Gearing Change Effecting Speedo Reading - Solution?

I see a few threads about changing sprockets/gearing and comments about effect on speedo reading. Is this because the speedo now comes from engine revs/standard gearing calculation rather than the old fashioned front wheel spindle drive?

If it is altered, is there a way of correcting it or do you just have to use mental arithmetic?

I ask because I have seen about a 10% difference between speedo and tomtom mph since I swapped

Russ

 

It is only an issue if the speedo drive is from the gearbox output shaft and the ease of solution will depend on whether the drive is mechanical or electrical and availability of alternative cigs and dip switches. Sometimes GPS is the easiest option.

 

Will it also affect the TC and ABS on the latest bikes ?

 

IIRC bikes with ABS read the speed from the ABS sensor ring on the rear wheel so no adjustment would be necessary from changing the sprockets/gearing

Bikes that electronically read from the output shaft should hopefully be able to be adjusted using TuneECU
You can alter the ratio by + or - a few % I think up to 10% either way

 

That's interesting ! May explain why they don't offer the speed healer for some ABS bikes (including S3..) cheers for the info

 

If you find no way of altering the changes.
Follow a friend at set speed limits take note and mark the speedometer at these points

 

Using the satnav I worked out it is about 10% over reading ie; 30mph when indicated 33, 70 at 77

 

got caught by N Wales plod doing 33 in a 30 last year - 1 speed awareness course later I am keen to observe in town speed limits.
Out of town is different - no point in trying to see the new drones

 

Dunno if it’s true but I thought you were allowed 10% speedometer error
3mph=10% at indicated 30mph
Think you could’ve argued against that one