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

I agree... there are definitely a lot of challenges. But I also wonder if it’s partly because the demand for small-torque motors is pretty niche in the overall ebike market.

Dunno, lightweight low assist systems seem pretty popular. Part of the issue may be that the more power you have, the more battery you need to actually have a usable range. And battery is generally where most of the system weight comes from.

Wow, you have a lot of experience with this! When you say ‘we were just asking it to do something it wasn’t designed for,’ apart from all the climbing and long hours, what else do you think was pushing it beyond its limits?

Catalyzt is absolutely right that I'd be very wary about retrofitting a super light carbon road bike. Hub motors have to turn against something when they are running. More powerful ones have a torque arm to brace against the chainstay, some less powerful ones seem to just brace against the dropout itself. But they all are trying to twist the rear triangle of the bike (newtons 3rd law: for every action theres an equal and opposite reaction; turning the wheel is going to try and turn the frame the opposite way). Super light bikes try and minimize carbon in areas where the frame doesn't need it. Whether the frame can handle those twisting forces, well, who knows. They definitely were not accounted for when the frame was designed though.

I mean, if the Scott Addict eRIDE is too heavy for you, you're probably best off just waiting for that class of bike to get lighter as tech progresses (which it will).
 
true, this would be a design idea to revive. I o think there is a market for it and with the current components it would be a more stable and robust poduct.
 
Wow, you have a lot of experience with this! When you say ‘we were just asking it to do something it wasn’t designed for,’ apart from all the climbing and long hours, what else do you think was pushing it beyond its limits?
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.
 
Unfortunately, Vivax -who owned the design - went out of business about 5 years ago. At that, the kits were $3-4k I think and are probably worth more now if any could even be found.
Which was right about the time the UCI woman cyclocross racer got busted for one when she pitted, took her pit bike, and "forgot" that it had a motor in it. UCI officials carry FLIR devices to detect them now. Nobody is going to pay $5K for a hidden motor to impress their friends on group rides. They will when there's 1500 euro on the line.
 
Wow, you have a lot of experience with this! When you say ‘we were just asking it to do something it wasn’t designed for,’ apart from all the climbing and long hours, what else do you think was pushing it beyond its limits?

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.

Dunno, lightweight low assist systems seem pretty popular. Part of the issue may be that the more power you have, the more battery you need to actually have a usable range. And battery is generally where most of the system weight comes from.



Catalyzt is absolutely right that I'd be very wary about retrofitting a super light carbon road bike. Hub motors have to turn against something when they are running. More powerful ones have a torque arm to brace against the chainstay, some less powerful ones seem to just brace against the dropout itself. But they all are trying to twist the rear triangle of the bike (newtons 3rd law: for every action theres an equal and opposite reaction; turning the wheel is going to try and turn the frame the opposite way). Super light bikes try and minimize carbon in areas where the frame doesn't need it. Whether the frame can handle those twisting forces, well, who knows. They definitely were not accounted for when the frame was designed though.

I mean, if the Scott Addict eRIDE is too heavy for you, you're probably best off just waiting for that class of bike to get lighter as tech progresses (which it will).
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.

Whoa-- and you guys just explained that in a way more granular way. Appreciate the more detailed description, I couldn't quite put it into words.

I've always been freaked out by CF, though I do ride a CF seat... it cost me all of $35 to save nearly a pound of weight, seemed crazy not to do it. I've had no problems with it.

When I heard about the Ocean Gate / Titan disaster, I happened to be across the street from the submarine base in Groton, where they build REAL submarines, playing a show (with Bill, of course.)

A lot of the guys in the local music scene have worked on subs, or worked at Electric Boat, it's the kind of town where people really take pride in doing things carefully, correctly and safely-- if you're working under your car in a driveway, and it's only supported by the kind of jack you'd use to change a tire, someone's going to cross the street and yell at you. So everyone was furious, obviously, that accident was totally preventable. Anyway, I got unreasonably spooked by the whole story and it activated my CF phobia. Terrible tragedy.

A lot of my friends on this board were talking me down for months: "You aren't riding your bike 12,000 feet underwater!"
 
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.

IMG_0076.jpeg
 
That's a really slick detail. Love how they eliminated a pain point for hub motors and turned it into a selling point.
 
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.




Whoa-- and you guys just explained that in a way more granular way. Appreciate the more detailed description, I couldn't quite put it into words.

I've always been freaked out by CF, though I do ride a CF seat... it cost me all of $35 to save nearly a pound of weight, seemed crazy not to do it. I've had no problems with it.

When I heard about the Ocean Gate / Titan disaster, I happened to be across the street from the submarine base in Groton, where they build REAL submarines, playing a show (with Bill, of course.)

