Recommendations for a 72V DD Hub motor in 20" wheel for 45mph (72km/h)

[Residents evil]

TLDR: Read Bold parts

After months of research, I'm fairly confident in terms of batteries and controllers and what I wish for my next build.
Motors, however, are hard to figure out for me, research led me almost nowhere.
In my place in Europe I'm restricted to 25km/h, so that makes buying a motor easy.
In the wild west of Mississippi, all bets are off, so I'm looking to get a DD motor that can ride up to 45mph (72km/h), to make my excruciatingly long stretch of commute a bit faster without going overboard.

Please recommend me what sort of motor I should pick up for a 20" fat tire (20x4) to hit those sorts of speeds.
Minimum over 31mph (50km/h), max 55mph (88km/h).
I know I can limit max speed, but I want to keep it within the most efficient band of rpms which is usually near top speed.

I don't have battery nor controller limitations, I'm making a full build. My motor needs will dictate the rest, but according to my frame limitations, I'm thinking, of a 72V 20S4P battery pack x2 (40Ah), can go up to 200A discharge rate with Molicel P50B cells. VESC Controller (Pronto 150A or Maxim >200A), regen optional but desired. Will use ferrofluid for cooling the motor. Aluminum frame, rear mount 175mm width dropout, can probably apply 2 torque arms if needed. Yes, I will also want to ring out the torque to at least 80Nm (What I have in my current setup) but higher is always nice. Spokes rim/motor preferred. Can buy from anywhere in the world, preference in Europe or USA to avoid import costs. Price is not an issue, I want the best/most long lasting solution.

 

[E-HP]

TLDR: Read Bold parts

After months of research, I'm fairly confident in terms of batteries and controllers and what I wish for my next build.
Motors, however, are hard to figure out for me, research led me almost nowhere.
In my place in Europe I'm restricted to 25km/h, so that makes buying a motor easy.
In the wild west of Mississippi, all bets are off, so I'm looking to get a DD motor that can ride up to 45mph (72km/h), to make my excruciatingly long stretch of commute a bit faster without going overboard.

Please recommend me what sort of motor I should pick up for a 20" fat tire (20x4) to hit those sorts of speeds.
Minimum over 31mph (50km/h), max 55mph (88km/h).
I know I can limit max speed, but I want to keep it within the most efficient band of rpms which is usually near top speed.

I don't have battery nor controller limitations, I'm making a full build. My motor needs will dictate the rest, but according to my frame limitations, I'm thinking, of a 72V 20S4P battery pack x2 (40Ah), can go up to 200A discharge rate with Molicel P50B cells. VESC Controller (Pronto 150A or Maxim >200A), regen optional but desired. Will use ferrofluid for cooling the motor. Aluminum frame, rear mount 175mm width dropout, can probably apply 2 torque arms if needed. Yes, I will also want to ring out the torque to at least 80Nm (What I have in my current setup) but higher is always nice. Spokes rim/motor preferred. Can buy from anywhere in the world, preference in Europe or USA to avoid import costs. Price is not an issue, I want the best/most long lasting solution.

Direct drive hubs with 175mm dropouts limits the available choices a bit. A QS273 would be pretty bulletproof.

 

[Residents evil]

Direct drive hubs with 175mm dropouts limits the available choices a bit. A QS273 would be pretty bulletproof.

I've seen that motor suggested multiple times in my research, but I've given up on it because, as far as I can see in QS Motor's website, all options require 200mm dropouts. Did I see it wrong?
Not only that, all rim sizes are not for 20". Don't think I would be able to run a 19", and bigger is physically impossible in my frame.

 

[E-HP]

I've seen that motor suggested multiple times in my research, but I've given up on it because, as far as I can see in QS Motor's website, all options require 200mm dropouts. Did I see it wrong?
Not only that, all rim sizes are not for 20". Don't think I would be able to run a 19", and bigger is physically impossible in my frame.

I was assuming you’d lace the new motor to the existing rim. Get the 3T winding. You’ll need to do radial lacing with a big hub in a small rim anyway.

 

[Risky Rob]

Why do you choose a 20" fat tire bike when you want to go fast on the street?

