Middrive vs hub acceleration

[speedyebikenoob]

Anyone tested the acceleration of a middrive and hub motor side by side? Would a 3kw middrive motor running through a 7 speed or 8 speed be able to compete with something like a 6 kw hub motor 0-20 mph because of gearing? Curious to see if anyone has any experience with this.

 

[Balmorhea]

Anyone tested the acceleration of a middrive and hub motor side by side? Would a 3kw middrive motor be able to compete with something like a 6 kw hub motor 0-20 mph because of gearing? Curious to see if anyone has any experience with this.

If you’re talking about single gear ratio systems in both cases, then acceleration will always trade off against top speed, and more power will either accelerate faster, or top out faster, or both.

 

[speedyebikenoob]

Anyone tested the acceleration of a middrive and hub motor side by side? Would a 3kw middrive motor be able to compete with something like a 6 kw hub motor 0-20 mph because of gearing? Curious to see if anyone has any experience with this.

If you’re talking about single gear ratio systems in both cases, then acceleration will always trade off against top speed, and more power will either accelerate faster, or top out faster, or both.

I don't mean a single gear ratio. I mean the middrive would be running through a conventional 7 speed or 8 speed cassette.

 

[Tommm]

Anyone tested the acceleration of a middrive and hub motor side by side? Would a 3kw middrive motor running through a 7 speed or 8 speed be able to compete with something like a 6 kw hub motor 0-20 mph because of gearing? Curious to see if anyone has any experience with this.

Depends on the top speed of the hub. The only thing you really need to know is the Power and Unloaded top speed of each motor in a gear.

Take any motor with a known top speed. If you are on a 32t rear, go to a 16t. Now what you get:
2x Unloaded top speed, 0.5x acceleration.

Mid drive gears is the same as a hub motor's winding. Only the winding you can't change.

So a mid drive with 3kw in a gear with 30 mph unloaded top speed will perform the same as a hub motor with 3kw with a 30mph unloaded top speed. Take it from there.

 

[Balmorhea]

Anyone tested the acceleration of a middrive and hub motor side by side? Would a 3kw middrive motor be able to compete with something like a 6 kw hub motor 0-20 mph because of gearing? Curious to see if anyone has any experience with this.

If you’re talking about single gear ratio systems in both cases, then acceleration will always trade off against top speed, and more power will either accelerate faster, or top out faster, or both.

I don't mean a single gear ratio. I mean the middrive would be running through a conventional 7 speed or 8 speed cassette.

By shifting gears, you can keep the motor in its peak power range for more of the time/a larger fraction of operating conditions. So if the hub motor is set up for maximum top speed, the mid drive may out-accelerate it. And if it’s set up for good acceleration and efficient cruising, the mid drive may have a higher top speed.

My subjective experience is that a multi-geared mid drive performs comparably to a hub motor of 1-1/2 to 2 times as much power. But putting 3kW through a bike’s gears is a mistake and you’ll regret it.

My own comparison is between a 48V, 25A BBS02 versus hub motors with 48V, 35A and 40A controllers. The BBS02 outperformed the hubs in acceleration and climbing, while also having a higher top speed.

 

[Tommm]

But putting 3kW through a bike’s gears is a mistake and you’ll regret it.

This depends on the gearing. You can get 3kw (3x human sprint power) by having 3x the max human rpm (120x3=360rpm) and human torque. Torque kills the chains, not power.

 

[Balmorhea]

But putting 3kW through a bike’s gears is a mistake and you’ll regret it.

This depends on the gearing. You can get 3kw (3x human sprint power) by having 3x the max human rpm (120x3=360rpm) and human torque. Torque kills the chains, not power.

Sure. But humans can’t sprint all the time. If they did, they’d wreck their chains and sprockets pretty quickly.

It like assuming 11t sprockets are OK for mid drives because they’re normal for pedal bikes. The reason they sort of work for pedal bikes is because they’re used so little of the time. When people use them often, like leaving their bikes cross-chained in small/small gear all the time, they wear that stuff out fast.

