26" steel mtb conversion - donor suggestions?

[2hr8c73hr9wdgsi47]

I have a Yuba Mundo classic cargo bike and right when COVID hit got a no name shop in NYC where I then lived to convert it to electric with a rear wheel motor.

I no longer live in NYC nor use it as a minivan and after it has sat for a while I'm itching to restore the yuba to its stock configuration and then take my ebike parts and affordably convert a regular sized frame and use it for hilly commuting including segments on a train where the yuba is too big.

It has 26"x2" wheel/tire set, I would need probably a 21 inch frame or maybe 20, the biggest challenges I already grasp are: the motor wheel needs a wider over locknut distance than the donor bike will likely have. The shop hadn't done this adequately for the yuba but Iater successfully cold set the frame to accommodate the extra width. So I'm thinking a 26" steel mountain bike frame that I can cold set to accommodate my motored wheel. But to handle the extra weight and power it needs also to take the disc brakes I now have which rules out a lot of the market of old steel MTBs I see on marketplace, craigslist, etc.

Any suggestions?

 

[gromike]

I haven't had much of a problem putting a standard motor wheel in a standard bike of 135mm space between the rear lugs. Proper disc brake rotor alignment sometimes has been a problem.
A quality, lightly used, properly stored 26" mountain bike with decent forks and disc brakes is what I would look for. It should be inexpensive. I have bought 15 year-old full suspension mountain bikes for under $150. I personally have had no problems with using aluminum frames.
Avoid a full suspension MTB in order to make battery fitment easy.

 

[2hr8c73hr9wdgsi47]

Thanks for the reply. Unfortunately the motor wheel I have I think has seemed definitely wider than 135mm locknut to locknut, more like 155 to 160mm.

Edit: or so I have believed for years, but inspired by your comment I just fussed with it and my sons bike which I measure at 135mm OLD and it near well slides in there. I think that, like my original set-up, it wouldn't be able to use the full range of gears at this width but would ride with adjustment to the disc brake fit. I'm puzzled and scratching my head but have renewed faith I don't need a unicorn frame. Thanks!

I haven't had much of a problem putting a standard motor wheel in a standard bike of 135mm space between the rear lugs. Proper disc brake rotor alignment sometimes has been a problem.
A quality, lightly used, properly stored 26" mountain bike with decent forks and disc brakes is what I would look for. It should be inexpensive. I have bought 15 year-old full suspension mountain bikes for under $150. I personally have had no problems with using aluminum frames.
Avoid a full suspension MTB in order to make battery fitment easy.

 

[neptronix]

So I'm thinking a 26" steel mountain bike frame that I can cold set to accommodate my motored wheel. But to handle the extra weight and power it needs also to take the disc brakes I now have which rules out a lot of the market of old steel MTBs I see on marketplace, craigslist, etc.

If you use a direct drive motor, rear vbrakes is no probem.
Regen + vbrakes will provide stronger and more durable braking than a disc could.
If you have a sufficiently large DD motor ( 35mm width ), then the motor can do 100% of the braking in the rear. If tuned for high regen amps, it would be stronger than the strongest disc brake... and fade a lot less.

 

[2old]

The rear brake is (reportedly) only responsible for 30% of braking. I've discovered that rear linear brakes are adequate on my DD street bikes. Accordingly, a hardtail with a front suspension fork is adequate and some 90's steel frames (even aluminum since your motor fits 135 dropouts) would be adequate. If necessary, there are new Rock Shox forks for $100 - $150 that will improve the front end markedly. Just look for one without a tapered steer tube.

 

[E-HP]

Thanks for the reply. Unfortunately the motor wheel I have I think has seemed definitely wider than 135mm locknut to locknut, more like 155 to 160mm.

Edit: or so I have believed for years, but inspired by your comment I just fussed with it and my sons bike which I measure at 135mm OLD and it near well slides in there. I think that, like my original set-up, it wouldn't be able to use the full range of gears at this width but would ride with adjustment to the disc brake fit. I'm puzzled and scratching my head but have renewed faith I don't need a unicorn frame. Thanks!

You didn’t mention it, but you need an axle washer on the inside of the dropout on each side to provide proper freewheel clearance, brake alignment, and to protect the dropouts.

 

[neptronix]

If you have 150mm dropouts, you should buy a 150mm motor.

 

[99t4]

If you use a direct drive motor, rear vbrakes is no probem.

Unless it is assembled to a rim that is non-rim brake compatible.