Good thinking. Not many people consider rim width versus tire size and many tire manufacturers often show as 'acceptable' rim widths that seem way too narrow for the tire, IMHO.

But I just peeked into the garage at my XJR wheels/tires (they're residing on a Ser III right now) and the 255/45s don't have the *appearance* of being too wide for the wheel....no 'pinched in' look at all, FWIW.

An extra 1/2" would probably be better for proper sidewall function/support but in this particular case I think it comes down to tire design/tread design more than rim width vs tire width. That is, 8.0" versus 8.5" probably isn't a major contributing factor in the notorious tramlining problem. IMHO of course.

Cheers
DD

 

So I did some checking with some tire size comparison calculators and a 245/50-17 would be quite a bit off from the stock 255/45-17, but is very close to the 225/60-16 stock XJ6 size.

XJR stock tire comparison.

255/45R17 Imperial Metric Section Width: 10.04 in 255.00 mm Rim Diameter: 17 in 431.8 mm Rim Width Range: 8 - 9.5 in Overall Diameter: 26.04 in 661.30 mm Sidewall Height: 4.52 in 114.75 mm Radius: 13.02 in 330.65 mm Circumference: 81.79 in 2,077.54 mm Revs per Mile: 798.91/mi Actual Speed: 62.14 mph 100.00 kph Speed Variance: - Diameter Variance: -

Tire Size 1 235/50R17 Imperial Metric Section Width: 9.25 in 235.00 mm Rim Diameter: 17 in 431.8 mm Rim Width Range: 6.5 - 8.5 in Overall Diameter: 26.25 in 666.80 mm Sidewall Height: 4.63 in 117.50 mm Radius: 13.13 in 333.40 mm Circumference: 82.47 in 2,094.81 mm Revs per Mile: 792.32/mi Actual Speed: 62.65 mph 100.83 kph Speed Variance: 0.82% too fast. Diameter Variance: 0.83%

Tire Size 2 245/50R17 Imperial Metric Section Width: 9.65 in 245.00 mm Rim Diameter: 17 in 431.8 mm Rim Width Range: 7 - 8.5 in Overall Diameter: 26.65 in 676.80 mm Sidewall Height: 4.82 in 122.50 mm Radius: 13.32 in 338.40 mm Circumference: 83.71 in 2,126.23 mm Revs per Mile: 780.61/mi Actual Speed: 63.59 mph 102.34 kph Speed Variance: 2.29% too fast. Diameter Variance: 2.34%

XJ6 stock tire comparison

Section Width: 8.86 in 225.00 mm Rim Diameter: 16 in 406.4 mm Rim Width Range: 6 - 9 in Overall Diameter: 26.63 in 676.40 mm Sidewall Height: 5.31 in 135.00 mm Radius: 13.31 in 338.20 mm Circumference: 83.66 in 2,124.97 mm Revs per Mile: 781.08/mi Actual Speed: 62.14 mph 100.00 kph Speed Variance: - Diameter Variance: -

Tire Size 1 235/50R17 Imperial Metric Section Width: 9.25 in 235.00 mm Rim Diameter: 17 in 431.8 mm Rim Width Range: 6.5 - 8.5 in Overall Diameter: 26.25 in 666.80 mm Sidewall Height: 4.63 in 117.50 mm Radius: 13.13 in 333.40 mm Circumference: 82.47 in 2,094.81 mm Revs per Mile: 792.32/mi Actual Speed: 61.26 mph 98.58 kph Speed Variance: 1.44% too slow. Diameter Variance: -1.42%

Tire Size 2 245/50R17 Imperial Metric Section Width: 9.65 in 245.00 mm Rim Diameter: 17 in 431.8 mm Rim Width Range: 7 - 8.5 in Overall Diameter: 26.65 in 676.80 mm Sidewall Height: 4.82 in 122.50 mm Radius: 13.32 in 338.40 mm Circumference: 83.71 in 2,126.23 mm Revs per Mile: 780.61/mi Actual Speed: 62.17 mph 100.06 kph Speed Variance: 0.06% too fast. Diameter Variance: 0.06%


Summary

Compared to OEM XJR 255/45-17 tire:
235/50-17 .82% too fast
245/50-17 2.29% too fast


Compared to OEM XJ6 225/60-16 tire:
235/50-17 1.44% too slow
245/50-17 .06% too fast

And then comparing the 225/60-16 XJ6 tires with the 255/45-17 XJR tires, we find that the XJR tires are interestingly 2.23% too slow.

