The Great "Gearing vs Hub Motor" Debate

[TylerDurden]

More power isn't neccessarily pointless, but rather just a means to overcome resistance; be it wind, grade or rolling.

To move something, you can reduce resistance and apply force (power). Less of one means less of the other, and vice-versa.




All technologies have their practical limits.

From the "freaks and sculptures" section of the old V...

 

[xyster]

Since the advantages of gearing is that it widens the speeds on which you can go (and offers a wider range of climbing torque) it makes the most sense to be talking about gears in the case of a highly streamlined and small wattage motor bike. With this small motor and gears you can either climb a very steep hill or go really fast with very limited energy required.

The reverse is also true. A bike that has high wind resistance (your classic mountain bike with a "sit up" position) will hit a virtual "wall" of wind resistance at about 30 mph and by 40 mph you need to exceed the legal limits for power to go any faster. For this reason the "tractor" (hopefully that's not being taken as too offensive a term... see below) approach is best accomplished by a hub motor.

I agree, mostly. Riding my bike on the flats, no-tuck, it takes me roughly:

5 amps to maintain 20mph.
10 amps (double) to maintain 25 mph.
20 amps (double double) to maintain 30mph.

As we all know, that progressively harsh wall of wind requires progressively more power to overcome. That extra power could come through high wattages on a geared motor, or the more usual higher wattages on a hubmotor, both of which (for continuous riding) require a larger motor. There just isn't much room for the requisite bigger motor anywhere on a bicycle except the middle of a wheel (unless one designs a frankenbike like the insane-o-cycle).

No, "tractor" isn't even remotely offensive to me. Is "80's bike racing has-been now in midst of deep midlife crisis seeking to compensate physical limitations of age and relive past glory with electricity and long-term uncomfortable positioning" offensive to you, Safe? :lol:

 

[safe]

No, "tractor" isn't even remotely offensive to me. Is "80's bike racing has-been now in midst of deep midlife crisis seeking to compensate physical limitations of age and relive past glory with electricity and long-term uncomfortable positioning" offensive to you, Safe? :lol:

No that sounds about right. Well, sort of. I'm a retired computer guy who is closing in on fifty, so I'm old enough to be less physical than my younger years, but not old enough to want to spend my life in a rocking chair.

For me it's about creating something that is fun for me and something that other people will get really excited about. It's an "intellectual challenge"... something that people do when they have lot's of brain power to spare and little to use it for. So taking on a whole new field (electrical motors) is fun for me. It's fun to learn new things.

As for the so called "uncomfortable position"... have you ever ridden a "road racer" motorcycle before? If you get the foot peg location correct then it's pretty good because your legs help to "balance" your upper body and you last longer. Most people have NO IDEA how to get the foot peg location correct and so they either have them too far back (uncomfortable because it forces too much weight onto your hands) or too far forward. (uncomfortable because it's harder on your legs and back)

When you are aggressively turning you naturally want to get your body forward and down to get the weight on the front tire. The motorcycle road racers even push their motors as far forward as they can to get the weight bias towards the front. (this is in part to keep the front end from lifting into a wheelie when the power is on full)

Anyway, for people that know what they are doing it's pretty comfortable and I love riding in a racing tuck, so that part you have completely wrong.

Nothing feels better than leaning forward, rolling to the side and dragging a knee...

(and don't forget to keep those shoulders FLAT... a common "rookie" mistake! This guy in the photo is doing it correctly)

Since in the "old days" I used to ride for 6 hours straight, the ability to ride full speed for one hour on an electric bike is really no problem. I'm usually just getting warmed up when the hour is over.

I make no apologies for old age... it happens to everyone...

 

[safe]

More power isn't neccessarily pointless, but rather just a means to overcome resistance; be it wind, grade or rolling.

To move something, you can reduce resistance and apply force (power). Less of one means less of the other, and vice-versa.

All technologies have their practical limits.

From the "freaks and sculptures" section of the old V...

Your sense of humor is appreciated... (the "jet scooter" sort of sums up the overpowered bike concept)

 

[safe]

Conclusions?

