on any of the XJ’s as we keep the overall tire diameter within manufacturer specs.