Frustrating Cruise Control

[FunkyFez]

My Cruise Control seems to work a treat up to 60MPH, when it just gives up. I've heard rumours that tire size can have an effect on this. The previous owner has fitted 245 45 ZR17's at the rear, but i believe this should be a 40 sidewall.
Is it likely this is the issue, or should i be looking into this more?

 

[Dieselman]

The tyres are the problem here.

 

[stevesey]

Yep, car will be detecting a difference between front/rear wheel speeds and treating it as an error (effectively think there is some loss of traction on one axle and deciding it might be a good idea to disengage CC).

My old Vectra was sensitive enough that when I put the (on the limit) spare on the back with a nearly full tread tyre on the other side the ABS light would come on after about 10mins at 80mph (a different reading from each side for a long period making it think there was a sensor fault).