Smaller rear wheel

Hi again everyone I have now started getting the bike (1975 Mk3 850 E/S) pulled into shape and have a quandry with my rear wheel and tyre . The wheel is 16'' but the tyre is a high profile american add on the difference in outer diameter including tyre is approx 2'' smaller from the standard bike which fortunately there was one at my pals workshop where the bike is ATM to compare, how will this difference affect the gearing if it is lower I need to raise it as I like to keep up with modern traffic without the engine screaming at me also the rear wheel is not in the best of condition so it will almost definitely be removed , BUT I have not the longest legs and ATM the positioning when stationary is comfortable the tyre on it ATM is a Dunlop MT90-16 and no other visible info so do I try and refub this wheel or a WM3 18'' or go back completely standard which I know my short arse would not be comfotable with, also if someone could avise me on the simplest way to up the gearing advise would be very much appreciated

Fit a larger front sprocket, but what's fitted now?

Hi L.A.B. and thanks for your reply I have not yet been in that deep to accurately find out any suggestions for identifying it while in situ it has to stay movable as it will be coming back home shortly as I hope to use it if we have not had our summer the other day !!! and then in the winter pull it down completely

Lie on the floor under the bike. Paint one tooth on the gearbox sprocket in a bright colour. With the bike in top gear and the plugs out, you can turn it over via the rear wheel and count the teeth until your painted tooth reappears.

Then you’ll know what sprocket yer got.

Mark Savage said:

...or just put it in neutral!

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Yeah that’d work!

Misfire in the brain dept…!

Obvious when you have been told (my brain hurts)

Measure the diameter of the 16" tyre that's on it at the moment. Then look on the Avon website at their tyre fitted diameters. See what the difference is between 18" or 19" tyres. 18" or 19" the O.D. of the tyre is very similar, in fact the O.D. of the 18" x 4.00 Road rider is the same as the 90/100 x 19" road rider. If you not going to strip the primary off to fit a bigger g/box sprocket till the winter, it will save bother now, just ride it as is and come the winter then count the teeth and do a sprocket change.
Then again, if your going to rebuild the wheel back to 18" or 19" it might be better to resculpt and lower the seat.

chrisf1 said:

Hi L.A.B. and thanks for your reply I have not yet been in that deep to accurately find out any suggestions for identifying it while in situ it has to stay movable as it will be coming back home shortly as I hope to use it if we have not had our summer the other day !!! and then in the winter pull it down completely

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The front sprocket can be seen (and marked with paint etc.) by looking between the swinging arm and lower chain run.

Yes.
Gritty chain needs a good scrub.

Re the small wheel and the effect on gearing, play around with this site to ascertain the overall set up:

Torontonian said:

Gritty chain needs a good scrub.

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Yes, although it isn't a recent picture and the chain has been replaced since it was taken.

L.A.B. said:

Yes, although it isn't a recent picture and the chain has been replaced since it was taken.

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That’s a bit obsessive innit ?

You cudda just cleaned it…

L.A.B. said:

Yes, although it isn't a recent picture and the chain has been replaced since it was taken.

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You tell them L.A.B chains don't get dirty and wear out by sitting in a garage!
I like a bit of muck for the street cred.

If a short wheel has been put on it surely they would have changed to gearing, have you ridden the the bike to find out, but best to get a stock wheel or 18" if you want to go that way, usually they go 16" when the do a chopper, on a stock bike why???

I have only ridden it a 100yds up road and back as running badly and at that time I had not even noticed the back wheel was smaller by an inch on the profile of the tyre