Smaller wheels and hub motors

[taiwwa]

It seems that especially for hill climb, smaller wheels are better with hub motors. Why 700c to begin with? I generally don’t notice a difference with 700c and 650b. The difference between 700c and 26 isn’t that large either. It just seems that 700c is traditional. Too small does change handling characteristics and bumps are felt more acutely.

A smaller wheel, 24 or 26 inches, would not only have better hub motor efficiency and power, but also is easier to pack and stow away in cars or airplanes. Size of 700c wheels makes them hard to pack for airplanes but with smaller wheels you can fit in a suitcase.

 

[neptronix]

Yep.

The larger the wheel, the lower the RPM, the less power you can extract from a DD hub.
Another thing that happens in small wheels is we often see an efficiency increase in addition to the extra continuous power capability and torque.

On a bike with 26" wheels, 22" and 24" are the sweet spot, any lower than 22" and your cranks are hitting the ground often.

Me and e-HP are both big fans of 24" rear, 26" front configurations. Another upside is that this creates a slacker fork angle, and gives you more of a crank forward positioning when pedaling, which is comfortable. You can also run a honker of a 24" rear tire if you wish.

22" will also accept 18" motorcycle tires ranging from 2.25" wide to ~5" wide.

On the other hand, a lot of geared motors work excellent in the larger wheel sizes because they are typically overgeared a bit. The low RPM of the wheel doesn't matter as much. In smaller wheels, the torque gets ramped up but the efficiency can go down on certain models because now, gear friction is a higher percentage of the load. So really small wheels ( < 22" ) are out of the question because there will be compromises.

 

[ebike4healthandfitness]

In smaller wheels, the torque gets ramped up but the efficiency can go down on certain models because now, gear friction is a higher percentage of the load.

Is this modeled in the ebikes.ca motor simulator?

 

[neptronix]

Is this modeled in the ebikes.ca motor simulator?

Absolutely, and bears true in real life

Extreme example, 20" versus 29":
Motor Simulator - Tools



Huge difference in thermals, efficiency, and continuous power handling.

On a semi recumbent bike you can really take advantage of this by driving the RPM into the stratosphere.. sprints to 60mph possible on this small motor now



Volt up, gear down my dudes

 

[ebike4healthandfitness]

Absolutely, and bears true in real life

Extreme example, 20" versus 29":
Motor Simulator - Tools

View attachment 357762

Huge difference in thermals, efficiency, and continuous power handling.

On a semi recumbent bike you can really take advantage of this by driving the RPM into the stratosphere.. sprints to 60mph possible on this small motor now

View attachment 357763

Volt up, gear down my dudes

Oh yes I do know in non geared motors like the GRIN and leaf bike 1500w that for any given voltage, amps and unloaded speed the faster wind with a smaller diameter tire always beats a slower wind and larger diameter tire. We see this happen with the 4T leaf bike 1500w with 20" tire vs. 5T leaf bike 1500w with 25" tire. Both have the same unloaded speed when used at X volts and X amps but the 4T/20" is more efficient and powerful.

Yes, that part I understand.

What I am asking about is geared motors like the MAC. (i e. the part you mentioned in the last paragraph of your first post)

 

[neptronix]

What I am asking about is geared motors like the MAC. (i e. the part you mentioned in the last paragraph of your first post)

Also in the simulator and modeled.

 

[ebike4healthandfitness]

Also in the simulator and modeled.

Can you point out an example?

For example, 72v and phase runner using a 20" tire and MAC 8T beats a 29.13" tire MAC 12T in efficiency at almost all points (except for the very highest speed where it is just a hair less efficient) and the 20" tire 8T wins in power at 11 mph onward (from 0 mph to 11 mph it merely ties the 29.13" 12T for power):

(The tire diameter of 29.13" was used with the 12T winding so it would have the same unloaded speed as the 20" diameter tire and 8T winding)

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

 

[Chalo]

For appeasing hub motors, stowing in cars, shipping in airplanes, yes small wheels are best.

For riding, the bigger the better.

What is your bike for?

 

[bengxe]

Me and e-HP are both big fans of 24" rear, 26" front configurations. Another upside is that this creates a slacker fork angle, and gives you more of a crank forward positioning when pedaling, which is comfortable. You can also run a honker of a 24" rear tire if you wish.

22" will also accept 18" motorcycle tires ranging from 2.25" wide to ~5" wide.

Depending on the bike, the slacker head angle isn't always an upside. I had to lower my fork 30mm to compensate for my 24" rear wheel. The front end always felt too light when sitting, especially with some wind force pushing on my chest. But the drop in standover height was a big benefit for me.
I'm still interested in trying a 22" with an 18" moped tire, but I'm finding inconsistent info on what works and what doesn't. Do you know of a specific rim and tire that work with each other?

 

[Papa]

I'm still interested in trying a 22" with an 18" moped tire, but I'm finding inconsistent info on what works and what doesn't.

20" 406 rims and tires works just peachy. The only time MC tires are suggested is when flats become an issue - the stiff sidewalls produce a harsher ride, and you suffer an increased weight penality.

