Carbon Frame -- prone to cracking?

[MysterySandwich]

Hey guys, relatively new to eBike's (I usually run a gas one for a lack of funds)
I wanted some input on Carbon Frames, specifically this eBay chinese $400 road frame
http://www.ebay.com/itm/171156705977?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2648

I was thinking of getting that, a single speed crankset, all the other parts to put it together (obviously haha) and a Magic Pie V3.

The only concern is that I know carbon frames are prone to cracking, so is it recommended to just avoid carbon frames especially since it'll be an electric bike?
-thanks

 

[mattrb]

I have a fazer frame and I noticed that the original one was carbon fiber and the newer ones or chromoly. supposedly the difference in weight is 2 pounds. Getting stuff on Alibaba isn't always the best idea.

 

[MadRhino]

To build with a hub motor, a good DH racing carbon frame is all right if the swing arm is alu, but a light weight carbon XC or street bike isn't.

 

[MysterySandwich]

But it's eBay with the PayPAl protection not alibaba

So you think the carbon frame and hub motor will be a good idea? I don't want to spend $400 on a frame that will crack in a year or two
What is a swing arm?

 

[efMX Trials Electric Freeride]

carbon frame is not designed engineered for extra weight of ebike..
therefore the frame will likely break if overloaded w a lot of power/weight..
carbon bikes are usually designed to be light weight not a good platform for ebike imo.
however if you build light w less power it can be done
see this thread: super commuter :
http://endless-sphere.com/forums/viewtopic.php?f=6&t=47139&start=325
however, my recommendation is use a quality steel frame or high/mid level full suspension..
best luck..

 

[USAEBIKECO]

Steel is the only way to go for electric because of the weight.

 

[Kepler]

Plenty of good advice here.

Just like to echo the general sentiment. However if you have your heart set on carbon, make sure it is a lightweight low powered build. This means small motor and small batteries. Make sure you never drill the frame to fit components and be very careful with clamping parts to the frame. Even a small hub motor needs a torque arm to protect the dropouts. This is even more important on a carbon framed bike. Make sure you come up with some sort of solution for this.

My carbon frame is holding up very well however it is a mountain bike frame with aluminium dropout inserts built in. Also consider dampening rather than rigid. I started off with skinny road tires and rigid forks. Fine for smooth roads, but not so good for anything else. I found that the bit of extra weight coupled with the higher speeds associated with an ebike made the ride very uncomfortable, much more so than my unassisted carbon road bike. Going to a good set of suspension forks and wide tires made a huge difference with very little loss in rolling efficiency.

 

[dogman dan]

As I see it, the real problem is how to secure the needed torque control device.

In most cases, a torque arm is clamped to the strut on the frame, and loads that part perpendicular to the direction the load was designed to be.

With metal, you often just get away with this. But on carbon, it could be fatal to the chainstay. Just the clamp pressure could crush it.

A carbon frame can easily be designed for that load, but the non electric frame won't be. So chances are, if you ever get a loose nut and load the torque arm, the frame will snap.

However, if the motor is low power, and the nut never loosens, you could ride for years with no problem. Justins experiments showed how just the nut pressure is quite effective and enough to hold lower torque motor axles in place. It's just that the slightest loosening of the nut will nearly guarantee breaking the frame. So check those nuts often. 8)

 

[Kepler]

Totally agree with not clamping a torque arm to a carbon chain stay.

This was the solution I came up with.





This attachment point is designed to handle braking forces which are essentially the same rotating forces that a hub motor creates.

 

[dogman dan]

Knew you'd have a smart solution. Using the brake attachment point of the frame makes sense. It's designed and built for a rotational load. A carbon bikes chain stay is very likely to fail under a side load, or just the clamp crushing it.

It might be possible though, to build a very long, rubber padded clamp that would spread the loads out over most of the length of a chain stay. Then attach the torque arm to that extra long clamp.

 

[MadRhino]

So you think the carbon frame and hub motor will be a good idea? I don't want to spend $400 on a frame that will crack in a year or two
What is a swing arm?

