Carbon cross bike conversion to ebike - bad idea?

Hi there

I am very new to the forum, but I have been doing a bit of Googling. I currently commute on a road bike around 50k a day (25 k each way), I have a couple of busy roads where I would appreciate some e-bike assistance to get up to the same speed as the cars. I currently do around 30-40kph, but to be safe I would like to be able to get to 50 (ish).

Most of the bikes I see customised are fairly robust, I am proposing a carbon framed cyclo-cross bike, with decent disc brakes (I have most of these items), with a bafang 250w 36V motor, and a reasonably light battery (something about the same as a bottle cage size).

To do around 50kph on the flat, I would be looking to put out about 250-300 watts of pedaling power, with the motor providing the rest.

Does anybody have any experience with Carbon frames. I have ridden carbon frames road bikes and mtbs, and they are very strong (just not good at taking impacts.

I understand the bafang motor is around 3kgs, I assume the battery would be about the same and with other lightweight componentry I would expect a bike around the 15kg mark. If this is a really bad idea - can people please give me some advice before I start buying bits and pieces. And would I have to fudge around with the speed sensor, wheel size, programming in order to utilise the bursts of power idea.

Thanks for your help

Sorry should have added it was for mid drive system.

Personally I prefer a hub motor for my road bikes. Too much drag in the BB series motors when just wanting to pedal.

Just make sure you get the right kit to fit your bb and the accessories as most CF bikes are press fit these days and even then there are choices.

Besides having press fit BB's , many modern bikes have a through axle rear axle. so at the present time a rear hub motor would not work , since the Chinese Still have not made a through axle rear hub motor.

Do you live in a area with Rain ?

Do you have any steep hills you have to go up ?

If not the Kepler Friction Drive would be a good and very light weight option.

I think the BBS02 is heavier than 3 kg . better research that more. the TSDZ 02 is a little less weight.

But if you do not have any steep hills to go up and have standard rear dropouts for the rear wheel then a hub is often better.
It is said that Hub motors are a better option for 80 % of people who want to do a conversion.

As you can already see you will get as many different opinions as you do answers. You stated you wanted to use a BBS02 mid drive so in my opinion that is what you should do, if possible.

First make sure it will fit your bottom bracket. They were made to fit in place of the standard 3-piece square taper cranks, but there are adapters available for some other bottom brackets.

On a regular bike the chain alignment has been a problem for some. If necessary you may need to add some guides and/or tensioners to eliminate chain drops. An IGH, such as the NEXUS 8, is also a good solution to eliminate shifting and chain issues.

There are about half a dozen different display units available for the BBS02, and they also control some of the functionality of the controller. For instance, some limit the top speed to 40 kph, but others allow speeds up to 99 kph, so none of the fudging with wheel diameters, etc. would be necessary. You might need to use a programming cable to get all the controllers parameters set the best for yourself.

There is very little drag from a BBS02 when you just want to pedal without using the motor. Probably about the same as a geared hub motor and way less than a direct drive hub motor. I expect a highly tuned rider like yourself will notice even a minor drag (I don't notice it at all) and also the extra weight involved.

Anyway, I think the BBS02 is an excellent choice for your frame because it won't stress any of the more sensitive parts, but I have no experience with carbon frames. Good luck with your project, no matter which way you decide to go.

Thank you everybody who has replied. I really appreciate the feedback and the time you have taken to share it with me.

I will continue to do some more research.

Cheers

Carbon Frames have thicker re-enforced BB moulding so the BB is typically thicker than 3mm which makes it real hard to fit a BBS mid-drive.




That said, a BBS02 at 52V will get you 50km/h on a cross bike with a 48t Chainring as stated in my build thread ( I run 29er tires which is same rim profile as 700c and close enough to what you're thinking of building ).

I built mine in 2015 and it's still going good, so I may be an outlier to the horror stories you might read... I did pack the shit out of it with Marine grease as soon as I got it though.

It sounds like you are a fairly strong cyclist looking to keep his bike lightweight but also get some extra assist to go a bit faster on a bike that still feels like a bike. You might want to read the thread below. This fellow's general approach is to use a small geared hub motor with a suitable winding. That keeps the bike relatively lightweight and provides enough extra power to get up to around 30mph (50kmh).

https://endless-sphere.com/forums/viewtopic.php?f=2&t=90904

Of course, if you want a mid drive, then by all means, go for it. But I've been thinking about adding electric to my road bike. I'm pretty sure I'd follow the above approach since it is simple and should keep the bike looking and riding a lot like a regular road/cross bike.