 

[Residents evil]

I was assuming you’d lace the new motor to the existing rim. Get the 3T winding. You’ll need to do radial lacing with a big hub in a small rim anyway.

I think I haven't properly grasped the process of picking and assembling a motor.
When the motors mention 200mm dropouts, it means I need 200mm width between my dropouts for the motor to fit, right?
I just re-took measurements and my dropout is definitely 175mm width. Current rim is near 16" (42cm), the tire (inflated, edge to edge) is almost 23" (58cm), which is super confusing to me because I'm 200% certain I'm running 20x4" tires... so, what do they refer to when saying 20"? I thought this was the rim size without tire. I'm missing fundamentals that I cant figure it out after months of searching and reading (Hence the thread).

I assumed my frame limitations by what the tire said, and sorry for making you have to assume anything. I'll probably get the motor and rim, instead of repurposing the current rim.

PS: Measurements are not exact, +/- 1cm. Didn't have tools with me to remove it from the frame to check with precision.

 

[Residents evil]

Why do you choose a 20" fat tire bike when you want to go fast on the street?

It's definitely a dumb and impractical decision, makes my options much slimmer. It's just the fact that I love the frame I have and couldn't find anything similar that could take bigger rims. Saw and bought a cheap used chinese frame for cheap online, but I would never trust the thinness of that chinese frame for the speeds I'm aiming for. I'll make a city slow cruiser out of that chinese one

 

[E-HP]

It's definitely a dumb and impractical decision, makes my options much slimmer. It's just the fact that I love the frame I have and couldn't find anything similar that could take bigger rims. Saw and bought a cheap used chinese frame for cheap online, but I would never trust the thinness of that chinese frame for the speeds I'm aiming for. I'll make a city slow cruiser out of that chinese one

If you like the bike, ride it as is and build a bike with larger wheels if you want to ride faster.

 

[Risky Rob]

It's definitely a dumb and impractical decision, makes my options much slimmer. It's just the fact that I love the frame I have and couldn't find anything similar that could take bigger rims. Saw and bought a cheap used chinese frame for cheap online, but I would never trust the thinness of that chinese frame for the speeds I'm aiming for. I'll make a city slow cruiser out of that chinese one

I have a 26" hardtail with a 1500W rear hub motor, and conventional tires. It goes plenty fast, but not 45mph.

 

[MxusMick]

If you are gonna go 45mph, you better have a tubeless tire or a moped rim with moped tire. I have 2 ebikes with 20" rear hub motors, and they are a hoot, the front tires are 26", and the handling is like Tron bro. You got the right idea, but 72v is probably 50 lbs, keep things realistic.

 

[neptronix]

You probably want a 9C type motor ( that describes most less expensive direct drive hub motors for bike wheels ) with 35mm wide stator.
Leafbike will sell you one with various axle lengths, you just need a regular QC dropout and a pair of very good torque arms.
I'd consider getting a 5T 1500w rated one which should result in 42.5mph on a 22 inch effective wheel on 72v.
It will weigh 16lbs and it's the lightest motor you can get away with.

Here's some consideration though, you're in Europe and they enforce max speed limits on ebikes out there quite heavily.
I'd be very nervous about owning such a fast ebike out there. Especially if it has fat wheels or otherwise looks like an ebike.

I think if you build a very fast ebike then you should use it's full capabilities as infrequently as possible and it should not look like a regular bike as much as possible.

This bike did 45mph on 48v and 59.9mph on 72v using a leafbike 1500w ( 35mm ) motor and some very strong batteries. No problem for me. I could pedal up to the max speed and aalways pedal. But nobody enforces ebike law out here in the suburbs of the USA. I'd definitely get in trouble in the city!

 

[99t4]

I would never trust the thinness of that chinese frame for the speeds I'm aiming for.

"Frame thickness" does not always correlate to frame strength.

 

[Risky Rob]

You probably want a 9C type motor ( that describes most less expensive direct drive hub motors for bike wheels ) with 35mm wide stator.
Leafbike will sell you one with various axle lengths, you just need a regular QC dropout and a pair of very good torque arms.
I'd consider getting a 5T 1500w rated one which should result in 42.5mph on a 22 inch effective wheel on 72v.
It will weigh 16lbs and it's the lightest motor you can get away with.

