1kW Front Hub Motor on Cheap Chinese Folding Bike

EVGator · Apr 3, 2021

Ok, I know this sounds crazy but hear me out? I want to lace a generic 1000W hub motor into a cheap chinese folding bike front wheel.

Why you ask? For the same reason that some jackass would put an LS motor in a Yugo. Is it a bad idea? Yes. Inherently risky? Yes. Is that part of the reason that I am doing it? Yes. I know it is a bad idea, and I know that I will have to beef up the front forks which are luckily made of steel. I have plenty of electrical and mechanical experience. What I don't have, is wheel building experience and the breadth of knowledge associated with it. I know that several of you on this forum do have that knowledge, and I would love some input as to how to make this a reality. I've attached some pictures of the 20" folding bike wheel assembly. I see the wheels often referred to as 20" despite the rim size being 16". Is that correct to say? This would be a 20" 406 wheel?

Some specs:

20" x 1.75 tire on what looks to be a 16" rim

1000W motor which is currently laced into a 26" wheel

14 gauge (2.0mm) spoke size on the 20" wheel

12 gauge (2.6mm) spoke size on the hub motor

Bike rim has 28 spoke holes

Motor has 36 spoke holes

Bike front dropout width is 100mm

Motor dropout width is 100mm

Motor axle length is 160mm

I am attempting to use Grin's spoke calculator to determine the spoke length that I will need, which can be found here: https://ebikes.ca/tools/spoke-calc.html. Does anyone have a better way to do this?
I don't have all of the info to fill out the spoke calculator yet. ERD, Offsets, Cross pattern (0, 1, 2?), Nominal Diameter (20" 406 I think?) still need to be determined/measured. Then, should I invest in a spoke threading tool set and cut the longer spokes to the length that I need?

I've got plenty of research ahead of me, but any feedback you guys can give will be greatly appreciated. I'll even make a sweet video of the shear torque ripping the front end off of the bike. The goal is to try prevent that from happening, but it's not outside the realm of possibility. Some of you will instantly shoot this idea down, but maybe someone with an open mind will see this as comical enough to lend a thought or two towards it.

markz · Apr 3, 2021

Folding bicycles have different dropout spacings then regular bicycles.
Do keep that in mind when purchasing a motor.

Another thing to keep in mind is that there are a lot of new styles for wheels to attach to the frame, like thru-axles. Do keep that also in mind when purchasing the bicycle. While most motors are still old school (axle flats) that you can slide into the dropouts, there is a motor with a thru-axle design. Then theres another snag, there are several different diameters of thru-axles out there. But the guess is your cheap chinese folder will be old school slide in, and very possibly might have some odd dropout width because I will say that I bought my fat bike from Costco which had old school slide in, but 120mm front fork dropout width, where 135mm is the normal. So, it was very hard to find a 120mm front hub to replace stock hub for traditional riding. My motor was 135mm axle width, so I had to spread the forks a tad.

https://sheldonbrown.com/frame-spacing.html

fatty · Apr 3, 2021

EVGator said:
I see the wheels often referred to as 20" despite the rim size being 16". Is that correct to say? This would be a 20" 406 wheel?

Careful -- most folders take a 20" tire on a 16" (406mm) rim, but Brompton folders take a 16" tire on a 13.7" rim. Your donor/frame should indicate which.

EVGator said:
I am attempting to use Grin's spoke calculator to determine the spoke length that I will need, which can be found here: https://ebikes.ca/tools/spoke-calc.html. Does anyone have a better way to do this?

Grin is best if it has your motor.

EVGator said:
I don't have all of the info to fill out the spoke calculator yet. ERD, Offsets, Cross pattern (0, 1, 2?), Nominal Diameter (20" 406 I think?) still need to be determined/measured. Then, should I invest in a spoke threading tool set and cut the longer spokes to the length that I need?

ERD and offset are specs from the rim.
Cross pattern is a function of spoke count: to get closest to tangential, spoke count divided by 9 and rounded down. If 36: 36/9 = 4 cross is tangential.
No, you calculate the spoke length that you need and order that length.

markz · Apr 3, 2021

Keyword in the title being CHEAP CHINESE folding bike, so the seller might not even have that info but its pretty basic info to know right. Like with generic hub motors, the sellers wont even know the Kv of the motor. The next problem is the communication barrier when you start to investigate and send off emails. On one hand they may just tell you anything to get a sale so be careful in how you write the email. Dont say, oh I have a 20" rim and what size of wheels does your bike use. No no, you dont give them any info on what you have, just ask them what size of wheels do they use if its not spec'd on their website.

fatty said:
Careful -- most folders take a 20" tire on a 16" (406mm) rim, but Brompton folders take a 16" tire on a 13.7" rim. Your donor/frame should indicate which.

