In this thread I'll input all the information I've gleaned regarding XJ-S/XJS wheel specs and possible upgrade choices.


1976–1996 Jaguar XJ-S/XJS WHEEL BASICS

Here are the basic specs on the XJ-S wheels:

PCD (bolt pattern): 5 X 4.75" (5 X 120.65mm)
Hub diameter: 73.85mm as measured by digital caliper
Wheel CB (center bore): Published as 73.8-74.1mm based on various sources
Factory ET (offset): 28.5mm


I'll begin with a discussion of the "ET" value—offsets, which is a measurement of how far the wheel mounting surface is from the wheel's centerline. Higher offset values push the wheel inward, while lower values push a wheel outward.


Rear Wheels

Here's how I'm calculating the ideal REAR offsets for upgrade XJS wheels. I'm assuming that most want to upgrade to a wheel at least 8" wide, so we'll start with that width as our first example.

From Bernard Embden's excellent site, the outer edge of a 235-width tire on an 8" wide rear wheel just clears inner edge of the rear fender flare when the wheel has a 20mm offset. However, even though this offset barely clears the outside visible fender lip, the outside edge of the tire actually does rub the inner fender lining at full upward suspension travel. So it would seem that 20mm for an 8" wheel is pretty much the minimum offset value to prevent rubbing on the outer edge, with 25-30mm being ideal to push the wheel a bit more inwards and provide enough clearance so as not to hit the inside of the fender lining. But less offset than 20mm on an 8" wheel with 235-section tire and the wheel will not only hit the inner fender liner—it will also likely scrape the inner edge of the fender lip.

Now let's increase the wheel width to 9" and suppose that we start with the wheel centered in the same position (having 20mm offset) as the 8" example discussed above. A 9" wheel with this same 20mm offset splits its 1" of increased width with 1/2" more wheel on the inner side, 1/2" more wheel on the outer side. Since the rear wheels run into interference on the outside first, increases in wheel width must be compensated by shifting the wheel further inward, meaning offset must be higher. In the case of a 9" wheel as compared to an 8" wheel, the 1/2" in increased width towards the outer side must be compensated for by increasing the offset to push the wheel inward by 1/2". So it needs an additional 1/2" (12.7mm) of offset (inward shift) to keep its outward edge equal to that of an 8" wheel with 20mm offset. This gives us about 32.7mm minimum rear offset on a 9" wheel, with a slightly higher ideal offset of 37.7-42.7mm for a 9" rear wheel to give us the same amount of extra clearance that a 25-30mm offset would have provided for an 8" rear wheel, so as not to allow the outer tire edge to impact the inner fender at full suspension travel.

Now a 9.5" rear wheel. For a 9.5" wide rear wheel, half of the additional 1.5" width (as compared to our 8" starting wheel) goes to the inside—half to the outside. As we did with a 9" rear wheel, we'll just add half of the additional 1.5" width (which is 19.05mm (3/4")), to the 8" wheel's 25-30mm ideal offset range to arrive at the 44.05-49.05mm ideal offset range for a 9.5" wide rear wheel, with 39.05mm being the absolute minimum offset for a 9.5" wide rear wheel in order for the outer edge of the tire not to scrape the inner edge of the fender lip.

Note, however, that at 9.5" of width, (and possibly with a 9" wheel) the inner clearance becomes an issue, and any offset greater than 40mm or so requires one to shave material from the bump stop and possibly grind away material from adjacent body seams so as not to interfere with the inside of the wheel/tire combo. So for any wheel width 9"–9.5" wide (depending on exact offset), you need the offset to be within a very narrow range to ensure the wheel is almost perfectly centered between the outer and inner contact points. So at 9.5" the offset target is actually around 40-45mm, slightly less than the otherwise ideal offset for a 9.5" wide wheel on the rear of an XJS.


Front Wheels

Note that on the rear I mainly discussed how far you could push the rear wheels outward (the MINIMUM amount of required offset) before the rear tire's outer edge hits the fender lip. Up front, though, as wheel width increases and offset stays the same you run out of room on the inner side first and experience interference with suspension components before you run out of room on the outside edge and experience intereference with the fender lip. You actually may have to run 1/4-1/2" lower offset (pushed further outwards) in front than the rear, assuming identical wheel/tire widths front/rear. So in the front we are more concerned with the GREATEST offset tolerable, with the goal being to not go much higher than this in order to maintain as small a difference as possible between front/rear offset.

