Why do hub motors use the older freewheel hub?

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thunderstorm80   1 kW

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Why do hub motors use the older freewheel hub?

Post by thunderstorm80 » Sep 20 2016 1:24pm

Hi,
I understand that for a wide stator machines, there is no room left for a cassette-hub, while the older (but short) freewheel hub thread allows to put just the one sprocket you need or few of them.
But - for moderately (and narrower) powered motors, like the H35XX series - why don't they use cassette-hub? In those days, 7 speed gears is a thing from the past and belongs to the very low end bicycles. Downgrading your gearing system from 9spd to 7 seems unrealistic for a bike which is supposed to be a pedal assist bicycle - in my case.

Grin has 9C 30XX rear motors with the modern cassette-hub, but seems they stopped stocking them. I wonder why?

And now more specifically - I consider the H3525R rear DD motor for a touring bike I build from an 8 speed bike. I must have the full gearing range, can't compromise there.
Is it possible to fit an 8 speed cassette if my rear dropout is a standard 135mm one? Do such 8 speed cassette for the old freewheel hub exist?
I heard rumours that even if you manage to fit it there, it's not recommended - since the length of the cassette is already causing significant bending torque (the hub threads are quite short in length), which results in bent axle over time. Is it true?

Roy

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Re: Why do hub motors use the older freewheel hub?

Post by motomech » Sep 21 2016 10:10am

I can only speak about geared mini motors, but since they have the most narrow stators, my experience probably transfers to the new crop of larger "CST" motors.
And my experience w/ CST mini's is, that they make for a problematc build, or at the very least, an unaesthetic build.
The length of the spline required to fit a 9-speed or 10-speed cassette pushes the motor so far to the left that severe dishing or lot's of "Rube Goldburg" mods(like spreading the chain stays or stacking washers under the caliper mount)are required to center the rim.
... 7 speed gears is a thing from the past and belongs to the very low end bicycles. Downgrading your gearing system from 9spd to 7 seems unrealistic for a bike which is supposed to be a pedal assist bicycle - in my case.
Perhaps this is true of pedal only bikes, but it's a common misconception that E-powered bikes need lot's of gears, they don't.
A couple of years ago, I built what must be one of the lowest-powered systems ever, a Q100C on 9S(34V) and a 15 A controller w/ the intent to use all 9 gears on the cassette.
Well, that didn't last very long. Even on 500 Watts, the time it took to shift though all the gears actually slowed me down and it was tiring to be shifting all the time. I ended up using 3 gears on that build most of the time.
The DPN free wheels have gotten better and while they seem "clunky" in one's hand, they work quite well when the derailleur is adjusted for the 2 or 3 gears that the majority of Ebikers use.
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Re: Why do hub motors use the older freewheel hub?

Post by Kodin » Sep 24 2016 3:55pm

Honestly the main reason is shaft diameter. Cassettes require bearings inside to support the clutch assembly and that eats into the maximum thickness the shaft can be coming out of the motor on the gear side. We're talking 14mm max, 15 if you want to modify the cassette to almost be dangerously thin-walled, and most designs are usually 12mm. Do you trust a heavier hubmotor on a 12mm steel shaft? Maybe if it was chrome molybdenum, but what manufacturers use chrome moly for their shafts?

In comparison, it's very common to have 16mm+ thick axles coming out on the gear side when using a freewheel.
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Re: Why do hub motors use the older freewheel hub?

Post by John in CR » Sep 24 2016 6:18pm

thunderstorm80 wrote:...Downgrading your gearing system from 9spd to 7 seems unrealistic for a bike which is supposed to be a pedal assist bicycle...
Good electric bikes need no more than a very few gears. Upgrade your thinking, because 9 speeds is not an upgrade over 7, but instead just BS bicycle equipment manufacturers have sold to keep people buying new and more expensive stuff. Guess what else, even a few kg doesn't make a hill of beans difference with an ebike, much less hundreds of grams. For certain types of riding where both wheels don't stay on the ground, where the extra ebike weight is located certainly has an impact, but since you're talking DD hubbies it doesn't apply to you.