Here's some consideration though, you're in Europe and they enforce max speed limits on ebikes out there quite heavily.
I'd be very nervous about owning such a fast ebike out there. Especially if it has fat wheels or otherwise looks like an ebike.

I think if you build a very fast ebike then you should use it's full capabilities as infrequently as possible and it should not look like a regular bike as much as possible.

This bike did 45mph on 48v and 59.9mph on 72v using a leafbike 1500w ( 35mm ) motor and some very strong batteries. No problem for me. I could pedal up to the max speed and aalways pedal. But nobody enforces ebike law out here in the suburbs of the USA. I'd definitely get in trouble in the city!

View attachment 383485

Did you have any issues with the controller exposed, and mounted so low?

 

[neptronix]

Did you have any issues with the controller exposed, and mounted so low?

Nope. It was outside the bag because the bag was full of battery and that controller needed air cooling at 80A.
Controllers have become much more compact since then!

 

[ZeroEm]

Can not compare bike tires to motorcycle tires. If someone who knows off hand can chime in. If not will look up the old thread discussion.

Note: 19" motorcycle wheel is more like a 26" bicycle wheel.

 

[Residents evil]

If you are gonna go 45mph, you better have a tubeless tire or a moped rim with moped tire. I have 2 ebikes with 20" rear hub motors, and they are a hoot, the front tires are 26", and the handling is like Tron bro. You got the right idea, but 72v is probably 50 lbs, keep things realistic.

I do realize my request is nearing limits of what's possible with current tech and my specific rim size request. It's sort of a aim for the sky, settle on reality kinda deal. Anything above my current 28mph (45km/h) would be an upgrade.
That's also the reason I'm getting another rim, wouldn't trust the factory rim for such speeds, and need something sturdy to mount a proper tire.

 

[Residents evil]

You probably want a 9C type motor ( that describes most less expensive direct drive hub motors for bike wheels ) with 35mm wide stator.
Leafbike will sell you one with various axle lengths, you just need a regular QC dropout and a pair of very good torque arms.
I'd consider getting a 5T 1500w rated one which should result in 42.5mph on a 22 inch effective wheel on 72v.
It will weigh 16lbs and it's the lightest motor you can get away with.

Here's some consideration though, you're in Europe and they enforce max speed limits on ebikes out there quite heavily.
I'd be very nervous about owning such a fast ebike out there. Especially if it has fat wheels or otherwise looks like an ebike.

I think if you build a very fast ebike then you should use it's full capabilities as infrequently as possible and it should not look like a regular bike as much as possible.

This bike did 45mph on 48v and 59.9mph on 72v using a leafbike 1500w ( 35mm ) motor and some very strong batteries. No problem for me. I could pedal up to the max speed and aalways pedal. But nobody enforces ebike law out here in the suburbs of the USA. I'd definitely get in trouble in the city!

View attachment 383485

I know from ebikes.ca that wattage rating is just a ballpark for motor survival (A "made up" number, if you will), but I was expecting that I'd need a lot more rated wattage to obtain such speed in a small wheel. For comparison's sake, the QS273s that I've seen recommended many times elsewhere go up to 8000W, hence why I was even worried about building bus bars into my battery to withstand >150A, due to peaks. Even if I 4x the rated wattage of a 9C, it's only 83 Amps.

Also because, when I simulated the top speeds in ebikes.ca a while back with my planned build, I was only getting around 35 mph (I probably messed up somewhere, and that thing is still quite hard for me to grasp, I was never good with numbers).

In Europe is wild, everyone's running fat bikes doing 28mph (45km/h) daily, through the city centers. My commute there is in the outskirts with long stretches and no intersections, and I ride a legal, 15.5mph (25km/h) bike. Had another which I did ride at 45km/h like everyone else, and I didn't like feeling "in danger" on the daily. Thankfully the issue solved itself (It broke down, like all my vehicles do lol)

 

[Residents evil]

"Frame thickness" does not always correlate to frame strength.

The Super73's look beefy compared to that frame I'm mentioning, yet they're known for breaking near the headset and downtube.
Mine might look thin but actually be very solid... but I'll go with my gut and relegate it to a cruiser, it's that frame's style anyway

 

[Residents evil]

Can not compare bike tires to motorcycle tires. If someone who knows off hand can chime in. If not will look up the old thread discussion.

