The Great "Gearing vs Hub Motor" Debate

[safe]

Takes me about 10 seconds to reach the 28mph point of 80% hubmotor efficiency. That's very little time out of a typical 1-3 hour ride.

But that's because you have a 3hp motor. Think about the consequences of running a 1hp motor... given the same weight you all of a sudden can take 20 - 30 seconds to reach your peak power depending on your gearing. In fact, it's pretty much impossible to even achieve the same range of speed and hill climbing abilities with a hub motor that only has 1hp.

So let's make a general rule:

"Roughly speaking, it requires about three times as much power in a hub motor to achieve the same results as a geared bike."

If there are no limtations on peak power (no laws to comply with) then the hub motor seems to do just as well as the geared bike and has many benefits like simplicity and increased power.

3 to 1 makes the Hub Motor more Fun?

 

[Lowell]

I wasn't really thinking wheelspin at speed on an ebike.... :lol:

Now what would be really cool is a shifting system that cuts power to the motor so you can full throttle through the gears.

Depending on the shifter it should not be to hard to rig up, just setup a micro switch so that it pulls in as you press the lever to shift.
Why not just use a hub or derailleur that doesn't mind shifting loaded?

I wouldn't trust a derailer with 4-5hp. If something broke, you'd be really screwed. No pedals AND no motor

 

[Lowell]

Takes me about 10 seconds to reach the 28mph point of 80% hubmotor efficiency. That's very little time out of a typical 1-3 hour ride.

But that's because you have a 3hp motor. Think about the consequences of running a 1hp motor... given the same weight you all of a sudden can take 20 - 30 seconds to reach your peak power depending on your gearing. In fact, it's pretty much impossible to even achieve the same range of speed and hill climbing abilities with a hub motor that only has 1hp.

So let's make a general rule:

"Roughly speaking, it requires about three times as much power in a hub motor to achieve the same results as a geared bike."

If there are no limtations on peak power (no laws to comply with) then the hub motor seems to do just as well as the geared bike and has many benefits like simplicity and increased power.

3 to 1 makes the Hub Motor more Fun?

Darn right it's more fun 8)

I've owned more cars than I can count easily, and none of them have been automatics. I was never a fan of the production semi auto gearboxes, tiptronics, etc. Even the last generation BMW M3 really sucks with the paddle shifters. However, the newest generation of DSG boxes from VW/Audi/Porsche etc. are really fantastic, and will outshift just about any manual transmission. While they do take some of the fun out of using the clutch, anything that makes it faster sounds fun to me.

 

[safe]

Darn right it's more fun 8)

It's really hard for laws to be made that make any sense. When they passed the 750 Watt Law (granting universal permission for them) they did so in a cautious manner so that people could get around, but they weren't going to be doing any "wheelies" because of so much horsepower. While people are inventing 4-5 electric bikes it's doubtful that a large percentage would ever grant legal status to them if anyone ever bothered to look. There is still a sort of "Wild West" atmosphere about the electric bike world and the government (in America) seems willing to wait and see how it all pans out.

My state of Missouri openly defines an electric bike as having up to three horsepower. So I could get a pretty decent ride going with that (and I will be making a 2 hp bike one day) but I also want to test what the limits of performance are with the national law.

In then end this is about having fun, affordable and efficient transportation. If you can do all three well then that's a "good thing" no matter how you do it...

 

[Lowell]

Fun? Yes.

Affordable and efficient? To me that's pumping gas into your sport bike and doing a lot of riding, not charging batteries, messing with electronics, wiring and speed controllers. (but I do it anyways :lol: )

It's kind of like shooting airguns instead of real guns... no smoke, less noise, no permits or licenses of any kind, but they cost more, and don't do the job as well. Need fiddly air tanks/compressors.

 

[Geebee]

I wasn't really thinking wheelspin at speed on an ebike.... :lol:

Now what would be really cool is a shifting system that cuts power to the motor so you can full throttle through the gears.

Depending on the shifter it should not be to hard to rig up, just setup a micro switch so that it pulls in as you press the lever to shift.
Why not just use a hub or derailleur that doesn't mind shifting loaded?

I wouldn't trust a derailer with 4-5hp. If something broke, you'd be really screwed. No pedals AND no motor

Just carry a chain breaker (available on folding bike tools these days) and you can convert to single speed in a few minutes.
I was thinking electric assist not motor bike, I have used a derailleur setup with a 600w peak motor plus similar input from me, zero problems and all low end components.

