Switching to a larger frame

[Adamsavage79]

I'm mulling over getting a better quality bike, however the bike I'm currently thinking about is the Trek Marlin 5 which has 29 inch wheels. This is obviously is not going to to work, without different spokes. My question is, can I use the wheel that comes with the bike, and cut it's spokes out and replace them with shorter spokes that are what I have now, but obviously a little longer. If so, how would I figure out the length I need. Do I need an adapter for the back wheel to support a disc brake ?

[Bikemad]

Check out this post to find out how to properly measure the ERD of the new rim and how to calculate the length of the new spokes that will be required.

Take a good look at the rear dropouts to make sure the Magic Pie 5 will fit into them OK ensuring there is sufficient room to accomodate torque arms and the much larger axle nut:



The brake disc appears to be a standard six bolt fixing type, which will hopefully bolt straight onto your MP5's disc mount/cooling fan unit.
Just make sure the fixing bolts aren't too long or the ends of the thread will rub against the controller's heatsink causing severe binding of the wheel and damage to the controller. 

Alan
 

[Tommycat]

Hi Alan,
Very nice post on the wheel lacing. (bookmarked)

I needed to have some wheel dishing to center the rim in my frame when I installed my MP5 and a 7 gear freewheel. My first build so I made the sides different lengths to account for the offset.( a difference of .6mm) With your build experience would you say this is overkill and that using the same length for both sides would be adequate?   (just adjusting the nipples to account for different lengths...)


Regards,
T.C.

[Adamsavage79]

How do I make sure ? I'm not sure if the bike shop will phyically have the bike in stock, for me to look @.

[Bikemad]

I needed to have some wheel dishing to center the rim in my frame when I installed my MP5 and a 7 gear freewheel. My first build so I made the sides different lengths to account for the offset.( a difference of .6mm) With your build experience would you say this is overkill and that using the same length for both sides would be adequate?   (just adjusting the nipples to account for different lengths...)

As the flanges on the Magic Pie hubs are very close together it doesn't take much to offset the rim slightly.
If you play with the offset figures in the ebike.ca spoke calculator it should show you what the difference in spoke lengths might be.

The rim on my original Magic Pie was about 7mm off centred and I couldn't fit a 26 x 2.35 tyre without it jamming against the frame.
I ended up making an additional flange ring to allow the rim to be correctly centred, and I re-laced the modified wheel using the original length spokes. 

How do I make sure ? I'm not sure if the bike shop will physically have the bike in stock, for me to look @.

Do a google search and see if you can find some better photos of the rear dropouts, as the camera angle on the above photo could be making it look much worse than it actually is.

Alan
 

[Adamsavage79]

What do you input for the hub, on the Spoke Calculator? Magic pie 3 looks to be the closest to what I have, which is the 5.

[Bikemad]

What do you input for the hub, on the Spoke Calculator? Magic pie 3 looks to be the closest to what I have, which is the 5.

I have updated the previously linked post to avoid any confusion. It now says select the "Magic Pie 3" which you would use for all MPII, MPIII, MP4 and MP5 hubs.

If the flange spacing measurement does not match your particular hub, you simply enter the measured figure for greater accuracy, but I would expect the default 22mm width to be close enough for most applications.
I physically increased the flange width on my original Magic Pie by ~6mm and the original length spokes still fitted fine, and I have not experienced any failure of the original spokes or nipples since the wheel was rebuilt, and that was over 10 years ago. 

Magic Pie II, III, 4 and 5 hubs with laced rims all use the same paired hole measurements.

Using the ebike.ca spoke calculator, select the "Magic Pie 3" hub making sure the "Cross Pattern" is set to "0"  and I suggest you also fit the spokes with the elbows on the outside of the flanges for better lateral strength as shown here:

Hopefully this is now a bit clearer to understand.

Alan
 

[Adamsavage79]

That does help, but I noticed the spoke length can vary depending on the rim. The motor also needs a 36 spoke rim it seems. As for the trek bike, you were right. I would have clearance issues with it.

[Adamsavage79]

Bikemad, that spoke calculator is wrong for some reason. The original spokes for the wheel are 110mm. This has been measured by the bike shop a few months back, and confirmed with tech support for Golden Motor. It seems Magic pie 3 Hub is smaller than the Magic Pie 5. Also, if you lace the wheel with the elbows facing OUT, how much more would they stick out towards the frame, or would this even matter ? I'm more worried about the clearance on the bottom area of the frame, where you have a kickstand, disc brake, torque arm etc.

[Bikemad]

The rim shown in the calculations below is not a GM rim:

It has a much larger ERD and therefore needs longer spokes.

The spoke calculator is not wrong, but it can only give the correct spoke length if you enter the correct ERD value:



For the above calculations I simply entered a guestimated ERD measurement for the 26" Deep "V" GM rim, as I don't have a bare rim to measure accurately, but the value I used is probably within a couple of millimetres of the rims actual ERD. 

The Magic Pie III (Magic Pie 3) is definitely not smaller than a Magic Pie 5.
If you take a look at the picture below you can see that the MPII and MPIII use exactly the same length 110mm spokes for the GM 26" rim as the MP4 and MP5:



Putting the elbows on the outside of the flanges do not present a clearance problem as they are even further away from the chainstay than the side cover of the motor:



Hopefully this post has covered your concerns.

Alan

[Adamsavage79]

Hmm ok. Well I went ahead of and ordered a entire set of 36 spokes from Ebikes.ca as the the place I originally got them from, don't have enough in stock. Now that I have a frame that supports the wheel without any sanding of the dropout's, I can get it re laced properly without needing the wheel to pull over to one side. I also noticed the noise I was getting from the wheel, seems to be gone with it being in the new frame.