26" to 20" differences?

[vskid3]

Hello ES,

I've been bitten by the ebike bug. Started out with a Yescom 1kw rear motor on my Giant Revel 3 mountain bike and a 48v 15Ah Ping battery in a backpack. I put about 600 miles on the motor between May and August of this year before the rim started to split at the valve stem hole on the inner wall, causing it to chew up tubes. I bought an identical kit for my wife's Diamondback Response XE so we could ride together, with me using it to commute until I could swap out the rim.

Now I'm considering switching to a 20" wheel bike to use for commuting and leaving my mountain bike human powered. I would use my current motor, but replace the rim with a 20" instead of a 26". On the 26" bikes, I have the top speed limited to 28MPH as most of my commute is on 25MPH roads. Would this speed be an issue for a 20" wheel bike? My commute is all on roads, not really any potholes but many uneven seams and a few sets of railroad tracks. I would like to be able to still ride at 25-30MPH because that makes the ebike about as fast as commuting by car.

As far as bikes to use, part of the reason for using a 20" bike is the smaller size so I can throw it in the back of my Prius quickly. A folder would be nice, but they don't seem like they would be solid enough for doing almost 30MPH from what I've read here. The Cannondale Hooligan looks like it would be perfect, but they're $1000 new and I can't find used ones anywhere near me. I'm thinking a kids bike like the Diamondback Cobra 20" would be a decent place to start, adding BMX-style handlebars and a taller seatpost to mimic the ride positioning of the Hooligan. Anyone have any thoughts on using that bike or a better alternative (cheaper is better, but I'm willing to spend a bit if it'll be worth it)? Thanks!

 

[wesnewell]

Unloaded speed on a 26" wheel is ~36mph. On a 20" wheel it will be ~27mph. But you won't loose as much under load with the 20" wheel as you do with the 26" wheel. I'd guess it will still do 25mph loaded.

 

[Chalo]

If you put a 20" wheel on a 26" bike, you'll impair its ground clearance and its handling in a big way. Depending on the motor and the voltage, you may reap efficiency and power benefits. Do know that 20 inch wheels ride much rougher and have less traction than larger wheels. You have to judge for yourself what compromises are acceptable to you.

Note also that motor vehicles have settled on a minimum practical wheel diameter that is equivalent to 26" bicycle wheels, not 20".

 

[dogman dan]

I think he was thinking of a new bike, not adding a 20" to his 26" bike.

But I do agree, particularly since you must use a weaker radial lace with a large diameter hubmotor, it can be better to just stick with 26" wheels.

Carrying your bike needs a better solution than throw it in the back of the prius. Unless you do go to a folder, you'd be better off to put a 1 1/4 inch trailer hitch on the prius, then get a hitch mount bike rack to carry the bike. Preferably the type that holds the bike by the wheels. Sounds pricy, but the hitches are on the web for pretty cheap, and you can easily install one yourself. Once you have that nice rack, you will discover a wide world of riding in fun places to ride. And you can carry both bikes easy.

If you do go for the 20" bike, get a smaller diameter motor, such as a Mac or similar 500w gear motor. This will allow a bit longer spokes, for less wheel problems.

 

[miuan]

Second this, I am very happy with my radially laced 20 inch Bafang BPM, except it gets quite noisy above 35kph due to the gears moving so fast.
I built it myself with minimum lacing experience and it holds up great.

 

[vskid3]

Thanks for the replies and sorry for taking so long to reply.

wesnewell- The unloaded speed for the motor I got from Yescom is 42MPH, pretty much perfect for a 20" and the speed I'm looking for. I believe they're currently shipping a 9C clone. Thanks for posting about your experiences with your Yescom kit, they played a big role in my decision.

Yes, I meant a 20" bike as well. I was under the impression that with a large hub motor, radial lacing is fine? Or is that just with lower power motors?

Anyway, I'll probably just replace the rim with another 26" for now. A 2 or 3 bike trunk rack should hold one ebike just fine if I need an easier transportation solution for the bike. Now to figure out what spoke length I'll need...

 

[amberwolf]

If you use a good rim and good spokes and tension them correctly, then radial is ok even with higher power, as long as you're not jumping the thing off 2-foot curbs very often. :lol:

I used the Sapim spokes from ebikes.ca (grin tech) for my 20" ex-Zero rim (from Ypedal--you might check if he still has any left) built onto an HSR3548 on the rear of CrazyBike2. Actually, half of the spokes were already used in a previous failed wheel build (where the failed half were bent for 1x lacing, and it didn't work out very long), and half were new. I still (knock on wood) haven't broken any of them in the present wheel build, which I guess has been something close to a year, now? I forget when I relaced it; maybe it was only 3/4 of a year ago. Anyway, it's seen the same abuse on our roads here, or worse, than the other one saw.

And the stock Crystalyte-provided rim and spokes disintegrated pretty quickly (as did a previous 9C wheel), so it definitely makes a difference which rim and spokes you use.

 

[friendly1uk]

I don't imagine much of a speed change, if any. Your top speed is not limited by gearing in either setup.

You will get about a 5th more usable torque, which might be nice. It might even increase top speed.. I wouldn't like to call it.

The torque from a 1000w DD is very low indeed. The smallest of geared motors would likely beat it. I wouldn't worry to much about radial lacing, unless your going to clip in and add some serious power yourself.

I'm strongly considering a 20" bike myself. Also a folder. My 26" bikes are just to big for women new to the hobby that want a go. Also I have no real rear rack options for my car. It is not approved for towing, and has no roof.

 

[miuan]

My 20" folder is quite difficult to ride, let alone for an unexperienced woman. I'd prefer 26" for anyone starting out.

 

[torker]

I have 2 -2810 = low speed winding motors . One in 20" and one in 26" If I run the 26 @ 50v and the 20 @ 60 volts they are neck and neck at top speed. The 20 has a nice advantage off the line though. I think they run 24 mph. If my speedo is calibrated right.
Mine is in a YPedal Zero rim also. Spokes from JRHolmes radial lace .. To be fair I did put a little more solder on the shunt of the 20" setup 8)

 

[friendly1uk]

My 20" folder is quite difficult to ride, let alone for an unexperienced woman. I'd prefer 26" for anyone starting out.

Are you women quite tall then? Ours are short round and wear Carling tea-shirts wet from the pint glass they are spilling. They couldn't get their leg over much, although many double as bikes themselves. It sure aint Holland. Only the influx of women from cooler climates has woke us up to the idea we are breeding fat pigs here. It's all the benefits lot that are too stupid to do much else than breed, now that we have to support them. It mental. Their genes spiral down to almost extinction as nobody else will intermingle with them, then just as they bottom out, about to go out of existence, they fall into the perfect position to have more kids than anyone else. It's survival of the fittest turned upside down.

So... are your women tall?