Tyre size and speedo reading

[Southcoastbiker]

So I’m looking at buying a rear tyre that is 140 80 r18 instead of 150 70 r18 . Seeing that it is a taller tyre would it affect my speedo  reading  seeing that it is the rear tyre. I’m hoping it would bring the speedo reading closer to a true reading  if the tenere has to travel further for 1 revolution of the tyre, or would it work better if I had a larger front tyre.

[duibhceK]

A couple of things to consider:

The theoretical difference in diameter between an 150/70 and e 140/80 is only +-2%. When installing a 140 width tyre on a 150 wide rim the profile of the tyre gets flattened a bit because it is pushed out wider which pulls the circumference in. So in practice the difference in diameter between both is marginal.

 

all of the above is mute imho, because iirc the speed is read from the front ABS ring.