I fitted aftermarket 20" alloy wheels with 275/60/20 tyres on.
It has recently started to shudder quite badly on braking from speeds above 40-50 mph.
Front tyres have been balanced but not rears.
Does anyone know what could cause this and are there any steering dampers/stabilizers available?

 

Shuddering while braking is usually caused by warped front rotors.

 

Another cause is a loose belt in the tire. Been there before.

 

Thanks for reply but rotors have been checked fronts replaced about 10000 mile ago.
The shuddering is more like the whole truck shaking.

 

10000 miles they could be warped again. at least get them checked to rule out the possibility. If it only happens when braking, then it is brake related.

 

Ok, thanks again I'll get rotors double checked.