 

[Tommm]

But putting 3kW through a bike’s gears is a mistake and you’ll regret it.

This depends on the gearing. You can get 3kw (3x human sprint power) by having 3x the max human rpm (120x3=360rpm) and human torque. Torque kills the chains, not power.

Sure. But humans can’t sprint all the time. If they did, they’d wreck their chains and sprockets pretty quickly.

It like assuming 11t sprockets are OK for mid drives because they’re normal for pedal bikes. The reason they sort of work for pedal bikes is because they’re used so little of the time. When people use them often, like leaving their bikes cross-chained in small/small gear all the time, they wear that stuff out fast.

You wouldn't use 3kw either all the time. Peak compared to peak. 3kw would sling so fast you would be doing low highway speeds.

Yea, hub, low power mid, high powered mid, are all just fine when done right, but they are all completely different animals.

 

[LeftieBiker]

It like assuming 11t sprockets are OK for mid drives because they’re normal for pedal bikes. The reason they sort of work for pedal bikes is because they’re used so little of the time. When people use them often, like leaving their bikes cross-chained in small/small gear all the time, they wear that stuff out fast.

I've seen this assertion several times. I use my 11T gear almost every day, for about 1/3 of an average 10 mile ride. I have over 3,000 miles on the bike, and no derailleur issues. I think that you are not accounting for the fact that pedaling torque in that gear is likely to be quite modest, especially on an e-bike.

 

[speedyebikenoob]

Interesting, so looks like you can get much better acceleration from an equivalent powered middrive because hubs are geared much higher generally. My middrive does 20 mph in first gear, and I'm going to be running 4-4.5 kw peak thru it in a day or two, so in theory I should be as quick off the line as a 9 kw hub geared for a top end of 40+ mph, all other things equal?? If there can be such a difference between a middrive and hub I wonder what the difference will be like between an ice and a middrive

 

[MadRhino]

Don’t dream with 7 gears. By the time you will have shifted them all, the DD hub will be long gone. A powerful single gear mid drive can beat a big DD hub, up to a certain speed.

 

[speedyebikenoob]

Don’t dream with 7 gears. By the time you will have shifted them all, the DD hub will be long gone. A powerful single gear mid drive can beat a big DD hub, up to a certain speed.

Right, which is why I said 0-15 mph I could probably accelerate a much more powerful hub drive because I'm geared way lower. After a couple shifts though, I'm sure the hub drive would pull away.

 

[Tommm]

Interesting, so looks like you can get much better acceleration from an equivalent powered middrive because hubs are geared much higher generally. My middrive does 20 mph in first gear, and I'm going to be running 4-4.5 kw peak thru it in a day or two, so in theory I should be as quick off the line as a 9 kw hub geared for a top end of 40+ mph, all other things equal??

Yes, but only off the line. At 0rpm you have the same torque. At 20mph you have 0 toruqe (constant speed) but the hub has 50% of total torque. So at 10mph the hub has a 75% of total torque, and you have 50% of your total torque. Your total torques are the same so the hub is accelerating faster than you at 10mph.
In reality the hub is heavy so it might be a bit slower to spin up, but its only a few % difference.

But for doing slow steep climbs, wheelies and burnouts, etc, yea, a smaller mid can get along with much less kw.

 

[Balmorhea]

It like assuming 11t sprockets are OK for mid drives because they’re normal for pedal bikes. The reason they sort of work for pedal bikes is because they’re used so little of the time. When people use them often, like leaving their bikes cross-chained in small/small gear all the time, they wear that stuff out fast.

I've seen this assertion several times. I use my 11T gear almost every day, for about 1/3 of an average 10 mile ride. I have over 3,000 miles on the bike, and no derailleur issues. I think that you are not accounting for the fact that pedaling torque in that gear is likely to be quite modest, especially on an e-bike.

Right, if you're only pretend pedaling, then you won't wear things out. But we're talking about mid drives here, where the motor power runs through that tiny sprocket. Whether you're doing that or pedaling in 24x11 all the time, you tear up the chain drive. It's not hypothetical; I see it in the shop all the time.

