Is there a lack of 20" ebikes? why?

[Kin]

Ok, I'm tried searching the forums, (20", 20 inch, 20, ect), and I really see a lack of 20" bikes. I happen to have a citizen bike 20" gotham2 folding bike. I love it.

I've spent an easy 20 hours just browsing forums, conversions, ev tech, batteries, ect, but I haven't done enough work finding specifics (e.g, I still only vaguely understand the whole turnigy vs. ping vs. cell_man battle, have only found mediocre, not optimized, sla batteries, and have yet to find a cheaper-than-lithium NiMH seller).

In my dream build, that I think over the summer I might actually do, I'd convert my 20" bike to 48v system. But the lack of good examples (that i've found) of 20" bike conversions has me wondering whether there are inherent problems to a 20" bike. Of course, I don't have shocks, but I can't think of any other fault to 20" bike. Since I got mine I've loved that they're smaller and easier to store indoors, have a slightly different ride (as a comfort ride, I prefer it, it might just be the specific model). I think I might even be able to fit a battery system half between seat and front [probably I'd throw some batteries on the back, though], so that I can still fold the bike indoors while not having a ton of batteries on the back.


Do I not see many 20"bikes because
-I'm too nooby, need to get out more on the forums?
-20" regular bikes are just less common...statistics..
OOORRRrrrr
-There are serious problems I need to be thinking about when I consider my 20" ebike conversion?

P.s. I appreciate the responses so far. Pretty awesome forum to get that many active responses in a half day.

EDIT: I'm going to start filling in answers

1 Response) Potholes.
How do scooters avoid this? Are their small wheels ok because they have thick tires?
2) [I got a response that chvidgov.bc.ca has made a few of them]
--Thing to consider: [Front fork. Sometimes small. Can it fit the hub motor?]
3): [Bigger problem getting the gearing up higher. He used freewheel with 11 cogs, (This is relevant to me. I have a 7speed and I'd probably have to find new freewheel/shifter as well).
4): I might need to worry about the low wheel base [This has not been clear why I need to worry about it, but two different responses referenced it]
5) More responses about the gearing question. This seems to be the biggest barrier (and serious). 56t and 13t would only have me going 23 mph at an uncomfortable 100rpm (that just seems silly , 80 I think is more ideal cadence).
6) There are upgearing mechanisms (meaning things for my peddling front gear that seem to work like the opposite of a geared hub). The only seller found was cost prohibitive (800 dollars?)
7) Chicago Electric bikes sell one. I might ask them if they had a solution

Possible solutions to the gearing problem:
1) Don't peddle much, or not until the battery dies [boring].
2) Very expensive but cool super gearing gear that's made by some Australian company...for $800 . Page 2.
3). What I think is an internal hub gear Sturmey Archer 3 speed 8/9 rear cassette. LIMITS ME TO FRONT HUB MOTOR.
4). Go ridiculous on the gears. 60t front (what is that? About 20" probably ), 13t back. This still isn't much of contribution, even if I up my cadence (trying to figure out the calculator).

 

[neptronix]

Easy.. gear ratios and wheel diameter.

On a 20" wheel, you cannot go very fast with pedal power.
On my 26" wheel bike, i can pedal to 27mph maximum!! and that is me really spinning my legs quickly, so a more relaxed pace would be like 22mph. That is a 48t chain in the front to a 13t in the rear; those gear ratios are literally maxed out

I cannot imagine how bad the situation is with a 20" wheel.
This is why 700c bikes are so fast. The larger diameter of that wheel is a huge boost for your gearing.

20" may be good for a bike that you do not pedal anymore.. hehe...

 

[dogman dan]

Tons of 20" bikes, bmx bikes for one.

But big wheels roll easier, so adults tend to prefer at least 26"... for pedaling.