A lot of the guys in the local music scene have worked on subs, or worked at Electric Boat, it's the kind of town where people really take pride in doing things carefully, correctly and safely-- if you're working under your car in a driveway, and it's only supported by the kind of jack you'd use to change a tire, someone's going to cross the street and yell at you. So everyone was furious, obviously, that accident was totally preventable. Anyway, I got unreasonably spooked by the whole story and it activated my CF phobia. Terrible tragedy.

A lot of my friends on this board were talking me down for months: "You aren't riding your bike 12,000 feet underwater!"
The problem with Ocean Gate was the CEO's rush to charge people $250K a pop to visit the Titanic. It was driven by both ego and necessity. You won't have that problem. But the lack of materials science engineering and testing before deployment would be similar. You wouldn't implode, but you could get hurt, and hurt others with you. If you do go this route, take it in steps. Have a test plan and do it in steps. Inspect, inspect, inspect.

My approach has been to buy a stock bike, strip it down piece by piece, and replace. The core stress points are the ones designed and tested by Cannondale. It's amazing how much weight that you can cut off a bike this way.
 
The issue with carbon, as a material, is its strength is highly dependent on the direction/type of the weave. An aluminum plate will generally be equally strong no matter how its oriented, but a carbon plate could be super strong one direction but very weak another if thats how the carbon layers are oriented. So designing something like a bike frame (which has all sorts of forces acting all sorts of different directions) requires weaves running in various directions at various thicknesses, dependent on exactly where in the frame the carbon is and what forces are expected there.

If you're starting with, say, a mountainbike frame, its less of an issue because they overbuild those frames and there is definitely extra carbon layers all over the place for redundancy, impact resistance, etc. If you're starting with a super light road frame though, there probably isn't nearly as much extra weave/design margin in the frame design. So introducing new, additional forces in places the original designers didn't consider is something to be very carefully considered. I would not personally do it. Especially when there is literally an ebike version of the same bike available.
 
they’re serving a very different market, with nothing even remotely as light as the X20 that @Katrina92 is trying to improve on.

The X20 weighs 1.39kg. a typical hub might weigh 200g, so the delta is more like 1200g. I am not aware of anything else that light, and while it’s bigger than a normal hub it’s smaller than either a disk rotor or most any modern cassette.

I don’t think there’s much need to make it smaller. lighter is always better but you can bet that if it was easy to do so, mahle would have done so given that the entire purpose of the x20 is for stealthy, light e-bikes.

to the OPl as mentioned in one of your other threads on this, mahle now makes a complete system around the X20, the XS, which incorporates everything into just the battery and motor. total weight is 2.5kg. you are not going to get it lighter than that with readily available current technology!
also.… the addict e-ride is a very nice bike, maybe pick up a used one? it’s essentially the bike you are trying to build yourself.

notice that 1) you can’t even see the motor and 2) the chain stays are substantially reinforced relative to the regular addict. the additional dimension also integrates the electrical dropouts, so the power to the moto or is completely invisible and no wires need plugging in. this is as clean as it gets in 2025.

View attachment 193109
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.
 
Dunno, lightweight low assist systems seem pretty popular. Part of the issue may be that the more power you have, the more battery you need to actually have a usable range. And battery is generally where most of the system weight comes from.
Exactly, it all depends on what people need. Personally, I don't need a super powerful motor--250 w is enough. And for battery range, I've seen in this forum that the majority of users only use e-assist for about 30% of their rides. So I think the required range actually varies from person to person.
 
Unfortunately, Vivax -who owned the design - went out of business about 5 years ago. At that, the kits were $3-4k I think and are probably worth more now if any could even be found.
Yeah, I've looked into that design. It's around $3,500. It's completely hidden inside the seat tube. But the installation is really complex—no way we could do it ourselves. So I think the price and difficulty in installation might be why it went under.
 
true, this would be a design idea to revive. I o think there is a market for it and with the current components it would be a more stable and robust poduct.
feel the same way. It shouldn't just be large companies like Mahle to design something like this. Otherwise, we'd have no other option but to buy fully assembled e-bikes with Mahle's e-assist systems.
 
Which was right about the time the UCI woman cyclocross racer got busted for one when she pitted, took her pit bike, and "forgot" that it had a motor in it. UCI officials carry FLIR devices to detect them now. Nobody is going to pay $5K for a hidden motor to impress their friends on group rides. They will when there's 1500 euro on the line.
Ah ha! So it all comes back to the original intention of the design. If it's just about making yourself seem stronger during group rides, no one would spend $5,000 on it.
 
Like TQ HPR mid-drive motor on Trek Domane+ or Specialized SL 1.2 mid-drive motor on Creo 2? :)
I mean, Mahle’s edrive sysytem only available on complete e-bikes. But it would be great if there was a standalone rear hub motor, similar to Mahle, that could fit any bike with a 142mm thru-axle.
 
And for battery range, I've seen in this forum that the majority of users only use e-assist for about 30% of their rides.
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.
 
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