Forget about 400$ CF frames if you are after some interesting power. What I am talking about is more in the likes of 3000$ for a proper frame with shock. A swing arm is the rear part of a suspension frame, no high torque from a powerful hub motor is possible on a CF swing arm. Many DH racing frames are made with CF front triangle and an ALU swing arm, that is what you are looking for if you want to build power on a CF frame.

Examples:

Santa Cruz V 10

Specialized Demo 8

 

[Drunkskunk]

I'd say its a great big NO to using that frame and a magic pie.

Road bikes are designed to be light. They are designed to qwithstand the power of One human at normal bicycle speeds on a normal road. A Carbon fiber bike is built to be even lighter, and often shaves the safty margin of stringth down further to save weight. They aren't likely to survive much extra power. Especialy some generic Ebay frame made in some back alley "factory" someplace in Asia.
That frame might be ok for 250 wat hub motor, but I wouldn't try it.

Check out http://www.bustedcarbon.com/ for pics and stories of broken CF frames and parts failing under human power alone.


Carbon fiber isn't a good choice for Ebike frames. the added weight of a motor and batteries quickly offsets the weight savings of the CF, and the CF is less forgiving than steel.

 

[d8veh]

I'm sure if you thought about it enough, you could find a way to strap your Majic Pie into that frame without it breaking, but what's the point?What advantage are you trying to achieve? If you want more speed, get a faster motor. If you want light weight, get a lighter motor and smaller battery. I could understand it if you said you wanted to fit a 328 rpm Q75 motor or a Keyde system into that frame, but why a Majic Pie? ......and please don't tell me you want to put four 12aH SLAs on a rack behind the seat.

 

[MysterySandwich]

Thanks guys wow a lot to respond to lol.

How do you guys feel about aluminum chinese frames?
http://www.aliexpress.com/item/Frame-visp-trx790-aluminum-alloy-frame-rack/1426155112.html

Also I wanted a MP3 because I've heard that they're pretty solid in their performance and reliability with a good number of features (regen braking, cruise ctrl, water proof...)
And no, I wasn't going to slap on 4 SLA batteries, I was thinking of one LifePo4 battery

 

[dogman dan]

No problem with alloy frames in general. Just use a torque arm, or make a torque plate.

Looks like your link is to a fixie or single gear bike frame. Make sure you select something with 135 mm wide rear dropouts. You can't bend out alloy frames to fit. Many bikes made for fixie use a narrower rear width.

Look for big flat dropouts if possible, that make installing torque plates easy. Weight of the frame is not that big a deal, since you plan to add about 25-30 pounds of motor and battery. So you could look at steel stuff too.

 

[MadRhino]

How do you guys feel about aluminum chinese frames?

Like anything Chinese: You use it if you can't do otherwise. For a motor we don't have much choice, but for a frame it is easy to find better.

 

[Drunkskunk]

Thanks guys wow a lot to respond to lol.

How do you guys feel about aluminum chinese frames?
http://www.aliexpress.com/item/Frame-visp-trx790-aluminum-alloy-frame-rack/1426155112.html

Also I wanted a MP3 because I've heard that they're pretty solid in their performance and reliability with a good number of features (regen braking, cruise ctrl, water proof...)
And no, I wasn't going to slap on 4 SLA batteries, I was thinking of one LifePo4 battery

Those aren't frames. read the fine print. Frame visp trx790 aluminum alloy frame rack
Package Weight:
0.500kg (1.10lb.)
Package Size:
30cm x 20cm x 10cm (11.81in x 7.87in x 3.94in)
sure, the pic is of a frame, but no frame would be that lite once packaged, and wouldn't fit in a box that small unless it had been run through a wood chipper.

That's an add for a bike rack. Since they don't show a pic, its hard to tell if they mean a rack to mount the bike on, or a rack to mount on the bike.

Even if it was the bike frame in the picture, it would still be a poor choice for a Magic Pie. The Magic Pie is a large sized, medium-heavy motor that produces a medium-high level of torque. You need a stronger frame than a road bike to handle it's size, weight, and torque.