does changing a diff make a difference to a speedo when the pickup comes from the engine??

The speedo will still read the same as it always did...

BUT

The car will now be travelling at a different speed.

A cable drive/electronic OEM speedo is taken from the output shaft on the RWD box.

[Edited on 7/10/06 by SeaBass]

its a bike engine.

If your road speed signal comes from your engine and you change the diff then your road speed will be wrong.

If you have a BEC then you will need to fit / reprogramme your speedo healer. If you have an aftermarket speedo then it will need to be reprogrammed / recalibrated if possible. There may be some DIP switched on it to do this. If you are using a mechanical speedo then you can sometimes get different gears to reduce / increse the speed.