Wheel Alignment

[DougX]

Having had an MOT on my car recently, it was indicated as an advisory that my two rear tyres were wearing on the outside edges. 2.70 and 2.80. Centre measurements were 4.30 on both tyres and inside edge were 3.00. As I am going to undertake a number of miles this year, I decided to change them and brought Dunlop SP Sportmaxx tyres. It was suggested that I have the wheels aligned to. I had this undertaken at another location and the results were as follows:
Front Nearside Wheel Camber -1.19 (Green) Front Offside Wheel Camber -0.51 (Green)
Front Nearside Wheel Caster -5.56 (Red) Front Offside Wheel Caster 5.48 (Green)
Front Nearside Wheel Toe 0.04 (Green) Front Offside Wheel Toe 0.04 (Green)

Rear Nearside Wheel Camber -1.32 (Red) Rear Offside Wheel Camber -1.15 (Green)
Rear Nearside Wheel Toe 0.06 (Green) Rear Offside Wheel Toe 0.06 (Green)
REAR
0.13 (green)
TOTAL TOE
0.00 (Green)
THRUST ANGLE
Can anyone explain why some of these reading are in RED? Should I be concerned?

[BrianG]

Doug,
Anything reading RED is out of spec and needs attention. Your nearside front Caster reading suggests to me that the suspension may have had a bash and knocked it rearwards, e.g. pothole damage. It could be within adjustable range, but may indicate damaged parts needing replacement are required. If you have not had this sort of alignment check done before it may have been like that since before your ownership.

Note also it's possible that if you have had tyres fitted and wheel alignment done by your local "gorilla" tyre firm that they have messed in areas they should not have touched. I had to take my XJ8 to the local Jag main dealer to have the whole car put right after Nationwide Tyre chain had talked me into having the front and rear tracking done whilst I was there; according to their equipment the tracking was "all OK". The main dealer has a super machine which gives "before and after" printouts of any adjustments made. Lots of RED areas found and it took about 2 hours to reset everything to spec, but well worth the (then) £100 fee.

[DougX]

Thanks Brian for your interesting take on this issue. I had new tyres fitted at one place and took the car to another tyre place where they had the equipment to all wheel alignment. Some local garages were only to undertake the front tracking. Bearing in mind there was more wear on the rear inner and outer edges of the rear tyres, I took the car to a garage that was able to do all wheels.

[JimMann]

Hi Doug, the readings of your rear wear would, to me, indicate that your rear tyres have been running under inflated. If you refer to any of the handbooks, it typically would show an over inflated tyre as having a central section high point, whilst the under inflated diagram would show a more "W" shape, with the centre section not touching the surface, therefore the wear is on the 2 x outer edges.

Jim Mann

[DougX]

Hi Jim, that is something that was suggested by the garage that undertook the wheel alignment. However, the type pressure guide in the centre console of the XK8 indicates the pressure of 20” wheels as 30 psi. That is what I always ensure they are and undertake monthly pressure checks, with them very rarely found to be below that pressure.