Wheels

[Andy_G]

Hello all, I would like some info on wheel sizes/measuring. I have a Bonny T140V chop (rigid) with a 500x16 rear wheel which doesn't run in line with the front wheel.  The rim is 3/4" to the right of centre. Any less offset would cause the chain to foul the tyre so I have concluded the only feasable option is fitting a narrower rim and reducing the offset by 3/4" What I need to know is what width rim I need to achieve this? Anyone able to advise please? I would prefer like to stick with a 16" diameter rim to keep the old '70's chop look but I'm not sure what tyre I'd need on the narrower rim to maintain the look.

[L.A.B.]

Rim/tyre fitment chart: http://www.hagon-shocks.co.uk/WheelTab.htm

[Andy_G]

Thank you L.A.B. I must be having a blonde moment as I'm not sure how this helps though?

Andy

[Searchguru]

A suggestion is take the wheel out and put the wheel spindle back in then sit the back end on a suitable stand or box. Acquire a cheap lazer pointer with straight side, hold it against the flat side of the gearbox sprocket and shine it onto the rear wheel spindle. Mark that then add on the distance of the lazer lens to its casing. That will show you on your rear spindle where the outside of your rear sprocket should be. The standard gearbox shaft and sprocket position dictates that you should use a standard wheel, anything wider and you get the problem you have. You will almost certainly need to have a modified gearbox shaft so that the gearbox sprocket can sit further out. You really need to speak to someone with proper knowhow like: http://www.thefont.pwp.blueyonder.co.uk/bikes/index.htm  or  
http://www.thefont.pwp.blueyonder.co.uk/bikes/index.htm

[Andy_G]

I'm not fussed about keeping the wide rim, just need to know what width I can get away with to leave me sufficient clearance between tyre and chain when the wheel is central.

[L.A.B.]

I'm not fussed about keeping the wide rim, just need to know what width I can get away with to leave me sufficient clearance between tyre and chain when the wheel is central.

OK, thanks for clarifying that, as I wasn't sure if you still wanted to use a wider than standard rim/tyre combination.

So if you wanted to set the wheel rim centrally to the frame, and keep the chainguard then a 110 section tyre (with a WM3 rim?) is about as wide as you can go with the standard T140 swinging arm rear end.
A 120 tyre would fit, but you will probably have to remove the chainguard or cut some of it away in order to gain enough tyre clearance.

As your T140 has a rigid rear end, then it is something of an unknown quantity, so you may have to do some careful measuring to see what will actually fit in there? 

[Andy_G]

Thanks for that, I'll have a measure up and see what's what. Give me an engine to rebuild any day. I remember you, you helped me with my gearbox back along. I'm still impressed

[Andy_G]

Hopefully this will clarify a little better...

[L.A.B.]

OK, well, what I would do would be to measure the distance between the frame centreline and the chain, less a small amount deducted for running clearance, maybe about 5mm?

If you double the amount, then that should give you an idea of the widest tyre section you will be able to fit, but note that tyres are not always exactly the nominal quoted size.
A suitable rim can then be selected to match the tyre from the selection chart link I posted earlier, and provided you don't go too wide on the rim size then this shouldn't be a problem.