Carbon Fibre

[Freddyflatfoot]

Couldn't seem to find any threads on this, so I thought I'd start one!
First, I'll describe the project, and then I'll welcome some meaningful discussion!
I want to build a light, nimble e-bike, Looking at a small, lightweight front hub motor, similar to, a Nano, with a LiFePo batt pack.
My project bike is a flat bar road bike, carbon fibre front forks, and carbon fibre rear seat stays. Rest is Al frame.
All the research I have done on carbon fibre forks so far, has indicated that carbin fobre is at least as strong as a steel fork, depending on how they are 'layered'.
I'm thinking that with a relatively lightweight motor, and 250 watts of power, that my current forks will suffice.
Does anyone have any experience with using carbon fibre on an e-bike?
I'm more interested in anyone that has had experience, rather than opinions. And if no-one has any experience, then I guess that would make me the guinea pig!
Rob

 

[fechter]

And if no-one has any experience, then I guess that would make me the guinea pig!
Rob

Crash test dummy

With something in the 250w range I don't think you'll have a problem. It's the actual dropouts you have to be careful with, which I'd guess are metal on a carbon fiber fork. Some kind of torque arm might be a good additional safety feature.

 

[knightmb]

With something in the 250w range I don't think you'll have a problem. It's the actual dropouts you have to be careful with, which I'd guess are metal on a carbon fiber fork. Some kind of torque arm might be a good additional safety feature.

Yeah, a lot of "pre-fab" torque arms exist on the cheap. While I don't think a 250 watt motor would break away that easily, better safe than sorry. The only catch is, he's going for light weight and the torque arm is going to add an extra pound or two. Suggest going with some very strong front forks as the weight might offset a big heavy torque arm.

 

[TylerDurden]

I ride a 250W ebike. A motor that small will not make a "nimble" ebike, no matter how lightweight it is, unless you overvolt that sucker to the max.

A 500W motor might get you into nimble territory with milder overvolting.

:?

 

[BiGH]

I ride a 250W ebike. A motor that small will not make a "nimble" ebike, no matter how lightweight it is, unless you overvolt that sucker to the max.

A 500W motor might get you into nimble territory with milder overvolting.

:?

I think you're better off staying with the CF flat bar bike, BUT buying a set of alu front forks with beefed up dropouts. I'm a massive CF fan. I'd LOVE an all CF e-bike, but there are numerous problems associated with CF.

As my LBS guy demonstrated, its not as strong as steel - and you have material joins to deal with - ie where the CF joins the metal dropout. He showed me a campag record crank arm that had... .actually thats right i took a picture!!: cracked and failed completely at the join.

I'd say you could do it - but personally i'd be very worried about front fork failure. - if you could put the motor in the back (safer since you've got rear carbon stays but not carbon chain stays. This means in case of failure of the carbon the wheel will fold up and hopefully the resulting crash won't be a bad bad one. imagine if the front fork broke like that crank arm did.

finally you need to look at how much weight is actually saved over an aluminium fork. probably not that much, you could always spend money on making everything else lighter, like seat + post, handlebars + stem or even go a bit more crazy - and carbon rear wheel / higher spec drivetrain.

Also i notice your current e-bike is a chaindrive setup. I've found that to get the best out of a hub motor, more power and volts were in order. For example my 408 was very slow at 36v and had range issues due to early cutout from the controller. at 48v it is about where i'd want it to be for an ebike, this is where it felt zippy.

