Building a robust rear wheel for a mid-drive

[RageNR]

Alright, so there are many threads about wheel building, but I have yet to see any of them that pertain directly to building wheels for mid-drive setups. Most of them discuss building wheels with a hub motor.

With the high torque forces applied with some of the more powerful mid-drive kits, building a proper rear wheel to handle the stress seems quite important.

This is my first wheel build, but I have been planning to do this for several years now. Advice from seasoned wheel builders will be helpful and appreciated.


I will be sacrificing a bit of weight to build a stronger wheel. Here are the components I'm using:
- Alex DX32 rim, 26in, 36hole (ERD: 545.6mm)
- Novatec Hub, 36hole [not sure the M#] (Spoke hole size 2.3mm, O.L.D. 135mm, Spoke Circle L-62mm R-68mm, F.T.F. 58.1mm, L.C.F. 35.95mm, R.C.F. 22.15mm)
- DT Swiss spokes, preferably 2.0mm/14gauge (not sure which of their product lines to go with)
- Brass nipples (again, have not decided with product to go with yet)


I used prowheelbuilder.com to calculate the spokes. Someone check my math and make sure I got all of this right.


According to the calc, looks like I need 260mm spokes. That is using a 3 cross pattern.
Also, I am aware of the reputation and reliability of Novatec. I am limited on options due to having a 36hole rim, and the Novatec hub I will be using is one of their highest end products meant for enduro.


Here is the second half of this thread...
What would be most durable and capable of withstanding the twisting forces applied through the drivetrain into the wheel?
I think 3 cross pattern will be adequate, but how about the type of spokes?

Reading through Sheldon Brown's excellent site and info, he mentions that some builders opt to use stronger spokes on the drive/derailleur side. Considering the forces applied from the mid-drive, this seems like it would make even more sense in this application.



I am super excited to build my first wheel. Just need a little advice from the vets of this sport. Spoke recommendations?

 

[ferret]

With the high torque forces applied with some of the more powerful mid-drive kits, building a proper rear wheel to handle the stress seems quite important.
...
Reading through Sheldon Brown's excellent site and info, he mentions that some builders opt to use stronger spokes on the drive/derailleur side. Considering the forces applied from the mid-drive, this seems like it would make even more sense in this application.

RageNR,
A powerful disk brake setup, 200mm rotor and 4 piston caliper, such as can be found in DH and enduro bikes, should be able to to generate more torque than most mid drives. Especially true if the all the power is transferred through the derailleur.

You did not mention the motor and bike setup you are using, but I would guess that any quality DH/enduro type of wheel or wheel parts will be strong enough for your needs.

Avner.

 

[RageNR]

The rim and hub I have chosen should be more than capable of holding up to the abuse.
(Alex DX32 36hole rim, Novatec enduro hub)

I am more concerned with spoke choice for such a high power application. As I explained in the OP, Sheldon Brown mentions that some wheel builders opt for stronger and sometimes thicker spokes on the drive side.
But I see your point about a good disc brake applying more forces than the drive side could. Make sense.

As for my setup, I have that Cyclone 3000w kit on a Klien Mantra, which has a URT design. There should be little to no flexing from the bottom bracket to the rear axel. I am also going to experiment with pushing the Cyclone to roughly 5kw in short duration.

You did not mention the motor and bike setup you are using, but I would guess that any quality DH/enduro type of wheel or wheel parts will be strong enough for your needs.

I didn't include the details in the OP since there is a link to my build thread in my signature.

 

[12-C]

Good topic, I with it had gotten more attention.

I'd say that a disc in the rear can't transmit as much torque as a hard launch on a powerful middrive..... weight transference to the rear on launch and the opposite for applying a rear brake.... you will break traction with a skid on hard braking.

Anyone interested in bringing this back to life and chiming in on wheel building?

 

[Balmorhea]

I'd say that a disc in the rear can't transmit as much torque as a hard launch on a powerful middrive.....

Maybe. But a front disc can probably transmit more torque than a mid drive, depending on weight distribution. You don’t hear about those wheels failing in torque, because they don’t. It’s an overblown concern. Calculate the tip-up torque for your bike, then divide by the number of spokes in the wheel. Then divide that number by the flange diameter, and you know the change, plus or minus, in one spoke’s tension due to torque.