To illustrate this, note that many XJ-S owners run the 17" X 8" XKE "revolver" style wheels front and back, which have a 33mm offset. Most space the front wheels outward about 1/4" to prevent interference that would otherwise occur when the wheels are used as-is. True, some say they run the fronts without a spacer and that the inner-side interference is slight and infrequent, but I think the majority of folks would prefer NO interference on the inner side. If we assume 1/4" is about the minimum amount of spacing the 33mm offset 8" revolver wheel needs, then the GREATEST offset possible for an 8" wheel is about 27mm. More offset (inward shift) than that and you risk hitting suspension components.

Note that many people have used '94-97 XJR 17" X 8" wheels on an XJ-S, and these wheels have a 25mm offset, for a good reason. 25mm is about as far OUTWARDS an 8" wide rear wheel can be (within a few mm) without rubbing the fender lip, and about as far INWARDS (within a few mm) an 8" front wheel can be without hitting the front suspension. (Rear wheel offset can actually be as low as 20mm without hitting the fender lip, though at this point it may impact the inner fender liner on full suspension travel.)

So this means that if one wishes to upgrade to 8" wide wheels with the same offset front/back, you have to get wheels in a very narrow 20-25mm offset range. So the late-90s 17" X 8" XJR wheels, with this "magic" offset and identical bolt pattern and hub bore are the easiest way to upgrade to a 17" X 8" wheel on the XJ-S.


The Effect of Fender Lip Rolling And/Or Fender Pulling

It should be noted that the ideal offsets cited above for each wheel width could be decreased, moving the wheels outward, if one were willing to roll the fender edge and/or pull the fender outward. If the fender lip is rolled inward (bent inward to lie flat against the inner fender), you could get away with having wheels of each size protrude another 10-15mm outwards, meaning you would subtract 10-15mm from the ideal offset ranges mentioned above. However, in the rear the tire would still slam against the inside of the fender liner a couple inches above the inside of the fender lip at full suspension travel due to the shape of the rear fender flare, and I don't believe there is much room for the inner fender liner to be banged out of the way. Because rolling the fender lip doesn't solve the problem of the inner fender liner, a better solution is pulling the fender outward a bit using force along with heat to soften the metal (google "fender pulling" for more details). The amount of offset that could be subtracted from the ideal values mentioned above, which will result in the wheel being pushed outward, will depend on how far outwards the fender is pulled. I've seen fenders pulled as much as a full inch (25.4mm) outwards without causing an obvious distortion in the body lines of the car.


Wheel Width Vs. Tire Width

The ideal offset values mentioned above assume that the tire width being considered is approximately the same as the actual width of the wheel. For example, a wheel quoted/advertised as 8" wide is actually 9" wide when the flanges are factored in, which is about 230mm. Recall that in Bernard's case he used a 235 section tire on the 8" wheel, almost the same as the actual 230mm width of the wheel. For handling purposes this is ideal. If anything, it's best to have a slightly larger tire than actual wheel width to provide the wheel lip a bit of protection.

So if you are using a 9" wheel (so 10" total width with flanges), the ideal offset ranges mentioned above are valid assuming you are using a tire width similar to the actual 10" width of the 9" wheel, which would be about 255. If you instead planning on putting a 275 series tire on it, you have to realize that that tire is 10.7" wide, .7" greater than the 10" actual width of a wheel advertised as 9". Since half of this increased width goes to the inside, half to the outside, you have to adjust your offset to compensate for the .35" extra width that comes from using a larger tire as compared to the wheel width.

So in other words, it's not really how wide a WHEEL will fit the front/rear of an XJS—it's how wide a TIRE will fit. The ideal offset of a 9" wheel would be the SAME ideal offset of a 10" wheel when the same tire width is being considered for both wheel widths. It always amuses me when I see someone claim that no more than a 9" wheel can fit in the back, but they're running a huge 285 width tire. Another person swears that a 9.5 inch wheel will fit, and he is perfectly correct since he is only using a 265 series tire.

So again, the ideal offsets assume that a tire is being used of a similar width as the actual wheel width being considered (advertised wheel width + 1 inch for the flanges).

If anyone else has different values or input, feel free to add.

 

This interests me as I want to use 17x9.5 or 10.

I think the TWR offset for the 16x8's was +33 so it sounds like you are on the money there with 32.7.

