Still searching for the perfect ultra-light ebike kit for road bikes — here’s the idea in my head

See what you're saying. My friend said there's still room for reducing the size from the structural point, and technically, it can be done. Moreover, Mahle products are not so versatile. If we could create something that's more versatile, that would be awesome.

of course it could be smaller, but unless your friend is proposing starting a motor company to design and have manufactured a motor (which would surely cost hundreds of thousands of dollars for the first unit) it really is irrelevant what he thinks. if it was so easy, such a product would exist.

the closest thing I see to the mahle system (which you could certainly get your hands on if you were determined) is a 1.6kg front hub motor, like the bafang G370. this and a cadence sensor and a bottle battery and the controller would make a compete system, it would look good awful, but wouldn’t weigh all that much.

another approach is the elevate conversion kit, which attaches a toothed ring to the rear brake disk and uses a small motor to turn that. it’s $2200 though, and not that light… you could buy a used x20 based carbon road bike for $2500.
 
You've seen that on EBR?? After almost 3 active years here, I'd say that the vast majority of members always ride with assist. Why? Because their ebikes are a pain to ride in OFF — even on the flats — and for their purposes, that's OK. (Not knocking that, just a fact.)

We definitely have a small minority of members who like to ride in OFF under suitable conditions, myself included. But we have the ebikes for it — e.g., Scott Addicts or Specialized Creos or original Vado SLs. Lightweight, lower-power, lower-torque, smaller-battery ebikes like these are very uncommon in the wild, and 70% of saddle time in OFF seems highly unlikely even in this group.
When I’m cycling, I usually ride faster than the motor’s speed limit for more than half of the time. The only time I struggle is when I’m climbing hills and I want some e-assist. I saw on this forum that parts of other people are in the same boat as me.
 
It's not that it can't be done. Plenty of manufacturers make carbon framed electric bikes. The issue is, they are designed from the frame up for this purpose.

Carbon fiber is manufactured as a woven material. The weave itself is geometric, with various densities. The material itself, along with the resin that binds it together, does not have a lot of strength by itself. It derives its strength by laying up multiple layers of fiber in directions (vectors) that are perpendicular to the expected forces. Each frame design takes these forces into account. It's not that different than the way steel frames were built, its just more complicated with carbon fiber. Because it is a laminate material, if you get the force vectors wrong, the material de-laminates. That's very dangerous.

Now add the instantaneous torque of an electric motor, and now you have two independent sets of torque vectors to design around. The motor, and you. Add the weight of the battery, and you have another set of vectors to consider. You could overkill the design, but then the weight goes up.

A properly designed carbon fiber electric bike is an engineering marvel. Carbon bikes even without motors are as well.

You can cobble something together, and it may work for a while. My concern would be what happens when it doesn't.
Mahle's motor can deliver torque gradually and actually adjusts its power based on real-time conditions, like climbing or on flat roads. It might avoid those sudden jolts of power that stress the bike frame.
 
When I’m cycling, I usually ride faster than the motor’s speed limit for more than half of the time. The only time I struggle is when I’m climbing hills and I want some e-assist. I saw on this forum that parts of other people are in the same boat as me.
Are you referring to the EU's 25 kph (15.5 mph) assisted speed limit, or one of the 32 kph (20 mph) or 45 kph (28 mph) limits in the US?
 
Are you referring to the EU's 25 kph (15.5 mph) assisted speed limit, or one of the 32 kph (20 mph) or 45 kph (28 mph) limits in the US?
I refer to the EU's 25 kph. I've been looking at a lot of converting kits from UK brands before. I'm not sure what the usual speed limit is for motors on Ali Express, and if it's possible to remove the speed limit on the motor myself.
 
of course it could be smaller, but unless your friend is proposing starting a motor company to design and have manufactured a motor (which would surely cost hundreds of thousands of dollars for the first unit) it really is irrelevant what he thinks. if it was so easy, such a product would exist.

the closest thing I see to the mahle system (which you could certainly get your hands on if you were determined) is a 1.6kg front hub motor, like the bafang G370. this and a cadence sensor and a bottle battery and the controller would make a compete system, it would look good awful, but wouldn’t weigh all that much.

another approach is the elevate conversion kit, which attaches a toothed ring to the rear brake disk and uses a small motor to turn that. it’s $2200 though, and not that light… you could buy a used x20 based carbon road bike for $2500.
I don't think making a product like this is quite easy, but it doesn't mean we shouldn't keep innovating. When you mention the 'elevate conversion kit', are you talking about something like Bimotal? Those seem more geared towards MTBs.
 
Just those two things, particularly the long, steep climbs, but it's a fair question because I don't KNOW that for sure. It's just an educated guess.

Everyone told me, 'hub motors aren't designed for steep climbs!' but I ignored them, and it seemed to be fine... until it wasn't. I sometimes think, "Well, Bill didn't do the subtle little things I did, like back off the throttle a bit sometimes even when I didn't feel like it, just to rest the motor. Maybe it would have survived if I'd been riding it." And he's also at least 20 pounds heavier than me.

But he's also stronger; he's a drummer, works as a contractor, also works out at the gym, and is totally ripped. After the motor died, he insisted on riding Survivor unpowered to the top of the hill and most of the way home -- and with motor and battery, that bike was 40 pounds.

I think I MADE him get off the bike and walk it slowly up the last hill, right before my house. I didn't want him to die, he was 65 at the time, and I was 63. We're both crazy as bedbugs.