 

[Freddyflatfoot]

Firstly, let me say that my bike is fairly nimble ATM, even just human powered!
My MTB is not too bad with 250 watts at about 30 kg,s. So I figure my road bike with the same power, and half the weight, should perform fairly well. Trying to work (loosely)within our power restriction of 200 watts.
I must stress, that I am using the motor as an assist, to supplement my own power, so not looking for power only performance.
Already a keen cyclist, just appreciate the extra power increase when commuting, especially up hills and against strong headwinds! I find that my daily commute to work is much more pleasurable, and sweat free!
I don't want to overload the bike with etra weight of batteries, so limiting battery power/weight and motor power for that reason. Reckon if you go too high powered, then you would need to increase your available watt/hrs for reasonable range.
Also don't want to affect the bikes handling too much, and that is my definition of 'nimble', not necassarily performance!
If I end up replacing the forks, I will probably get some steel 'cyclocross' forks, but I am curious to see how the CF goes!
It seems, so far, that no-one has actually used CF front forks with a hub motor before?
For BigH, I have overvolted my other motor to 36 Volts, but hated the extra weight! So went back to 24 volts.
As an aside, I will be trying a nominal 24 volt LiPo pack, that is actually 29.6 volts, with a cutoff of 26.5 volts, so that should give me better performance, especially with no voltage sag!
Rob

 

[safe]

If I end up replacing the forks, I will probably get some steel 'cyclocross' forks, but I am curious to see how the CF goes!
It seems, so far, that no-one has actually used CF front forks with a hub motor before?

Carbon fiber is an "all or nothing" material. Either it will be able to handle the loads completely or it will fail dramatically. My guess is that they build a pretty considerable safety margin into the forks and have done enough testing to be certain of the reliability. Unless you weigh more than 185 lbs I'd guess that the forks will be fine. If you were above 185 lbs and then add the hub stress then I'd start to question things. I'm guessing (and you don't really want to hear that) that you will be fine.

I think that a 5 lb hub motor like the Nano is so lightweight that it will also not be a problem.

It's the big 25 lb hub motors with several horsepower that tear things to pieces... you should have no problems with your setup...

 

[Freddyflatfoot]

BigH,
I thought steel was preferred over aluminium, because Al fails with constant stress? That a reason why i was thinking that CF might be a better choice, not necessarily the 'best' choice. Actually CrMo might be better, but I 'm just considering using what I already have.
Rob

 

[BiGH]

Hi Rob,
Yes i'd probably rait Alu as higher strength (for dropouts) than entry level CF. You're main issue is that you want the highest strength. Alu and all single metal forks would probably be stronger than a CF/metal combination (metal for the actual dropouts). CrMo would be very good too. the thing that it really comes down to - how much extra weight would CrMo be over CF anyways? i'm guessing not very much - under a KG?

Honestly if your bike currently uses CF forks, test it to see if you can get the motor going nicely, also if you don't treat the forks badly it could be fine. But i'd be checking for hairline cracks before every ride, and if you decide that the bike (its an interesting idea to run a light weight bike - would be interesting to compare to a a heavier bike).
Take Care,
Haydon

 

[mvadventure]

One more opinion and this from a CF fan. A fork failure at 25 MPH will hurt and will not provide any warning. Steel front forks with a torque arm will definitely weigh more but will that extra two or even five pounds amount to anything? Is pretty worth a busted face, arm, hand, leg or involving someone else in an accident?

Nimble is as nimble does and it's hard to be nimble with a face full of road rash and the bone sticking out your arm. The medical bills would have bought the best ebike every built several times over.

Strictly an opinion as I rinse the mud off my steel forks.

Mike

 

[Malcolm]

I'm no expert with carbon fibre, but being a fibre it's properties are highly directional. This means that each component has to be designed to suit the stress pattern it will be subjected to, and the material is then laid up so that it gives maximum strength where it is needed most and in the direction of maximum stress. In the case of a carbon fork, the manufacturer is unlikely to have considered the possibility of someone fitting an electric hub motor, so the fork will not be designed to cope with the very special stress pattern that a hub motor produces.

Even with a torque arm fitted, a hub motor will induce a much higher torque at the tip of the fork than was ever expected by the designer. A steel fork, and to a lesser extent, an aluminium fork, have much more redundant strength to cope with such a situation, because they are relatively isotropic materials – they are equally strong in all directions.

Personally, if I was looking to shave weight to a minimum and couldn't put the motor in the back, I'd go for a carbon fibre frame with steel forks. That way the carbon fibre is still doing exactly what it was designed to do.

