My rear tyres are shot and I'll be replacing them soon. What worries me is that the inner 2" of tread are a lot more worn than the rest of the tyre. I have about 4-5mm left in the middle, 3mm on the outer edge, but only 2mm on the inside edge. Both rear tyres exhibit much the same wear.

I took a spirit level to all 4 rims (yes, I know, not very accurate...), including the front, and the camber seemed significantly off vertical on each of them. I had to move the top of the level away from the wheel about 8-10mm to get the bubble in the middle (see photo).

Would this explain the increased tyre wear on the inner side, i.e. more pressure being constantly excerted on the inner side of the tyre?

285/30x20 Pirelli Rossos

 

Factory settings call for some Negative Camber on all 4 Wheels for good Cornering.

Rear Tire wear due to Negative Camber is compensated for (to some extent) with Rear Toe-In.

When I installed Lowering Springs, I also observed increased Negative Camber (Using your Level method).

I installed 7.5mm Axle Spacers (replacing the Factory 4mm units) and the Camber appears to be back in factory range (again, using your Level method).

This actually produced less Camber than the Front Tires, but handling seems OK, and no noticeable inner tire wear.

 

Frog, how often have you been rotating tire position on your car?

.

 

If you have lowered your car without adjusting the camber, than it will be to negative, resulting in more inner tire wear. Another disadvantage of to much rear camber is you get less traction.

 

Thanks for your input so far

I haven't lowered my car, or changed any of the suspension settings, but I have installed 15mm spacers on the rear hubs only. I can't rotate any of the tyres as they are staggered and also direzionale.

 

In theory because of the lever effect, it will lower your car slightly, so increasing the negative camber, but I have no experience with spacers (other than negative vibration ones and thru them away long time ago), so can’t say if that would be the main cause.

If you make a picture from the rear of the car as low as possible, I can guess the camber.

Personally I would double check the geometry settings, and don’t forget to do this with a full tank.

 

Do you have any before/after pics of the 15mm spacers? How do you like them Frog? I had 1'' spacers on my 18'' wheels but am considering a set for my 20'' Detroits...

 

I may be barking up the wrong tree and apologise if I am, but it seems that there is only 1mm difference between either outside edge of the tyres, with the biggest difference being the central section. This would suggest to me that perhaps the problem is under-inflation of the tyres rather than a significant camber problem.

 

My 2 cents:
With 15 mm spacers on each of the rear hubs, you have extended the distance from center to the outer edge of the tire, thereby changing the geometry of the independent rear suspension and increasing the negative camber. While driving straight, the inner portion of the tire will wear at a faster rate than the center or outer edge. The XKR specs call for a certain degree of negative camber, which is desired for cornering to prevent side slippage. As mentioned in the previous posts, when lowering or extending the length of distance from centerline to the outer edge (creating longer leverage), the camber must be readjusted.

 

I agree that tire pressure may be too low.

 

I checked the pressure on all 4 wheels: it was too low, but not massively so. I know the spacers aren't very kind on the suspension, but I think they look better. Big question: how easy is it to reduce the negative camber just a little to compensate for the spacers? Is it just a matter of tightening or loosening a bolt?

 

Here are a couple of before & after shots. I went with H&R, as I know they are high quality. The thinnest they offer for our wheels is 15mm, but I would have gone for 10 or possibly 12 if I had been able. 15 is ok, though


BEFORE:



AFTER:

 

Adjusting camber to rear wheels is not necessarily an easy task. Shims are required between the axle and differential axle flange. Jaguar has shims from 3.5mm-7.5mm. Your vehicle will have shims; therefore, an alignment calculation is required to fit the proper shims for the camber you desire. I have read that .5mm shim is approximately .2 degrees. If camber adjustment is what you're seeking, additional items may also contribute to negative camber - weak coil springs, upper shocks mounts and plastic spacers (Jaguar refers to this as packing) above coil springs. My previous post regarding the spacers contributing to negative camber was just one possible camber problem. A curiosity question - should you remove the spacers, do you still have as much negative camber? That would isolate the spacers as contributing to excessive negative camber and inside tire wear.