 

[The Mighty Volt]

A 20" ebike gives lesser ground clearance than other sized rims, it gives more torque but a reduced top speed, it makes bikes harder to ride as one wheel is invariably bigger than the other. It improves efficiency but presents the problem of adapting the bikes brakes, as the post-mounts for the stock brakes will now be nowhere near the rim.

 

[Kin]

Easy.. gear ratios and wheel diameter.
On a 20" wheel, you cannot go very fast with pedal power.
On my 26" wheel bike, i can pedal to 27mph maximum!! and that is me really spinning my legs quickly, so a more relaxed pace would be like 22mph. That is a 48t chain in the front to a 13t in the rear; those gear ratios are literally maxed out
I cannot imagine how bad the situation is with a 20" wheel.
This is why 700c bikes are so fast. The larger diameter of that wheel is a huge boost for your gearing.
20" may be good for a bike that you do not pedal anymore.. hehe...

My 20" has pretty reasonable gear ratios. I waste my downhills and slight downhills a bit, but I'm ok because I don't use a helmet right now. I can always change the gear ratio though to put me at a better top speed; if I'm on a 60lbs+ ebike (rather than the 23lbs bike i have now), I feel like my limit won't be as bad. (If I got into ebiking though, in a winter climate, or anything more serious than this campus commuting, then I'd use a helmet. helmets are cool with me)

Tons of 20" bikes, bmx bikes for one.
But big wheels roll easier, so adults tend to prefer at least 26"... for pedaling.

Oh! I've never been around bmx people. I forgot about that. That's great, thanks for reminding me. I was also originally considering BMX / Motorcycle conversions, but I think I'll start with ebikes. I really like them right now. As for big-wheels-roll easier, I was thinking about that. I imagine with a smaller diameter it is more important that my wheel is a true circle, but simultaneously, a bigger wheel is easier to deform, so I don't really know how a 26" rolls easier.

A 20" ebike gives lesser ground clearance than other sized rims, it gives more torque but a reduced top speed, it makes bikes harder to ride as one wheel is invariably bigger than the other. It improves efficiency but presents the problem of adapting the bikes brakes, as the post-mounts for the stock brakes will now be nowhere near the rim.

Ground clearance is a valid point. I have a milk crate instead of panniers, because I didn't want to have to find a pannier that was appropriate. I don't understand the one wheel invariably bigger than the other. Both wheels are 20". Sorry I was not planning on throwing a 20" wheel on a 26" frame , but I've seen a few clown bikes like that. Please let me know if I misunderstood you.



Thanks for the responses so far.

 

[The Mighty Volt]

I thought you might be copying SteveO. He has a "penny farthing" type arrangement where his rear wheel is noticeably smaller than the front, to get the most of the 5304 torque arrangement.

 

[vanilla ice]

I imagine with a smaller diameter it is more important that my wheel is a true circle, but simultaneously, a bigger wheel is easier to deform, so I don't really know how a 26" rolls easier.

I think the reason larger diameter wheels roll easier is in the physics of rolling resistance..
http://en.wikipedia.org/wiki/Rolling_resistance

Where r is the radius and F is the force of the resistance.

 

[spinningmagnets]

Potholes...

If you hit one at 20-MPH it can be a problem with a smaller wheel and a shorter wheelbase. At 30-MPH they could easily be disastrous if you are flung into on-coming traffic. I have built a longtail with 26" wheels and full-suspension using fat 2.5" tires. It handles potholes very well...or...as well as I can imagine them being handled. I do not hit potholes on purpose, but the old streets here are narrow and the crazy drivers often force me to bail into a puddle and/or pothole of significant size. When there is water in a pothole, I can't tell how deep it is. Small diameter wheel = risk.

That being said, I have an aluminum 20" bike in my RV because its easy to get in and out of the narrow door. No motor yet, but I have a "pop-off" friction drive that it will accept if needed. Longtail bike and friction-drive links are in my sig below.

 

[knoxie]

I have a bmx as one of my rides and I love it!! The smaller wheel provides more thrust not more torque, the torque is the same as the 26 inch wheel given the same conditions.