So here's a question probably no one knows.... is the XJR speedo calibrated to account for the XJR tires being 2.23% slower than a regular XJ6 tire? If not and the XJR and XJ6 speedos are calibrated the same, then indeed it looks like the 245/50-17 is indeed an almost perfect "+1" match to the XJ6 tire, at least in indicated speed and diameter. So if the XJR speedo is really off by 2.28%, this 245 tire would get it back to spot on accuracy.

Bottom line the 225/60-16 and 245/70-17 tires only have a .4mm difference in overall diameter. That's darned close.

And the load ratings for the 245/50-17 tires seem to be readily available in the appropriate 98+ load ratings, where the 235/50-17 seem mostly/all to be 96 load rated.


So I wonder if the 245/50-17 may actually be the ideal fit and if they would be narrower and/or taller enough to have the same positive effect reducing tramlining as the 235/50-17 has been reported to produce?


.

 

Uniroyal Tiger Paw GTZ All Season
Ultra High Performance All Season
Size: 235/50ZR17
UTQGL: 400AAA
Load/Speed Rating: 96W

This is the model I ended up with. $96 per tire.

 

Here's an interesting thread in the X308 section talking a bit about the subject of Jaguar choosing 255 tires for an 8" wide rim:

https://www.jaguarforums.com/forum/x...g-tires-70678/




.



I particularly found the following interesting:


If one looks at the specs I posted for a 245/50-17 wheel above, that 9.64" quote as the actual width of a 255 tire on an 8" rim is almost exactly the width of a properly fitted 245 wheel.

Seems like that gives even more creedance to a 235 or 245 tire being a more appropriate fit. That has to help with wear and possibly ride?

And again, while I've found no 235 tires (via a cursory, but not extensive search) that meet the 98/99 load rating of the OEM tires, I have found several 245 tires that do.

So maybe 245 is worth a test to see if it is a size as good at minimizing tramlining as the 235 tires have been shown to be?

It would be fantastic to hear if anyone has tried 245s and evaluated their impact on tramlining and general ride quality and performance.


.

 

I've not tried the 245s (or 235s) so I can't comment.

Besides tire size I think it would interesting to examine/research tread pattern and shoulder design and see where that fits into the tramlining issue.

We already know from years of commenting that different 255s behave differently, including significantly different degrees of tramlining. So size is only one factor, albeit it seems to be an important one as we know that if you make a significant enough reduction in width (and an increase in aspect ratio) you're virtually assured of eliminating tramlining.

As an aside (referring to the above quoted commentary) I get a bit of a kick about regarding 8.5" as a good rim width for 255s but calling 8.0" rim width 'extra-skinny'

Cheers
DD

 

Sounds like the X300 sub-forum might benefit from a tire recommendation FAQ/sticky one day identifying tires and their respective sizes that are a "good fit" and less likely to tramline for XJ6 and XJR applications.

Maybe we should start to solicit that feedback, compile it and then just make a list, much like the list for compatible OBD readers?

.

 

So, a little more fuel to the fire... guess what size tire is OEM spec for the 17x8 wheel on the XK8?

Yep, 245/50-17




.

 

..... and see posts #21 and #23 in the following 'differential' thread:

https://www.jaguarforums.com/forum/x...e2/#post640068


Doc mentions he played with tire sizes on his XJR to get his speedo accurate to coincide with the speed cameras. What tire size worked out to make the speedo accurate?