 

I'm no expert as this post will attest to.

I also can't remember if Frog's car is RHD and mainly driven on the 'wrong' side of the road.

But, as most roads are laid with a high point in the middle and lean down towards the edge.

Would a UK spec car be set up differently in terms of suspension geometry to a car permanently driven with the driver and hence weight at the bottom of the slope rather than at the top as is the case for cars with the steering wheel on the correct side for the country where it is supposed to be driven?

I hope that this is fairly clear.

In other words, are US specs different to UK specs, or should some calculation also take place to compensate for the issue of the car permanently being driven at the 'wrong' angle? due to road construction.

Over 20 odd years with RHD cars in Europe, my right hand tyres always wear faster than the left side, so should the 0.5mm shims etc be transposed to the other side of the vehicle?

Evidently we have members in this thread that could think about this one.

BTW Frog, I'm OK with the spirit level, my last comp V8 LR chassis was welded together using one and some 2x4 cut wood as frame guides.

 

I seriously doubt it. Non-track vehicles should be set up without bias of this sort.

 

You would need to check the specs book for the figures to determine if there is a lateral bias. There should be specs for UK, JP, DE, NA and ROW. Consideration for driver weight on RHD Jaguars is complicated by the battery also being on the same side.

If there is a bias then transposing it would make sense. When roads in North America were more likely to be crowned it was common to bias the settings to create a more centered feel. Older texts cover this in detail.

If Brutal drops by, he'll tell you for sure.

 

An interesting theory, Translator. Hadn't thought of that

 

How much camber change did you observe with the new shims?

 

The JTIS Suspension section specifies the differences in setup for the different world markets, RHD and LHD. For the rear suspension there are no differences in the market requirements and left and right wheels have, therefore, the same limits for camber and toe settings.

It's the front that's more complex! There are different settings for 1. RHD/Japan, 2. USA, Canada and Mexico and 3. Rest of the World. On top of that there are differences in the actual upper wishbone lengths as described in this quote from JTIS

''The close tolerance machined alloy subframe installed on NA vehicles with VIN up to 031302, precludes the necessity for adjustment of front suspension geometry during vehicle manufacture. Eccentric lower wishbone fulcrum bolts are available as service items, but should only be fitted when directed by Jaguar Technical Support.

On RHD and Japan market LH drive SC vehicles with VIN up to 031302, eccentric fulcrum bolts securing the lower wishbone to the front crossbeam, facilitate adjustment of wheel camber.

All RH drive and Japan market LH drive vehicles from VIN 031302, incorporate a long upper wishbone on the RH side of the vehicle and a short upper wishbone on the LH side. There is a 2mm difference between the two wishbones, measured from the centers of the ball joint location and the fulcrum bolt location. The longer wishbone is identified by a countersunk hole in the upper surface adjacent to the ball joint location.

All other LH drive vehicles from VIN 031302 onward are fitted with the shorter upper wishbone on both sides. These measures counter the effects of road camber on steering and eliminate the necessity for adjustment of suspension geometry.

The vehicle must be checked to establish that it conforms to the Jaguar original specification, e.g. wheels, tires, tire pressures, etc.The 'space saver' wheel must not be installed on any of the hubs when measuring suspension geometry.The vehicle must be unladen and the fuel tank full when measuring suspension geometry.''

That final comment about having a full fuel tank is contradicted elsewhere in JTIS, where it suggests only 9 litres/9.5 US quarts (Showroom Condition) Take your pick!

 

This is Data from another user who changed the Shim Thickness with the measured results. There is still a small amount of Negative Camber (Within Factory Specs).



Not shown in the Above Diagram is the Measured Final Camber at -0.34 deg (vs the expected -0.63 deg).

This indicates about 0.46 Deg Camber Change per 1mm of Shim Thickness.

Although I only used the "Spirit Level" method of measurement, I seem to have similar results.