EVGator · Apr 3, 2021

You're right about it being the open end/slide in type of front fork. The dropout width for the front seems to be the standard 100mm. At least I believe that's the standard. The hub motor is a "front hub motor" so it also has a drop out width of 100mm, which matches. I'll take some pictures of the hub motor and the forks for better visualization. Thanks for the info!

markz said:
Folding bicycles have different dropout spacings then regular bicycles.
Do keep that in mind when purchasing a motor.

Another thing to keep in mind is that there are a lot of new styles for wheels to attach to the frame, like thru-axles. Do keep that also in mind when purchasing the bicycle. While most motors are still old school (axle flats) that you can slide into the dropouts, there is a motor with a thru-axle design. Then theres another snag, there are several different diameters of thru-axles out there. But the guess is your cheap chinese folder will be old school slide in, and very possibly might have some odd dropout width because I will say that I bought my fat bike from Costco which had old school slide in, but 120mm front fork dropout width, where 135mm is the normal. So, it was very hard to find a 120mm front hub to replace stock hub for traditional riding. My motor was 135mm axle width, so I had to spread the forks a tad.

https://sheldonbrown.com/frame-spacing.html

EVGator · Apr 3, 2021

fatty said:
EVGator said:

I see the wheels often referred to as 20" despite the rim size being 16". Is that correct to say? This would be a 20" 406 wheel?

Click to expand...

Careful -- most folders take a 20" tire on a 16" (406mm) rim, but Brompton folders take a 16" tire on a 13.7" rim. Your donor/frame should indicate which.

EVGator said:

I am attempting to use Grin's spoke calculator to determine the spoke length that I will need, which can be found here: https://ebikes.ca/tools/spoke-calc.html. Does anyone have a better way to do this?

Click to expand...

Grin is best if it has your motor.

EVGator said:

I don't have all of the info to fill out the spoke calculator yet. ERD, Offsets, Cross pattern (0, 1, 2?), Nominal Diameter (20" 406 I think?) still need to be determined/measured. Then, should I invest in a spoke threading tool set and cut the longer spokes to the length that I need?

Click to expand...

ERD and offset are specs from the rim.
Cross pattern is a function of spoke count: to get closest to tangential, spoke count divided by 9 and rounded down. If 36: 36/9 = 4 cross is tangential.
No, you calculate the spoke length that you need and order that length.

This folder seems to have the 20" 406 wheel/tire combo. I took measurements and it was listed as such on the website.

So it is less popular to make your own spokes? I saw a video of a guy rolling the threads into the spokes using the correct tooling but honestly, I'd rather just buy the length that I need. Thanks for the info!

LewTwo · Apr 3, 2021

Just for a bit of perspective this is a large direct drive motor laced into a 20 inch wheel ... notice the cross pattern ?
https://www.ebay.com/itm/20-Mountain-Bike-Modified-Kit-48V-500W-Front-Wheel-E-bike-Conversion-Kit/193873734848

Of course one could avoid the spoke problem altogether (provided the axle fits):
https://www.ebay.com/itm/36-48V-20inch-1000W-Front-or-Rear-Ebike-Integral-Motor-Wheel-Motorized-ebike/233342882159

EVGator · Apr 3, 2021

The rim measures 16" exactly in diameter with a tape measure. 406mm is like 15.98", so it looks like a 16" rim, with a 20" tire.
The Grin calculator has a selection for 20" (406) for nominal diameter in the Rim settings section. I think this is right?

markz said:
Keyword in the title being CHEAP CHINESE folding bike, so the seller might not even have that info but its pretty basic info to know right. Like with generic hub motors, the sellers wont even know the Kv of the motor. The next problem is the communication barrier when you start to investigate and send off emails. On one hand they may just tell you anything to get a sale so be careful in how you write the email. Dont say, oh I have a 20" rim and what size of wheels does your bike use. No no, you dont give them any info on what you have, just ask them what size of wheels do they use if its not spec'd on their website.

fatty said:

Careful -- most folders take a 20" tire on a 16" (406mm) rim, but Brompton folders take a 16" tire on a 13.7" rim. Your donor/frame should indicate which.

Click to expand...