 

[Kin]

I think the reason larger diameter wheels roll easier is in the physics of rolling resistance..
http://en.wikipedia.org/wiki/Rolling_resistance

Where r is the radius and F is the force of the resistance.

Ok I'll compile some answers soon. Thanks for the link, I never thought about that form of resistance that the wheel offers (It makes sense, playing squash where the squash ball heats up a lot, but I never though about that in the context of bike. I'm not sure it causes a significant amount of friction, but that could be relevant).

Potholes...
If you hit one at 20-MPH it can be a problem with a smaller wheel and a shorter wheelbase. At 30-MPH they could easily be disastrous if you are flung into on-coming traffic. I have built a longtail with 26" wheels and full-suspension using fat 2.5" tires. It handles potholes very well...or...as well as I can imagine them being handled. I do not hit potholes on purpose, but the old streets here are narrow and the crazy drivers often force me to bail into a puddle and/or pothole of significant size. When there is water in a pothole, I can't tell how deep it is. Small diameter wheel = risk.

That being said, I have an aluminum 20" bike in my RV because its easy to get in and out of the narrow door. No motor yet, but I have a "pop-off" friction drive that it will accept if needed. Longtail bike and friction-drive links are in my sig below.

:S potholes. Yeah, that's pretty serious. Not much else I can say. Totally valid point (I assume scooters avoid this problem because they have fat wheels?) I'll take a look at the friction drive you mentioned (curious).

 

[Kin]

I have a bmx as one of my rides and I love it!! The smaller wheel provides more thrust not more torque, the torque is the same as the 26 inch wheel given the same conditions.

So, I think more torque will give more thrust. The thing about 20" wheels and torque/thrust though is that from what I understand it's all optimized to the relative standard of ebikes. So a 20" wheel, because it is essentially on a lower gear than a 26"bike, will simply be optimized so it has a higher rpm. I would plan on setting up me 20" bike so that it would have a comparable speed to 26" wheels, and not really make use of the theoretical lower-gear advantage (and disadvantage).

 

[spinningmagnets]

I'll take a look at the friction drive you mentioned (curious).

Since I am making them and selling them, you might think I'm their greatest promoter. Actually, I most recommend a hub-motor for best bang-for-your buck and for better performance. FD's are power-limited in that, somewhere about 3-HP (2100 watts) the roller breaks loose and grinds on the tire a bit until acceleration catches up.

My friction-drive (and others, *wink*) have a tendency to slip a little when the road is wet. A weekend sport-rider can choose their rides, but a commuter must travel regardless of the weather. And I also imagine the driven tire will wear a little faster.

The major benefit to a seat-post mounted friction-drive is that by flipping the lever on the seat-tube clamp and pulling off the throttle-wire plug, I can then remove the drive and battery (connected to the seat-post and seat) to carry it inside for charging and security...while leaving the bike outside (a limited customer base).

I am living on the third floor of an apartment building, and I have cheap used $20 bike outside that I am not too worried about if it gets stolen. There is a large college nearby with many students in the same position, and I thought a few of them might want one. I've seen frame-mounted friction drives before, but the tiny RC-motors, controllers (ESC), and LiPo batteries have made the light and small pop-off drive possible...

edit: I have seen aluminum folding bikes with 16" wheels (can be carried onto a train/bus, or stored inside a tiny apartment), and although they fold into a VERY compact form, I would put up with a lot of hassle to have at least the 20" wheels...if I really needed a folder.