 

[Freddyflatfoot]

Malcolm, you are right about the strength of CF being directional, and the more lightweight forks use less CF, but layered specifically to suit the stress patterns for the fork.
As my bike/fork combo is more entry level/generic, I would think that this fork has not been optimised for weight, but more for the stress requirements of a general cyclist. Not sure if this means a weaker fork or a stronger fork! But it certainly isn't the lightest on the market. If I try it and it fails, then thats ok (as long as its not HS!) Can be easily replaced.

 

[flip_normal]

The only way to make a 250W motor useful at speed (assuming that's what you mean by nimble) is by running it through the gears, isn't it? That would exclude a 250W hub motor altogether. You'd need to have it mounted down near the bottom bracket and run it via a chain onto a chainring with a free-wheel mechanism or something similar, wouldn't you?

 

[Freddyflatfoot]

Maybe Flip, I'll post a fuller reply under the bantam lightweight thread,
Rob

 

[fechter]

There's an idea. You could mount one of the very small hubmotors near the bottom bracket and do something like a Stokemonkey. No fork worries. There would be a bit of weight for the motor mount and some complexity in the freewheel arrangement, but having gears might be very good at lower power levels.

 

[Malcolm]

You could mount one of the very small hubmotors near the bottom bracket and do something like a Stokemonkey

Yes there's a lot to be said for that. Low weight, built-in gearing, near-silent running, good efficiency. The main drawback I can see is that the entire motor spins on its axis so it would really need to be shielded in some way. I'm not sure whether the pedals would clear a hub motor either. You might have to mount the hub outside the path of the pedals.

 

[BiGH]

you really got me thinking about bike weights today. No idea why .

(nb this is slightly off topic) but as a newbie to e-bikes i find it very interesting: anyways there isn't much point i've realised going from a midrange bike gear to top of the line gear for the SOLE purpose of saving weight (there clearly is a reason with some components such as suspension and brakes): point in note:

Avanti Ridge Rider mountain bike, with h-disk brakes weight: 15kg $800 AUD
Scott scale LTD bike - 8.6kg. ~$5000 AUD

so going from $800 to $5000 saves you 6.4kg

now while this is quite a lot - we need to look at it in the great scheme of things:

i weigh about 85kg
LiFEPO4s (72v) at about 9kg (inc controller)
408 - 7.5kg
Avanti: 15kg or scott- 8.6kg
Total avanti: 116.5kg
total scott: 110.11kg

hardly makes spending that extra money seem worth it. esp when $4200 AUD would easily buy you two pumas controllers and a substantial amount left over. Which brings me to this conclusion. Additional funds for spending on the bike are much better spent on extra batteries, and upgrading the power side of the bike rather than the actual components of the bike. I guess the exception would be if there were no more electrical upgrades that could be made.

6.4kg is a lot but so is $4200! reckon its worth it guys?

 

[Miles]

Weight off of the bike makes a much bigger difference to the handling of the bike than weight off of the rider....

Weight off of the rider actually saves money, though....

How about reducing your weight to 75 kg and putting the money saved towards a few lightweight components

 

[BiGH]

Weight off of the bike makes a much bigger difference to the handling of the bike than weight off of the rider....

Weight off of the rider actually saves money, though....

How about reducing your weight to 75 kg and putting the money saved towards a few lightweight components

yes true, but weight off both?

i was in the bike shop yesterday -they had a full carbon mountain bike with rear ALU dropouts. wonder how that'd fair with a massive set of torque arms and a rear motor.

 

[BiGH]

Found some people are making their own carbon fibre bicycle frames... wonder how well it could be made with some large steel dropouts? could be a possiblity for a ligher weight bike - ie custom oversize dropouts using THICK steel.

that'd be an interesting bike.

 

[LockH]

[Bump] So. About nine years down the road... OP was looking for "a light, nimble e-bike, Looking at a small, lightweight front hub motor, similar to, a Nano, with a LiFePo batt pack."