245/50-17

 

Who makes a 245/50/17 tyre to suit our cars?
I couldn't find one in Australia when I bought mine would have loved to try the 245,s out its nice to have an accurate speedometer

 

Hi Doc, a little confused by your question above as your post linked below seemed to suggest you installed 245/50-17 tires to get the speedo spot on accurate:

https://www.jaguarforums.com/forum/x...e2/#post640068


Am I perhaps misunderstanding your question?


But, here in the US there are a lot of 245/50-17 tires to choose from that are appropriate load rating and speed rating. I shopped at tirerack.com and found quite a few mainstream brands.

http://www.tirerack.com/tires/TireSe...50&diameter=17


Hope that helps answer your question about general availability.


.

 

Yeah must have Got that one wrong somewhere

Got 235/50/17,s on it

I did see the 245/50/17,on Tirerack thought I might try ordering a set to deliver them to Australia next time seems Tirerack do ship to Australia

But don't think I,ll be needing them soon the XJR6 is in the garage with trickle charger under a cover up for sale haven't driven it in 3 months

Just got my XJ8 X350 sorted last Friday for it only to break the nipple of the header tank Saturday morning on the way to get it washed and refuelled for a trip to Brisbane
oh well got to watch plenty of TV shows recorded and none of them by the wife LOL

 

X308 Asteroids with 245/45 x 18 Toyos go well.
Tramline a bit, but not bad if a good alignment done

However Asteroids are getting scarce in NZ
I got a new boxed set as spares, at great expense from sbwheels.co.uk - he gives great service but shipping from UK to NZ is $$$

 

I might've mentioned that I've been running 225/60x16 tires on my XJR for many years now. However, encouraged by so many happy results using size 235/50x17 I decided to jump on the bandwagon myself.

I bought "Sumitomo HTR Enhance". These have a V-speed rating, 600 treadlife rating, and A-A traction-Temp rating.

The load rating of '96' is a bit lower than I'd prefer but obviously not to the extent that I feel unsafe using them

So far I happy report: no tramlining, slightly nosier than the previous BFG Advantage tires but certainly not excessively so. The ride is a tad firmer and the steering a bit sharper....to be generally expected, I reckon, when going from a 60-series to a 50-series.

In my neck o' the woods wet traction is very important. I'll be able to report on that in a few weeks.

Only $100 each before $50 mail in rebate.

No complaints

Cheers
DD


PS- I forgot a very pleasant bonus. The last bits of vibration are finally gone! I think one of the old tires had gone a wee bit lumpy with accumulation of age and miles.

 

Did you mean 235/50x17 or 245/50x17?


Heh, nevermind, went and looked at the specs. Looks like the 235 is what was available and is a good size match.



.

 

Anyone have any experience with the new Pirelli P7 Centurato?

I started a thread in the "Tires & Wheels" section, but no one has replied.


https://www.jaguarforums.com/forum/w...rience-126266/


.

 

I know it's not the same chassis, but I'm running 235/50-18s on my VDP. That is the stock tire size, but I've got them on 8.5 wide wheels, which is the maximum width wheel recommended for 235s. I made the mistake of putting 245s that run wider than most on the 8 in wide wheels on my GTO and it felt sloppy in hard turns compared to the 235s the stock wheels came with. I only went with 245s because the place I bought tires from because they couldn't source the 235s at the time that I wanted. They looked ballooned to me on the 8 inch wheel and that was a 40 series tire on that car.

 

I'm thinking about going with either the 245/50-17 or 245/45-17.

In looking through the 235/50-17 options, none except one Hankook tire meet the load spec for the XJR. Most in this size are 95-96 load ratings, where the XJR requires 98-99.

But the 245/45 and 245/50 sizes do come in the correct load rating. The 245/45 also has a lot more choices, especially for higher mileage tires like the Continental Purecontact and Michelin Sport A/S

The 245/45 is very close in size, but just a little bit smaller in diameter/circumference, losing about 5mm in sidewall height.

One can see the difference here:

255/45-R17 vs 245/45-R17 Tire Comparison - Tire Size Calculator


The 245/50 is the next runner-up but is a bit bigger, being about 8mm taller.