 

[chvidgov.bc.ca]

I've done several 20" ebikes, including a Raleigh 20, a Giant Revive, a 20" rear motored Rebike recument, and a Bazooka folder. The main issue with the Raleigh was you needed a fork replacement - like Dahon, the stock front forks are too narrow for 100mm hub motors. On the others, the problem was getting the gearing up higher - I needed to use freewheels with 11 tooth cogs (Shimano Megarange) that are hard to find (ebikes.ca has a clone 11 tooth freewheel). Many of the 20" bikes are six speeds, so you need to replace your shifters as well, if the seven speed will fit in there. And putting a bigger ring up front is tricky when the folding hinge conflicts with a bigger ring. And I needed all kinds of machinations to get longer seatposts and stems. The Revive with the Nexus hub is the best one, with the front hub motor. I do like the 20" form factor though.

 

[Kin]

.I am living on the third floor of an apartment building, and I have cheap used $20 bike outside that I am not too worried about if it gets stolen. There is a large college nearby with many students in the same position, and I thought a few of them might want one. I've seen frame-mounted friction drives before, but the tiny RC-motors, controllers (ESC), and LiPo batteries have made the light and small pop-off drive possible...

My advice would be to look up the college's clubs. At least in the U.S, a lot of colleges have numerous clubs, ect. You could easily find an outlet for people in any mechanically or technologically inclined club (Engineering clubs, like specific discipline clubs, engineering without borders, or other engineering related clubs, like areospace clubs, car clubs, ect). I'm speaking from the perspective of an quasi-engineering student, but I bet you get the drift (it's really not just engineer clubs). The reason why I suggest this is because those are people who are interested, could help you get into the college groups, and eventually be liasons for selling to less technologically inclined students, if you're ever interested. You would just start by searching the college's club list online, and sending an email to one of the clubs leaders letting them know your offers and possibly a demonstration.

you'd be part cannibalized by people insisting on "making their own" but I think eitherway they'd need you for help, support, and to be in some sort of dealer capacity. (the legal kind of dealer ).

 

[Kin]

I've done several 20" ebikes, including a Raleigh 20, a Giant Revive, a 20" rear motored Rebike recument, and a Bazooka folder. The main issue with the Raleigh was you needed a fork replacement - like Dahon, the stock front forks are too narrow for 100mm hub motors. On the others, the problem was getting the gearing up higher - I needed to use freewheels with 11 tooth cogs (Shimano Megarange) that are hard to find (ebikes.ca has a clone 11 tooth freewheel). Many of the 20" bikes are six speeds, so you need to replace your shifters as well, if the seven speed will fit in there. And putting a bigger ring up front is tricky when the folding hinge conflicts with a bigger ring. And I needed all kinds of machinations to get longer seatposts and stems. The Revive with the Nexus hub is the best one, with the front hub motor. I do like the 20" form factor though.

--Cool, I appreciate the advice and word from someone who has built them. My bike does not have shocks unfortunately :S, that's not really an issue for me, but might eventually be for my bike.
--I'm on spring break, and my gotham2 is in another state, so I can't measure the front fork width right now. :/ I don't know if it would fit the hub. that would clearly be a setback if it can't fit any quality hub.
As for the cogs, I never use my lowest 2 gears, and rarely use my lowest 3 [lowest meaning easiest to peddle], so I assume I could setup some situation in which I either increased the size of my front single gear, and/or got even smaller gears on the back wheel. I could really be over estimating my options and bike gears.
So I don't fully gather if the 11tooth cogs are for a seven speed bike. Mine is a seven speed bike.
--I couldn't find what you meant about "The Revive" [assumed it was a bike model] or "Nexus Hub". I got a few hits on the Nexus, but wasn't sure what made you say it was the best one.
--Also, is the recommendation for front hub simply because of the gearing challenges, or is there any other reason? I was concerned the 20" bike would have a greater propensity to flip over, because it looks top heavy, although in reality I've noticed it's a lot harder to do wheelies on it than my 26" bike [and don't know if that reflects anything]

Thanks for the response!

 

[neptronix]

My 20" has pretty reasonable gear ratios. I waste my downhills and slight downhills a bit, but I'm ok because I don't use a helmet right now. I can always change the gear ratio though to put me at a better top speed;

If you are going rear hub motor ( which is really the only way to go with a hub motor ), you can only go as low as 13t in the rear.

