Pedaling at high speeds - Hub motors compatible with wide range casettes

[TroySmith80]

I'd like to build myself something of a moped. Think of a sturdy cargo bike, or upgraded version of something like a Super 73 style. I want to be able to go about 40mph or so. I like to pedal and i'd like to use a torque-sensing bottom bracket and cycle analyst to implement pedal assist that (using different PAS levels) allows me to operate at normal bicycle speeds and up to 40 mph or so with similar effort levels.
Normally once you hit 15-20 mph I can't keep up with pedaling anymore and i just have to motor along. I don't like that, i still want to pedal, and with some resistance (not just ghost pedaling). So i'm thinking that if i can get one of the modern mountain bike cassettes, with a 10-52 tooth range, that 500% drivetrain range can allow me to use PAS all the way up to 40mph.

Two questions...
1. Does the above all make sense and seem like a reasonable goal to pursue?
2. Are there any hub motors powerful enough to do this, and that will accept a modern wide-range mt bike cassette (preferably SRAM XD)?

I'm aware of the Grin All-Motor and that's probably what i should do, it's spendy though and i'm just kind of experimenting at this stage. Is there a QS Motor or sometthing like that available for half the cost that would get me going?

 

[hillslayer@]

Tire size factors in, a 60 t chainring will pedal to 40 mph with 29er tires and 11 t cog .

 

[99t4]

What is your preferred cruising pedal RPM?

Small cogs (you mentioned 10t?) are problematical, prone to short longevity, chain skipping, etc.

 

[TroySmith80]

Good points/questions. I think I want to stick with 24 or 26-in tires. Or maybe 18 or 19 inch motorcycle or scooter tires. But remember I still want to be able to Pedal comfortably at 10 mph also. So regardless of tire size I need a pretty wide range of Gears available for pedaling.

Not quite sure what RPM I like to Pedal, a casual but engaged pace.

Small Cog should be fine because I'm not running motor power through it

 

[bananu7]

I don't think hub motors with support for more than 9-speed casettes are very common or affordable. They have enough problems already in fitting into typical bike dropouts.

In practice, I would say that as long as you get an appropriately big front sprocket, you'll be able to pedal at the necessary speeds, as during starting or climbs the motor power will fill the torque gap anyway.

Also, have you considered a 2x9?

 

[lnanek]

I use a 75t front cog so I can still assist by pedaling at 30mph:

https://a.co/d/aACUeRA

I also once installed an efneo front gearbox:

Gearbox

www.efneo.com

The problem with low teeth rear gears is that you have to progressively upgrade your wheel to support smaller and smaller ones. Freewheels and Hyperglide freehubs typically only go down to 11 teeth and you have to upgrade to XD or microspline for 10 teeth. I think I only saw an XD freehub motor listed once ever. I think e*thirteen might have a couple odd cassettes or freehub adapters too that might mix things up.

If I had to try something next it would probably be one of these single speed 9 tooth freewheels:

9 Speed Cassette Sprocket Flywheel Bicycle 9T Mountain Bike Freewheel Cog | eBay

Performance car 9-tooth flywheel 9T bearing hub bicycle flywheel. Bicycle flywheel 1.

www.ebay.com

That gives up all the higher tooth gears, but I typically stay on high gear and use wide open throttle to accelerate after a stop light anyway to get back up to speed, so it's only a brief period where I'm going slow enough those would make sense anyway.

 

[hillslayer@]

I use a 75t front cog so I can still assist by pedaling at 30mph:
https://a.co/d/aACUeRA

You must have had small tires, I can do 30 mph 60 t to 17 t on the 14 t I can get 35 mph . 29 tires and 152 mm cranks .

 

[Chalo]

So i'm thinking that if i can get one of the modern mountain bike cassettes, with a 10-52 tooth range, that 500% drivetrain range can allow me to use PAS all the way up to 40mph.

Once you're going much over 30 mph, you won't make enough power at the pedals to offset the increased drag you make by stirring your legs in the airflow. So pedaling at 40 mph will cost you range.

10T small end is a SRAM standard that I haven't seen on any hub motors. Likewise Shimano Microspline. It will be easy enough to find an 8, 9, or 10 speed Shimano Hyperglide standard cassette with 11t high gear and 48t to 51t low gear.

 

[TroySmith80]

Once you're going much over 30 mph, you won't make enough power at the pedals to offset the increased drag you make by stirring your legs in the airflow. So pedaling at 40 mph will cost you range.

10T small end is a SRAM standard that I haven't seen on any hub motors. Likewise Shimano Microspline. It will be easy enough to find an 8, 9, or 10 speed Shimano Hyperglide standard cassette with 11t high gear and 48t to 51t low gear.

I would prefer not to have a 2x or 3x setup with multiple front rings.

Not worried about aero, just want the experience of pedaling.

9 spd with 11-48 would probably be good enough. Which motors will accept that? Anything that can reliably get me the speeds i'm after?