Forgive me if anyone disagrees, (you can always post a rebuttal) but I think over the course of this (long) debate we have more or less arrived at a set of conclusions:

1. If the laws in your area encourage one type of bike over another you should obey your local laws.

2. If you have a bike with high wind resistance then gears don't help all that much and so you should use a hub motor.

3. If you have low wind resistance and a small motor then you should use a bike with gearing if your goal is to maximize top speed and still be able to climb hills.

4. If you can run an enormous motor then you can do pretty much whatever you want and it doesn't really matter.

 

[Geebee]

Conclusions?

Forgive me if anyone disagrees, (you can always post a rebuttal) but I think over the course of this (long) debate we have more or less arrived at a set of conclusions:

1. If the laws in your area encourage one type of bike over another you should obey your local laws.

2. If you have a bike with high wind resistance then gears don't help all that much and so you should use a hub motor.

3. If you have low wind resistance and a small motor then you should use a bike with gearing if your goal is to maximize top speed and still be able to climb hills.

4. If you can run an enormous motor then you can do pretty much whatever you want and it doesn't really matter.

I agree with all except number 2.
Why would you want to lose the gears, the steepness of the hills hasn't changed and the head winds will be worse.
ALTERNATE 2. If you value simplicity and/or quietness above all else go for a hub motor.

 

[D-Man]

cancel

 

[safe]

Why would you want to lose the gears, the steepness of the hills hasn't changed and the head winds will be worse.

Well you simply give up on the top end speed because it's not practical with high wind resistance to try to achieve it. Since the top speed is excluded you can gear the motor (internals) so that they run at lower speeds and get more torque. Basically you are in first gear all the time, but you don't care because you can't really go much faster anyway. In any situation there is a "top rpm" and a "bottom rpm". The closer these are to each other the stronger the argument for a hub motor. When the spread is larger (like a small motored low wind resistance bike) the gears help to cover more torque/rpm possibilities. Put simply it's easier to have a powerband that only needs to go 0-30 mph than one that must go 0-60 mph if you are assuming the same engine size. Rule 4 basically means that if you use a big enough "hammer" (large motor) you can ignore everything else. (except be prepared to pay for a huge battery pack)

But the other ones about simplicity and noise are a strong arguments too. :wink:

 

[xyster]

The closer these are to each other the stronger the argument for a hub motor. When the spread is larger (like a small motored low wind resistance bike) the gears help to cover more torque/rpm possibilities.

Well stated. I'd add something to the beginning like: "When power is limited relative to power requirements to reach a certain speed, climb a certain grade, or accelerate at a certain rate...the closer these are to each other..."

Electric drag racers and electric sports cars with wide rpm range sometimes use a 2-speed tranny.

After all, if enough power is available to break traction anywhere in the desired rpm range, and under any conditions one is riding in, then gears became superfluous unless concern for super-duper peak efficiency makes up for the added complexity.

 

[safe]

Electric drag racers and electric sports cars with wide rpm range sometimes use a 2-speed tranny.

I've heard also that some will start at one voltage and then switch to double the voltage half way down the strip. I have no idea what those voltages are, but imagine wiring your bike for low speeds as 36 Volts and then switching to 72 Volts for high speed. You could with the same battery pack have double the amps available at low speeds and then with the high voltage you could get the top end speed but with only half the power.

It's not a bad idea... maybe run two separate controllers and separate wiring somehow...

Isn't that what a "relay circuit" does?

 

[knightmb]

Electric drag racers and electric sports cars with wide rpm range sometimes use a 2-speed tranny.

I've heard also that some will start at one voltage and then switch to double the voltage half way down the strip. I have no idea what those voltages are, but imagine wiring your bike for low speeds as 36 Volts and then switching to 72 Volts for high speed. You could with the same battery pack have double the amps available at low speeds and then with the high voltage you could get the top end speed but with only half the power.

It's not a bad idea... maybe run two separate controllers and separate wiring somehow...

Isn't that what a "relay circuit" does?

Seems it would be easier to have one controller that can handle 72 volts and just use a switch to go between series and parallel mode (36 volts parallel, 72 volts series) for the batteries. Don't know if the controller would be hurt by a sudden jump in voltage though, might even kick the bike around with a sudden speed burst.