My '80rpm' pedaling speed is 24.6mph, on your bike it would be 18.5mph.
You may not even be able to fit a 48t front crank on that bike either.

The problem becomes the fact that the electric motor becomes stronger / faster than you and you can no longer pedal to add more mph. Even a 250w kit can do 15-17mph.

Also yes.. short wheels and wheelbase are a problem. Taller wheels is always better.

 

[Hillhater]

Easy.. gear ratios and wheel diameter.

On my 26" wheel bike, i can pedal to 27mph maximum!! and that is me really spinning my legs quickly, so a more relaxed pace would be like 22mph. That is a 48t chain in the front to a 13t in the rear; those gear ratios are literally maxed out

I cannot imagine how bad the situation is with a 20" wheel.
This is why 700c bikes are so fast. The larger diameter of that wheel is a huge boost for your gearing.

...

Not strictly true...
A 700c wheel with a typical 28mm tyre is the same diameter as a 26" wheel with a 1.9" tyre.
Roadies use a 11T rear cog for more speed ( and a much faster cadence !)
And a Rohof geared front BBracket could overcome any of those issues.

 

[neptronix]

Easy.. gear ratios and wheel diameter.

On my 26" wheel bike, i can pedal to 27mph maximum!! and that is me really spinning my legs quickly, so a more relaxed pace would be like 22mph. That is a 48t chain in the front to a 13t in the rear; those gear ratios are literally maxed out

I cannot imagine how bad the situation is with a 20" wheel.
This is why 700c bikes are so fast. The larger diameter of that wheel is a huge boost for your gearing.

...

Not strictly true...
A 700c wheel with a typical 28mm tyre is the same diameter as a 26" wheel with a 1.9" tyre.
Roadies use a 11T rear cog for more speed ( and a much faster cadence !)
And a Rohof geared front BBracket could overcome any of those issues.

You're right, but a 20" tire can only get so tall.
Can a Rohof geared bottom bracket be added to a standard bicycle?

 

[Gordo]

I've done several 20" ebikes, including a Raleigh 20, a Giant Revive, a 20" rear motored Rebike recument, and a Bazooka folder. The main issue with the Raleigh was you needed a fork replacement - like Dahon, the stock front forks are too narrow for 100mm hub motors. On the others, the problem was getting the gearing up higher - I needed to use freewheels with 11 tooth cogs (Shimano Megarange) that are hard to find (ebikes.ca has a clone 11 tooth freewheel). Many of the 20" bikes are six speeds, so you need to replace your shifters as well, if the seven speed will fit in there. And putting a bigger ring up front is tricky when the folding hinge conflicts with a bigger ring. And I needed all kinds of machinations to get longer seatposts and stems. The Revive with the Nexus hub is the best one, with the front hub motor. I do like the 20" form factor though.

Have you had any trouble with the spoke angles or spoke nipples with the 20" wheels? I have had 2 suppliers tell me they could not lace the hub motor I wanted into anything smaller than a 24" wheel.
Thanks;
Gordo

 

[Kin]

If you are going rear hub motor ( which is really the only way to go with a hub motor ), you can only go as low as 13t in the rear.
My '80rpm' pedaling speed is 24.6mph, on your bike it would be 18.5mph.
You may not even be able to fit a 48t front crank on that bike either.
The problem becomes the fact that the electric motor becomes stronger / faster than you and you can no longer pedal to add more mph. Even a 250w kit can do 15-17mph.
Also yes.. short wheels and wheelbase are a problem. Taller wheels is always better.

Shoot, I was really going to edit and clarify myself on that. I realized my explanation that "I don't think that would big deal on an ebike". What it really meant was that if I was going to let my bike take over and it died of juice, then having a mediocre top speed is ok, since peddling a heavier bike is hard. But a much better solution would be to get a gear ratio that I could still contribute to the fast speeds.