Note: 19" motorcycle wheel is more like a 26" bicycle wheel.

Oh, right... On my research for proper tires (much much longer ago) I do remember being confused as to why I couldn't just pick a 20" motorcycle tire.

Just went to check my notes and had this tire as an option: Shinko SR567, which doesn't have 20" measurement.
Found this in my notes too:
3.00-3.5x16 and 110-80x16 (Motorcycle tires) = 20x4 Bicycle tires
Though at the time, I didn't look much deeper than that, so do not take this information as the truth

PS: Sorry for the spam folks. I tried to do multiple-quote on a single comment but couldn't figure it out.

 

[MxusMick]

If I was starting from scratch and money was no issue I would have a tubeless tire for my rear 20" hub motor, to cancel out the possibility of a flat . My front 26" wheel would have an insert to prevent a full blowout. I have never gone 40 mph on my ebike, but consider the idea borderline stupid without a full face helmet, gloves, jacket, pants. I have a Honda CRF 450 that shakes at 65mph, a bicycle could shake itself apart. I had a fork tube snap once years ago on a MTB, maybe I'm paranoid?

 

[neptronix]

I know from ebikes.ca that wattage rating is just a ballpark for motor survival (A "made up" number, if you will), but I was expecting that I'd need a lot more rated wattage to obtain such speed in a small wheel. For comparison's sake, the QS273s that I've seen recommended many times elsewhere go up to 8000W, hence why I was even worried about building bus bars into my battery to withstand >150A, due to peaks. Even if I 4x the rated wattage of a 9C, it's only 83 Amps.

On my 26" leafbike 1.5kw wheel, 45mph cruising speed took about 2500w and it could do it for ~5 minutes at a time before getting too hot.
Once i added cooling, it could do that for 30 minutes.

On a 22" wheel, you'll have a bit more continuous wattage and it may take 10 minutes to overheat. Add cooling mods and you'll have a better time than i did on a 26".

Yeah this is the minimum of motor you need for mildly hilly terrain; the next step up would be a MXUS 3kw rated hub which is 18lbs vs the leaf's 16lbs.

If you keep to 35mph peak, lower continuous, then you could use a smaller ~10lbs hub motor.

 

[Residents evil]

If I was starting from scratch and money was no issue I would have a tubeless tire for my rear 20" hub motor, to cancel out the possibility of a flat . My front 26" wheel would have an insert to prevent a full blowout. I have never gone 40 mph on my ebike, but consider the idea borderline stupid without a full face helmet, gloves, jacket, pants. I have a Honda CRF 450 that shakes at 65mph, a bicycle could shake itself apart. I had a fork tube snap once years ago on a MTB, maybe I'm paranoid?

I did ride my 28 mph (45km/h) bike with almost full gear: ECE 22.06 full helmet, boots, gloves. I'm lacking the pants and jacket, that will come when I get this project done. Haven't got them yet since all my fast vehicles died for this or that reason. People have mocked my attire to ride a bicycle, but I prefer that than what I've seen some acquaintances suffer from falls. Road rashes are gnarly in your face.

On that bike, I am running Taunus armor, a foam insert that has proven it's worth. About 6200 miles (9800 km) in that bike and no flats, whereas the other ones... But anyway, I'm thinking proper motorcycle tire for this build, for a variety of reasons.

I know this is me deluding myself, but my commute has zero bumps in the road, so my fork doesn't suffer from stress. Surely it wont break... surely.... Given my luck with vehicles, I'll add to my shopping list a reputable fork for this bike.

 

[Residents evil]

On my 26" leafbike 1.5kw wheel, 45mph cruising speed took about 2500w and it could do it for ~5 minutes at a time before getting too hot.
Once i added cooling, it could do that for 30 minutes.

On a 22" wheel, you'll have a bit more continuous wattage and it may take 10 minutes to overheat. Add cooling mods and you'll have a better time than i did on a 26".

Yeah this is the minimum of motor you need for mildly hilly terrain; the next step up would be a MXUS 3kw rated hub which is 18lbs vs the leaf's 16lbs.

If you keep to 35mph peak, lower continuous, then you could use a smaller ~10lbs hub motor.

