Hi All,

My bike is a WM20 1943, but i'm not fussed about keeping it authentic, and it wasn't before.

I've seen the sprocket spec for WM20 and the civy M20, but my bike did not match either, and I have a few sprockets to choose from now.

clutch is 43t and rear wheel is 42.

My eng was 20t and G/box was 17t

I have Eng, 17, 19,& 20 and G/box 17 & 19.

So my question is what is my best option ?, before bike seemed to sit on 50/55 no problem and wound out to 60 but not sure how accurate the speedo is.

Thanks for your help as always.

Cheers
Mick

email (option): mskehan@komatsu.com.au

Hi Mick
Mine is STD gearing except I have a 20t engine sprocket since last year

Since putting this on instead of the STD 19t I have noticed the following
Less motor stress/ vibration (at "higher" speeds 50mph)
50 / 55 more easily achieved & maintained
Slightly better fuel return
However, it needs a shift down to 3rd gear more often on the hills, but my top end does need a little work !
I think a 21 might be a step too far if you have lots of hills but should give you a good top end
Just my experience Mick
:-)
Jo'b

email (option): Jonnyob1@googlemail.com

Mick, your current gearing provides an overall reduction ratio of 5.31:1, which is very close to the standard 5.28:1 ratio. You an work it out as
(Clutch x Wheel) / (Engine x Gearbox)
but be aware that a non-standard rear wheel diameter, or even (to a limited extent) different tyres, also have an effect on road performance.

As you are seeing 60mph I don’t think there’s much to be gained from swapping things around, but you could experiment with using both the 19T engine and gearbox sprockets together, giving an overall ratio of 5.00:1 and a slightly over-geared but perhaps more relaxing ride (and maybe 65mph with a good tail wind!), very similar to that which John has just described.

ChrisJ

email (option): chris.joy@btinternet.com

Thanks for the info John & Chris, i will give the 19 & 19 (civilian) gearing a go, with the formula I can now calculate the various options, thanks again for your help.

Cheers
Mick

email (option): mskehan@komatsu.com.au