But the damage was probably cumulative. I bet it would have died a few months later anyway. I should add: what actually got fried was the controller, but I think the motor was never quite the same after that, either. The controller was under warranty, Clean Republic / Hilltopper replaced it, and it ran for another hundred miles or so out of it before it failed completely-- the wheel would spin under no load, but not under load, Hiltopper said it was the battery BMS, but...

Oh, I don't need to go down the whole rabbit hole! The point is, controllers do fail due to overheating, and the system is not designed for quite such extreme load.
Are you using a hub motor with a throttle on it? When you're riding, do you mostly pedal or do you rely more on the throttle to give you a boost? I also want to know is the controller built right into the motor?
 
Thinking about the rear hub motor a bit more, i wonder how much the design of a frame for disk brakes takes into account similar forces, applied rather suddenly?

The seat stays on a lot of super light modern carbon road bikes are seriously thin, which make sense if they go into tension in braking. They’d see compression in acceleration, and some amount of bending, but how much, i have really no idea.

the x20 integrated connection dropout has a simple rectangular metal reinforcement which connects to a fairly large flat area of the frame, very unlike the small junction with only a circular through axle hole in a regular carbon road bike.
I totally get where you're coming from. That's definitely something to think about.
 
I don't think making a product like this is quite easy, but it doesn't mean we shouldn't keep innovating. When you mention the 'elevate conversion kit', are you talking about something like Bimotal? Those seem more geared towards MTBs.

definitely targeted at MTBs, not sure i’ve ever seen a road bike with 4 piston brakes but i imagine it’s possible. probably easier than inventing a new motor and adapting a rear hub motor to a carbon frame with a regular through axle. ;)

anyway, i agree wholeheartedly that continuing innovation on the lightweight side of e-bikes is great. i disagree that that’s what you’re doing here - you’re speculating, not developing a product, and the product you want doesn’t really exist. adapting a lightweight hub motor like the X20 or the Bafang i mentioned to your addict would be a challenging but interesting project. contemplating a new even smaller motor as a consumer, not that useful.
 
Just saw this, a new Taiwan lightweight/road bike rear hub motor. Can't tell if it's a B2B or a DIY kit like Bafang, suspect it's the former to sell to frame brands etc.

The speed with which Chinese bike companies seem to be innovating I expect there could be several new lightweight hub motor systems out in the next couple of years.


 
Are you using a hub motor with a throttle on it? When you're riding, do you mostly pedal or do you rely more on the throttle to give you a boost? I also want to know is the controller built right into the motor?

Past tense, I no longer have this motor, but it was really a mix. On flat terrain, I rode without any power, but while climbing, I had a trigger throttle that provided variable assist/ However, it was a low power motor, so there were not many increments to the amount of assist! I would say that it was like having three levels-- almost nothing, something, and maximum for that motor, only there were no click stops or detents in the trigger-style thumb throttle. A little pressure would give you a little power, add a tiny bit more, nothing happens, add a little more, you have medium assist, keep adding pressure, and eventually it will provide max assist.

The controller was located in the housing for the battery, which fit into the water bottle screws. I know this because the controller failed and was replaced under warranty, and that was the part they sent me.

It's an odd kind of assistance compared to mid drive. You can go about 17-18 MPH with no pedaling at all, but... when does the motor actually stop helping you when you are pedaling? I could never determine that-- if you think about it, the answer is ephemeral. If I was going 25 MPH with max assist, did it feel like I was giving less effort than I would have been without a motor? Yes, it did, but who knows?

I'd have to dig up my oldest posts to figure out what the range was. I think 12 miles was typical with lots of steep hills, sometimes I did better than that, but sometimes I'd do worse. Once, I was just on flat terrain going around the reservoir, and the battery died at 10 or 11 miles. I think there was more wind that day than I realized. There was a lot I liked about the kit, but range anxiety was severe.

It did seem crazy that I could go up just about any hill-- I'd say over 15% for sure, probably more than that-- in granny gear, though it took a lot of effort, and I did have to lean forward to avoid the front wheel spinning in the most extreme situations. And again, sometimes the two-wheel drive was amazing for handling.

This gets into the issue of mid-drive torque vs. hub drive torque. I will tell you that it was easier to pedal than my 40nm 46-pound FS mid-drive emtb, but far, far less versatile. At one point, when I tested it, I figured out that putting in maximum effort, I could climb about 5-8% faster on the hub drive, but my overall times were far quicker on the mid-drive. A lot of this didn't have that much to do with the motor, it was that the emtb is way more stable going downhill, and as a result, I would descend much, much faster, with 39 MPH being not unusual and max speeds in the low 40s. Max was 43 MPH; the 40 lb hub drive, with only stem and seat post suspension, would have been terrifying at the speed. The emtb felt like a motorcycle, just glued to the road.

Here is my review of the kit:

 
I personally like the DM02 motors from ToSeven. I can supply discerning folks miles away with factory support in English from someone who knows the ins and outs, me. The motors are light, universal fit, and robust. Here is one on a trike. These are fully end user programable, challenge me on that. 90Nm. I can walk people through the entire install and programing. They kick azz over anything retail to the huddled masses like Specialized. How many degrees of angle do you want before kick-in 2, 3? What about perkey responsiveness vs. smoothness. That is all yours and more to dial in. The palmed sized silver thing between the pedals is the motor.
 

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