The largest wheels tyre I have seen on an XJS with no modification to the wheel arch apart from rolling the lip are 18x10 with 285/35's these were on a very stiffly sprung car and the owner advised they do rub slightly on the track.

255's on an 8" rim fit easily as long as the offset is correct. I think you could squeeze 275/35 on 18x9.5 with standard springs if you do not lower the car.

BTW any combo you will need to ensure the offset is correct otherwise they will rub.

cheers
Warren

 

i want 18x 10 in the rear, i am getting springs that are 1 inch lower and 25 percent stiffer, what offset should i get?

 

The later facelift cars have much more room for wider tires than the earlier cars. Find a corvette wheel/tire that you can borrow for a test fit before you buy anything. I don't think what you want will fit on a 1985.

Dave

 

18x10 will fit but if you lower the car 25% stiffer springs will not be enough you will have issues with rubbing. You will need to roll the lip, the inner guard rolls upwards so when the suspension is in bump the tyre will rub on the inner guard. The suspension needs to be stiff enough so it does not hit the bump stop or you need to modify the inner guard.

 

i was already planning on rolling the lip, what offset do you think ill need?

 

You will need to measure the off set. From memory it is about 38. Don't forget to measure it at ride height.

 

The offsets for XJSs is the same as the XJ and XK, this is why 18s from these cars will fit, the biggest issue is clearing the grease cap on the front hub, the back of the wheel needs to be machined to give clearance.

Basically the offset is 18-20mm

 

18x 10 require a larger offset or the guards have to be flared. XKs 18x 9.

 

My bad I was meant to say the 18-20 is the standard size so you need to compensate if you go wider... I have 17 X 13J on my XJS

 

what size are you running on your xjs?

 

What most people seem to forget about is that the main purpose of offset has nothing to do with preventing tires from rubbing, it has to do with handling, alignment, excessive wear, etc.

As designed, the vertical centerline of the tire/wheel are designed to be in a certain position between the inner and outer wheel bearings (usually centered). If you put on tires/rims that change this relationship, you will have excess bearing wear.

The vertical centerline also is designed to intersect the camber axis at a certain point. If it does not, again, excess wear along with compromised handling.

There are other things in with this, such as are the rims "hub centric" or "lug centric", my brain is just too rattled at the moment to comment on the others.

Some of the alignment issues can be corrected by special alignment.

Tim A.

 

What you are refering to here is Scrub Radius and is relevant to the front steering geometry. We were talking about rear wheels where this has no relevance.

You are correct that incorrect scrub will affect tyre life especially if it is Zero, Psoitive or negative Scrub will also increase steering feedback and weight. Scrub can change significantly with higher profile tyres as the sidewall flexes. Offset is needed for 2 things and that is keeping the tyre from rubbing and if this is done correctly Scrub will not be effected to any major degree.

BTW as the Jag is wishbone Scrub can be changed by altering the camber (this is not so for Macpherson Strut)

 

I didn't think I was communicating very well.

What I was trying to say was that the offset shouldn't be changed *****-nilly. The offset selected should be such that it will keep the centerline of the tire/wheel in the original position.

 

will the stock offset with 18 x 9 in the rear fit? what size tires should i run? i am also dropping the suspension an inch

 

Scrub is a funny thing and increasing either pos or neg scrub will not have a great effect on handlng it will increase steering effort. What will have a major effect is if the Scrub is close to Zero


It should be close - I did some measurements last night, and my stock starfish rims are 15x6.5 28.5 offset with 215 65 15 - measuring the total tyre width it was 9" about half way down the sidewall. So based on this an 18x9 with 255's should go close to fitting with a lip roll - though not ideal. Any wider in the tyre will need an increrase in offset.

Based on my very quick measurements in the dark garage I estimate an offset increase of around 20-25mm would be about the most I would be comfortable with. This would leave 15-20mm clearance beween the tyre and raduis arm.

BTW the 16x8 TWR rims were 33 offset from memory.

Best to measure hub face to guard lip and hub face inwards to the farthest point - which is either the radius arm or bumpstop. Then take these measurements to a tyre shop.

 

My post here has about as detailed a review of XJ-S offsets as you can find:

https://www.jaguarforums.com/forum/x...-wheels-65576/

 

For aesthetic reasons, the gap between the top of the tire and the fender should always be less than the sidewall height of your tire.

When you upsize your wheels, the sidewall height of your tires decreases and causes the fender gap to look larger, by comparison, than it did when appearing above a taller tire. This is why many people lower their cars after upsizing their wheels—so that the fender gap remains in proportion to the tire sidewall height.

In other words, lower the front a bit. With those narrow-profile tires, it's causing the fender gap to seem excessive, like the car is jacked up a bit in the front. After you correct this aesthetic issue, THEN I would see how it looks.