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Re: Why do hub motors use the older freewheel hub?

Post by spinningmagnets » Sep 24 2016 7:13pm

Vendors will stock whatever customers consistently buy. I think your question might more accurately be phrased: "why don't hubmotor customers want 8 or more gears (requiring a cassette)"

Hubmotor customers are notoriously price-sensitive, and a hub costing just a few dollars more so it can have a cassette freehub is often enough that cassette hubs don't sell very well.

The last two hub bikes I built up had a single-speed and a 6-speed freewheel. And even then I operate the 6-speed as if its a 2-speed. First gear is for those times when the motor isn't working, and sixth gear is for those times when I want to pedal along with the motor at medium speeds. At top speed, any pedaling I do is just for show...

There is a market for cassette-freehub hubmotors, its just not very big compared to the others...

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Re: Why do hub motors use the older freewheel hub?

Post by Kodin » Jan 13 2017 2:02pm

The whole point of more gears is added efficiency when accelerating. Just like a car with 3 gears vs. one with 6+; the one with 6 gears will get better gas milage in-town where there are lots of stops and starts. A car with a 3-speed vs. a 6 speed will do the same gas milage in top gear, but during acceleration, the bigger the hops between gears, the more loss you have as your power source isn't running at it's optimal range. In the case of bikes, that may only be tens-of-watts, but if you're racing, you notice the difference. Going from 7-speed to 9-speed cassettes I noticed it was easier to accelerate quickly, but only marginally so. Hubmotors typically make most of those considerations irrelevant as the power output is SO much more than the rider can generate.
Tank Bike - (Previously YAG - Yet Another Genesis) - LeafBike 1500W 5t, custom shaft, 9 speed cassette, Chinese "Tank" EEB clone frame, Sabvoton SSC048150

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Re: Why do hub motors use the older freewheel hub?

Post by teslanv » Jan 13 2017 4:44pm

There have been lots of advancements in non-powered bicycle technology in recent years, with the cassette freehub being a useful design in that realm, but it doesn't carry over well to hub motors.

1. It's cheaper to provide a cover with a simple threaded shaft for a freewheel, vs. the complexity of a cassette freehub.
2. What Kodin said about axle diameter/strength with a freewheel design.
3. Freewheels can be either single speed, or up to 7 speeds, and allow wide stator motors to fit in standard width drop-outs (135mm, 170mm, etc.)
4. On an adequately powered ebike, you don't need more than 7 speeds. Unless you lose power. After years of riding high-power ebikes, I gave up on trying to pedal at speed. Now I just use a single speed freewheel, of the 22T variety for pedaling when I lose power. This simplfies everything greatly. If I want some exercise I'll ride a mid drive on light pedal assist, or non-powered bike.
5. Most manufacturer's use standardized hub covers that will fit a variety of motors and applications. This keeps things simple and cost-effective.
6. Replacing a freewheel that is worn out is pretty easy and parts are readily available, vs. having to replace the entire motor cover with an integrated cassette freehub assembly (from the factory that made the motor).
7. You can get some really nice single speed freewheels (White Industries comes to mind).

The only real advantage to having a cassette freehub is the availability of 11T small cogs, vs the freewheels, of which there are only a couple manufacturers that offer 11T cogs. - But I revert back to note 4. Just install a large single speed freewheel and make your ebike simple.
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Re: Why do hub motors use the older freewheel hub?

Post by Kodin » Jan 13 2017 5:13pm

Also you lose power efficiency below 13t sprockets. 11t is nice, but does make you have to pedal harder.
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Re: Why do hub motors use the older freewheel hub?

