Tire Load Rating for XK8
 

Just saw my new tires mounted on my new (used) rims. NICE!! Up'd to an staggered set of 18" rims with the fronts being 245/40/18 and the rears 275/40/18 on the rear. The tire dealer mentioned I might be light on the "load range" on the fronts which are a LR of 97. Anyone know if this might be too low on the load range? I haven't mounted these on the car yet as it's still in the shop getting a recolor paint.

I don't know if it changes with rim size!?7

But for 20" rims it is 97 front and 99 rear.

I think you'll be okay. My wife's XK8's Yokohama YK580 tires are 94 up front (245/40/19) and 100 in back (255/40/19). Absolutely no problems thus far....

Seems odd to me that the same tires, just one size difference apart, would have such dramatically different load ratings.

<shrug>

There must be a good reason...


Cheers
DD

The XK8 and XKR curb weight is about 4,000lb. The Gross Vehicle Weight Rating (GVWR) is about 4,800lb, and would give you about 1,200lb per wheel, or an index of 88. Using an index of 94 is already 1,500lb and 99 is 1,710lb per wheel.

Based on that, you are more than OK.

I have found that most of us buy higher spec tires than we really need. Don't get me wrong, I will not compromise on quality, but I don't need a load index of 99, and I can use S-rated tires instead of V-rated. If S-rated max speed is up to speeds of 112mph (180kmh), how many times will I need or exceed that speed? In any case, that is when it is loaded up to its load index and I know that you can drive safely over the rated speed, as long as you do it for very short periods. Just my 2c...

Here in the UK, if you fit lower spec. tyres etc., than Jaguar states, our insurance companies will use it to not pay out on a claim!!!

In the case of tyres it may also be a problem with the MOT test!?

The rating given by Jaguar is not based just on weight.(extra load is also part of the Jaguar spec.)
They also take into account the, expected, sportier driving style, with higher speed cornering etc. so it is also to do with the side wall strength/rigidity, flexing etc. and how the tread actually sits/contacts the road surface.

Although I've never comes across anything that specifically says so (not have I looked very hard) I'm thinking the max load rating is taken at maximum allowable pressure as shown on the sidewall and drops significantly at lower pressures.

If I'm correct (am I?) you'd have to run max pressure to keep your margin of safety.

I have 98 or 99 rated tires on my XJR (can't remember this early in the morning) and the max pressure is something like 45 psi. But I typically run 34 psi. So, how much of my ample load rating have I lost?

I dunno!

Cheers
DD

Doug, there are two standards used - the index is based on tire pressure 35 psi and 36 psi respectively.

Derek, yes I agree there are countries where the law / insurance will force you to to install tires that meet the manufacturer standards or higher. There are also differences in tires of the same size and rating between manufacturers, and then there is also rim size on the car. My car's 17 inch will behave very different than the same car with 19 or 18 inch.

I do not disagree that if you want to drive more "spirited", get the best tires. Trust me, I have learnt my lesson with motorcycles. But, I also believe that a lot of the manufacturer recommendations is more to avoid lawsuits than engineering.

Based on the original question from Padrino, I believe that an index of 97 is more than sufficient for his car.

Where did you get this info? (I'm asking, not being argumentative)



Cheers
DD

WILL use it to deny a claim or MIGHT use it to deny a claim?

This comes up quite often. Years and years ago I asked every UK guy I could reach if he had every heard of a claim *actually being denied* for this reason. None had.

<shrug>

Presumably (hopefully?) this would only apply if the tires were somehow related to the accident?

Well, anyway, I guess you wouldn't want to fit lower spec tires and then find out the hard way that your claim is denied!

Cheers
DD

I'm finding this very interesting and reassuring I bought tires (tyres) in the right load range but my question back to this thread, is there a published Jaguar load range requirement also??? I've never seen one.

Padrino, I have found this on the Internet from a XK Series 2002 Vehicle Care Handbook.

Hope this help.

Here are copies taken from the Jaguar XK8/XKR user manual, of the tyre and weight specifications:

Great piece of data Stumpy and JSC. Thanks.