Oops - Wrong Tire Size - Alignment Issues Ahead?

Well, I just discovered that the new Acceleras I put on the front of Superblue last week were not of the specified factory width (i.e. 235) but rather 225. No idea how that goof happened or why the WM tech didn’t notice the mismatch when he went to put them on in place of the old Cooper Cobras and let me know. :blush: And here, I have just ordered another pair of them for the rear. :slightly_frowning_face:

I talked to a friend of mine who used to work at a large tire chain retailer about what happened, and he opines that my going to 225s probably won’t make a noticeable difference in things, but only the “height” would be changed slightly by the switch. Strangely enough, Superblue seems to handle better with these 225s on the front than with the OEM 235s. :thinking: I’m not all that knowledgeable on tire measurements, but from what I have found out online that seems to mean the new tires are a slight fraction “shorter” and “narrower” than the OEM ones, given that the aspect ratio is unchanged (i.e. 60). :confused:

So, does anyone see any problems from my going with the 225s? Will that “incorrect” size prevent me from getting a proper wheel alignment next month? :grimacing:

btw, I know earlier I opined that I did not care for the Acceleras and they seemed to ride hard. However, I have changed that opinion and actually like them … Maybe it takes 20-30 miles of usage on new tires to get them to “fit in”? :confused: I also notice now they are quiet - quieter than my Coopers were. :+1:

Well, found this handy tire calculator online which compares the dimensions of my old 235 Cobras to the new 225 Acceleras:

Tire size 235/60 R15 Right arrow. From one size to another225/60 R15

Copy result link!

Old New Diff %
Diameter 26.10" 25.63" -0.47" (-12.00 mm) -1.81% Smaller sign. Arrow down
Width 9.25" (235.00 mm) 8.86" (225.00 mm) -0.39" (-10.00 mm) -4.22% Smaller sign. Arrow down
Sidewall Height 5.55" (141.00 mm) 5.31" (135.00 mm) -0.24" (-6.00 mm) -4.26% Smaller sign. Arrow down
Rim Diameter 15" 15" 0" 0.00%
Ground Clearance -0.24" (-6.00 mm) Smaller sign. Arrow down

So, it does look like my ground clearance (ride height) with the new tires would be reduced almost 1/4", so that’s telling me a new wheel alignment might not bring things back to snuff … ? :confused: Or, is there some way they can recalculate the alignment dimensions at the shop with the new tire size so that it will still come out O.K. and be within tolerances, either with or w/o the use of mid-laden tools?

geometry shouln’t change much (ie you won’t notice any difference) for those 6mm

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Will not affect alignment or the ability to do one.

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I what respect? Just wondering. In any case the improvement might come down to the design of the tire more than the size.

Or maybe it is the size. What wheels do you have? Jaguar used 6.5" wide wheels for many years…which is really a bit too narrow for the 235 tires. You won’t get the best out of a tire when the sidewalls are pinched in to fit on a narrow wheel. The 225s would be a better fit; less pinched.

Nope and nope !

Cheers
DD

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The geometry should stay the same. The new tires are just wider, not taller. No ground clearance should be affected. If you can make a turn and not have the wheel make contact with the wheel well, you should be good to go!

Atty went from 235 to 225, so they are narrower and slightly shorter.

i have 215-65-r15… works fine… again the geometry comes out about the same as original

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Original tires on the XJ-S are 215/70/R15. Sounds like a previous owner already went to a wider/shorter tire on your XJ-S?

I went wider and shorter. To 225/60/15. Which is what you now have. I would have thought the 235/60-15s would rub up front on wide turns? Also, much more selection at 225/60. And I think it makes the car look sportier.

You will see no differences in alignment. Only difference is a bit more space in wheel wells, and your speedometer will be off a tiny bit. If the speedo gear was never changed, then your speed will be about 10% off, reading higher than you’re really going. Same with odometer.

For my 88, I simply changed the plastic gear that reads the transmission speed. I think yours is at the differential. Not sure how that’s done.