255/45-R17 vs 245/50-R17 Tire Comparison - Tire Size Calculator


Any thoughts on issues or preference with either choice in size.

I could also stick with the OEM size of 255/45-17 as I've gotten fairly used to the tramlining now to tell you the truth.... but all of the tires in this size have very poor mileage, and I need something with 50k or more treadlife given how many miles I drive.

.

 

I faced the same quandry. I'm not sure it quite correct to say that the car 'requires' 98 or 99 load rating. Jaguar elected to use a 98 or 99 load rating tire. Obviously, though, you want a tire that'll support the weight of the car and then some.

The XJR/6 has a curb weight of 4200 pounds and a max allowable gross weight of (something like) 5000 pounds. That is, five passengers + luggage = about 5000 pounds max.

'96' load rating = 1565 pounds x 4 = 6260 pounds
'98' load rating = 1653 pounds x 4 = 6612 pounds

So, you gain 352 pounds of additional margin.

Since I drive alone 99.99% of the time (I don't think the back seat has been used six times in as many years) I decided the '96' tires wouldn't pose any unreasonable risk.

An owner driver who drives with under-inflates tires, due to simple laziness or neglect, is more likely to need that extra 352 pound margin. I'm quite sure you keep on top of such things, though !

In the end I'd say it's a valid concern but I wouldn't let load rating alone disqualify a tire that you're otherwise happy to consider. I didn't

Just my two cents.

Cheers
DD

PS- one word about the tire size calculators:

These are a real boon BUT do double check tire specs from the manufacturer. The standards here seem to be a bit low. For any given size designation you can sometimes find manufacturer-to-manufacturer differences in actual, final dimensions. I've seen as much as 5% in some cases.

 

Thanks Doug

Question though, if you (or anyone else) had to choose between the slightly 'shorter' 245/45 or more than slightly 'taller' 245/50 tire on the XJR, where would you lean and why?

I have my thoughts to some degree, but am curious what others may consider that I haven't.



As an interesting aside, for what it's worth.... the 1997 XK8, also fitted with 17x8 rims, has 245/50-17 size as the OEM size.

As another interesting thought/question: Does anyone know if the XJR speedo with the OEM 255/45-17 tires is accurate, or is actually a bit 'off' and still calibrated to the non-XJR XJ6 225/60-16 tire/rim size?

Because, it appears that the closest match (NEARLY IDENTICAL) in diameter/circumference is between the XJ6 225/60-16 and XK8 245/50-17:

http://www.tacomaworld.com/forum/tir...0r16-245-50r17



*If* the XJR speedo is still really calibrated against a regular XJ6 225/60-16 tire size (versus the XJR 255/45-17), *and* the XK8 17x8 rim is spec'd for a 245/50-17 which is apparently almost exactly the same diameter/cirucmference as the XJ6 225/60-16 tire.... PHEW

.... well then that may argue that the ideal tire size on the XJR really is 245/50-17


Much appreciated

.

 

All else being equal I'd go with a bit taller. Why? I favor a taller sidewall. My personal experience (on various cars, including Jags, and including the XJR) with 40 and 45 series tires has been rather poor. My personal experience with 50-55-60 series tires has been generally good.

You'd think the difference between 45 series and 50 series wouldn't amount to a hill a beans but it seems to be an important 5%.

Back when I was running the 255/45 tires one of my big complaints was road damage. I had to replace several tires and have a couple wheels repaired, over a period of 3-4 years. I've never had that happen with 50-or higher series tires. Pure coincidence? I dunno. Obviously there are variables but maybe, for a 4200 pound car, the difference between 45 and 50 just sorta puts things over the edge?

(Aside: I don't know how the guys running those 25-30-35 series tires tolerate all the road damage problems. You can read about here and on other car forums. It's quite common)

As far as the actual driving performance of the tire goes I doubt the 45 vs. 50 difference, in and of itself, would make much difference. Any difference you feel might well come down to the design of the tire (tread, casing, compound, etc) as much or more than the 5% difference in aspect ratio

Cheers
DD