EVGator · Apr 3, 2021

Interesting. I think I ran across these before, but they weren't ever listed with more than 500W. No cross pattern, just radially laced. I don't know enough theory about lacing patterns, crossed vs. not but I suppose I should read up on it

LewTwo said:
Just for a bit of perspective this is a large direct drive motor laced into a 20 inch wheel ... notice the cross pattern ?
https://www.ebay.com/itm/20-Mountain-Bike-Modified-Kit-48V-500W-Front-Wheel-E-bike-Conversion-Kit/193873734848
20 inch wheel 01(400).jpg

Of course one could avoid the spoke problem altogether (provided the axle fits):
https://www.ebay.com/itm/36-48V-20inch-1000W-Front-or-Rear-Ebike-Integral-Motor-Wheel-Motorized-ebike/233342882159
20 inch wheel 02(400).jpg

EVGator · Apr 3, 2021

More photos of the hub motor fitting between the forks and into the dropouts. It definitely looks like it fits?

LewTwo · Apr 3, 2021

Measure the diameter of the axle. Then measure the width across the flats.
You need these dimensions to get the proper torque arms and yes use one set on each side of the fork.

EVGator said:
I don't know enough theory about lacing patterns, crossed vs. not but I suppose I should read up on it

Not my area of expertise either but I do know that one of the problems with short spokes is the "angle of the dangle". The spoke nipples are limited to what angle they should be laced.

fatty · Apr 3, 2021

LewTwo said:
Just for a bit of perspective this is a large direct drive motor laced into a 20 inch wheel ... notice the cross pattern ?

Radial spokes are loaded entirely in shear and provide no rotational strength. This is fine for front rim-brake wheels only, but not appropriate for driven nor hub-brake wheels.

fatty · Apr 3, 2021

LewTwo said:
Not my area of expertise either but I do know that one of the problems with short spokes is the "angle of the dangle". The spoke nipples are limited to what angle they should be laced.

Well, there are two limits:
1) Spokes cannot exit the hub beyond tangential -- the spoke count divided by 9 limit.
2) On small diameter spoke flange circles, exactly tangential spokes can overlap with the spoke head of the adjacent spoke. This is generally not a concern on hub motor flanges, which are obviously much larger diameter.

Tangential spokes are stronger because they are loaded entirely in tension, with no shear load.

LewTwo · Apr 3, 2021

fatty said:
Radial spokes are loaded entirely in shear and provide no rotational strength. This is fine for front rim-brake wheels only, but not appropriate for driven nor hub-brake wheels.

Personally I have no horse in this race (not even a lame mule). I do note that there are varying opinions on the matter as exemplified by this old thread: https://endless-sphere.com/forums/viewtopic.php?t=46618

markz · Apr 3, 2021

https://endless-sphere.com/forums/viewtopic.php?f=3&t=108540&p=1587985&hilit=radial+strength#p1587985

Cross pattern has almost no effect on a wheel's strength

https://ebikes.ca/tools/spoke-calc.html

Cross Pattern: Most hub motors are laced with a single cross pattern. There is no point at all in having 2 or more crosses with the large flange diameters of most hub motors, and doing so will usually result the spoke entering the rim at a very difficult angle. Small geared hubs can be laced into large diameter (>26") rims with a double cross pattern OK, and large direct drive motors in small (<=20") rims usually can only be laced radially with 0 cross. If you have a motor with paired spoke holes, then a 0 cross pattern still has a spoke angle for transmitting torque, and there is no need for even single crossing the spokes.

LewTwo said:
Personally I have no horse in this race (not even a lame mule). I do note that there are varying opinions on the matter as exemplified by this old thread: https://endless-sphere.com/forums/viewtopic.php?t=46618

fatty · Apr 3, 2021

LewTwo said:
I do note that there are varying opinions on the matter as exemplified by this old thread: https://endless-sphere.com/forums/viewtopic.php?t=46618

Yeah, I looked through it, and I just don't think anybody should buy the argument that because some Chinese hubmotor wheels are laced radially, that it's okay. There's plenty of nonsense coming out of China.
Yeah, if you use motorcycle spokes it'll last longer, but that doesn't make it acceptable design.

Just like radial-laced disc-brake wheels, I think it's okay to say "no, that opinion is incorrect" and not perpetuate inaccuracies. It equally obvious why radial-laced driven wheels are a fail, whether pedal-driven or motor-driven.

fatty · Apr 4, 2021

markz said:
Cross pattern has almost no effect on a wheel's strength

Click to expand...

