Optimal Wheel size rear hub/rear drive configuration

[LI-ghtcycle]

I have sorta a weird question lol!

I rode motorcycles for years, and I have just come to wonder if part of the reason it takes more room to u-turn on my 26" bicycle is the wheel size.

Also, I am looking to get the most all-around performance in my next e-bike build, and I have noticed people putting smaller rear wheels on.

On a motorcycle, the typical size on a high-performance sport bike is 17 inches.

Would putting a 20 inch rear hub motor or just a 20 inch wheel with rear disc mounted sprocket increase my acceleration considerably?

I don't want to hurt top speed TOO much, but I would like to put more emphasis on hill climbing and acceleration and still maintain 20 mph+ on the flat.

My concern is using the current Amped Bike 36v brushless 500watt rear hub motor on the bike I helped my father build, it struggles on steep grades (7%-9%)

and I would like to keep the bike at the legal limit of around 20 on the flat, but I'd really like more than 3-4 mph (motor power only) on the steep stuff.

Is it doable by decreasing my rear wheel diameter to gain some "gearing" (also looking to use a geared rear hub on my kit) for hill climbing?

Conversely, if I go with the smaller rear wheel, and a geared frame mounted motor driving a second sprocket on the disc break mount, what wheel/sprocket

combination would give me the optimal hill climbing ability and yet allow me 20 mph on the flat?

P.S. I am thinking either going with a high voltage set-up or high amperage, which ever is optimal for my needs, I have seen where some run 70+ volts and low

amps, or run 48 volts and high AH. I am currently considering 4 dewalt 28V a123 packs left intact, running 2 in series then those in parallel for 56volts and 9.2

AH (if my math is correct) with Kfong's circuits to use the battery's built-in BMS.

Any and all advice greatly appreciated!

 

[dogman dan]

Going to a 48v battery and controller will help. But mid size motors like 9 cont, aotema, clyte 408 will struggle some on hills above 5%. Most of us more energetic riders simply downshift and pedal a bit more to get up a 7% hill of less than a mile of length. Gearmotors like bafangs have more torque for sure, but when run at low wattages, I don't find hill performance all that spectacular, at least for top speed up a hill. But a gearmotor may be the best option for you, since you mention not pedaling.

A real hill, 7% for more than 2 miles, or 10% for at least a mile, will take more motor. One favorite is the bmc gearmotors, but even they will overheat if run hard enough up that hill for long enough. the clyte 5305 still rules for long hard hills, and it can tolerate overvolting enough to go to whatever volts it takes to get the job done at the speed you like. But,,, it won't be cheap, especially the batteries.

Wheel size matters, but so does winding count. My hill bike is a 5304, but it's in a 24" rim that gives it perfromance similar to a 5305 in a 26" rim. The real hill climbers are running 20" rims, and enough volts to still hit 30 mph.

Riding technique matters too, my 36v aotema bike will get up 13%, but not fast. To do it, I use the lowest gear, and pedal along using the motor only as an assist, and travel less than 10 mph. It does get me up the hill, but nothing like the full throttle ride I do on the flats. I watch motor temps on an internal sensor so I don't fry a motor climbing too steep for miles. I'd have to stop every 2 or 3 miles.

 

[Drunkskunk]

turning radius is mostly a factor of wheelbase: the distance between the axles. the longer it is, the wider the turns you make.


If you have the same motor and same gearing, a smaller wheel will act like reducing the gear ratio, so it will go slower, but accelerate and climb better. you could get the same effect with a large wheel and chain drive by increasing the size of the rear sprocket. The underlying principle is having a ratio were the bike moves X number of inches for every 1 revolution of the motor. If the bike moves 10 inches every time the motor turns once, it doesn't matter if the wheel is 20 inches tall, or 20 feet tall. the torque and speed will be the same.

If you're running a direct drive hub motor, then the only way to reduce the gearing for better acceleration is to reduce the wheel size. you of course have a slower motor now, but if you then increase the voltage to compinsate, you end up with a motor that is just as fast but more powerfull.

The alternitive to changing the physical wheel size is to change the winding count of the motor, which will also act like gear reduction. more turns of copper means slower RPMs, which combined with more voltage means more torque.

 

[LI-ghtcycle]

Good to know, I also had an idea for conquering the hills, what if I had a set up that allowed me to put all batteries in series, for short bursts, i.e. this 7-9% grade here in town (it probably isn't even 1/4 of a mile, just steep) and upped my voltage?

I'd much rather spend more and replace less, so if you could recommend a set up that would be misery on power, yet allow for high voltage bursts, I was thinking using the dewalt 28 volt packs since I can get them cheaper than the 36 volt, and having somewhere in the neighborhood of 4-6, and 4 is better if I can get away with it, not looking to race up hill, but just maintain around 12 - 15 mph with pedaling with out working too hard.

Maybe it would be a good compromise to goto a 24" wheel as you have, and then get that clyte 5304 (geared?) hub motor. I'm not afraid of going up in voltage, just not wanting to start turning it into a hot-rod that burns it's self up too easy.

