Suzuki Club UK

Hi folks, I have a 21 plate Vitara Allgrip mild hybrid and have just fitted some larger tyres on it which looks pretty cool, but my cruise control disables itself after driving for a few minutes whether turned on or off. I understand the speedometer will be slightly out ( by about 10% I reckon) and I guess this is part of the problem. Any ideas how to recalibrate it? I've phoned a few re map "specialists" but non of them would try, even the Suzuki dealer can't help. Anyone else had the same trouble?
Cheers in advance.