I was talking to a guy a couple of months back at the all British day and he has 18X10 +35 with 285-30 on the rear. His comment was that they do rub slightly but only on the track, he did have the the lip on the outer flare rolled and quite stiff suspension. But they do fit.

 

Warren, I just rewrote half of my original post so there might be some extra info that could be of use if you re-read it. I typed the original in a hurry.

With a 285 tire, the offset needs to be such that the fender will pretty much have to be rolled. The problem is that the tire will still impact the inner fender liner. His suspension must be pretty stiff for this not to be happening.

 

Everything seems spot on to me. Wheel spec wise you did a great write up and a good baseline to go off of. The only thing that needs to be addressed is that tires are not all the same size. Even when listed as the same size two tires can vary quite a bit in overall dimensions. features like sidewall width, rim protectors and even lettering on the tires sidewall all vary from make to make and even between models of the same make. Hell even tire pressure can effect that.





BUT the wheel specs are great.

 

You make a great point. Two tires may have the same 265 tread/section width, but one make/brand could have a sidewall that balloons outward 1/2" (12.7mm) more than the other.

So once you are at 9.5" widths and above where the tire must be perfectly centered at the rear to prevent fender pulling/lip-rolling and/or inner component grinding, tire brand may make a difference.

 

Yes the tyre will hit where the inner guard starts to roll inwards. I have made cardboard cutouts for a 275 tyre. This size should be ok and not rub as long as offset is correct and the car is not lowered.

 

Warren,

Correct of the offsets for the XJR-S: 19 mm front and 33 mm on the rear.

If you haven't already seen this, check out what this XJS owner has done. Really impressive.

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The information from this post has now been moved to the first post.

 

I just added a new introduction to the thread that lists the XJ-S wheel specs and mentions that other information other than offset info will be included.

 

If i bought a set of 18x.75 with a 40 mm offset would those work on my 97 xj6 vanden plas? thanks for the help!!

 

sorry, 18x7.5 Thanks!

 

Sorry—not sure if inner/outer clearances on an XJ6 are identical to those of an XJ-S.

 

I just bought a set of Coventry Whitley 17"x8", 5x120.65 bolt pattern, 73.9mm hub 25mm off set the seller recommended 235/50r17 as in this post I then talked to Tire Rack to order the tires they talked me into buying a set of 225/55r17's as they where concerned about clearance in the rear wheel wells. so I bought the 225/55r17's installed today no clearance problems in the front the rear at full compression to bump stops gives only 1/4" clearance with inner wheel well lip. So the 235/50r17 may be a bit to wide. Also speedometer is very accurate at 70 mph as the 225/55r17's are a bit taller.

 

Would love to see some pics. I'm finally back in the States for a bit and hope to finally install the 17" wheels I bought years ago for my '86.

Btw, you would have been fine with the 235s, as the extra 10mm is split in half, with it being only 5mm closer to the inner fender liner, which at .20 is slightly less than the .25" you say you have to play with. Nothing wrong with giving yourself a little extra, though.

 

I did not think to take pictures when I was at the resto shop the other day but her are some from my parts car taken today

Tire specs Firestone Firehawk Indy 500 225/55r17 Tread width 7.5" section width 9.2" Diameter 26.8" (26.8" is also the original diameter of the 215/70r15 tires) The 235/50r17 Firehawk has an 8.1" tread width 9.7" section width and a 26.3" diameter. This is only my second post so not quite sure how every thing works yet.

 

Hi - this looks like the right thread for this question - I have a 95 and a 96 XJS - I'm thinking of swapping wheels on them (for a variety of reasons) - is there any change between the two years in terms of bolt pattern or offset?

 

[/QUOTE]The bolt pattern off set and hub are the same from1975 to 1996[/QUOTE]

 

The bolt pattern is 5x120.65 same a chev for entire XJS model run.

Offset will depend on the width of wheel you intend to fit. 8" rims front 19 offset and rear 33 offset, this is a good starting point.

 

Update on
COVENTRYŽ - WHITLEY Gloss Black with Mirror Cut Lip (17" x 8", 5x120.65 Bolt Pattern, 73.9mm Hub) Tires 225/55R 17

Wheels clear back edge of inner fender by 1/4" and front edge of lower valance panel by 1/4" as well the rear clear the inner wheel well lip by 1/4" too. close but no contact.

 

will this work on my 1988 jaguar xjs ...17 x 9 wire 100 spoke rims with 215/50/17 ?