Why do e-bikes have tiny chainsets?

Electrically assisted bikes, trikes, etc. that are legal in the UK
Racingt
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Why do e-bikes have tiny chainsets?

Post by Racingt »

Just looking into e-bikes for my wife and I’m seeing chainwheel sizes of 17 teeth through to 40 teeth. I really don’t see the point of a 17t chainwheel, or anything under 32 actually.
Am I correct in thinking that 17*11 is around a 40 inch gear?
What’s the point of the motor if a 40inch gear is the highest gear?
Sorry if this has been covered previously or I’m completely missing the point!
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horizon
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Re: Why do e-bikes have tiny chainsets?

Post by horizon »

Don't you mean 40 -11?
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Racingt
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Re: Why do e-bikes have tiny chainsets?

Post by Racingt »

Nope! The chain wheels are 17, and smallest rear sprocket 11 so I do mean 17*11.
You find it incredible too??
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horizon
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Re: Why do e-bikes have tiny chainsets?

Post by horizon »

Racingt wrote:Just looking into e-bikes for my wife and I’m seeing chainwheel sizes of 17 teeth through to 40 teeth.


Do you mean on the same bike or lots of different bikes?
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
Racingt
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Re: Why do e-bikes have tiny chainsets?

Post by Racingt »

Sorry, I haven’t been clear. E-Mtbs have the tiny 17 tooth (&smilar) chainwheels.
The hybrids, 32 or rarely 40.
I just dont get it. My lowest is 22, and it’s too low to be useable for me.
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horizon
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Re: Why do e-bikes have tiny chainsets?

Post by horizon »

Racingt wrote:Sorry, I haven’t been clear. E-Mtbs have the tiny 17 tooth (&smilar) chainwheels.
The hybrids, 32 or rarely 40.
I just dont get it. My lowest is 22, and it’s too low to be useable for me.


I find 22 very usable with a 34T rear sprocket giving about 17" AFAIK - that's with a fully loaded bike going up a steep hill. I'm guessing that that gear is useful if your e-bike weighs in at say 20 kg and you need to get up that hill with a flat battery. But it could be there is a technical reason in that you aren't going to use the high gears with a motor - I don't know. But it may also be that the BB motors have their own gearing which obviates the need for large chainwheels i.e. the gearing isn't what you think it is.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher
Mike_Ayling
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Re: Why do e-bikes have tiny chainsets?

Post by Mike_Ayling »

Is there an IGH in the rear wheel?

Mike
Cyril Haearn
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Re: Why do e-bikes have tiny chainsets?

Post by Cyril Haearn »

If the chainwheel is so small there is a gearbox in the BB so the effective chainwheel size is 40-50 teeth I think

The 'pinion' drive has this set up
Seems unsuitable to me, energy is lost, too complicated

Looks a bit queer, could be good for starting conversations but attractive to thieves who do not know about bikes

There are lots of e-bike variations including fwd, have a look at some in a shop and ask the 'experts' there to advise you, take test rides
Do not buy yet! Wait a while until you can decide yourself
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Racingt
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Re: Why do e-bikes have tiny chainsets?

Post by Racingt »

Thank you! I didn’t consider the possibility of an internal B.B. gearing. Clearly need to investigate further & take test rides.
Thanks!
loafer
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Re: Why do e-bikes have tiny chainsets?

Post by loafer »

Racingt wrote:Thank you! I didn’t consider the possibility of an internal B.B. gearing. Clearly need to investigate further & take test rides.
Thanks!

these guys will tell you ...very well informed http://www.pedelecs.co.uk/forum/
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Re: Why do e-bikes have tiny chainsets?

Post by Cyril Haearn »

Seems crazy to have such a small ring to take electric drive too, it must wear very quickly
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robgul
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Re: Why do e-bikes have tiny chainsets?

Post by robgul »

For a centrally mounted motor like the Bosch the stated chainring size needs to be multiplied by 2.5 to get a close comparison with a conventional chainring - so a 17T = approx 42T - if you use that notional size with a gear inch calculator (SHeldon has one) it all makes sense. It's all to do with the gearing in the motor itself.

[I've been through all this with a customer at the shop who wanted to raise the gearing ... and also - although we had nothing to do with it - then tweaked the software to double the maximum speed under power]

Rob
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Racingt
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Re: Why do e-bikes have tiny chainsets?

Post by Racingt »

Thanks Rob. I guess the chainwheel rotates faster than the cranks then?

Regarding derestriction, I’ve heard a number of people doing this, I’m guessing, that by using the extra power on the public highway they risk immmediate driving bans due to lack of MOT, insurance, helmet, perhaps licence as the bicycles status becomes a motorcycle powered by electricity. Of course, using off road, probably all legal, but I would emphasise caution as eventually the Police will latch onto this and start prosecuting.

Thanks for the response, there are certainly some attractive models for sale now.
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robgul
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Re: Why do e-bikes have tiny chainsets?

Post by robgul »

Racingt wrote:Thanks Rob. I guess the chainwheel rotates faster than the cranks then?

Regarding derestriction, I’ve heard a number of people doing this, I’m guessing, that by using the extra power on the public highway they risk immmediate driving bans due to lack of MOT, insurance, helmet, perhaps licence as the bicycles status becomes a motorcycle powered by electricity. Of course, using off road, probably all legal, but I would emphasise caution as eventually the Police will latch onto this and start prosecuting.

Thanks for the response, there are certainly some attractive models for sale now.


AIUI the situation with over-clocking to higher speed, licence etc and prosecution is as you say - off-road/private land you can do what you like.

[EDIT : Graham : . . . . . . ]

Rob
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chris_suffolk
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Re: Why do e-bikes have tiny chainsets?

Post by chris_suffolk »

Racingt wrote:Thank you! I didn’t consider the possibility of an internal B.B. gearing. Clearly need to investigate further & take test rides.
Thanks!


Surely any gearing in the BB as part of the motor set-up and is just incidental. All it (and the motor) does is provide more wattage to the system. The gearing is still whatever the chain ring and sprocket are - i.e. whatever the chain goes round, unless I've totally mis-understood how gear inches are calculated (one revolution of the pedals relates to gear inches (for wheel diameter of an old penny farthing?)) Await somebody with more knowledge of these things than me.
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