 

[safe]

Seems it would be easier to have one controller that can handle 72 volts and just use a switch to go between series and parallel mode (36 volts parallel, 72 volts series) for the batteries. Don't know if the controller would be hurt by a sudden jump in voltage though, might even kick the bike around with a sudden speed burst.

I think the idea would be to raise the current limit as you switched. Also, with the wires PHYSICALLY changed you change the amperage limits.

So:

36 Volts - 4 Amps

72 Volts - 2 Amps

...would be the same pack. (and you can multiply those much higher for each if you want to exceed the rated currents in AH)

So in a "burst mode" setting

36 Volts - 20 Amps

72 Volts - 10 Amps

 

[Geebee]

But for a motor to reach 30 mph and climb a 25% hill unless its a monster its still going to need gears.
My view of e-biking is severely coloured by my enviroment.
On an unpowered trike any trip from home will mean breaking the speed limit with in 200m from my gate and prolonged 5kph climbs to return home.

 

[safe]

But for a motor to reach 30 mph and climb a 25% hill unless its a monster its still going to need gears.
My view of e-biking is severely coloured by my enviroment.
On an unpowered trike any trip from home will mean breaking the speed limit with in 200m from my gate and prolonged 5kph climbs to return home.

Your motor restrictions in Tasmania seem excessive. In America we have a minimum allowed motor of 750 Watts and most states allow up to 1500 Watts. At 1500 Watts you can basically produce "tractor power" if you want (and some people are even going beyond 1500 Watts!) and all the subtle issues about performance pretty much get thrown out the window. We Americans seem to love the big "muscle cars" and I guess we love our "muscle electric bikes" too.

Gears are a requirement below 500 Watts if you want to be able to do much of anything...

 

[safe]

After playing with the numbers on the 1200 Watt machine I figured I'd post them.

1200 Watt Unite Motor
48 Volts
75 Amp controller (or 100 Amps and waste the extra)
1771 Watt Peak Power
185 lb Rider
100 lb Bike
Lowracer with Tail
8 speed

Top Speed - 56 mph!

Gears 1 and 2 get you to 40 mph and the remaining six get you from 40 mph to the top speed. So it's like NASCAR or Indy cars, most of the gears are just getting you up to speed where things plateau.

 

[safe]

It's kind of funny.

I just realized that on this 1200 Watt bike the first gear gets you to the legal limit (30 mph) and 2, 3, 4, 5, 6, 7 and 8 are all illegal. (useful for getting to higher speeds, but illegal to use)

From a legality standpoint the hub motor clearly wins!

But I also realize that a manufacturer could sell this bike "speed ready" (with the fairings and the overall "speed friendly" design) but sell it initially as a fixed gear bike. People could then on their own "trick it out" by adding the multi-speed gearing. So there's a way to get this past the laws. Of course that won't stop you from getting a speeding ticket, that's of your own doing!

56 mph on a bicycle...

 

[xyster]

I just realized that on this 1200 Watt bike the first gear gets you to the legal limit (30 mph) and 2, 3, 4, 5, 6, 7 and 8 are all illegal.

If true, there goes your justification for gears over a hubmotor...

 

[safe]

If true, there goes your justification for gears over a hubmotor...

Well, I added something after that.

The manufacturer could sell these trick looking brightly colored "road racer" electric bikes with fixed gears on them. The top speed would be 30 mph. Then the person goes about "tricking" his bike out by adding the multi-speed gearing. The law can't prevent the bikes from being sold "fixed" and so it gets them out there. If someone gets pulled over for speeding then they get a speeding ticket and in a worst case scenario a "fix it" ticket to go back to a "fixed" gear which is the same as a hub motor.

The laws weigh the heaviest on the person SELLING a bike. You can get away with home grown stuff more easily. The manufacturer can't break any laws.

