700c Road Bike / Commuter Project

Meer123

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A high-end mountain bike is nice and a 29'er is even nicer but neither is inexpensive and most will be heavier and rougher riding than needed for normal commuter duty. That being the case, "700c" style road bikes and hybrids are generally lighter and more efficient especially when fitted with slimmer fast rolling tires. There are many makes and models available and there's one right for every budget.

I am writing because the "Electric Powered" scene seems to be dominated by 26 inch kits and to a lesser extent, 20 inch kits. The 700c kits are out there but not in the same volume ?

Who has a 700c electric powered bike ? Any suggestions or words of wisdom to share ? Do you know which 700c hub kit is best ? Do you recommend a "Cyclone" style kit over the hub kits ? I'm building a commuter to use to work and hope to use a 36V 15A Li Battery ... I dont need to race anyone but I need to move smartly (30mph bursts - 16mph to 18mph cruising speed - 9 miles each way) ... looking for the best affordable solution given these parameters ? Any input will be much appreciated. My budget for this build is $800 to $1100 (kit + bike) the less I spend the better but I do need these minimum requirements to be met - is this mission impossible ?
 
J

JemmaUK

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Its do-able, but has some major inherant problems.

You will find that you might get frame and wheel mount failures because of the 0-100% torque on electric motors (hence why they are used in train motives and such) - also the skinny tires will be taking a fearful pounding and the last thing you want is a wheel collapsing on you at speed.

The thing with a 700c bike is that its optimised for speed given that the motive power unit is going to be a human... its the superbike option when all you have are your legs providing the go. Therefore they are generally pared down weightwise in order that they can make the most of the power available.

The problem comes when you try and motorise them because there simply isnt any free tolerance to stress and vibration (the latter not being so much of a problem in this case) that something like a Cruiser frame or MTB is designed for.

Most of the kits will work with the larger wheel (hub motors are just a replacement of the hub that is laced in), although that will change the gearing and they should manage to make the cruise speed you are aiming at without problem... my only worry is the durability of the frame/wheelset with all the extra weight and speed induced stresses. You might loose a little acceleration with the larger tyre (higher gearing) but it is entirely possible to do.

This is only my personal opinion you understand, but I think you would end up with a more reliable and less highly strung machine if you were to get one of the hub motor kits and put it on a reasonably priced MTB frame... since if you are anything like me - you are likely to use the machine more as a electric moped... and in that case weight saving is not so much the issue..

hope that helped...

Jemma xx
 

veloman

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Unless you're mounting a 2000watt + motor on a road bike, there won't be any problems. A quality road bike (not dept store) can easily handle the torque that a strong rider puts through it in a sprint, then it can definitely handle a 1000 watt electric motor.

My road wheels have no problem handling my standing start accelerations (pedal power) of 0-20 in under 2.5 seconds. Show me a *realistic* electric motor with more torque than that on an ebike.

The problem is, handling. A 20lb road bike with tall wheels and higher center of gravity, and especially high pressure narrow tires don't mix well with adding 20-40lbs of weight. That's the issue. Using 700 x 38c tires would solve much of that though.
 

wheelbender6

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You are better off with a mountain or cruiser bike, but 700C should be fine if you run the largest available tire (40mm or so). You will appreciate the fat tires the first time traffic forces you into a pothole or off the road.
An aluminum frame should be OK for electric assist.
I frequent a forum site that is dedicated to electric assist and the Cyclone kits get good reviews there. I think they just look cool, compared to a hub motor.
 

Tanaka40

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The problem with electrifying a 700c is first and foremost is to make sure your dropouts can handle the torque. Alminum frames OK, Aluminum forks NO way!!
 

veloman

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I've never used a powerful hub motor, so maybe I'm in the dark. But from what I know, most hub motors have nowhere near the torque as a strong cyclist. If you close that quality skewer tight, you should have no problem.

As for forks: I would think slamming the brakes on would create immensely more torque than a motor could.

Or are you hub motor riders doing 0-15mph in < 1 second?
 

Tanaka40

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First most if not all hub motors do not use skewers or QR., Second Yes these 500 watt (or more ) hub motors have alot of initial torque and can literally RIP the dropouts right out the bike or even worse round them out and allow the motor to spin and wrap up all the leads into a smokin' ball.
When you brake, the torque stops at the point of contact (the rim or brake disc) and is transfered to the frame through their attachment points (cantilever mounts or disc mounts) NOT the dropouts.
 

veloman

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I'll take your word for it, I have no experience with them, just intuition. Maybe their high torque is only for a fraction of a second, at essentially 0mph.

I still don't believe your point on the front dropouts not experiencing torque. They are the only point actually holding the wheel on. That seems like a simple statics lesson.
 

Tanaka40

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That one little point holding 500 to 1000 watts of power is the hair that broke the camels back. I have a standard 500 watt hub motor but did not install it becuase I discovered I have alum. forks on my MTN Bike. So, I decided to install a GEBE kit on the back because the price of LiPO4 batts are too expensive for the range I desired. ($400 to 600 for 48V 30A)
There are pics on the indestructables website of chewed up dropouts and twisted wires. Be careful and you will be OK.
 
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