Excuse the ignoranc...
 

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[Closed] Excuse the ignorance but why do e-bikes have such small front chainrings?

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As above, I have just got back from a trip abroad & have seen first hand that E-bikes are now mainstream, which was surprising as I was in Croatia/ Slovenia which I had obviously wrongly assumed as places where people didn't spend the equivalent of £3-5000 on a bike. But one thing got me, they all had small, like 20 tooth, front chain rings even in the flatter lake regions, why? I had assumed that with assistance a bigger than normal front ring would be required?
Why have I got this the wrong way around?

Cheers.


 
Posted : 15/08/2017 7:50 pm
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I have no idea but motorbike ones are even smaller.


 
Posted : 15/08/2017 7:52 pm
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Could it have something to do with helping reduce torque demands from the motor meaning a smaller lighter motor can be used?

Just an idea I threw in my thought wok!


 
Posted : 15/08/2017 7:58 pm
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no idea mine has a 30t and a sram 10 40 something cassette it rides just like a normal big fat heavy bike


 
Posted : 15/08/2017 8:02 pm
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A lot of the chainrings aren't driven directly from the cranks and there's a gearbox in between the two, so the chainring size isn't comparable to normal bike gearing.


 
Posted : 15/08/2017 8:24 pm
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Chief, that makes sense to me, but surely it would add weight?

Cheers anyhow for all the answers.


 
Posted : 15/08/2017 9:32 pm
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Probably because most of them will rarely go above 25 KPH so low gearing is what they need .


 
Posted : 15/08/2017 10:16 pm
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The motors are low torque motors and you want them to last as long as possible on a single charge. Also at some point the, usually, overweight and unfit person sat on top of the e-bike will have to pedal the bike at some point, and they wouldn't stand a chance without low gearing. Have you felt the weight of an e-bike? I wouldn't want to pedal it unassisted for any length of time.


 
Posted : 16/08/2017 6:00 am
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As above, I have just got back from a trip abroad & have seen first hand that E-bikes are now mainstream

We're in Somerset and every other bike we've seen (and there are lots) has a motor.


 
Posted : 16/08/2017 4:35 pm
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We're just back from 3 weeks wandering around France and there were a lot more E-bikes there than I'm seeing here in the UK. Mostly cheapo ones though, and being ridden even slower than my wife and I were going on our cheap non-electric folding bikes (although that was on the flat - probably would have spanked us uphill).


 
Posted : 16/08/2017 4:43 pm
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Unsure all ebikes cost over 3k...mainland Europe has far more cyclists than the UK and things are priced differently so more people have access to affordable biking...
I have no opinion on them other than they are good if it gets more people biking...


 
Posted : 16/08/2017 5:45 pm
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Power = speed x torque.

Torque = size/cost

if your electric motor only goes slowly it needs to make a lot of torque, which means it's big and costly. Make a small fast motor to save money, and fit a smaller front chain ring so you don't need to gear the motor down as much as before. Riders torque can be applied at a further reduction ratio


 
Posted : 16/08/2017 6:18 pm

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