The 215/70x15 was used for many years. Circa 1989 Jaguar began using 235/60x15 tires (and the “Lattice” wheels) as standard issue…at least for the USA market cars.

Cheers
DD

No issue as I see it. The actual size of the tires vary from one maker to another. very slight, albeit

Usually, new tires handle better than older ones.

Any speedo difference is negligible. Possibly now closer to real speed than before.

A drastic difference in diameter would effect alignment. here rthe difference if, any is slight and has little or no effect.

My XJ6 wears 15" lattice wheels from an XJS. I like them a lot. 215.70/15 B.F. Goodrich touring tires. Better rie and handling from the old hard tires. ,

225 were original equipment on the XJ-S – just not in the US.

Its a good conversation, which I tried to convey in my suspension thread. I’ve gone to a larger wheel size and a fairly low profile tire for better handling but not so much a soft ride. I’ve noticed that my drivers side unidirectional tire seems to be wearing uneven on the outside tread. The car is not out of line but then I suspect bushings, ball joints, camber, caster, toe in the whole nine yards. I will get this sorted but was wondering after reading an extensive thread on the E-Type forums about shims etc. I was also looking at trying to keep the speedometer readings close to the same as original based on the findings of Bernhard Embdens site.
Im likely going to go back to the the 235 50 R17’s as the 215 70 R15’s were garbage with the Pirellis when you went into a hard cornering situation
Personally speaking if you want the right look , ride and handling on an XJ~S probably shouldn’t go much more than a 16” Rim and a set of 225 60 aspect ratio. My two cents…

After years of 14”-16” rim size obsolescence the classic crowd has been pigeonholed into selecting the sloppy seconds of the few that put little effort into producing mediocre tires that fit a diminishing crowd.

The XJS is rightfully befitting of a proper high speed tire, so in order to stay in the game, moving up to a 17”, or 18” rim size is the only alternative.

Of course if your not actually driving the car and just puttering around town locally on small jaunts it doesn’t much matter what your rolling on.

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(what DoubleD said) x

mine. (88) had 235-60-15 Pirellis… too hard to get and costly around here. so decided to go with Hancook…215-65-15 although my spare is Pirelli… and another spare albeit like new Pirelli… all on lattice wheels

Thanks, guys … ! :smiley:

Wow, you guys aren’t kidding. Just less than two years ago, I purchased 225/60-15 Kumho Ecsta LX Platinum, V speed rating (149mph)! Just checked, no longer manufactured in that size.

I’m definitely staying in the game and won’t be putting the 15” Starfish wheels back on anytime soon, even though they’re still sitting in my garage with a brand new set of Pirellis 215 70 R15’s on them. I switched to the 17” rims and run a speed rated Dunlop Dirtezzo ( trying to keep with the British theme). I’m just wondering when I made the change if it’s a direct swap or does the geometry change at all due to different wheel sizes, and stresses on the front suspension. Once I tackle the project this winter and land on the new tires I’m going to start changing all the bushings and check the camber , caster. Toe in etc…Not sure if a person is supposed to set this up with 150 lbs weight in the drivers seat and 130 ibs in the passenger seat or not. Does it make any difference. They say a well sorted Jaguar steering and suspension rides like no other car. Just got to find the sweet spot I suppose .

I don’t have any definitive proof, but I have been led to believe that the car should be aligned correctly with a chosen set of wheels and tires. In other words, if the car was properly aligned with 15” wheels, it should then be re-aligned when moving up to a 17” or 18” wheel as well.

The proper weights on the seats will simulate real world suspension compression. I don’t remember reading about the 150, and 130 lb. seat weights, but those seem to be arbitrary numbers to me. It would be much better to just go with whatever your true weight is and that of your passenger.
The fuel tank should be full as well, or at least simulated with the correct amount of weight in the trunk. You basically just want the car to be weighted down the same as it normally would be.

In the case of our modern day drivers the sweet spot is more likely to be whatever it is to you and not so much what the Jaguar vision was.