||I have 165/15 tyres on the front of my 96. Am I correct in thinking that this will cause my speedo to underread? Reason I ask is I got one of these roadside speed warning signs to light up at a lower indicated speed than in my other car at the same place.
||Yes but it will on be a very small percentage - 8mm additional radius, maybe a couple of mph at most?
||usually most 165's for the Saab have a 80 profile with no great increase in tread width.
||I've noticed that those speed warning signs pick up cars travelling in the oppsite direction, also they don't always seem to be that accurate!
||also speedos are allowed to be 10% out and still deemed 'accurate'.