Min power+max lightweight efficiency VS. more power+weight

Discussion in 'General Questions' started by Impala, Apr 16, 2007.

  1. Impala

    Impala Guest

    I posted the description of my ideal in the "introduction" forum, and it's pasted below. I've now had a chance to look around the forum, and here's my impression:

    There are two approaches to motorized bicycles. One is to take advantage of the power of even a very small IC motor compared to a human "motor" by attaching it to a vehicle that is heavy and "clunky" compared to a state-of-the-art mountain bike. You have so much power to spare that having a really efficient platform isn't that important. This appears to be the most common approach seen on this site. (This approach also allows greater "personal expression" by individuals who may be just a bit - eccentric. ;-) )

    The other approach is to take advantage of the inherent efficiency of the bicycle, especially a state-of-the-art one, to minimize the size, weight, fuel requirements and output of the motor. My "ideal" described below is based on this approach.

    This forum helped me realize that when I dreamed this up I did so with the idea of being able to "portage" the bike in an off-road or broken-road situation, such as across a stream, say. In other words, being able to pick it up and carry it almost as easily as lightweight mountain bike. Also, I was thinking in terms of retaining full mountain-bike efficiency for non-motorized operation. Actually, the context of all that is a "survivalist" situation, but the application for more prosaic and realistic scenarios is obvious. Among these would be use in undeveloped parts of the world, and off-road touring. Or just bopping around town in a low-profile fashion.

    So without further ado, here's my ultra-high efficiency ideal:

    - Virtually the same weight as a standard high-tech mountain bike that has a full suspension, except for the addition of a tiny motor, I mean like 25 CCs or less, just enough to propel the bike at around 25 mph (40 kph) on flat pavement with no headwind.

    - A gasoline motor like the one described above. (I picture a chainsaw or weed-whipper motor.)

    - Transmits the power to the front sprocket of a mountain bike derailleur, so that the small amount of power available could be used in the most efficient way possible via the 15, 18 or 21 gears available. I picture a motor mounted behind and beneath the saddle, with the chain going to the front sprocket (I think chains are very efficient, if a teensy bit heavy.)

    - Has fat tires like a mountain bike, but slightly optimized to give better traction on pavement for safety. (With standard mountain bike tires an option for off-road use.)

    - Has wheels that are almost as light as those on a high-tech mountain bike, but just a teensy bit more robust to stand up to sustained speeds on pavement that are slightly above typical pedal-bike speeds.

    - Has top quality mountain bike disk brakes for safety. They cost more and are a bit heavier than rim brakes, but give better, more consistent brake performance in all conditions - critical given sustained, higher-than-average speeds on pavement.

    - (Perhaps) has a "self sealing" gas tank for safety. This is very simple - it just means a foam liner that prevents the gas from pouring out when punctured, unless is really gets smashed.

    - Has full-bicycle functionality, and even allows the user to quickly remove the motor and appurtenances.

    This would be the ultimate 'green vehicle' for around town use. It would not be allowed on freeways, obviously, but if you didn't mind only going 25 mph you could cross a continent with it, using less than 15 gallons of gas!

    They could probably sell around 300 million of these in China and the third world. Except it wouldn't be cheap - it only works by using expensive high-tech materials and technologies. Still, it should be possible to make this for around $3,500, given the cost of high quality mountain bikes.

    A recumbent version could have all the same features. in a slightly heavier but more comfortable and aerodynamic package.
    Last edited by a moderator: Dec 15, 2015

  2. Guest

    Guest Guest

    I subscribe to the "build it cheap at home and know it intimately" school.

    The bike you describe would be a "big boys' toy" like general aviation is compared to the ultralighhts, or H-D riders are to small road bikes, or the yatch club compared to the outboard motor guys.

    No one in China or third world country will buy one, though the market potential is great.

    2-4 hundred is a long way off from 3500.

    But- the great thing about these "motored bikes" is the vast choices for building a custom bike to fit your wants and needs.
  3. Impala

    Impala Guest

    You're right, it would be a "big boys toy" - right now. But - the "super-duper expensive state-of-the-art" mountain bike technology found in $2,000 bikes 15 years ago is in $500 bikes today. Progress advances apace, and we'll be able to say the same thing 15 years from now. So this approach has value beyond the immediate.

    You are also right in suggesting a "let 100 flowers bloom" approach.
  4. I'm all for the build it heavy add a chevy V8 trailer pusher behind kind of guy.
  5. Hi,

    Hmmmmm, small engine heavy bike or great bike and small engine???

    How about the combination.....Max hi tech lightweight fully suspended mountain bike coupled with a high output 70 or so CC with gearing (either gears or CVT)....Oh yeah...that's my vote! ;-)

  6. SirJakesus

    SirJakesus Guest

    A Staton NuVinci on a full suspension MTB would be as close you could get to a go anywhere do anything bike. They make them with engines as small as 33cc 4-stroke hondas or subarus however their gearbox I've heard is a bit heavier than you would like. Remember as well that the lighter you make these things the higher chance of parts and even the frame breaking down under the extra stress of having a motor. The Staton NuVinci drive is around $900 on their site and it should fit on any frame out there with a 26in wheel. The NuVinci has mounts for a rear disc brake and is a CVP which would remove the need to run a second chain to the front gear (as well as the problem of freewheeling the crank)
    You could probably make this kind of system for around $1600-2000 considering a $600-1000 bike to put it on (including accessories like lights)
    From what I've read here the Statons are extremely durable and the gearbox is lifetime guaranteed. I saw a thread by ZombieBuilder (i think) where he used the NuVinci hub on a custom chopper bike and it generated enough torque to bend his dropouts without reinforcement. I believe he was using a large displacement chinese 2 stroke on a jackshaft. Good luck on your project.
    Last edited by a moderator: Feb 1, 2008
  7. Just a question Sirjake...why do yo put a front freewheel crank as a problem?
    I don't see more problems there than a on motorcycle, if you are refering to the chain and front sprocket grabing your pants. I rode motorcycles(and had a few pants damaged, but not more than that) for many years in the past.
  8. SirJakesus

    SirJakesus Guest

    I've only seen a freewheeling crank available on a couple Ebike sites where the electric motor runs through the front crank and it seemed like availability was a problem. So without a freewheel front crank/sprocket your pedals are going to spin wildly with the motor running. The other problem I see with running motored power this way is during gear changes. They would have to be done very slowly as I know I've jammed chains very easily when just riding a pushbike hard and switching gears whereas the nuvinci cvp can be shifted smoothly even under power without jams, jolts or skipping.
    Furthermore I wouldnt trust standard thin mountainbike chain with a couple HP through it. I've popped them in half just muscling up hills before. If it was easy to find the parts to run a right side drive very low displacement engine clockwise mid-frame with a readily available freewheeling crank I'd be all for it. Unfortunately a kit like that doesn't exist to my knowledge and this poor guy would have to engineer and fabricate it (engine and all.) If he managed to do all that I'd gladly kiss his feet and buy his kit :) until then he may have to settle for an already manufactured and proven kit.