0-15mph acceleration of 250W electric bicycle?
- Thread starter carlston49
- Start date
"How long does it take a 250W electric bicycle to accelerate from 0-15mph without pedal assistance?"
A very long time (clue pedelec ;-)
"How fast do they go uphill?"
Depends on a number of factors, Cranks drive or hub and type of, and gradient of hill. But somewhere between a few mph to 15 odd mph.
A very long time (clue pedelec ;-)
"How fast do they go uphill?"
Depends on a number of factors, Cranks drive or hub and type of, and gradient of hill. But somewhere between a few mph to 15 odd mph.
With a sim fit man they zip off like a rocket and climb at 15 mph.
With an old fat asthmatic they still go not badly and climb reasonably well.
Of corse the steepness of hill etc all count too.
Oh the 250 watt is a fudge most legal motors can max at over 600 watts some can hit a Kw and gearing helps too.
A 500watt direct drive can struggle on a fairly simple hill as no gears and it really won't do 750 watts or it would be sold as such.
With an old fat asthmatic they still go not badly and climb reasonably well.
Of corse the steepness of hill etc all count too.
Oh the 250 watt is a fudge most legal motors can max at over 600 watts some can hit a Kw and gearing helps too.
A 500watt direct drive can struggle on a fairly simple hill as no gears and it really won't do 750 watts or it would be sold as such.
Very few ebikes have throttles.
Mine goes no where if you do not pedal
Up hill, very fast or very slow
D
Deleted member 4366
Guest
Lets estimate:
The average torque of a 250w motor below 15 mph would be about 24NM. You can get that from the Ebike.ca simulator.
The radius of a 26" wheel is about 30cm, so the force at the tyre would be 24/.3 , which is 80N.
Acceleration is force divided by mass. Lets say a 75kg rider on a 25kg bike, so 100kg total. That means that the acceleration is 80/100 = 0.8 M/S/S
The first equation of motion says that final velocity = initial velocity +acceleration x time or V=U +AT. Turning that around, you get V-U=AT or T=(V-U)/A
U is 0, V is 15mph, which is 15x1500/ 60/60 M/S = 6.25 M/S
Therefore we have T = (6.25-0)/ 0.8. which is 7.8 seconds.
QED.
The average torque of a 250w motor below 15 mph would be about 24NM. You can get that from the Ebike.ca simulator.
The radius of a 26" wheel is about 30cm, so the force at the tyre would be 24/.3 , which is 80N.
Acceleration is force divided by mass. Lets say a 75kg rider on a 25kg bike, so 100kg total. That means that the acceleration is 80/100 = 0.8 M/S/S
The first equation of motion says that final velocity = initial velocity +acceleration x time or V=U +AT. Turning that around, you get V-U=AT or T=(V-U)/A
U is 0, V is 15mph, which is 15x1500/ 60/60 M/S = 6.25 M/S
Therefore we have T = (6.25-0)/ 0.8. which is 7.8 seconds.
QED.
Last edited by a moderator:
With pedaling (I only have a pedelec to test with) under 4-5 seconds, I don't ride with a clock so that is from counting in my head. Healthy, reasonably fit 78 kg slightly asthmatic 61 year old man on +25 kg bike.
I have stopped riding up hills at 25 km/h in order to save the battery and go further so now I am at between 16 and 19 km/h in assistance level 3.
I have stopped riding up hills at 25 km/h in order to save the battery and go further so now I am at between 16 and 19 km/h in assistance level 3.
Calculations like that at 1am, that's incredible.
What's one decimal place among friends?
It's Christmas 0.78, 7.8 or 780 very well done.
D
Deleted member 4366
Guest
Yes, it was late. I got my units mixed up like any schoolkid. The units of mass are kg not N, so it's out by a factor of 10. The correct answer is about 7.8 seconds. I edited the one above now.
It would be interesting to have a race between a hub-motor and crank-motor with exacly the same controller. Which one would win and why? That's your homework for tonight.
It would be interesting to have a race between a hub-motor and crank-motor with exacly the same controller. Which one would win and why? That's your homework for tonight.
Last edited by a moderator:
Well I'm impressed. But then I get confused working out the various machine ofsets for a mortice and tenon.
Not being funny, I hope, but get on one and find out. That would be my best suggestion for your best answer.
Not being funny, but it's freezing cold outside...so I'm not going anywhere. Besides, we all know it's 7.8 seconds now!
They vary due to a number of factors, mine is faster than that.
Reasons: My 65 kilos, bike has controller capable of delivering over 28 Amps, rear hub motor is in 20" wheel.
.
Uphill speeds depend on the motors winding, and the amps allowed by the controller,also battery voltage,same bike same hill same motor at 48 v with 30amp controller i can do 11mph with a bit of help,48v with 10amp controller and its down to about 7mph with a lot of help,and it feels like hard work,36v with a 18amp controller about 9mph with a little help,same on the flat more volts and more amps accelerate much quicker,but drain the battery far quicker,this is on a hill that most lycras get out of the saddle for, and a lot of people get off and push.
Im going for the hub motor on all but the steper hills, when the crank motor can start in a lower gear and gradually build up speed through the gears.
Is that correct?
My impression is that actually out there in the world, the bulk of bikes are Chinese and do have throttles.
Both of mine have.
D
Deleted member 4366
Guest
I have 8 ebikes at the moment. They all have throttles. My neighbour has two, and they both have throttles as well. In fact, I'm pretty sure that every ebike I've ever seen out and about in Telford (at least 100) had throttles except two Kalkhoffs.
It's rare to see an ebike in a shop now with a throttle, but many seem to grow one not long after they left the showroom.
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