Ferrofluid is my go-to cooling mod, think I'll skip the dissipation fins and just go easy on the motor instead. One of the reasons to have a higher top speed is to also be able to reduce a bit from full throttle and ride below top speed to thus ease the load and heat buildup in the motor. 35mph would already be an upgrade from my regular 28mph, I was just dreaming of doing 40mph continuous regardless of battery level (Assuming 5mph is lost for low charge in the battery), hence the 45 mph target.

I'm also conscious in motor usage and always coast it at every opportunity of potential hazard, red light or descent.
I'm also expecting to be reminded of limits by programming the VESC to cut me off when the motor isn't happy about temperatures. I've toasted cheap geared hubs before due to lack of such temperature readouts, don't want to do it again with this build.

Don't think the 2lbs will be a deal breaker, I'll lose weight instead haha (Yes I know, rotational mass makes a lot of difference for battery life and whatnot). Will take a look at all those motors properly hopefully this weekend and try to decide. Thanks for the suggestions : )

 

[E-HP]

If I was starting from scratch and money was no issue I would have a tubeless tire for my rear 20" hub motor, to cancel out the possibility of a flat . My front 26" wheel would have an insert to prevent a full blowout. I have never gone 40 mph on my ebike, but consider the idea borderline stupid without a full face helmet, gloves, jacket, pants. I have a Honda CRF 450 that shakes at 65mph, a bicycle could shake itself apart. I had a fork tube snap once years ago on a MTB, maybe I'm paranoid?

The more time you spend going fast, the closer you are to crashing when riding above bicycle speeds. I've never seen the top speed of my ebike because of that, since I'm not going to wear a full face helmet on a bicycle. That would really attract the cops. I attempted to a full speed run once, but shut it down at 53mph when my brain cell kicked in to tell me to stop being stupid.
I've had two motorcycle crashes above 70mph, but I had the right equipment on and a lot of luck, and I'm pretty sure the survival rate on a bicycle going 50 with a bicycle helmet is a lot lower than 70 with full gear on, even with a lot of luck.

 

[Alex12345]

TLDR: Read Bold parts

After months of research, I'm fairly confident in terms of batteries and controllers and what I wish for my next build.
Motors, however, are hard to figure out for me, research led me almost nowhere.
In my place in Europe I'm restricted to 25km/h, so that makes buying a motor easy.
In the wild west of Mississippi, all bets are off, so I'm looking to get a DD motor that can ride up to 45mph (72km/h), to make my excruciatingly long stretch of commute a bit faster without going overboard.

Please recommend me what sort of motor I should pick up for a 20" fat tire (20x4) to hit those sorts of speeds.
Minimum over 31mph (50km/h), max 55mph (88km/h).
I know I can limit max speed, but I want to keep it within the most efficient band of rpms which is usually near top speed.

I don't have battery nor controller limitations, I'm making a full build. My motor needs will dictate the rest, but according to my frame limitations, I'm thinking, of a 72V 20S4P battery pack x2 (40Ah), can go up to 200A discharge rate with Molicel P50B cells. VESC Controller (Pronto 150A or Maxim >200A), regen optional but desired. Will use ferrofluid for cooling the motor. Aluminum frame, rear mount 175mm width dropout, can probably apply 2 torque arms if needed. Yes, I will also want to ring out the torque to at least 80Nm (What I have in my current setup) but higher is always nice. Spokes rim/motor preferred. Can buy from anywhere in the world, preference in Europe or USA to avoid import costs. Price is not an issue, I want the best/most long lasting solution.

I can recommend QS159.8, it's a relatively small direct drive hub, designed for 175mm and capable of 72V, with a posted max torque of 90Nm. It's about 11.5 rpm/v give or take, I'm actually running it in an underpowered setup with 48v battery and very limited current, nevertheless during my build before setting up a speed limit I was able to get a loaded speed of 30mph. So I presume it will def beat your minimum speed req with a 72v pack. It has a fairly good description and tech drawings on QS websites. I am running it with some spacers in a 190mm dropout, but based on the drawings you should be able to fit it in 175. Overall it's comparable to grins all axle fat in weight, but is wider and smaller diameter, which makes lacing easier in a smaller wheel.