Custome Electric conversion of a Carbon Fiber Road Bike

[Texyclist81]

Ok, so I own a carbon fiber road racing bicycle (non-motorized; 07-08 Giant OCR C3). What I want to do with it is to add a super lightweight motor/battery system that is throttle only, to be engaged exclusively for cresting hills. Mainly, I want to avoid getting off the bike on longer or steeper hills and turn what would normally be the hardest part of a ride into a rest period for my muscles so that I can pedal for longer rides. Any suggestions as to what type of custom configuration might work best here?

 

[m@Robertson]

The carbon fiber frame is going to make mounting an issue that is either going to be tough to address, or kill the idea entirely. Lekkie makes some adapters for carbon fiber frames/bottom brackets, but the general consensus is c/f frames are poorly suited for the stresses of a mid drive unless they were designed to handle one from the start.

Compounding the problem is this is a road bike frame. DIY conversions usually stick to bikes with stronger stays, which also get subjected to higher twisting forces thanks to the new motor. So thats another knock against this.

The prejudice against cf in DIY is rooted in the fact that, when it is stressed, steel bends but cf shatters. Alloy is handicapped as well but nowhere near as badly as cf.

If this can be done at all, I would use a BBS02 once I confirmed the adapters are available for the bottom bracket. I have seen the '02 de-tuned such that it becomes survivable with old-school road bike frames with spindly stays (i.e. Columbus, Reynolds et al). Also tuning guides are widely available for this class of motor (I wrote one you'd do well to emulate given what you are proposing, via the flat land tune that is low-powered). You could also look at motors from Cyc and ToSeven, but both of them have reliability and configuration issues whereas the Bafang motors are known troopers, long time players and replete with wide aftermarket and youtuber support.

But honestly, I think this is just about the last kind of frame (carbon fiber road bike) you would want to add assist to. I wouldn't feel good even about a hub motor given the need for torque arms, what that would do to your chain stays, and the stress on the dropouts.

 

[m@Robertson]

One more thing: If you are wanting this for just part of the hill climb, thats not going to happen. The OCR C3 has a triple front crank and I am sure you would expect to use it. I'm guessing you have a 52-42-32 now. A mid drive takes over the front chainring, and that means your bike is going to become a 1x. So you'll need a pie plate in back, and the one chainring you will keep is going to be something like a 42T, and your chainline on a short-stay bike with a BBS02 is not going to be great. But regardless of those issues, having one 42T ring up front means you can forget about leaving the motor inactive except for a small segment of your ride. You will no longer be geared to reach the higher speeds of your outer ring, and of course your inner ring will be gone, as will be your front derailleur.

And to get that pie plate in back to get back some of your gear range, you'll want to change your derailleur to one that can handle said pie plate. So add a new derailleur and shifter.

I suggest you re-think your project. Starting over makes a whole lot more sense. And when you get to that point, everything here would work on a gravel bike config getting a bbs02:

How To Build An Ebike From Scratch

You want to build an ebike, but the project seems overwhelming. Lets de-mystify the entire process, including planning, parts and perfecting the end result.

talesontwowheels.com