Plunger A10 Rear QD Rim Offset

[MikPowl]

Help! I'm confused.  Searching thro earlier posts I found the reference to S/Sheet 79 giving rim offsets.  This provides a set of wheel codes with appropriate offset and someone has written in notes of which code applies to which bike. It seems the most appropriate to mine is the 'A7 Star Twin Plunger' (The other A7 & A10 variants may be s/a - it's not clear).  This gives the offset as '9/16" - edge of rim to face of hub centre'.  What exactly does 'face of hub centre' mean? Is it the edge of the crinkly bit, and if so which side?  Is it the face of the hub central tube opposite the splined side or is it the edge of the spline itself?  On top of this, having carefully marked up the bike centreline on the hub with the hub in situ, this gives an offset different from all of the above!

[Rex]

I'd say it was meant as measuring from the face of the splined end, but that just my interpretation.
Why not build the wheel to this dimension then adjust when mounted in the bike, if required?

[MikPowl]

Yes. that suggestion makes perfect sense, except that I was going to have someone skilled (not me!) to true the new wheel and he/she needs a dimension to work to.  I think the workaround will be for me to 'build' the wheel finger tight then a trial fit will tell me if any offset adjustment would be needed for the final 'pro' truing.  But out of curiosity I'd still like to find out what the terms used in s/s 79 actually mean!

[Miker]

This is what I used as a reference for wheel offsets 1951 a10. Saved from the forum years ago. Credit to forum member that originally put it on. Hope it is helpful.

[MikPowl]

Thanks, Miker, that is indeed helpful.  The dimension you have between rim and the end of the spline is 19mm whereas I'm seeing 14mm. Also, my rim is slightly narrower than your 2-3/4" rim (about 4mm slimmer) so I should be seeing 20+mm.  I shall have to go back to re-check my method for finding the frame c/line on the hub - either i've got that wrong or something is bent!   Not sure any of this will make much difference in the end but I might as well try to get it right.

[Rex]

You need to find the frame centre line on your rim, when built, not on the hub.
Two long parallels (one either side of the rim) up past the frame tubing works best. Obviously the centre of the rim should be equidistant either side of the tube.
{And it's amazing (when following other bikes) just how many have wheels off-set from each other}

[Swarfcut]

  Literature on wheel building stresses the importance of measuring "offset" on an existing wheel, and in the case of the crinkle design the splined end of the hub makes the most sensible datum. This is the same for all variants, the other side differs with the type of bearing cover or as on the unit models, the speedo drive.

  One thing to remember is that even new wheels are never absolutely perfect, and an example  used wheel may not be to factory spec anyway after years of use, abuse and spoke tightening. Makes sense to see how badly out of true any wheel is, before taking measurements from around the rim and taking a mean figure.

 If rebuilding a wheel with a new rim at least this gives a starting point, again assuming the new rim matches the old exactly in profile but at the end point, Rex says it all, forget published data, just set the rim centrally in the frame, with bearings, spacers etc in place and the spindle tightened. Plunger frames do flex a little bit, but with the rear mudguard off, the bolt on the centre of the footrest forging makes a good central reference point.

 Swarfy.

[MikPowl]

I think it's more or less sorted.   I built up the rear hub/brake assembly off the bike and measured the span of the assembly (179mm, or a tad over 7").  Then I marked up the centre of the assembly on the crinkle hub.  After taking apart the assembly I measured the distance from the base of the spline to the mark on the hub and subtracted half the rim width. This gave me the size (16mm) for offset-setting wooden blocks. I've built up the wheel so that spokes are about finger tight and put the whole lot back onto the frame. Although this dimension is a bit less than the 19mm suggested on Miker's sketch things look fine and central but I'll check again before passing the wheel onto someone for truing.   I'm still curious about the wording in the s/s 79 but it occured to me that they may have intended to give a dimension that can quickly be checked with the wheel on the bike simply by putting a straight-edge across the off-side hub flange and measuring the gap to the rim.  Thanks, All!

[Rex]

Surely if you've got the wheel built to roughly the correct off-set and the spokes are all now finger tight, you've done the hard part so why not carry on and tighten those spokes to finish the wheel off?

[MikPowl]

Finger tight but very wobbly!  I'll have a go but not easy without a truing jig.  Let's see how it goes.

[Rex]

You have got the perfect truing jig though...where it sits in position in the frame.
Tie-wraps around both lower frame tubes work as an indicator for checking the wobble.

[Bsalloyd]

If you look at the service bulletin there is a column named complete wheel minus tyre and brake. The number under that column gives you the parts number listed in your parts manual. Just eliminate the first three numbers given for each wheel listed.