Something like this maybe?:

More:

Wouldya believe right now US $292 FOB unit price from China?

Seen here:
http://szlcyp.en.made-in-china.com/...ducts-Carbon-Fiber-Electric-Folding-Bike.html

LiFePo batt pack? Have to upgrade yerself. Hehe (Battery Capacity: 288wh, but can be supplied w/cells from Samsung or LG... or Chinessy-quality...)

"Max. Load 120kg"... Watt may not suit EVerybuddy in NA. [sigh]

 

[Mündawg]

I wouldn't trust a Carbon Fibre fork with my life. But if you are really cheap or lazy (seems like only reasons to stay with carbon) then go for it. But please let us know how it goes so we can avoid the danger in the future

 

[sgds23]

I've been using a CF fork (and CF rims) with hub motors in both front and back for two to three years.

1) Clearly part of the appeal is fetishistic-- as others have noted, saving a small amount of weight doesn't matter much in terms of performance. (For a host of reasons, starting with you make up what you lose...) I do think that saving rotational weight (ie CF rims) leads to a noticeable difference, but I've seen equally smart people, armed with equally complex equations, come to opposite conclusions on this. For me, the main issue is that I want to be able to carry my bike up stairs. This means I use a lot of weight weenie type components.

2) As I related on my own build thread, the "fragility" of a CF fork probably kept me from more serious injury. (Short version: hit a car at high speeds, cracked my CF fork in two. If it hadn't cracked, more of the force would have been transfered to my body instead.)


s.

 

[cycleops612]

Maybe Flip, I'll post a fuller reply under the bantam lightweight thread,
Rob

You will find the going hard here mate. Its very USA centric. Under 750w is ungodly and way under the radar.

Nimble is up to you, but it would be nice to put us in the picture w/ the most vital stat - riders weight?

It comes down to power to weight ratio.

I believe you, because not everyone is huge. My 70kg on a 2-250w roadbike (the EU rules limit here in oz - long story, but 250w is ~kosher), would indeed be nimble, with occasional, gentle pedaling. I figure ~11kg bike, 2kg of lipo battery & 1kg of geared hub motor.

Personally, i would prioritise torque to get me up to speed and up hills - ie, the lowest rpm version of the hub motor (esp given roadbikes have big diameter rims). As u say, a key object is to sweat less, so prioritise dealing with hills.

I think the clear message from posts here is, use a rear hub. Failure is less likely AND less catastrophic. Has to be simpler than new front forks. No complex torque arms seems a reasonable risk to take on the rear? Why is rear hub a drama? for you?

pros & cons to both hubs, but i really like a qik release front wheel as a surefire simple roadside repair kit. Remove wheel & throw the bike in a taxi. Front hubs make it messier.

Self evident perhaps, but bears saying, that on an indoor cycling track, a roadbike needs 100w to maintain 25kph/15mph. Each extra 5kph needs another 100w. Over 25kph, the main enemy is wind by far. It is not other forms of friction.

Just saying, drop bars and lycra helps.

 

[chas58]

you could read my post if you are interested in a light nimble bike. I built a road and mountain bike, just around 30lbs each. The big difference is a light battery that is now possible (I had mine custom built). but you could build a 24v10ah battery with 18650 cells that weigh about 1kg.

Almost no one here can understand what a light nimble ebike like that feels like, because 99% of the bikes here weigh over 40 or 50lbs, and have fairly big batteries. More power us the not so subtle theme.

But a light ebike is an amazing thing to ride!

As for Carbon fiber - the weak part on the front fork is the aluminum drop out. It is not designed to take that twisting fork, will crack if stressed or mounted improperly or if you spin the wheel, and then you are going down hard. I don't worry about a carbon fork, I worry about the front drop outs cracking. That said, low current 24-36v battery isn't too bad, but spinning a wheel or improper mounting, can cause the aluminum dropouts to fail on the front fork.