The other thing i'd thought of was having my pedals just run a tiny generator or clutch pack or some other form of resistance, that could be metered and fed to the cycle analyst for throttle input. So I wouldn't even be driving the wheels at all. That is a more complicated project though, and probably would not have a satisfying feeling.

 

[E-HP]

9 spd with 11-48 would probably be good enough. Which motors will accept that? Anything that can reliably get me the speeds i'm after?

Unless you’re pedaling without assist, those lower gears are useless on a hub motor since you need to maintain reasonable speeds to avoid overheating. You’ll probably only use 3 or 4 cogs total, and mostly higher gears. With a 40mph bike, you may only use one or two gears 90% of the time. I pedal, but I only shift a couple times a year.

 

[Mclewis1]

...

10T small end is a SRAM standard that I haven't seen on any hub motors. Likewise Shimano Microspline. It will be easy enough to find an 8, 9, or 10 speed Shimano Hyperglide standard cassette with 11t high gear and 48t to 51t low gear.

Grin's All Axle hub motor has an XD spline option (on the more more expensive torque sensor model) that according to the specs will accommodate a native 12spd SRAM cassette with a 10t low gear.

And you can almost get there (SRAM 12spd) on some other hub motors ...

Sunrace sells 12 speed SRAM compatible cassettes that are also HG spline compatible (and MTB 11spd width so should fit many newer hub motors) ... BUT they don't go down to 10t ... only 11t. Oh so close

 

[Chalo]

9 spd with 11-48 would probably be good enough. Which motors will accept that?

Any cassette freehub model motor would do it. Those aren't usually very powerful, and they always have a skinnier weaker axle end on the right side compared to a threaded freewheel version. I don't know of one that can do 40 mph with a full sized adult on board.

 

[classicalgas]

I would prefer not to have a 2x or 3x setup with multiple front rings.

Not worried about aero, just want the experience of pedaling.

9 spd with 11-48 would probably be good enough. Which motors will accept that? Anything that can reliably get me the speeds i'm after?


The other thing i'd thought of was having my pedals just run a tiny generator or clutch pack or some other form of resistance, that could be metered and fed to the cycle analyst for throttle input. So I wouldn't even be driving the wheels at all. That is a more complicated project though, and probably would not have a satisfying feeling.

Driving a generator with the pedals (no pedal to wheel mechanical connection) involves more losses than a chain that's in decent shape. For a trike, that *might* make sense ( since trikes have long chains, with multiple idlers and/or guide tubes adding friction ) but the problem is that most ebike laws require a mechanical pedal to wheel connection to be legal, so you'd have to register it as a motorcycle to be strictly legal. If you're going 40 mph on a regular basis, that would probably be a good idea anyway.

 

[TroySmith80]

Any cassette freehub model motor would do it. Those aren't usually very powerful, and they always have a skinnier weaker axle end on the right side compared to a threaded freewheel version. I don't know of one that can do 40 mph with a full sized adult on board.

so, back to square one (or question 2) Are there any hub motors powerful enough to do this, and that will accept a modern wide-range mt bike cassette (preferably SRAM XD)? OR a wide-ratio freewheel, 11-5X

 

[neptronix]

I exclusively use cassette gears instead of freewheels so i can consistently get a 11T lower gear.
A 52T with an 11t gear in the cassette is enough to pedal up to 31mph on a 24" wheel.

With a DD, you'll find that a fairly narrow range cassette will work just fine.

On a leafbike 1.5kw, i used to pedal up to 40mph with a 11t lower gear mated to a 62T chainring on a 26" wheel. What you're looking for, gearing wise, is not impossible and doesn't require exotic parts.

 

[TroySmith80]

I exclusively use cassette gears instead of freewheels so i can consistently get a 11T lower gear.
A 52T with an 11t gear in the cassette is enough to pedal up to 31mph on a 24" wheel.

What motor will accept one and is powerful enough to get to 40mph?

 

[neptronix]

Grin's RH212 would be an ideal choice for up to 35mph duty. more torquey than the leafbike 1.5kw and 2lbs lighter.
Leafbike 1.5kw if you want 40mph or beyond.
In either case you'll want two very good torque arms for that kind of power.

Both can take cassette gears.

 

[TroySmith80]

Leafbike might be a good choice thanks! I was looking at that but didn't see that it is available with a freewheel.
Also wasn't looking at the RH212. More torque and less-high speed IS what i'm after, so that might be a better choice.

Thanks for the specific tips!

are there any geared hub motors that will get that kind of speed/power without melting gears or breaking clutches? I like the lighter weight and better torque of those.

 

[neptronix]

RH212 actually puts out more torque in the low to mid range RPM.
The taller stator + additional poles help here and it's a better design for large bike wheels.
Adding ferrofluid would probably turn the RH212 into a 40mph continuous motor.

No geared hub motor can take 40mph continuously, they just can't shed heat well. The MXUS XF-19 would be the biggest geared motor you can buy.. but it's weight is verging on a DD

 

[TroySmith80]

Great info, thank you!