Front Chain Ring Sizes

[Ebiker33]

So I was looking at a website that was giving options for front chain ring sizes for their motors
They say a 52T is the fastest for their motor, but the 44T has the most torque.
I thought this was mainly controlled through the rear gears.
The Watt Wagon has a 60T with Gates belt

Yet sometimes you see small very chain ring sizes up front, what is really the best for an Ebike?

 

[Nova Haibike]

So I was looking at a website that was giving options for front chain ring sizes for their motors
They say a 52T is the fastest for their motor, but the 44T has the most torque.
I thought this was mainly controlled through the rear gears.
The Watt Wagon has a 60T with Gates belt

With a mid-motor, the torque is multiplied through the gears. While you cannot change the front chainring (unless the motor can accept multiple chainrings such as some Yamaha units), the size does matter. A larger ring trades torque for speed.

Yet sometimes you see small very chain ring sizes up front, what is really the best for an Ebike?

Older Bosch mid-drives used a small chainring because the ring rotates at approximately 2.5 times the speed of the crank.

 

[kmccune]

So I was looking at a website that was giving options for front chain ring sizes for their motors
They say a 52T is the fastest for their motor, but the 44T has the most torque.
I thought this was mainly controlled through the rear gears.
The Watt Wagon has a 60T with Gates belt

Yet sometimes you see small very chain ring sizes up front, what is really the best for an Ebike?

Its a matter of "gearing" ,look at most simple ICE units, the motor pulley(if you will) is generally a good bit smaller then the pulley on the "work side of things, to increase the torque ,we trade rpms for the ability to move things . The mechanical advantage lies in the fact( going back to simple machines) the load does not have to move as far for a given time.
I have seen people try to motorize a bicycle with an overgear system, you couldn't even get the small gas engine to "fire'or hear it doing so when you towed the blessed thing.
That's the advantage of electric motors very good torque at stall. whereas when you gear these things for speed you see how quickly you lose ability to go fast or tackle hills, so a smaller chainring will give you better gearing for pulling ability, like the old 3 ring MTBs the power chainring was the small one. My cadence his become so lacking I have to go really down in the gearing to move a heavy EBike due to friction, wind resistance, etc( It amazed me when I used to ride an old 10 speed how much a slight headwind held me back.-When I was young I never noticed the wind or slight inclines-Ebikes brung me, so EBikes will send me home)

 

[TrevorB]

So I was looking at a website that was giving options for front chain ring sizes for their motors
They say a 52T is the fastest for their motor, but the 44T has the most torque.
I thought this was mainly controlled through the rear gears.
The Watt Wagon has a 60T with Gates belt

Yet sometimes you see small very chain ring sizes up front, what is really the best for an Ebike?

Best chainring size depends on what max speed you are after and gear ranges. For 9-11spd cassettes smallest cog is 11t, a 38t chainring good for 35-40kmhr, 44t 50kmhr. For 32kmhr motor 38t is ideal for commuting, could go to 34t if MTBing. 45kmhr motor 40-44t, depends on your cadence. If you want to sit on cutoff may need to try different chainring to match you cadence.

I can't sit on my bikes 32kmhr cutoff 13t is bit to high and 15t is 28kmhr. Really need 14t rear cog for 38t chainring or 13t with 36t chainring.

 

[TrevorB]

With a mid-motor, the torque is multiplied through the gears. While you cannot change the front chainring (unless the motor can accept multiple chainrings such as some Yamaha units), the size does matter. A larger ring trades torque for speed.

Older Bosch mid-drives used a small chainring because the ring rotates at approximately 2.5 times the speed of the crank.

14t=35t chainring 15t =37.5t, 16t =40t

 

[Sierratim]

So I was looking at a website that was giving options for front chain ring sizes for their motors
They say a 52T is the fastest for their motor, but the 44T has the most torque.
I thought this was mainly controlled through the rear gears.

A larger chain ring allows you to develop more speed at lower torque with a given cassette while a smaller chain ring will develop more wheel torque at lower speed with the same cassette. You can think of the chain ring as setting the mid-point of your desired bike performance and the cassette then offering a range of opitons from that mid-point.

eEMTBs often have smaller chain rings for improved climbing ability. One of my sons rides a Trek Rail eMTB that's equipped with a 34t ring. With the 10-51t cassette this provides a huge amount of torque, but a more limited top end speed than my ebike with a 48t chain ring and a 11-50t cassette.

What's best for you? Depends on your riding ability, typical ride profile, and overall intended use. More torque for steep terrain and/or more rider assistance, more speed for flatter terrain and/or stronger riders. Test riding is a really good idea. Our LBS rents ebikes by the day so it's easy to get one out on a trail you'd actually be riding.

BTW - This Gear Calculator can compare various gearing combinations for chain ring and cassette options. The rider's preferred cadence range can also be considered when comparing bike speeds with various gear setups. There are several other calculators available; to the Google!

 

[tomjasz]

In my world these chainring discussions are frustrating. Mid-drive kit builders often want to squeak every MPH possible out of their motor. Or ride it like a moped. Just throttle away regardless of appropriate gear use. Want to go 30? Buy a 30MPH bike/kit. Bought a less powerful bike than you want? Upgrade or just ride it like you stole it.