No effect on lateral and radial strength, but huge effect on rotational strength. Drawing out the force components for radial vs tangential spokes shows this dramatically.

markz said:
Cross Pattern: Most hub motors are laced with a single cross pattern. There is no point at all in having 2 or more crosses with the large flange diameters of most hub motors, and doing so will usually result the spoke entering the rim at a very difficult angle. Small geared hubs can be laced into large diameter (>26") rims with a double cross pattern OK, and large direct drive motors in small (<=20") rims usually can only be laced radially with 0 cross. If you have a motor with paired spoke holes, then a 0 cross pattern still has a spoke angle for transmitting torque, and there is no need for even single crossing the spokes.

Click to expand...

Good point -- don't exceed the rotation allowed by the spoke nipple. I switched to internal nipples with spherical contact surface, so I don't have this problem.

But I would clarify that 0-cross does not equal radial, which does not have spoke angle for transmitting torque.

amberwolf · Apr 4, 2021

fatty said:
No effect on lateral and radial strength, but huge effect on rotational strength. Drawing out the force components for radial vs tangential spokes shows this dramatically.

Despite this, practically it often makes no operational difference.

I'm still running short radial spokes on my 20" rear wheels with large diameter DD hubmotors on SB Cruiser, with no problems due to the radial lacing. I've destroyed rims on potholes, but not spokes and they stay tight, using 13/14g single-butted, and good eyeletted doublewall rims. This is a very heavy trike, that can weigh half a ton with a cargo load plus me (more with a trailer load of stuff, like a piano, etc), with around 4kw of power between the two rear wheels, and I am not gentle on the startup power from stops.

I've broken plenty of spokes on wheels (of various sizes) where the nipple / spoke angle was so great that it forced the spoke to bend right out of the nipple, or where the nipple itself couldn't seat fully inside the rim and had all it's load on one side of the lip, causing it to eventually shear off at that lip.

So...build the wheel well, and even radial lacing will work, and it will probably work better than any cross lacing that bends the spoke at the nipple, or forces the nipple to be angled so far that it isn't fully seated all around it's base inside the rim.

Ideal? No, but a better compromise than the others.

LewTwo · Apr 4, 2021

amberwolf said:
...
I've broken plenty of spokes on wheels (of various sizes) where the nipple / spoke angle was so great that it forced the spoke to bend right out of the nipple ...

That was what I was referring to with my comment about the 'Angle of the dangle'. I have looked for a picture showing a spoke bent in such a manner but could only find one. Unfortunately it is in a copyrighted E-book, so I can not insert it here. On page 78 of Roger Munson's book "Professional Guide to Wheel Building, 6th edition" he has such a picture. He cautions the reader "As the number of crosses increases the spoke entry angle becomes more acute and the nipple may not swivel enough to match the natural spoke line." The picture used to illustrate this condition has a spoke bent where the spoke enters the nipple. The nipple is brass and the rim has eyelets.

I note that on the next page he also comments on "Radial wheels". He shares the conventional wisdom that radial lacing should not be used in the case where the hub needs to transmit torque (i.e. disk brakes or motors).

Alas some of this is theoretical and sometimes the real world application defy the validity of the theory. Man's knowledge is not absolute. I am reminded that years ago people would say "in theory a helicopter can not fly" as they watched them take off and land.

2old · Apr 4, 2021

Don't know if this was mentioned, but bicycle wheels are defined by the outside diameter of the wheel plus tire, while motorcycle by the diameter of the rim. The first thing I would do is purchase a 20" rim with 36 holes. This will make your task much easier. The wheel, even radially laced, which seems the only option, should be strong enough. Too bad Chalo didn't respond; he would be a great help here. I put a 1000w, 48V (operated at 52V) motor on a cruiser, which had only a coaster brake, and survived.

fatty · Apr 4, 2021

amberwolf said:
Despite this, practically it often makes no operational difference.

Well, it depends. My background is racing, and I build with either Sapim Super CX Rays for J-bend, or DT Swiss Aerolite for straight-pull, so in my application it makes a huge difference. And in general terms of understanding physics/design (which I think matters more than practical implementation), it definitely matters...

amberwolf said:
So...build the wheel well, and even radial lacing will work, and it will probably work better than any cross lacing that bends the spoke at the nipple, or forces the nipple to be angled so far that it isn't fully seated all around it's base inside the rim.

Ideal? No, but a better compromise than the others.

...but yeah, you can get by with radial lacing if you use 12g motorcycle spokes. It's not correct design though, and choosing spoke gauge like that is sort of self-limiting, since spokes that thick can't be crossed or bent. Some bend at the nipple is okay -- indeed, normal spokes are bent at the hub flange.

