just wandering are there any? will the speedo read faster or slower than actual speed, or does it not make a difference(i think this one)

lol, stuck on my race spare wheels with tyres to get me through the winter legally, with an 18 on the rear, and it already jacked up with the nitron track shock, plus i have the forks through the yokes 5mm, my balls are well squished against the tank, haa haa. will adjust the forks again at weekend if i have the time.

You will be going faster than your speedo is reading.

This is because the speedo 'knows' the rolling circumference of your tyre and works out how far you travel in a set amount of time based on how many times the wheel turns.

if you go up to a 18 then this 'calculation' will be out as each rotation will cover more distance.

It will also affect your gearing.

FWIW flat out the speedo was under-reading by over 20mph in comparison to the GPS on my TDM with it's 17 rather than 18 inch front.

Druid

anyone know the diameter of a tired up 18 and 17??

These are a few measurements I have taken over the years.

18" Rear Tyre Dimensions

BT092 150 (636mm spec) 631mm measured - New
BT020 160 (647mm spec) 633mm measured - Worn to minimum tread depth indicators
BT014 160 (648mm spec) 646mm measured - New

Regards,

Dave.

DAC wrote:These are a few measurements I have taken over the years.

18" Rear Tyre Dimensions

BT092 150 (636mm spec) 631mm measured - New
BT020 160 (647mm spec) 633mm measured - Worn to minimum tread depth indicators
BT014 160 (648mm spec) 646mm measured - New

Regards,

Dave.

is that diameter dave?

Diameter, yes - should have made that clear.
I don't have any measured data for a 17" wheel/tyre setup, but the Bridgestone website gives all the specifications for this size. I have found that there are slight differences between measured & specified values. Measured diameter will vary slightly with wheel rim width as well.

Regards,

Dave.