 

[neptronix]

I found that certain motorcycle tires had an innate suspension to them due to the massive amount of rubber. Loved how they ride on a very fast bike.

The smaller the diameter, the more hell they are to mount though. That's why i'd like to stop at 18" motorcycle size aka 22" bike size

 

[bengxe]

20" 406 rims and tires works just peachy. The only time MC tires are suggested is when flats become an issue - the stiff sidewalls produce a harsher ride, and you suffer an increased weight penality.

From what I've read, it seems that 22" rims and 18" tires aren't as directly compatible as 20" and 16". And a 16" tire that is tall enough to work for my frame geometry would be too wide to fit in the swingarm. The stiff sidewalls are my reason for wanting to swap, bicycle tires feel squirmy unless I run a lot more pressure than I want to.

 

[Papa]

Depending on the bike, the slacker head angle isn't alwas an upside

Slack headtube angles typically require an appropriate amount of positive trail. But there's three other attributes that needs careful consideration when fooling with steering geometry ..... and that's tiller, handlebar width and grip angle.

 

[neptronix]

From what I've read, it seems that 22" rims and 18" tires aren't as directly compatible as 20" and 16".

Hasn't been my experience. I hookeda Mitas 18" tire on a 22" fitbike co heel, no problem.

Seen in front is of it is a bike 20".

 

[Papa]

I found that certain motorcycle tires had an innate suspension to them due to the massive amount of rubber.

Schwalbe Tires states otherwise -- Instead of thick rubber for suspension, Schwalbe recommends increased tire width (read, greater air volumn), and thin supple sidewalls. Thin sidewalls offer less resistance to flexing and produces less heat.... AND...produces lower rolling resistance.

I never have problems or experience mounting difficulties with proper 406 tires on quality 406 rims. I've been solely on 406's for over 30 years.... It's all I ride Chief

 

[bengxe]

Slack headtube angles typically require an appropriate amount of positive trail. But there's three other attributes that needs careful consideration when fooling with steering geometry ..... and that's tiller, handlebar width and grip angle.

Trail isn't something you have control over without swapping forks, and it doesn't compensate for the front wheel being too far out in front. I would say bar height and stem length are both more important than the 3 you mentioned, but I have no idea what you meant by "tiller". I'm assuming grip angle means bar bend angles?

 

[bengxe]

Schwalbe Tires states otherwise -- Instead of thick rubber for suspension, Schwalbe recommends increased tire width (read, greater air volumn), and thin supple sidewalls. Thin sidewalls offer less resistance to flexing and produces less heat.... AND...produces lower rolling resistance.

I never have problems or experience mounting difficulties with proper 406 tires on quality 406 rims. I've been solely on 406's for over 30 years.... It's all I ride Chief

And if a tire manufacturer wants us to use their highest margin products in ways that minimize their lifespan, who are we to argue?

 

[bengxe]

Hasn't been my experience. I hookeda Mitas 18" tire on a 22" fitbike co heel, no problem.

Thanks for this, I'll keep those names in mind when I'm ready to do something.

 

[neptronix]

Thanks for this, I'll keep those names in mind when I'm ready to do something.

Ya welcome, for motorcycle or moped tires that come in narrow sizes, i usually recommend treatland.tv because their selection is excellent, and prices pretty good.

 

[neptronix]

Schwalbe Tires states otherwise

Schwalbe is far from an authoritative source on building very fast ebikes; they cater to the regular cyclists and don't understand the needs of the kinda stuff we build here.

 

[Papa]

Trail isn't something you have control over without swapping forks, and it doesn't compensate for the front wheel

Not true.

Within limitations, trail can be altered without swapping or modifying the fork. And..., repositioning the front wheel slightly forward, typically improves handling.

 

[G8trwood]

I thought it was amp up volt down, lol, For old and slow that is

The grin Fat slow and the Mac12T have very similar power graphs until the mo power go fast stages

 

[Papa]

Schwalbe is far from an authoritative source on building very fast ebikes; they cater to the regular cyclists and don't understand the needs of the kinda stuff we build here.

I never implied they were an authority. I'm merely pointing that Schwalbe's technical reasoning mirrors that of many performance tire manufacture's... and I concur e.

But by all means, choose what you feel is optimum for you. I chose to rely on physics... not opinions based on "seat of the pants"... which varies widely, to the point of confusion.

 

[ebike4healthandfitness]

Schwalbe Tires states otherwise -- Instead of thick rubber for suspension, Schwalbe recommends increased tire width (read, greater air volumn), and thin supple sidewalls. Thin sidewalls offer less resistance to flexing and produces less heat.... AND...produces lower rolling resistance.

I never have problems or experience mounting difficulties with proper 406 tires on quality 406 rims. I've been solely on 406's for over 30 years.... It's all I ride Chief

So basically a large attack surface for things like goathead thorns. That is just going to increase the chances for a flat tire.

 

[neptronix]

I use motorcycle tires specifically because they stand up to extremely long goat head thorns, which my region is littered with. No bicycle tire except a few models of very heavy kenda tire come close to the amount of rubber depth a mid weight motorcycle tire has.