Swap a 700c motor onto a bike with 26" wheels

[Solfatara]

Hi All,

I have been given an old delapedated bike that has a Bafang motor on a 700c wheel. Rather than fixing it which involves a lot of extra cost and effort as it is in a very bad way I was thinking of swapping the motor from the 700c wheel to a Dawes Red Feather which has a 26" wheel, together with the other electric parts.
Anybody got any suggestions on things to watch out for? Also how to work out the new spoke length that will be needed?
Thanks

 

[saneagle]

You buy your new rim first. Hopefully, they will tell you the ERD. Whether they do or not, you measure the internal diameter in at least two directions, then add 3mm and see if it's close to what they gave you. If it isn't, use what you measured plus the 3mm, and do the same if they didn't give you one, otherwise use what they gave you.

Next, measure the motor spoke holes pitch circle diameter and the width between the spoke flanges.
Finally enter the results into this spoke calculator:

Edd, an easy to use spoke calculator

An easy to use spoke length calculator with a large amount of hubs and rims in its database.

leonard.io

It'll work OK in a 26" wheel. You might want to check any markings to see how fast it is. If it's 36v 180rpm, it would be best to run it with 48v. In fact unless it's specifically marked as a high speed one, you'd probably be better with 48v anyway.

 

[Bikes4two]

If you can re-use the 26" rim (same number of spokes as 700c wheel) then that should be fine if keeping the cost down.

Then of course ensure the Over Lock Nut (OLN) of the motor is suitable for the 26" wheel bike.

Then Google how to measure the Effective Rim Diameter (ERD) as mentioned above and also for the motor's rim diameter.

Spoke lacing - 2 cross or 3 cross : I'm not sure what to advise - anyone?

 

[saneagle]

If you can re-use the 26" rim (same number of spokes as 700c wheel) then that should be fine if keeping the cost down.

Then of course ensure the Over Lock Nut (OLN) of the motor is suitable for the 26" wheel bike.

Then Google how to measure the Effective Rim Diameter (ERD) as mentioned above and also for the motor's rim diameter.

Spoke lacing - 2 cross or 3 cross : I'm not sure what to advise - anyone?

One or two cross, not three. It depends on the rim and size of the motor. Some rims don't allow much angle on the spokes. You can check that with the 700c spokes. Generally, it's not such a problem with 14g (recommended) spokes as with 13g.

 

[Solfatara]

One or two cross, not three. It depends on the rim and size of the motor. Some rims don't allow much angle on the spokes. You can check that with the 700c spokes. Generally, it's not such a problem with 14g (recommended) spokes as with 13g.

The motor is a Befang 250W and I think the original set up on the 700c wheel was 3 cross, I have attached a photo of it in case it helps?

 

[saneagle]

The motor is a Befang 250W and I think the original set up on the 700c wheel was 3 cross, I have attached a photo of it in case it helps?

Look at the bend by the nipple. On a a 26" rim of the same type, it would be worse, but what's more important is the rim itself. Every rim is different, some hold the nipples in a radial direction, which increases that bend at the nipple a lot. As I said, when you get your new rim, test the angle you can get with your old spokes and nipples, then you know which pattern to use.

You didn't tell us the markings on the motor.

 

[WheezyRider]

It doesn't look particularly well looked after, judging by the rust and general corrosion on that wheelset. I would be tempted, if removing it from the existing rim to put into another rim, opening it up and making sure it is properly greased inside and the clutch is in good condition. I wouldn't want to go to the hassle of building it into a new wheel and then finding it needs sorting soon after.

 

[Solfatara]

The wheel pictured is the old 700c one. I have swapped it for the intended 26" rim using 248mm spokes in a 3 cross lacing.
The problem that I now have is that having tightened the locking nuts to the drops the wheel does not free wheel. Any suggestions on what I have done wrong? On the cassette side I have used the large spacer inside the cassette, then a washer/spacer of approx 3mm, and then the torque washer insid the drop with a washer and locking nut outside the drop.
On the non drive side it is normal washer, torque washer, drop, washer & lock nut.

Not entirely sure what I have done wrong?