Sorry if I confused this thread with theory but not practical advice. I'd still suggest spoke count divided by 9 (rounded down) to get max cross. But then use a spoke calculator and work down from max cross to find bracing angle under 9deg if using standard external rounded (Polyax-style) nipples, or use internal spherical nipples.

markz · Apr 4, 2021

https://sheldonbrown.com/gloss_ra-e.html

Radial spoking
The oldest and simplest of spoke patterns. The spokes run straight outward from the hub to the rim. This is called "direct" or "radial" spoking. This pattern is not well suited for transmitting the torque of pedaling, or of a hub brake, but is suitable for front wheels.

Traditional cycling folklore holds that radial-spoked wheels give a "harsh" ride, due to the slightly shorter spokes they use. Jobst Brandt demolishes this fallacy nicely:

"...'radial spoking also gives you a very stiff wheel. You can actually feel increased bumpiness compared to a three- or four-cross wheel.'

"I think you are imagining all this. There is no change in radial elasticity between a radial and crossed spoke wheel with the same components, other than the length of the spokes. A 290 mm spoke is 3% stiffer than a 300 mm spoke of the same type. Since spokes stretch elastically about 0.1mm on a hard bump (not ordinary road ripples), the elastic difference between the radial and cross-three wheel is 3% x 0.1mm = 0.003 mm. Copier paper is 0.075 mm thick, and if you can feel that when you ride over it on a glassy smooth concrete surface, please let me know. You have greater sensitivity than the lady in "the princess and the pea" fable.

"If your story weren't so common, I would assume it to be a put-on, but it isn't. I find it amazing how humans love to believe unbelievable things, the more unbelievable the stronger the belief. It isn't new."

I would add that the deflection of the tire, the flex of the fork, stem and handlebars are each an order of magnitude greater than this theoretical deflection difference in the spokes. The difference in elasticity between spokes of different thicknesses is also much greater than the difference between spokes which differ in length by 3 %, but you don't hear the same complaints about wheels built with spokes of different thicknesses.

EVGator · Apr 5, 2021

Thank you guys for all of the input! I have been reading back through old forum posts and just trying to learn as much as I can. You all shared some good knowledge.

I am leaning toward a non-radial configuration and a spoke angle of somewhere between 50 and 70 degrees. I don't have solid math or free-body diagrams to back anything up, just flying by the seat of my pants for this initially. According to the calculators, there are a few different cross configurations I could go with. My hands are kind of tied until I can take an accurate ERD measurement for the new 36 hole wheel that I ordered. I decided to go 36 to match the hub motor instead of 28, so that I can connect every spoke 1:1 for more support. Once I have the measurements, I will a use a couple of different calculators to estimate the spoke length and order it. I considered purchasing the Hozan spoke cutting and thread rolling tools, but I don't know if I'll actually use it enough to justify the purchase. It would be nice to have though..

Going to just build it and either fail fast and re-adjust, or get lucky enough to have the wheel stay intact first try.

amberwolf · Apr 6, 2021

fatty said:
...but yeah, you can get by with radial lacing if you use 12g motorcycle spokes. It's not correct design though, and choosing spoke gauge like that is sort of self-limiting, since spokes that thick can't be crossed or bent. Some bend at the nipple is okay -- indeed, normal spokes are bent at the hub flange.

The bend at the flange (at the elbow, or when bending "over" the edge of a flange on an elbow-out/head-in spoke) is a very different thing than bending it at the threads at the nipple exit, where it is a stress riser area.

In my wheels, they are not using "12g motorcycle spokes". Using that thick of a spoke (which is what comes from just about all of the hubmotor wheel manufacturers; all the "kits" and such) has always resulted in broken rims on my wheels, because the bicycle rims are not strong enough to handle the tension required for that thick of a spoke.

But the Sapim 13/14 single-butted spokes I'm using successfully are 13g at the elbow (to help fit the overly large spoke holes in the hubmotor flanges without having to use washers or drill new holes in the flange ***) and 14g from around a half inch or so from the elbow to the end including the threads.

***which is what I ended up doing on the MXUS 450x motors anyway, so I could've used 14/15 instead...

fatty · Apr 6, 2021

amberwolf said:
But the Sapim 13/14 single-butted spokes I'm using successfully are 13g at the elbow (to help fit the overly large spoke holes in the hubmotor flanges without having to use washers or drill new holes in the flange ***) and 14g from around a half inch or so from the elbow to the end including the threads.

***which is what I ended up doing on the MXUS 450x motors anyway, so I could've used 14/15 instead...

I do like this approach. My first build used DT Swiss Alpine IIIs for the same reason, but I've since become a weight/aero weenie..

1kW Front Hub Motor on Cheap Chinese Folding Bike

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