I have Fibromyalgia, and although I am in good shape and can average about 15-17 mph under my own power on the flats, I want some insurance for when I become unexpectedly fatigued.

Can you recommend a seller with just such a kit? I am not set on hub motors by any means, but I am very interested in LIGHT motors, and from what I see most geared hub motors have more of the performance I am looking for, and are about 1/2 the weight.

What would you suggest for both 20 mph (talking motor performance alone no pedaling) and about 10 mph on a steep grade? BTW I weigh 170 lbs.

 

[Anonymous]

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[dogman dan]

I think I put pix of installing it on my aotema hightechbikes motor review thread. The sensor is just a bell brand indoor outdoor car thermometer from wallmart. Ten bucks. The outdoor sensors wires fit easily along with the power wires since that motor has no halls. The sensor was epoxied next to the windings. On my fusin, I couldn't fit the wires so I simply mounted the sensor on the end of the axle, and put some foam tape over it to keep the sensor from reading false from air cooling. Tests on the aotema showed that temps on the axle stub run 30-40 F less than inside, so on the fusin, when I see 130F on the axle stub I know it's time to stop. The readout was mounted to the hanldlebars. An infared sensor can be used, but they cost more.

To the OP, the performance you specify is not that hard to find. The fusin gearmotor 48v kit would do that, my 36v fusin nearly does, but they are front hub.

A 409 clyte, an Ezee kit, the slower winding 9 cont, bafangs, or bmc's would also go 20 mph and reasonably fast up a hill on 48v, 20-30 amps. I have some similar hills, but a bit shorter on my route. One is about 10% for 200 yards, and my 36v aotema easily gets up it at 15 mph if I start up it at 25 mph. Any longer though, and I'd slow down to 8 mph. Still, I'd get up it with no sweating.

This bike is to replace your dads? or for you to ride. For dad, get a gearmotor, like the ezee kit from Ebikes.ca. Then you can just overvolt the 9 c for you.

 

[LI-ghtcycle]

I think I put pix of installing it on my aotema hightechbikes motor review thread. The sensor is just a bell brand indoor outdoor car thermometer from wallmart. Ten bucks. The outdoor sensors wires fit easily along with the power wires since that motor has no halls. The sensor was epoxied next to the windings. On my fusin, I couldn't fit the wires so I simply mounted the sensor on the end of the axle, and put some foam tape over it to keep the sensor from reading false from air cooling. Tests on the aotema showed that temps on the axle stub run 30-40 F less than inside, so on the fusin, when I see 130F on the axle stub I know it's time to stop. The readout was mounted to the hanldlebars. An infared sensor can be used, but they cost more.

To the OP, the performance you specify is not that hard to find. The fusin gearmotor 48v kit would do that, my 36v fusin nearly does, but they are front hub.

A 409 clyte, an Ezee kit, the slower winding 9 cont, bafangs, or bmc's would also go 20 mph and reasonably fast up a hill on 48v, 20-30 amps. I have some similar hills, but a bit shorter on my route. One is about 10% for 200 yards, and my 36v aotema easily gets up it at 15 mph if I start up it at 25 mph. Any longer though, and I'd slow down to 8 mph. Still, I'd get up it with no sweating.

This bike is to replace your dads? or for you to ride. For dad, get a gearmotor, like the ezee kit from Ebikes.ca. Then you can just overvolt the 9 c for you.

This bike would be for me, I built dad's set-up (well I installed the kit, only thing I have "built" are the bracket for a trailer/torque arm and the battery holder and I have soldiered up chips to run the dewalts)

Just curious why you recommend overvolting a hub motor rather than a geared? Isn't a geared lighter and more efficient?

 

[dogman dan]

I meant going from 36v, to a 48v controller, with maybe some more amps too. You may be just running the 9 c on a lame battery too, are you using sla's now?

But even a gearmotor will need some volts and amps to climb fast.

My fusin 36v kit has a low amp controller, and though it can do 20 mph, it bogs down fast when going uphill or into wind. A 48v one would do much better I believe since it comes with a higher amp controler too. The right gearmotor would be good for you, but not a 250-350 watt one. Youbetcha it's efficient at 350 watts, but it climbs like a lame 350 watt bike. Another gearmotor like the bmc 600 watt would do ya for sure, but it's costly.

 

[ZOMGVTEK]

I dont have a issue climbing hills with my 1000W Golden Motor rear hub. With the controller at the stock 25A it was always clamped wide open. But with the controller modded to 60A, i can be going too fast up hills at times and need to let off. Now, these hills I speak of are all generally made of dirt, so its quite a rough ride.

I can only go about 23-24 MPH on flat road, but can do about 12-14 up a very steep grade. Id guess about 13-15º... Its steep enough that you would need to be in 1st or 2nd if you didnt want to kill yourself going up. The motor is much stronger than me up hills until its far far too steep for the motor and it just cogs, draws 3kw and goes nowhere. But that takes about 30º head on and no running speed.

 

[torker]

Dogmans right, the 9 c on 36 V is not a climber. If that is what you have then try 48 V . It will wake it up considerably. If it comes close to what you need then you could still lace it in a smaller wheel to gain even more torque ..