A 5304 at 72 Volts and 35 Amps CAN'T be sold by a store LEGALLY... (and most of the "legal" hub motors would be pretty lame)

Another possibility is to sell the frame, fork, clipons, fairings, etc as a "kit" and then let people decide how to build it themselves. One person might build his bike as a souped up hub motor and another might go with a small motor/ multi-speed setup. This is another way to get around the laws.

 

[xyster]

I prefer laws addressing behaviors (like speeding) to laws against certain configurations of consumer products -- especially when said laws are not applied equally. We don't limit larger vehicular speeds or power when misuse of those products causes far greater damage than misuse of small, one-person vehicles. Hence, I restrain how I ride, not how I configure my ride.

 

[safe]

I prefer laws addressing behaviors (like speeding) to laws against certain configurations of consumer products -- especially when said laws are not applied equally.

On that we agree.

One does wonder why something like the electric bike is given such an extremely tight set of rules when gasoline is such a big issue these days. By restricting these bikes so much they force people into the "motorcycle category" which means drivers licensing and lights and mirrors and registration. All this "red tape" make people throw up their hands and want to drive their Hummer around and waste the gas that is now down to BELOW $2 here in Missouri

It's as though one week the gas price is high and everyone makes a "New Years Resolution" that they will "change". Then a few weeks later the prices go down and they go right back to their old habits.

America should be changing NOW! Not later...

 

[safe]

14 Speed? More?

This is a 1200 Watt motor being run at a modest 35 Amps, but this time it has a Rohloff 14 speed rear hub. The peak torque is only about one half of the manufacturers recommendation so it would never break. The amazing thing is that you can climb a slope greater than 15% AT PEAK POWER (not in that lousy low rpm. low efficiency area) and the top speed is about 50 mph.

This gets me to thinking.... (a dangerous thing to happen? )

Why not use a FRONT and REAR derailler and set it up to run 18 speeds or up to 30 speeds? (you can get 8, 9, 10 speed rear deraillers these days) You could easily use a very small motor and if you had a wide enough gearing you could do anything you wanted because you have total control of the torque because you control the gearing.

The Stokmonkey uses a hub motor which runs slowly and would make it really easy. I would figure any hub motor would work. Ignore the idea of "pedals" for the moment because that just makes it more complicated, but just think of running triple chainrings on the front and a cassette with a derailler on the rear. From an efficiency perspective the good old fashioned chain is pretty good and if there is no "crank" (no pedals, no crank, but you do have the triple chainrings) you avoid all the friction of a bottom bracket. And this could be cheap too!

Just ideas...

The irony is pretty good too... the best way to beat the hub motor is with a hub motor...

 

[xyster]

Instead of 30 gears, how about an infinity?

New bicycle CVT design:

http://texturadesign.typepad.com/interbike/2006/09/ellsworthnuvinc.html

http://www.fallbrooktech.com/NuVinci.asp

 

[safe]

If perfected and made cheap, then sure!

In the here and now... the triple chainring / derailler looks good. (I've got a rear derailler on my present bike, but it just dawned on me how you could eliminate the bottom bracket and still get the triple chainring... that's the "wow" thought about it)

In my previous thoughts about the idea I was always stuck with the high rpms of the Unite motor which required some gearing down to get it to work.

 

[Geebee]

Safe, all the friction from the bottom bracket would be so low as to be negligible. if you are talking about mounting the cranks on the hub motor the motor rpms of all the ones I can think of will be to high, unless you build a custom front tripple with very small sprockets.
It will be a bitch trying to fit the pedal system with the rest of this as well.

 

[safe]

Safe, all the friction from the bottom bracket would be so low as to be negligible. if you are talking about mounting the cranks on the hub motor the motor rpms of all the ones I can think of will be to high, unless you build a custom front tripple with very small sprockets.
It will be a bitch trying to fit the pedal system with the rest of this as well.

The idea was to eliminate the pedals completely.

So it's "direct drive" from the hub motor with "attached" chainrings to the rear wheel cassette and derailler. Very, very low overall power losses and at an affordable price. A very simple design.

I figured with the gear calculator that a 300 rpm hub motor could use front chainrings of about 25 - 40 teeth to get the right ratios and that 's about right in what they sell for bikes. (mountain bike front chainrings tend to be very small)