 

[safe]

What he's talking about with 4-5 hp would actually even break the freewheel itself. The little "clicking" cogs that allow the freewheel to go one way and not the other will not withstand so much power. When you get above what appears to be about 2hp the calculated torque levels on the hub rise to a point that I doubt many bicycle components would hold up. Xyster is pushing enough power (and weight) to actually break spokes on (what sounds like) a regular basis.

My 175 lb MB5 (50cc) motorcycle only had about 5 hp and it used full strength motorcycle components. What is going to happen with these 4-5hp machines is they will either break lot's of parts or be forced to "hold themselves back" to such a degree as to make all the extra power more of a "bragging point" than a practical daily habit.

My attitude is:

"Whatever machine you are on, the 'most fun' is when you are riding it near it's limit because that's what makes riding fun..."

The actual limit doesn't matter (it can be slow or fast) it's the careful testing of the limits that provides the satisfaction.

 

[Lowell]

I wasn't really thinking wheelspin at speed on an ebike.... :lol:

Now what would be really cool is a shifting system that cuts power to the motor so you can full throttle through the gears.

Depending on the shifter it should not be to hard to rig up, just setup a micro switch so that it pulls in as you press the lever to shift.
Why not just use a hub or derailleur that doesn't mind shifting loaded?

I wouldn't trust a derailer with 4-5hp. If something broke, you'd be really screwed. No pedals AND no motor

Just carry a chain breaker (available on folding bike tools these days) and you can convert to single speed in a few minutes.
I was thinking electric assist not motor bike, I have used a derailleur setup with a 600w peak motor plus similar input from me, zero problems and all low end components.

No, I think I'll stick to my hub motor with no moving parts to break or wear out. Until someone comes up with a proven multi speed gear system that's as reliable as an X5 hub, I'm not interested. If it was only the chain that would break, that might be workable, but I suspect that would be the least of your worries if you put 5hp through a derailer system.

 

[Lowell]

What he's talking about with 4-5 hp would actually even break the freewheel itself. The little "clicking" cogs that allow the freewheel to go one way and not the other will not withstand so much power. When you get above what appears to be about 2hp the calculated torque levels on the hub rise to a point that I doubt many bicycle components would hold up. Xyster is pushing enough power (and weight) to actually break spokes on (what sounds like) a regular basis.

My 175 lb MB5 (50cc) motorcycle only had about 5 hp and it used full strength motorcycle components. What is going to happen with these 4-5hp machines is they will either break lot's of parts or be forced to "hold themselves back" to such a degree as to make all the extra power more of a "bragging point" than a practical daily habit.

My attitude is:

"Whatever machine you are on, the 'most fun' is when you are riding it near it's limit because that's what makes riding fun..."

The actual limit doesn't matter (it can be slow or fast) it's the careful testing of the limits that provides the satisfaction.

At looks as though the holes in the X5 hub are designed to accept larger spokes, and by lacing it with smaller spokes, it might create a stress point. I guess we'll see how they hold up for me, but fortunately a broken spoke won't ruin your day like a stripped freewheel would.

I'm not sure what you mean by break a lot of parts, as a hub motor is simplicity itself. Only a pair of cartridge bearings that move, and unless you fill it with water/mud, or actually burn the wiring out, there's not much to go wrong. Having pedaled bikes for nearly 30 years, I've had more than a few chain/derailer/shifter issues and many greasy fingers on the side of the road. No thanks

 

[xyster]

Xyster is pushing enough power (and weight) to actually break spokes on (what sounds like) a regular basis.

I've broken two spokes in 1,100 miles of riding now. Replacement was simple, and didn't require removing the wheel. The x5's should come with beefier spokes. Mine are 13 gauge. 12 gauge spokes would easily fit the hubmotor flange holes. I'll probably re-lace when it comes time to change the tire.

 

[Lowell]

Xyster is pushing enough power (and weight) to actually break spokes on (what sounds like) a regular basis.

I've broken two spokes in 1,100 miles of riding now. Replacement was simple, and didn't require removing the wheel. The x5's should come with beefier spokes. Mine are 13 gauge. 12 gauge spokes would easily fit the hubmotor flange holes. I'll probably re-lace when it comes time to change the tire.

A couple of spokes in 1100 miles is pretty good for a bike that's so much fun! Thicker spoke certainly can't hurt though.

 

[Lowell]

Takes me about 10 seconds to reach the 28mph point of 80% hubmotor efficiency. That's very little time out of a typical 1-3 hour ride.

But that's because you have a 3hp motor. Think about the consequences of running a 1hp motor... given the same weight you all of a sudden can take 20 - 30 seconds to reach your peak power depending on your gearing. In fact, it's pretty much impossible to even achieve the same range of speed and hill climbing abilities with a hub motor that only has 1hp.