 

[LeftieBiker]

Right, if you're only pretend pedaling, then you won't wear things out. But we're talking about mid drives here, where the motor power runs through that tiny sprocket. Whether you're doing that or pedaling in 24x11 all the time, you tear up the chain drive. It's not hypothetical; I see it in the shop all the time.

I don't pretend pedal except when I have to speed up quickly to get passed some maskless idiots or a dog. I ride to keep my heart functioning and my blood sugar down, and I put in real effort. (I also checked this evening, and I use top gear more like half the time.) I take your point about mid-drives, but I think that that is about the only case in which an 11T top gear is really problematic. You guys here make it sound as if a hubmotor bike with one is going to chew it up, and as far as I can tell that just isn't the case.

 

[spinningmagnets]

On flat ground, I'd use a hubmotor to get hard acceleration. I have a mid drive and a hub. I plan to keep them both, each has its benefits and drawbacks.

If I was building a bike for an acceleration contest, I'd use 2WD and fat tires on smaller rims. Rear hubmotor and a front geared hub. If I was running a contest, I'd limit the voltage to 52V and I'd provide the batteries to the contestants so everyone would have the same volts and amps.

 

[MadRhino]

... when I have to speed up quickly to get passed some maskless idiots or a dog. ...

Fear is more dangerous than dogs or Covid my friend. You got to work on that. :wink:

 

[Balmorhea]

I take your point about mid-drives, but I think that that is about the only case in which an 11T top gear is really problematic. You guys here make it sound as if a hubmotor bike with one is going to chew it up, and as far as I can tell that just isn't the case.

A hub motor e-bike is one of the cases when an 11t sprocket, or even a 10t sprocket, makes sense. It allows the rider to pedal along at unnatural speeds, without demanding the kind of power that it would on a pedal-only bike.

 

[speedyebikenoob]

Interesting, so looks like you can get much better acceleration from an equivalent powered middrive because hubs are geared much higher generally. My middrive does 20 mph in first gear, and I'm going to be running 4-4.5 kw peak thru it in a day or two, so in theory I should be as quick off the line as a 9 kw hub geared for a top end of 40+ mph, all other things equal??

Yes, but only off the line. At 0rpm you have the same torque. At 20mph you have 0 toruqe (constant speed) but the hub has 50% of total torque. So at 10mph the hub has a 75% of total torque, and you have 50% of your total torque. Your total torques are the same so the hub is accelerating faster than you at 10mph.
In reality the hub is heavy so it might be a bit slower to spin up, but its only a few % difference.

But for doing slow steep climbs, wheelies and burnouts, etc, yea, a smaller mid can get along with much less kw.

Can you explain this further? Is it the power curve of the motor? Is that why you're saying a hub will pass my mid at 10 mph? I assumed it would keep pulling away from the hub till 15-16 mph because that's where I feel the torque falls off and I have to upshift

 

[Tommm]

Interesting, so looks like you can get much better acceleration from an equivalent powered middrive because hubs are geared much higher generally. My middrive does 20 mph in first gear, and I'm going to be running 4-4.5 kw peak thru it in a day or two, so in theory I should be as quick off the line as a 9 kw hub geared for a top end of 40+ mph, all other things equal??

Yes, but only off the line. At 0rpm you have the same torque. At 20mph you have 0 toruqe (constant speed) but the hub has 50% of total torque. So at 10mph the hub has a 75% of total torque, and you have 50% of your total torque. Your total torques are the same so the hub is accelerating faster than you at 10mph.
In reality the hub is heavy so it might be a bit slower to spin up, but its only a few % difference.

But for doing slow steep climbs, wheelies and burnouts, etc, yea, a smaller mid can get along with much less kw.

Can you explain this further? Is it the power curve of the motor? Is that why you're saying a hub will pass my mid at 10 mph? I assumed it would keep pulling away from the hub till 15-16 mph because that's where I feel the torque falls off and I have to upshift

The torque curve of an electric motor is just a straigh slope.
Green is for a motor of double power but double high gearing/winding. Torque is same at 0 rpm.

