The standard tyre size for an XJR6 is 255/45 X 17. Mine came with 245/45 X 17 Michelin Pilot Sports.
Some say the narrower width reduces tram-lining? Yet I find it is still sensitive to pulling, following camber changes and lines in the road.
The narrower width also reduces the profile making the already hard ride even harder.

Ride is too hard. From member's experience, what size should I go for? 55 or 60 or 70 series?
Concern is altering overall gearing and loss of acceleration if I go too far with the profile.

Also, which make of tyre gives the most supple ride?

 

I had an XJR/6 as a daily driver for several years (140k miles) and had numerous tire issues and experienced the usual tramlining problems....which were sometimes almost terrifying. I tried quite a few supposed cures to no avail.

Long, long story short I threw in the towel and went with a wheel change and 225/60x16 tires for a number of years. No tramlining at all.

I also used 235/55x17 tires for a period of time and had zero tramlining.

There won't be any performance loss as long as you stay at or close to the overall diameter of the original 255/45x17 size.

Most supple riding tire? I don't know.

Cheers
DD

 

How was the ride on the 55 and 60 series compared to the original?

 

I have 235/50/R17 fitted and absolutely no problems, tramlining etc. All you are losing is the extra width. My research (post Dec. 2016) indicated 255 was over wide for 8" rims.
I have attached comparison chart -

John Herbert
1996 XJR

 

I have Dunlop Sport Maxx RT 225/50/ R17 98Y on mine. Very happy with the ride and handling, no tram-lining . The marketing department went way over the top with the width of the tyres from new.

 

I recently rebuilt the entire front suspension, including new bushings on the subframe, and that completely cured the tramlining on my car, so if you have that problem i suggest you take a look there first.
Also install some bushing spacers or wind some steel wire in the bushing gap to cure the excessive sideways movement of the steering rack.

I run 255/45/17 Toyo Proxes sport tires, and i would say the ride very much magic carpet style comfy - before changing the bushings it was a little bit on the harsh side.

edit: i used the rather expensive Original parts, not URO, except for the upper control arm bushings and lower shock bushings which were polybushings.

 

To be honest I don't recall any significant difference in ride quality. Softer shocks are more likely to give you the improvement you're after, IMO.

I recall that the steering was slightly less crisp with 60-series tires.

Personally I found the 45 series tires to be unsatisfactory for the rigors of daily, real world driving. Two or maybe three times I had to replace tires and repair wheels from pothole damage. And, at the time (this was many years ago) there were not any tires of the appropriate size that gave anything resembling decent tread life. I was getting 12k miles from a set of tires while driving 15k miles per year. (My first clue was buying the car at 30k and the second set of tires was already worn out!)

Cheers
DD

 

My XJ12 has 245x50x17 tires on XK8 factory wheels. Same overall diameter as XJ6 16" tires. No steering issues, ride is great, proportions of the tires and wheels are just right for the car. Sidewall is not too short. But the inexpensive tires are getting chewed up quickly by this heavy car. Or is it my driving?

 

You do need reinforced tires for these cars. Which exact ones are you using? I have long life out of my Dunlop SP Sport RT’s

 

It isn't expensive versus inexpensive. Nor the weight of the car....although you do need to look at load ratings.

Some tires are simply not designed with long tread life in mind. Look at the tread wear index when you buy the next set of tires; it does mean something. Many "high performance" tires are designed for maximum traction. They're often quite expensive, have high load and speed ratings....but horrible tread life ratings.

This is what is ran into years ago with my XJR. Staying with the original size I was getting 12k miles from tires costing $200-$250 each. I went to 225/60x16 tires and was getting 40k miles from tires costing $100 each.

Cheers
DD

 

My XJ12 has 235/50R17 tires on X308 Super V8/VdP SC 'Solar' wheels.

No complaints, although the stock 16" wheels with 60-series tires afforded a slightly cushier ride.

 

How did the 45, 55 and 60 series tyres compare for ride and crashing through?

 

One would expect the 60-series to feel different in terms of ride quality but I don't recall much difference, to be honest. But this was a number of years ago.

Most of the stiffness comes from the shocks and springs, I reckon

Cheers
DD

 

Odd, my shocks and springs are very soft. The hard ride comes from the 45 series tyres. So am considering what tyre to use based on other's experience?

 

You have an XJR/6, right?

The springs and shocks for that model were definitely harder than the standard XJ6.

Anyhow, you're best chance for maximum comfort would probably be 16" wheels with 60-series tires but even then variables come into play: surely not all 60-series tires are manufactured the same with respect to casing and sidewall stiffness.

Plus....the general condition of your suspension comes into play as well. If there's a lot of wear then its gonna feel like you're "crashing" over bumps no matter what tires you have.

Cheers
DD

 

Point taken about worn suspension bushes. Wanting to compare the ride of my XJR with 245/45x17 Michelin Pilot Sports, I just drove a standard X300 XJ with 215/60x16 Dunlop tyres and was surprised to find it was not much better. It also lacked the sharp response to steering input that the XJR has. CONCLUSION:- The X300 sure does not ride like the older Jags from the 70's

 

I know the feeling you're talking about. It's that "drive like velvet" thing. And, correct, X300s don't quite have it. And in XJR form, they have even less of it. Intentionally.

Cheers
DD

 

I have an XJR6 and recently changed from original dimension 255/45 x 17 tyres to 245/45 x 17. The reason for the change was based on the high cost of the original dimension tyres as apart from cheap poor performance Chinese brands I could only find Michelin in the original size. It is simply not a common size anymore and the Michelins were substantially more costly than a quality 245 wide tyre.

My car had minimal tram lining in the first place and neither it or the ride has changed with the new tyres. I do however prefer the slightly wider look of the 255 tyres.