So let's make a general rule:

"Roughly speaking, it requires about three times as much power in a hub motor to achieve the same results as a geared bike."

If there are no limtations on peak power (no laws to comply with) then the hub motor seems to do just as well as the geared bike and has many benefits like simplicity and increased power.

3 to 1 makes the Hub Motor more Fun?

I never really looked at the numbers first time around. Anyways, I've never timed 0-28mph, or 0-80% efficiency, but I figure 6 seconds would be a close estimate. I think "just as well" should be changed to "outperforms in every category"

As for 3x the power to get the same results? I don't see a 1000W geared bike having anywhere near the same speed as a 3000W hub motor, given equal drag numbers of course.

 

[safe]

As for 3x the power to get the same results? I don't see a 1000W geared bike having anywhere near the same speed as a 3000W hub motor, given equal drag numbers of course.

Well you have to think in terms of "speed range".

In order for a hub motor to work well it's powerband needs to be configured so that it's peak power occurs near it's intended top speed, but probably a little below it since you don't want to sacrifice all your low end. The geared bike is effectively "always" running at it's peak no matter if it is inching it's way up a hill or tapped out in high gear on a straight away. So the "range of speeds" that the 1000W motor can cover are roughly equal to the same effective range as a hub motor that has about three times the power. Remember the reverse argument... a geared bike stuck in one gear is a "hub motor" so all you have to do is compare a geared bike "stuck in one gear" verses it's same performance spread out over many gears. The "wild card" argument is wind resistance. If you are riding a mountain bike then the advantages are less for the geared bike because the "range" of speed is more limited.

So in the case of a mountain bike the ratio might be closer to about 2 to 1.

On my bike configuration it shows up on the spreadsheet as three to one, so for my purposes I would need three times the power, three times the battery, to get the same performance as I would using gears. If you have an unlimited budget for batteries then the hub motor is fine, but for us into "affordable" stuff we get "more bang for the buck" with the geared bike.

 

[safe]

3000 Watts of POWER

If you are running something like a PMG 132 and you are getting 3000 Watts of power out of it and you have gears to "get to" your top speed then your top speed (with lowracer level aerodynamics) should be right around 67.6 mph. If you are running a hub motor and getting less of a top speed than 67.6 mph from your 3000 Watts then you are NOT using the motor to it's full potential. Gears "stretch" the abilities of any motor because it effectively expands the powerband.

If you were on a track that was 10 miles in length and you had the choice between a hub motor able to go 50 mph or a geared bike that could go 67.6 mph in 8th gear then the geared bike would win.

The 3 to 1 ratio might be 2 to 1 for bikes with poor aerodynamics, but the more aerodynamic the bike the greater the geared bike has an advantage.

It's no surprise that the electric speed record was with a geared machine... (5 speed I think... they talked about it on a tv show... "Future Cars"... 300 mph)

 

[xyster]

Gears "stretch" the abilities of any motor because it effectively expands the powerband.

Multi-winding hubmotors, like the 406/409, 408/412, etc behave the same way. It's too bad there's no dual 5303/5305 :? It'd be even better to have a CVT built into the hubmotor -- but I think we've gone over that already. With the new small CVT's and hub transmissions coming to market now, hopefully somebody will commercialize a hubmotor w/internal CVT or multiple gears soon.

Point is, just because it's a hubmotor, doesn't mean it has to be single gear -- so long as 'gear' means any kind of device that trades rpm's for torque.

If I was on your side of the argument, looking to do the things you're looking to do, I'd broaden my definition of gears to include all such torque/speed converters, including solid-state electrical.

 

[safe]

With the new small CVT's and hub transmissions coming to market now, hopefully somebody will commercialize a hubmotor w/internal CVT or multiple gears soon.

Actually an "on board" motor with a built in CVT would be great. The final gear and chain is on average about 95% efficient and so bringing that 25lb "mass of steel" back to the center of the bike where it belongs is a good idea. If anyone worries about breaking their freewheel they can always use a track gear which would take just anything you could give it. If you could break a track gear on a hub then the spokes would likely break first. Or they could find some motorcycle hub if need be. Maybe an 80cc dirt bike hub? Those can handle about 10 hp or more and are very light weight.

