Which hub motor for 20inch rear wheel?

[Simon Knight]

Hi,

Last year I purchased a 48 volt Tongsheng TSDZ2 conversion kit from Woosh to fit to my recumbent trike. The kit required some of wiring to be lengthened but otherwise it was standard. Unfortunately while I mostly enjoyed how the kit performed I found that the wide and asymmetric Q factor (tread) hurt my knees. I tried shorter cranks and straight cranks but neither solved the problem. I looked at having a new boom built with an off centre bottom bracket but did not proceed as doing so not reduce the tread. I removed the kit and waited for my knees to recover.

I have decided to fit a rear hub motor. The issue is that, as far as I can discover, it is not possible to purchase a rear wheel motor built into a 20inch wheel. This means that I will have to purchase a hub motor and have it built into a wheel plus I will have to source a compatible controller and battery.

For any given cycling speed a 20 inch wheel spins at at a higher rate than a larger one meaning that motors designed for 26inch and larger wheels may not be able to drive the cycle to the legal limit of 15.5 m.p.h. However, some motors designed for smaller wheels are sold as high speed versions. I calculate that a 20inch wheel needs to rotate 26% faster than a 26inch wheel. From memory a typical geared motor for 26inch wheels spins at approximately 200 r.p.m meaning that a motor used in a 20inch wheel needs to spin at 252 r.p.m if it is using the same internal reduction gearing.

I have read elsewhere that an alternative approach is to purchase a motor sold as 36 volts and supply it with 48 volts.

My aim is to reuse my existing 48 volt battery in a system that uses a lighter weight hub motor combined with a small display and control buttons. I do not need a high torque monster as the rear wheel does not have the traction and I wish to keep the weight as low as reasonable so 40nm seems a reasonable target. I would consider a direct drive hub if it provided regenerative braking especially at higher speeds.
My questions:

1. Am I correct in my understanding?
2. As of July 2024 which hub motors do you recommend?
3. Are there any issues having a hub motor built into a wheel that I need to be aware of?
4. Will a normal wheel builder be able to build a motor into a wheel?
5. Which controllers should I consider?
6. Which small displays are available.
7. Which components are available from U.K. based suppliers?
8. Which far eastern suppliers have your trust based on experience ?

Thanks for reading,

best wishes

Simon

 

[Peter.Bridge]

Hi,

Last year I purchased a 48 volt Tongsheng TSDZ2 conversion kit from Woosh to fit to my recumbent trike. The kit required some of wiring to be lengthened but otherwise it was standard. Unfortunately while I mostly enjoyed how the kit performed I found that the wide and asymmetric Q factor (tread) hurt my knees. I tried shorter cranks and straight cranks but neither solved the problem. I looked at having a new boom built with an off centre bottom bracket but did not proceed as doing so not reduce the tread. I removed the kit and waited for my knees to recover.

I have decided to fit a rear hub motor. The issue is that, as far as I can discover, it is not possible to purchase a rear wheel motor built into a 20inch wheel. This means that I will have to purchase a hub motor and have it built into a wheel plus I will have to source a compatible controller and battery.

For any given cycling speed a 20 inch wheel spins at at a higher rate than a larger one meaning that motors designed for 26inch and larger wheels may not be able to drive the cycle to the legal limit of 15.5 m.p.h. However, some motors designed for smaller wheels are sold as high speed versions. I calculate that a 20inch wheel needs to rotate 26% faster than a 26inch wheel. From memory a typical geared motor for 26inch wheels spins at approximately 200 r.p.m meaning that a motor used in a 20inch wheel needs to spin at 252 r.p.m if it is using the same internal reduction gearing.

I have read elsewhere that an alternative approach is to purchase a motor sold as 36 volts and supply it with 48 volts.

