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Rear Wheel Offset


rcgods
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Hi,

I have a M91 Sherpa which has the early style rear hub with a bolt on spoke flange on one side and a 140mm x 40mm hub on the other.

Does anyone have a measurement of the offset for this type of wheel please?  I have measured mine however the rim is massively buckled no wonder the tyre touches the chainguard, shocks and swingarm!

Thanks

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Hi -    

You have my  sympathy - I know from my own experience how difficult it can be to obtain this sort of information, and I'm surprised that you've had no response so far. Not at all sure if I can help , but here goes :-

 Standard  M91 Sherpa rear wheel is the same wheel as M92 and also (late) M85, and features 17mm. dia. spindle, WM2 (1.85 X 18") Yellow label Akront flanged alloy rim, and butted stainless steel spokes with alloy nipples.  The outer spokes on the brake drum/sprocket side have an extra  bend in the butted portion at  the outer edge of the spoke flange - without this bend I imagine it would make achieving the required offset quite difficult. lf the chain comes off the rear wheel sprocket these 9 spokes are frequently those that get damaged.

Does your wheel have standard spokes and rim ?  Is the rim itself badly buckled, and if it is, what will you use to replace it ? Is the rim correctly laced to the hub (X2's pattern) ?

Here is a sketch I made of a M92 rear wheel, mebbe 40 or more years ago - ..........I can't of course claim that these are the standard offset figures (or that I was able to measure them with any accuracy, come to that..). However, as the bike and its wheel had only about 2 years use at the time - there's hope !

1958334393_BultacoSherpaM92rearwheelrimoffset.jpg.599ca42c57df41b5f1a9439550bd0629.jpg

Let me know if this is of any help at all, or if you need any more info.

A check on the M85 wheel gave a figure of 1.5" for the sprocket mount surface to rim outer edge, rather than the 1.21/32", but I rather fancy this is not right - I have a suspicion it's been laced incorrectly.

 

Edited by lorenzo
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Thanks for the information Lorenzo.  Much appreciated!  That is exactly the rear wheel I have, everything you mention matches up correctly even down to the extra bend in the spokes.  I know it is original as have owned the bike from brand new!  This wheel also has the bolt on flange for the non-drum side of the hub, I have seen others where this is riveted on, which makes adding the spokes tricky as they slot in and then get pulled into the spoke seat.

The rim is scrap so I am having it rebuilt with a new rim (with the flanged edge so it looks correct) it wasn't just buckled left to right it was up and down as well!  If the nipples hadn't been seized so badly I could have probably pulled the wheel back into something close to round, unfortunately I had to cut the spokes from the rim.

The main bonus with this rear wheel type is the steel liner, the main disadvantage is the weight!  I thought I had got another matching wheel but the offset is huge and is either from a Pursang or has been spoked incorrectly.

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