X-Trail alloy wheel discolouration - Big Ron
The nearside alloys on my X-Trail are showing marked discolouration on the spokes. This first manifested itself on the front wheel but is now also evident on the rear. There is no sign of it on the offside wheels.

The wheels do not appear to have been particularly scratched and there is no pitting, just a dull, rough patch on each of the splokes. I've tried to clean the wheels with a variety of cleaners but have had no joy.

I should say here that I regularly clean the alloys with car shampoo so that the wheels never get too dirty.

Anyone got any ideas on why this should be happening, and particularly to the nearside wheels?