According to Dynojet (206 wheel power) my speedo shows + 2.5 mph at 140 mph.

 

Measuring distance by the odometer and comparing with a 5km measured section on the road the S2K indicated 5.1 kms. I think this means my speedo would also read about 2% fast. (And my tires have about 23000 kms on them and are 80% worn down).

 

As speed increases, the speedo's accuracy decreases due to many reasons, such as tire pressure (expanding).

 

[QUOTE]Originally posted by SkipX
[B]This is normal. My '01 was off by +6 at 100MPH according to my K-15/II radar gun. However, according to Honda, a

 

I was wondering if getting larger wheels made it say I was going faster. I'll have to go out and check one of there days.

 

Dave, don't make the mistake of assuming the odo and speedo are synchronised. As I posted earlier, manufacturers will deliberately set the odo to operate accurately whilst giving you an optimistic indication of speed.

 

Going through a speed trap at a 1 mile track land speed racing event I was reading 143 and clocked 137.
-BS2KT

 

This is normal. A few years ago, Car & Driver had an article about speedometer error, I can't remember all the findings but they concluded that most Japanese cars had a built-in error of reading faster than actual speed, I too have confirmed this with my GPS. So if you have one that's dead-on, consider yourself lucky, or perhaps not because when you are clocked by a radar gun and the officer asks you if you knew how fast you were going, you can say yes! I actually like mine reading high, it's a built-in safety factor for when the occasional speed trap does catch me off-guard.

 

Larger wheels will make it read slower if you changed the overall diameter of the wheel/tire combination. If the diameter didn't change (stock is 24.8 inches) then the speedometer reading won't change.

 

The +2 at 60 and +4 at 100 agrees with my measurements with NEW or almost new tires. If you do the math you will see that the error will INCREASE (assuming it's reading high to begin with) by about 2% between new tires and ones that are down to the wear bars. It would then be about +3.2 at 60 and +6 at 100.