 

[Kin]

Have you had any trouble with the spoke angles or spoke nipples with the 20" wheels? I have had 2 suppliers tell me they could not lace the hub motor I wanted into anything smaller than a 24" wheel.
Thanks;
Gordo

[I am clearly not chvidgov.bc.ca, but] I've noticed golden motors doesn't sell a lace 20" motor- theres are just direct metal spirals (more like car's hub).

 

[neptronix]

yeah, again that is a problem with an eBike. If you are using a rear hub motor ( as you should ), you are limited to using a 13t rear gear at the lowest. And i don't think a 48t would even fit..

48t + 13t =

pedaling furiously at lowest gear on a 26" wheel: 28mph
pedaling furiously at lowest gear on a 20" wheel: 20.5mph

http://sheldonbrown.com/gears/index.html

That's a best case scenario for a 20" wheel. that's IF you can fit a 48t on the bike ( very unlikely )

Dontcha think it would suck to have your electric motor go faster than you, and thus not be able to contribute to the power it produces?

 

[Kin]

yeah, again that is a problem with an eBike. If you are using a rear hub motor ( as you should ), you are limited to using a 13t rear gear at the lowest. And i don't think a 48t would even fit..

48t + 13t =
pedaling furiously at lowest gear on a 26" wheel: 28mph
pedaling furiously at lowest gear on a 20" wheel: 20.5mph
http://sheldonbrown.com/gears/index.html
That's a best case scenario for a 20" wheel. that's IF you can fit a 48t on the bike ( very unlikely )
Dontcha think it would suck to have your electric motor go faster than you, and thus not be able to contribute to the power it produces?

I definitely agree, it would be very disappointing and a bit of a range waste. I'm trying to fully understand the problem with the gearing situation though. I'm not clear why, in the worse scenario, I can't stick a giant gear on my front (gearless, i.e, the peddle part). This would be regardless of whether I can get specialized rear tires, if I increase the radius of that front gear by 1.5, I presumably would vastly improve my ability to contribute.

edit: Ok, I think I am understanding it better. You are saying rear hub the smallest I could get is 13t, meaning 13 teeth. And for some reason the max I could possibly have for the front is 48teeth?

 

[neptronix]

I definitely agree, it would be very disappointing and a bit of a range waste. I'm trying to fully understand the problem with the gearing situation though. I'm not clear why, in the worse scenario, I can't stick a giant gear on my front (gearless, i.e, the peddle part). This would be regardless of whether I can get specialized rear tires, if I increase the radius of that front gear by 1.5, I presumably would vastly improve my ability to contribute.

edit: Ok, I think I am understanding it better. You are saying rear hub the smallest I could get is 13t, meaning 13 teeth. And for some reason the max I could possibly have for the front is 48teeth?

Yes, the smallest on a freewheel ( all rear hub motors use threaded freewheel at this time.. ) is 13t. There are 11t freewheels but they are total junk.. so cross that option off..

48t may not be the largest gear you can get, but this theoretical 48t would give you 20.5 mph, right?
a 56t would give you 23.9mph..

This is at 100rpm, which is just a notch below pedaling your ass off. It's not something that you could maintain for a long time.

The only reason i drive this home is because i went with a 26" wheel and regret it deeply. I have met the limits of my gearing and body at 27mph... and that's on a 1.95" tire. I could eke another 1-2mph out of the motor if i could pedal a few mph faster... sucks.

 

[Hillhater]

Can a Rohof geared bottom bracket be added to a standard bicycle?

Sorry, my mistake, it is not the Rohloff B'bracket ( that is another device) .. but the Schlumpf Speed Drive that gears up the pedal action.
. http://www.schlumpf.ch/hp/schlumpf/antriebe_engl.htm

and I believe they can be fitted to most bikes, but a modification is required to fit it ( minor machining using a special hand tool)