Wanted:diagram with measurements of Magic Pie 2 rear motor.

[Andrew]

As in title.

I need some measurements to replace a rim and get spokes made to the correct lengths.

Andrew

[atcspaul]

if you use a new rim you will need to remeasure for spokes. the way I did mine was I pulled a spoke off that was on the bike and measured it. then I measured the width of the new rim and the golden motor stock rim and subtracted the difference. I imagine their is an easier way but that worked for me

[Bikemad]

Hi Andrew, I have attached a drawing of the MPII spoke layout (PDF) but the spoke measurement shown for a 26" rim will be a bit too short as it does not allow for the dish angle, or the additional length of spoke inside the rim.

The threaded end of the spoke should ideally end up just below the head of the nipple when the spokes are properly tensioned:


To calculate the additional length you will need to measure the length of a nipple, and then insert it into the rim and measure the length of the nipple which is still protruding. Add 1mm to this measurement (to allow for stretching under tension) and then deduct it from the overall nipple length to determine the additional length of the spoke that should extend inside the rim.

So if the nipple is 16mm long, and only 10mm sticks out of the rim when it is fitted, you would deduct 11mm from the original 16mm to determine that the spoke needs to have at least 5mm of its overall length hidden inside the rim.

Alan
 

[Andrew]

The rim I will be using has a double eyelet, meaning a single deep isolated 'well' for each nipple. Could the spokes be slightly too long so the thread end of the spokes comes past the top of the nipple?

[Bikemad]

If the spokes are too long, the nipples may tighten against the end of the threaded section of spoke before the spoke has been properly tensioned.

If you screw a nipple onto an unfitted spoke until it cannot thread on any more, and then make a note of how much of the spoke is protruding past the head of the nipple, this will give you a rough idea as to when the spoke's thread bottoms out inside the nipple.

If during assembly, the amount of spoke protrusion is getting close to this amount, the spokes are likely to be too long.

However, if you are able to correctly true and tension the wheel with less spoke protrusion than you had with the unfitted spoke, then the spokes will probably be OK.

I strongly recommend fitting the spokes on the outside of the hub flanges so that all their heads are on the inside:



This ensures the spoke "elbows" are correctly supported against the flange, thereby reducing the likelihood of spoke failure due to fatigue, whilst also improving the lateral strength of the wheel and helping to use up a small amount of that surplus spoke length at the same time.

Alan

P.S. I have updated the PDF attachment in my previous post in order to correct the pitch circle diameter of the spoke holes.
I have shown it as approximately 300mm as the 305mm was definitely wrong.
One GM drawing showed it as 299mm, and I used a measured diameter of 297.6mm for the flange modification on my original MkI Pie. 

[Andrew]

Once again, thanks for the help and support. The numbers you given should do the job when ordering the spokes. The rim being used I have used before for a wheel build and has an ERD of 534mm. 
Do the maths if possible on a spoke calculator.....  http://ebikes.ca/SpokeCalc.shtml

I make it 118 to 119 mm depending.....

[Bikemad]

Andrew, the results of a conventional spoke calculator will not be correct for the MPII or MPIII because of the unorthodox hole spacing on the flanges:



The actual spoke length will be much shorter than a single crossed spoke layout, but also longer than a radial laced wheel (no crossed spokes).
Here are two spokes from Magic Pie wheels with identical diameter hub and the same diameter 26" rim.
The longer spoke at the top is for the conventional 1 cross spoke pattern used on the original Pie:


If you used Justin's Ebike Spoke Length Calculator with your rim and hub measurements and selected the radial option (cross pattern=0) you must then then add ~2mm to the calculated spoke length to allow for the 9° spoke angle on the 26" Pie.

If your ERD of 534 mm is correct, I would say that 119 mm will be very close to the ideal length.


 
Alan