 

[dogman dan]

Well, FWIW, the bike that killed it at the last death race held, was a mid drive. It clearly out accelerated the gas bicycles big time, but it looked to me like that bike also was out accelerating the other electrics. In that race, with its 50 mph straights and 25 mph corners, it was all about acceleration, and not laying it down on a corner.

But its also worth noting, that the first electric bike to show up at the death races, was me riding a 1000w aotema front hub. I did not win, but on the start I was at the back of the field, and beat almost all of the gas bikes to the first corner. Even that lame commuter bike slayed the entire field of china girl 50 and 90 cc, un modified gas kits.

Trying to say,,, even lame shit accelerates fast compared to gasoline bikes. anything with 4000w plus is going to fly, provided you can keep that front wheel down. I rode a 10,000w hub bike once, and could only use about 1/4 throttle before it wheelied.

I would stop worrying about which is best, and just enjoy the ride on whichever type you choose to build. But I would not suggest you put much more than 1500-2000w through bike chain and freewheels. For more, you need bigger chain, like the bike that won the last death race, or the gas bikes. You want giddy up, just build a 4000w+ hub motor bike. Easy, fast as hell, fun as hell. The one I built for the death race accelerated to 40 mph just about as fast as my BMW 1150 cc does now. It did not win because I crashed, and because my bike made the gassers go buy snowmobile engines that year.

 

[speedyebikenoob]

Interesting, so looks like you can get much better acceleration from an equivalent powered middrive because hubs are geared much higher generally. My middrive does 20 mph in first gear, and I'm going to be running 4-4.5 kw peak thru it in a day or two, so in theory I should be as quick off the line as a 9 kw hub geared for a top end of 40+ mph, all other things equal??

Yes, but only off the line. At 0rpm you have the same torque. At 20mph you have 0 toruqe (constant speed) but the hub has 50% of total torque. So at 10mph the hub has a 75% of total torque, and you have 50% of your total torque. Your total torques are the same so the hub is accelerating faster than you at 10mph.
In reality the hub is heavy so it might be a bit slower to spin up, but its only a few % difference.

But for doing slow steep climbs, wheelies and burnouts, etc, yea, a smaller mid can get along with much less kw.

Can you explain this further? Is it the power curve of the motor? Is that why you're saying a hub will pass my mid at 10 mph? I assumed it would keep pulling away from the hub till 15-16 mph because that's where I feel the torque falls off and I have to upshift

The torque curve of an electric motor is just a straigh slope.
Green is for a motor of double power but double high gearing/winding. Torque is same at 0 rpm.

Hmm interesting, I assumed torque for dc motors fell off at higher rpms. It feels that way atleast.

 

[speedyebikenoob]

Well, FWIW, the bike that killed it at the last death race held, was a mid drive. It clearly out accelerated the gas bicycles big time, but it looked to me like that bike also was out accelerating the other electrics. In that race, with its 50 mph straights and 25 mph corners, it was all about acceleration, and not laying it down on a corner.

But its also worth noting, that the first electric bike to show up at the death races, was me riding a 1000w aotema front hub. I did not win, but on the start I was at the back of the field, and beat almost all of the gas bikes to the first corner. Even that lame commuter bike slayed the entire field of china girl 50 and 90 cc, un modified gas kits.

Trying to say,,, even lame shit accelerates fast compared to gasoline bikes. anything with 4000w plus is going to fly, provided you can keep that front wheel down. I rode a 10,000w hub bike once, and could only use about 1/4 throttle before it wheelied.

I would stop worrying about which is best, and just enjoy the ride on whichever type you choose to build. But I would not suggest you put much more than 1500-2000w through bike chain and freewheels. For more, you need bigger chain, like the bike that won the last death race, or the gas bikes. You want giddy up, just build a 4000w+ hub motor bike. Easy, fast as hell, fun as hell. The one I built for the death race accelerated to 40 mph just about as fast as my BMW 1150 cc does now. It did not win because I crashed, and because my bike made the gassers go buy snowmobile engines that year.