My aim is to reuse my existing 48 volt battery in a system that uses a lighter weight hub motor combined with a small display and control buttons. I do not need a high torque monster as the rear wheel does not have the traction and I wish to keep the weight as low as reasonable so 40nm seems a reasonable target. I would consider a direct drive hub if it provided regenerative braking especially at higher speeds.
My questions:

1. Am I correct in my understanding?
2. As of July 2024 which hub motors do you recommend?
3. Are there any issues having a hub motor built into a wheel that I need to be aware of?
4. Will a normal wheel builder be able to build a motor into a wheel?
5. Which controllers should I consider?
6. Which small displays are available.
7. Which components are available from U.K. based suppliers?
8. Which far eastern suppliers have your trust based on experience ?

Thanks for reading,

best wishes

Simon

Topbikekit have been good

Just make sure you get the freewheel or cassette version depending on what you need.

AKM-100H 48V350W Ebike Rear/Front Driving Hub Motor 36holes with 16/20/26inch/27.5inch/700CC wheel rim [AKM-48V350W Rear motor 26/700cc] - $100.10 : Zen Cart!, The Art of E-commerce

Zen Cart! AKM-100H 48V350W Ebike Rear/Front Driving Hub Motor 36holes with 16/20/26inch/27.5inch/700CC wheel rim [AKM-48V350W Rear motor 26/700cc] - ★★★★★ AKM-100H 48V350W Ebike Rear/Front Driving Hub Motor 36holes with 16/20/26inch/27.5inch/700CC wheel rim Specification: 1. Voltage: 48V 350W...

topbikekit.com

AKM-128H CST 36V/48V 800W Rear Driving Hub Motor with 20/26/28inch wheel rim [AKM-128HCST 36/48V800W 700C] - $151.06 : Zen Cart!, The Art of E-commerce

Zen Cart! AKM-128H CST 36V/48V 800W Rear Driving Hub Motor with 20/26/28inch wheel rim [AKM-128HCST 36/48V800W 700C] - ★★★★★ AKM-128H CST 36V/48V 800W Rear Driving Hub Motor with 26inch or 28inch wheel rim Specification: 1. Voltage: 36V/48V. 2. Brake type: V-brake, rim brake and disc brake...

topbikekit.com

 

[Benjahmin]

I agree, Topbikekit is a good source of the main kit.
Really you need a motor of 328rpm for a 20" wheel. You either but a 48v motor specced at this rpm or buy a 36v specced at 220ish, running it at 48v will give the extra rpm + around 30% more torque. This will not damage the motor so long as maximum current is not pushed too far. 15A should be plenty.
Controller will depend on what maximum current you want / your battery is capable of delivering. The maximum current rating of your battery should be at least 10% higher than your controller maximum current. That said KT controllers (as supplied by TBK) have an adjustable maximum current.
Display can be any KT display although I understand the Lcd1 is not so good.
I bought my motor from TBK and, with help from here and Grin technologies videos, built the wheel myself. They have a calculator to work out correct spoke lengths to buy. Whole very enjoyable process took around 4 hours - haveing never done it before.
There's a whole load of motors on TBK. Lots are labelled 250w, some are labelled higher. Take your pick, link it here and you'll get pro's and con's.

 

[Sturmey]

.......... From memory a typical geared motor for 26inch wheels spins at approximately 200 r.p.m meaning that a motor used in a 20inch wheel needs to spin at 252 r.p.m if it is using the same internal reduction gearing. ....

1. Am I correct in my understanding?

About 25% extra rpm is often recommended as the power start to taper off at about 65-80% of rpm and very severely (due to back emf) as the motor approaches its final speed, and also to allow for normal battery voltage reduction under load and as it discharges.
This then gives you about 250 rpm for 26 wheel and about 325 rpm for your 20 inch wheel.

 

[Woosh]

Hi,

Last year I purchased a 48 volt Tongsheng TSDZ2 conversion kit from Woosh to fit to my recumbent trike. The kit required some of wiring to be lengthened but otherwise it was standard. Unfortunately while I mostly enjoyed how the kit performed I found that the wide and asymmetric Q factor (tread) hurt my knees. I tried shorter cranks and straight cranks but neither solved the problem. I looked at having a new boom built with an off centre bottom bracket but did not proceed as doing so not reduce the tread. I removed the kit and waited for my knees to recover.

