Roadbike, 125mm dropout

[francoisr]

Hi,

What a great forum. Lot of information, reviews, etc.

I don't have an ebike yet. I'd like to add a motor to my triathon roadbike. The frame and fork are CR-MO. Fork dropout is 100mm, standard. Wheels are 700c.

A dealer did not recommended to install his 500W kit on it. Is that a no-no for a front wheel hub motor? Even for a 36V, 350Watt system? I'm not looking for high torque at startup but speed (25MPH or so) and battery efficiency with medium pedaling.

I wouldn't mind a rear wheel kit. It's just that my rear triangle dropout is only 125mm instead of 135mm. The kits I've seen are for 135mm. Can I order one that would fit my narrow 125mm dropout. (I wouldn't mind 5 gears instead of 7 if the smalls gear is small (11 or 12)? Any recommendation?

Thanks in advance for you advice.

 

[Drunkskunk]

Cro-mo frame can be stretched. Its just 5mm each side, nothing to worry about. the steel has enough spring in it, I wouldn't even bother trying to expand the frame in the usual way, just pull it by hand as you drop the motor in.

As for front, a cro-mo fork would be the ideal fork to mount a 500 watt motor in. Just use good torque arms. I recommend 2, one per side.

Best hub motor kit for efficient cruising I know of is a 9 continents 9X7, also called the 2807. it does around 21-22 as a 36 volt, 27 - 29 as a 48 volt which would hold 25 in a headwind with some peddling.

 

[Zoot Katz]

Welcome to our obsession.
You might be able to substitute a heavier duty hybrid or cyclo cross fork if you don't trust your lighter weight race fork.

justin_le rode a front mounted X5 cross Canada on 36 volts without problems.
He's still rockin' a front hubby in steel forks on his Big Dummy.
He's also done a bunch of destructive testing of fork ends and torque arms.
http://endless-sphere.com/forums/viewtopic.php?f=2&t=14195&start=0&hilit

Spreading the rear triangle 10 mm could cause problems with chain line, ring clearance and alignment of the drop outs.
http://www.sheldonbrown.com/frame-spacing.html

 

[jag]

Front mount is easiest to deal with, and sufficient for medium power.
Rear makes sense for high power, or with a front suspension fork.

The 9C is an efficient and reliable motor, but at 7kg relatively heavy.

Geared motors are lighter.
An Ezee or BMC at 48V would also do 25-30mph and weighs 4kg.

With a bit of pedalling help maybe even a Bafang would do at 3kg.