Wait your 1000 watt hub out accelerates your motorcycle to 40 mph? Can a 1000 watt even do 40 mph? I've been running 3500w+ for 500 miles thru my middrive and haven't had any reliability issues yet as long as I keep tightening the bolts. But ofc that's only 3.5kw peak not continuous. I have fun shifting through the gears which is why I probably won't ever own a hub I was mainly just curious how a hub and middrive compare acceleration wise because my bike accelerates a lot slower in sixth gear (geared for just over 30 mph) than first gear (geared for 20 mph max). My middrive feels noticeably peppier than the last motorcycle I rode (a slow 220cc making about 20 horses), till a certain speed. Any details on that middrive that one the death race? I'm curious as to what kind of power levels were being run through it.

 

[Tommm]

Yes, but only off the line. At 0rpm you have the same torque. At 20mph you have 0 toruqe (constant speed) but the hub has 50% of total torque. So at 10mph the hub has a 75% of total torque, and you have 50% of your total torque. Your total torques are the same so the hub is accelerating faster than you at 10mph.
In reality the hub is heavy so it might be a bit slower to spin up, but its only a few % difference.

But for doing slow steep climbs, wheelies and burnouts, etc, yea, a smaller mid can get along with much less kw.

Can you explain this further? Is it the power curve of the motor? Is that why you're saying a hub will pass my mid at 10 mph? I assumed it would keep pulling away from the hub till 15-16 mph because that's where I feel the torque falls off and I have to upshift

The torque curve of an electric motor is just a straigh slope.
Green is for a motor of double power but double high gearing/winding. Torque is same at 0 rpm.

Hmm interesting, I assumed torque for dc motors fell off at higher rpms. It feels that way atleast.

Different controllers have different max phase amps and a different ratio compared to battery amps. So it does drop off later depending on controller ability. The graph used here shows phase amps.
If the controller can give max phase amps until a higher rpm (which means it is capped on the low end) it will drop off later.

 

[dogman dan]

In the paragraph about the 1000w bike, I was racing gas bicycles.

I said my 4000+ watt race bike accelerated about as good as a street motorcycle to 40 mph. After that, my bmw comes alive and REALLY accelerates from 40 to 120. Its problem 0 to 40 is simply that it weighs a ton. Lighter crotch rockets would do better, but 4000w on a sub 1000 pound bicycle will seriously haul ass from 0-40 mph.

I said you don't need mid drive to scream off the line in a drag race. I said you DO need to be able to keep that front wheel on the ground, if you go higher wattage than 4 or 5 kw. Power up a hub motor good enough, and all you worry about is staying on it, since they want to wheelie much more than a typical dirt bike. Part of this problem is that the throttle gets touchy when you put 72v into controllers. Its not as controllable as a gas motorcycle. This is one of the reasons it can be good to put 15 pounds of front hub weight on a bicycle with that much power. Or Battery, or just heavy fork and motorcycle wheel, whatever.

That mid drive that schooled all the gasoline bicycles in that race did not have such a wheelie problem. It had the motor and the batteries in the mid frame.

My 1000w commuter, which was the first ever electric bike to compete in these gas bicycle races, beat all the china girl bicycles to the first corner. Unmodified, 150 buck gas motor bike kits. It followed the modified china girl bikes, but still out did them on the longer straights. I just wanted to make the point that even lame 1000w electric hub motor bikes have pretty amazing acceleration off the line, to 30 mph. They go right away, while the gasoline bike is still slipping its clutch.

As you can see though, I've gone back to a big street motorcycle for my go fast fun. its nice to enter a mountain road corner at 30 mph, and exit it at 50, because I can trust those tires. And it runs 6 hours at a time on a tank, instead of 45 min. That short electric ride was fine when I was sick, and could only handle a 30 min ride. But now I like to go out all day and do 250 miles.