I'm just not "sold" on trying to race around on something where all that weight is in the hub. Think of it this way... if there was an advantage in placing all the weight at the center of the wheel the racers would be doing it already. But "unsprung weight" to my knowledge will forever relegate the "hub motor" to slower speed touring vehicles. (with great 10 mph - 30 mph torque thrills of course)

Imagine going over a set of bumps at speed with a hub motor! Geez... :lol:

 

[Lowell]

3000 Watts of POWER

If you are running something like a PMG 132 and you are getting 3000 Watts of power out of it and you have gears to "get to" your top speed then your top speed (with lowracer level aerodynamics) should be right around 67.6 mph. If you are running a hub motor and getting less of a top speed than 67.6 mph from your 3000 Watts then you are NOT using the motor to it's full potential. Gears "stretch" the abilities of any motor because it effectively expands the powerband.

If you were on a track that was 10 miles in length and you had the choice between a hub motor able to go 50 mph or a geared bike that could go 67.6 mph in 8th gear then the geared bike would win.

The 3 to 1 ratio might be 2 to 1 for bikes with poor aerodynamics, but the more aerodynamic the bike the greater the geared bike has an advantage.

It's no surprise that the electric speed record was with a geared machine... (5 speed I think... they talked about it on a tv show... "Future Cars"... 300 mph)

I don't see too many people riding around with lowracers, although I do see plenty of regular bikes with 4 and 5 series hub motors. Also, if I was going to race on a 10 mile long track, I'd bring something with at least 600hp 8)

 

[Mathurin]

Actually, the sram spark is a multi-geard hubmotor that exists.

 

[Lowell]

Actually, the sram spark is a multi-geard hubmotor that exists.

A quick search didn't turn up anything, do you have a link or more info?

 

[Toorbough ULL-Zeveigh]

Your spelling is thwarting the search.

http://sram.com/_media/techdocs/Sparc16V_Ins_EDFNlDkSv12_05.pdf

I was led to believe by his pontiff, Joshua G. that the Sparc was only available to OEMs in thousand lot quantity.

 

[Mathurin]

Also the motor part is single speed & I think 160w.
Guess it's still a nice boost compared to nothing.

 

[safe]

Hub Motor verses Motor with Chain

Just to keep this thread from being hijacked...

Why might someone choose a PMG 132 over a 5304 hub motor strictly on power and performance reasons and not even thinking about all the other issues?

Here's a comparision of the 5304 hub motor at 72 Volts able to reach 47 mph (with very good aerodynamics) compared to a similiar bike using a very big motor (PMG 132) that can also go 47 mph.

Basically you can get "more ideal" performance when you can fine tune a really well built motor to the desired speed. You could achieve this with a "perfect" hub motor (something that does not now exist), but it's EASIER to achieve really good performance if you start with a really good motor not constricted by the low rpms that hub motors require. The PMG 132 is the motor that most electric motorcycles run... it's really well built.

In this case the range of the PMG 132 is 50% better while both give the same top speed...

 

[safe]

Big Motor verses Small Motor

The other comparision is "big motor with fixed gear" verses "small motor with gearing".

How do these options match up?

Examples:

Small Motor
1200 Watt
5 speed
2.17 peak horsepower
Minumum Range 25 miles
Top Speed 51 mph

Big Motor
PMG 132
Fixed Gear
2.54 peak horsepower
Minumum Range 32 miles
Top Speed 51 mph

One thing you realize after observing the charts is that "throttle fiddling" (the idea of riding around with partial throttle) makes a lot of sense when you are using a big motor with a fixed gear, but doesn't make as much sense for the small motor with gearing. The torque is "further forward" (higher) in the powerband in the geared bike. So all the previous discussions that took place between Xyster and myself about how to use the throttle are "true" but they come from different bikes. Our "truths" were valid for our own bike realities.

As a general rule the bigger the motor and the more restricted the current limit the higher your overall efficiency. If your power is restricted by the law (like the 750 Watt law) then gearing can achieve much of the same things that the bigger motor can do. So either way works, but "bigger is better".

 

[fechter]

Now wait a minute,
Those last graphs, what is the X axis? Load? what are the units?

We need numbers and labels on both graph axes.

BTW, good luck getting 51mph with a 1200W motor unless you have a velomobile.

At low speeds, like under 25mph, the smaller motor will probably be more efficient than the large one, due to lower no-load current.

 

[safe]

What are the units?

The Power figures are divided by 25 otherwise they are actuals. I've gone over this before, I don't have access to high quality graphing software right now, so I can't put all the "bells and whistles" into the charts. (someone else could do that if they wanted to, the spreadsheets are "open source" and the numbers could be exported to other graphing software)

The aerodynamics are equal to a lowracer with a fairing or "road racer".

The results are valid. Basically you need a bigger motor and more horsepower to run a fixed gear, but if the efficiency is good enough you do fine.

When power is restricted (laws) then gears always win.

(this is sort of intuitively obvious isn't it?)