Post by thunderstorm80 » Feb 07 2017 3:26am

Kodin wrote:The whole point of more gears is added efficiency when accelerating. Just like a car with 3 gears vs. one with 6+; the one with 6 gears will get better gas milage in-town where there are lots of stops and starts. A car with a 3-speed vs. a 6 speed will do the same gas milage in top gear, but during acceleration, the bigger the hops between gears, the more loss you have as your power source isn't running at it's optimal range. In the case of bikes, that may only be tens-of-watts, but if you're racing, you notice the difference. Going from 7-speed to 9-speed cassettes I noticed it was easier to accelerate quickly, but only marginally so. Hubmotors typically make most of those considerations irrelevant as the power output is SO much more than the rider can generate.
You are right if it's a ride on a flat.
If it's an uphill, due to the human leg's narrow efficient RPM zone, the lack of gear range can make a striking difference in power efficiency.
More so, 9 speeds come with a bigger overall range than 7 speed cassettes.
Of course if you rely on motor power alone or pedal just for fun then even one gear can be enough, but if it's a pedal assist on uphill - then you DO want as many gears as you can.

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Re: Why do hub motors use the older freewheel hub?

Post by thunderstorm80 » Feb 07 2017 3:28am

Kodin wrote:Also you lose power efficiency below 13t sprockets. 11t is nice, but does make you have to pedal harder.
When you have a strong tail wind on a flat, even 11t can "spin-out" beneath your legs.

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Re: Why do hub motors use the older freewheel hub?

Post by Chalo » Feb 07 2017 3:54am

thunderstorm80 wrote:
Kodin wrote:Also you lose power efficiency below 13t sprockets. 11t is nice, but does make you have to pedal harder.
When you have a strong tail wind on a flat, even 11t can "spin-out" beneath your legs.
A bigger chainring accomplishes the same thing without adding a lot of friction and wear, like an 11t sprocket does.
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Re: Why do hub motors use the older freewheel hub?

Post by thunderstorm80 » Feb 07 2017 4:20am

Chalo wrote:
thunderstorm80 wrote:
Kodin wrote:Also you lose power efficiency below 13t sprockets. 11t is nice, but does make you have to pedal harder.
When you have a strong tail wind on a flat, even 11t can "spin-out" beneath your legs.
A bigger chainring accomplishes the same thing without adding a lot of friction and wear, like an 11t sprocket does.
That's true. The 11t gear shouldn't be used continuously. Exchanging 11t for 13t requires increasing the 48t chainring to 56t, which is highly uncommon. Do you know where I can find triple chainring set with 56t top gear?

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Re: Why do hub motors use the older freewheel hub?

Post by Chalo » Feb 07 2017 1:53pm

thunderstorm80 wrote:Do you know where I can find triple chainring set with 56t top gear?
Hostelshoppe.com has lots of sizes up to 73t. I have a 56t 110mm ring in my shed. This stuff is around, even if it doesn't come as original equipment on a crank.

There are limits to how big a ring you can use. Often the shape of the bike's chainstays prohibits using a ring much larger than its original spec. And there are limits on how much total gear range derailleurs can cope with.

Another thing to keep in mind is that over 30mph or so, it costs more power to pedal (by making extra aerodynamic drag) than the amount of power you're likely to make by pedaling. That's right-- sometimes you can pedal to go slower.
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Re: Why do hub motors use the older freewheel hub?

Post by thunderstorm80 » Feb 13 2017 5:05am

Chalo wrote:
thunderstorm80 wrote:Do you know where I can find triple chainring set with 56t top gear?
Hostelshoppe.com has lots of sizes up to 73t. I have a 56t 110mm ring in my shed. This stuff is around, even if it doesn't come as original equipment on a crank.

There are limits to how big a ring you can use. Often the shape of the bike's chainstays prohibits using a ring much larger than its original spec. And there are limits on how much total gear range derailleurs can cope with.

Another thing to keep in mind is that over 30mph or so, it costs more power to pedal (by making extra aerodynamic drag) than the amount of power you're likely to make by pedaling. That's right-- sometimes you can pedal to go slower.
True. I attempted installing a 26-38-48 crank on an MTB that has 22-32-42. The 48t chain-ring collided with the chain-stay tube, so it wasn't possible.
It needs to be a bike that already comes with very big chain-rings, otherwise it's almost certain that you will not have the space to expand...