I have decided to fit a rear hub motor. The issue is that, as far as I can discover, it is not possible to purchase a rear wheel motor built into a 20inch wheel. This means that I will have to purchase a hub motor and have it built into a wheel plus I will have to source a compatible controller and battery.

For any given cycling speed a 20 inch wheel spins at at a higher rate than a larger one meaning that motors designed for 26inch and larger wheels may not be able to drive the cycle to the legal limit of 15.5 m.p.h. However, some motors designed for smaller wheels are sold as high speed versions. I calculate that a 20inch wheel needs to rotate 26% faster than a 26inch wheel. From memory a typical geared motor for 26inch wheels spins at approximately 200 r.p.m meaning that a motor used in a 20inch wheel needs to spin at 252 r.p.m if it is using the same internal reduction gearing.

I have read elsewhere that an alternative approach is to purchase a motor sold as 36 volts and supply it with 48 volts.

My aim is to reuse my existing 48 volt battery in a system that uses a lighter weight hub motor combined with a small display and control buttons. I do not need a high torque monster as the rear wheel does not have the traction and I wish to keep the weight as low as reasonable so 40nm seems a reasonable target. I would consider a direct drive hub if it provided regenerative braking especially at higher speeds.
My questions:

1. Am I correct in my understanding?
2. As of July 2024 which hub motors do you recommend?
3. Are there any issues having a hub motor built into a wheel that I need to be aware of?
4. Will a normal wheel builder be able to build a motor into a wheel?
5. Which controllers should I consider?
6. Which small displays are available.
7. Which components are available from U.K. based suppliers?
8. Which far eastern suppliers have your trust based on experience ?

Thanks for reading,

best wishes

Simon

I have Shengyi DWG2NC rear hub in 20in rims if you are interested.

Woosh hub kits | Electric Bike Conversion Kits from Woosh

Woosh range of hub kits with choice of front or rear hub motors. Convert your bike into an electric bike.

wooshbikes.co.uk

 

[Woosh]

The DWG2NC has a freehub, suitable for cassettes up to 10 speed, 135mm dropout, 45NM maximum torque and screw type motor lid for easy maintenance. Standard 9 pin motor cable, internal speed sensor.

 

[saneagle]

You are correct. A 260 rpm 36v version of a motor is equivalent to its 328 rpm 48v version. There would me no difference whatsoever in the construction. Only the markings would be different. In other words, you can use any typical 36v motor for a 26" wheel and run it in a 20" wheel at 48v.

When you run at 48v, it gives more options for how much torque and power you get. I would say that you should run with 14A or 15A unless you're more than 100kg. You already get a lot of torque from any motor in a 20" wheel, so at 48v it'll climb cliffs.

 

[Simon Knight]

Saneagle : "You already get a lot of torque from any motor in a 20" wheel, so at 48v it'll climb cliffs." Unfortunately in a recumbent that torque will probably cause the rear wheel to spin, mind you that does mean that drifting becomes an option!"

Woosh : Yes I'm interested. I have just spoken with Andy and will be sending an email with a few questions. The DWG 2NC is not listed on the Shengyi website but he believes that it is similar to either the DGWX2C/DGWX2S-Rear Drive Motor-City Bike (https://www.syimotor.com/products/dgwx2c-dgwx2s-rear-drive-motor-city-bike.html) or the DGWH2C/DGWH2S-Rear Drive Motor-City Bike (https://www.syimotor.com/products/dgwh2c-dgwh2s-rear-drive-motor-city-bike.html). The first is 40nm the second 50nm and the masses are 2.9k.g. and 3.6k.g respectively. If there were a choice I would opt for the lighter one.

Both motors have a voltage rating of 36v~48v so although your kit is 36v it seems that as long as the controller is rated to 48v I should be able to use the battery I already own.