Ideal Offsets for XJ-S Wheels
#22
07-18-2018, 03:56 PM
Veteran Member
#23
04-16-2019, 10:22 AM
Senior Member
Time for tires. I've got Pirelli P600s that have excellent tread but are 14 years old. I've been experiencing a pulling to the right and can't seem to adjust it out by reducing negative castor (moving shims from in front to behind the ball joint).. Now I've noticed a shimmy in the right front at around 30-40 mph. I'd been anticipating getting tires and wanted an upgrade, so I bought used 17" Revolvers. Also bought .2" - 5mm spacers to reduce offset from 33 to 28mm as per suggested above. I would like to mount 235/50 - 17" tires. There seems to be mixed opinions on whether they will rub vs 225/55 -17s. I'm thinking of purchasing through Tire Rack, so I don't want to make a mistake. Spyhunter2K thinks they'll be fine, ProXJS thinks 225/55-17s are the way to go. What say you guys. BTW thinking of getting Continental Purecontact LS 235/50R17.
https://www.tirerack.com/tires/tires...omCompare1=yes
https://www.tirerack.com/tires/tires...omCompare1=yes
Last edited by Fla Steve; 04-16-2019 at 10:26 AM.
#25
02-24-2020, 10:36 PM
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ok so I can use a 9 inch wheel with a 285 tire max if I ET is 37.7 -42.7 offset with a 18 inch wheel or 265 tire with a 9.5 inch wheel. I am a little confused because I am not a car guy but trying to get custom wheels that will work well with a totally orginal 1987 HE xjs 12. This will be my first upgrade and I was told I can go up to 18 inch wheel with no problem.
#26
02-25-2020, 01:17 PM
Im running 18 X 8 all around. 245/45-18 up front 255/45-18 in the rear with no rubbing. Offset is 40mm which is perfect. Could easily run a 9" wheel in back but may have to shave the bump stop.
You can get a lot of wheels with this offset. The only issue is the big hub on an XJS. I got a local shop to skin the bore of the wheels to fit. Only needed 1.5mm. The ride is still good
You can get a lot of wheels with this offset. The only issue is the big hub on an XJS. I got a local shop to skin the bore of the wheels to fit. Only needed 1.5mm. The ride is still good
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BitDrive (08-15-2021)
#27
02-25-2020, 02:20 PM
#28
11-20-2020, 09:41 PM
Adapters move the wheel outwards in the same manner/rate as would occur if you decreased the wheel's offset value. So if you had rear wheel with 20mm offset (maximum offset/minimum number value possible on the rear for an 8" wheel running a 235 tire—ideal would be closer to 33mm as mentioned above), and you added a 20mm spacer, that would be the same as having a 0 offset wheel, which would stick out.
So if adapters are planned, you must start with a high offset wheel to begin with to allow for the thickness of an adapter.
Instead of adapters, you can also run BMW wheels (5 X 120) (some of which come in 74.1 CB and others in 72.56 (which would need to be bored out to at least 74)), and then take care of the ever-so-slight variance in bolt pattern with PCD variation lug nuts (AKA "wobble bolts").
#29
03-23-2024, 05:18 PM
#30
03-24-2024, 12:53 AM
Sorry to necrobump this thread, but I have a 1979 XJ-S and am looking at some new wheels and tires...
Would these 17x8 ET25 wheel with 245/50R17 fit fine with no clearance issues?
Would these 17x8 ET25 wheel with 245/50R17 fit fine with no clearance issues?
running 17x8 et 28 now with same tires and it never rubs.
the rear is a challenge. Lots of room in front.
also, there is wrong information earlier in this thread. XJR wheels are 17x8 et 33.
#31
03-24-2024, 01:47 AM
i ran 17x8 et20 245/45R17 and it barely cleared fender lip in the rear. Occasionally, dips in the road would rub(just barely.
running 17x8 et 28 now with same tires and it never rubs.
the rear is a challenge. Lots of room in front.
also, there is wrong information earlier in this thread. XJR wheels are 17x8 et 33.
running 17x8 et 28 now with same tires and it never rubs.
the rear is a challenge. Lots of room in front.
also, there is wrong information earlier in this thread. XJR wheels are 17x8 et 33.
#32
07-17-2024, 01:49 PM
The forum won't let me edit the original post anymore because of the time that's passed. It would be nice if a moderator could correct this information at the beginning.
#33
07-18-2024, 10:31 AM
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.
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.
Then if you want the original Group 44 flairs will handle 15x10 wheels & 27x15 racing slicks
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