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Re: Why do hub motors use the older freewheel hub?

Post by rborger73 » Feb 13 2017 10:24am

thunderstorm80 wrote:
Chalo wrote:
thunderstorm80 wrote:
Kodin wrote:Also you lose power efficiency below 13t sprockets. 11t is nice, but does make you have to pedal harder.
When you have a strong tail wind on a flat, even 11t can "spin-out" beneath your legs.
A bigger chainring accomplishes the same thing without adding a lot of friction and wear, like an 11t sprocket does.
That's true. The 11t gear shouldn't be used continuously. Exchanging 11t for 13t requires increasing the 48t chainring to 56t, which is highly uncommon. Do you know where I can find triple chainring set with 56t top gear?

11t 48t for close to 19,000 miles for me. Always stays in that gear. No problems ever. Same chain as well for that matter. And I pedal always. Other than the normal coming fast around corners, or when pedaling creates drag coming down big hills. Other than that I've pedaled every mile the bike has on it.

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Re: Why do hub motors use the older freewheel hub?

Post by thunderstorm80 » Feb 13 2017 10:47am

rborger73 wrote: 11t 48t for close to 19,000 miles for me. Always stays in that gear. No problems ever. Same chain as well for that matter. And I pedal always. Other than the normal coming fast around corners, or when pedaling creates drag coming down big hills. Other than that I've pedaled every mile the bike has on it.
We are talking about a non-mid-drive, right?
If so, It's a huge difference. In fact, the chain has barely any wear when you always pedal along with a hub-motor. The force of tension is way way lower. So yes, if you just help the motor, your chain may last forever.

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Re: Why do hub motors use the older freewheel hub?

Post by rborger73 » Feb 13 2017 11:34am

thunderstorm80 wrote:
rborger73 wrote: 11t 48t for close to 19,000 miles for me. Always stays in that gear. No problems ever. Same chain as well for that matter. And I pedal always. Other than the normal coming fast around corners, or when pedaling creates drag coming down big hills. Other than that I've pedaled every mile the bike has on it.
We are talking about a non-mid-drive, right?
If so, It's a huge difference. In fact, the chain has barely any wear when you always pedal along with a hub-motor. The force of tension is way way lower. So yes, if you just help the motor, your chain may last forever.

Apparently the conversation changed somewhere? Must be in the middle. lol Thread was started discussing freewheels and hubmotors. Ya I only see one mention of mid drive in the thread... So... ya...

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Re: Why do hub motors use the older freewheel hub?

Post by Chalo » Feb 13 2017 3:35pm

rborger73 wrote:11t 48t for close to 19,000 miles for me. Always stays in that gear. No problems ever. Same chain as well for that matter. And I pedal always.
Have you checked your chain for wear? I think it might be educational for you. 12 inches of chain should measure between 12 and 12-1/16" from pin to pin. When it reaches 1/16" over, it's time to replace the chain. More than that, and it's time to replace the rear sprockets too.

A bike shop can do it if you don't feel like measuring it yourself. They can also check your sprocket's observable wear. The 11t outer sprocket is the only one that's available as a loose replacement, so lucky you.

If you don't actually apply power when you pedal, then chain wear will of course be diminished versus someone who does. And a worn-out chain won't skip like it would if you were pedaling hard.
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Re: Why do hub motors use the older freewheel hub?

Post by rborger73 » Feb 13 2017 6:00pm

Pedal all the time. I know how to check a chain. I don't need a bike shop to check it... I lean back pulling on my handlebars giving full power to the pedals, and my legs are very strong. No slippage, and I live in a super hilly area. When you ride the same bike for almost 19,000 miles, you know if anything changes.. I keep chain and any moving parts lubricated. Every 3 days or less they get sprayed. I clean the chain with kerosene every few months. Keep the grit out, keep it lubed.

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