18" Rear wheel offset?

Joined
Aug 26, 2005
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59
Hi all - I am rebuilding a 69 commando rear wheel using an 18" rim. From my research the correct offset for a 19" rim is 3/16 to the right, (Roy Bacon).

For an 18" rim I assume the same offset will be OK. anyone have some experiance with this?

Many Tks in advance for your comments!
 
Joined
Apr 7, 2004
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1,691
Did you already break down your stocker? If the rims are the same width 18-19 they would be the same offset from center.
 
Joined
Aug 26, 2005
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I have another bike I can examine (a 71), I will look....

The rim I am installing is a - 18", WM 3 - 18 if that helps clarify.

How is 3/16 offset best measured? Center hub to center rim? hub brake side to rim edge? other?????

TKS!!
 
Joined
Apr 7, 2004
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Because rims vary in speck so much it is best to first find the dead center of the rim. Use a piece of tape across the rim and mark the center with a pen. Now all offsets can be called out from known surfaces using a long straight edge. When you reinstall the new rim use the tape again. In this way the the relatively meaningless rim width doesn't creep in and throw the new wheel off the true line.
 
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Jan 10, 2005
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For what my 2c is worth the offset seems to vary from bike to bike. I have seen them at 3/16" and 1/4". Mine was .25" at the rear ISO and .31" at the front resulting in a skewed power train, swing arm & wheel. I'd check the front since that is relatively easy to remove and build the wheel offset to suit. That way, assuming the head tube is not off centre the rear wheel will align with the front, if the rear ISO is similar.

On the same thread can anyone explain the reason for engine offset?
I never have got a proper explanation from the specialists when it's come up in conversation.
 
Joined
Aug 26, 2005
Messages
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"Mine was .25" at the rear ISO and .31" at the front resulting in a skewed power train, swing arm & wheel."

Re: your quote above, the ISO shims on the left front & right rear as you describe not being equal could skew the drive train but you will only know if you determine what are the specs on the shims on the other side (of the frount & rear). In theory the ISO should have the same shim thickness on ether side of the frount & on the rear ISO.

I know when I rebuilt my ISO's to obtain the correct clearence I ended up with slightly different thickness on one side on both frount & rear. I put the greatest thickness on the sides I couldn't latter easily reshim (the front right & rear left) in anticipation of it needing additional shimming latter & the extra shims being on the opposite side will be actually be improving alignment of the drive train. After break-in I did have to add 15 thou to the rear ISO (right side)...

Having said all this the recomended way to check the wheel aligment is using two straight edges against the front & rear tires. I havn't had to try this however as my commando handles great as is.
 
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I have Norvil verniers and with the rear nipped up and the front assembled with just the rubbers installed right side clearance was 060" less than left side. Basically with everything in place the front mount was being forced over to one side and with vernier adjustment being on the right another 010" was being added. Settled for machining and adding spacer to left side. I think with shims I'd have had them all on one side!
Sure the age old recommended method for aligning wheels works with a straight edge but on mine the rear was so far out it was badly compromising the chain line to get them in line.
Like you say if it ain't broke.......
 
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