250w vs 500w

[CerIs]

Hi, ebike newbie here and legalities aside im torn beside a 250w and 500w motor. Originally the 500 appealed for the extra speed/power but as I was driving the car at 20 yesterday I thought "I really dont need to be doing any more than 20mph on a bicycle", ill be using it for a 16 mile round trip to work.

So my question is how hard is it to get an ebike from 15mph to 20mph, given flat ground and reasonably fit rider? I ask because I read on another post here that going from 15 to 20 is not same as 0mph to 5mph, wind resistance etc? Any advice appreciated.

Thanks C

 

[JohnCade]

Depends on the bike and tyres fitted and how well it rolls. I can get my Kalkhoff Agutta up to over 20mph on the flat but can’t hold it there too long as the weight tells when the road rises just a tiny bit. Just under that at about 19 mph can be held much better. The Kalkhoff cuts out at a smidgin over 17mph and is legal.

Lighter 250W kit converted bikes would be easier to keep the speed with even if the cut out was left at 25kph. Many people change the cut out on the Chinese bikes LCD and then the bike can hold over 20mph quite easily. If illegally. You don’t need a 500W bike for that.

 

[RobF]

Wind resistance means each extra mph is harder to get the faster you are going.

That applies to any bike, powered or not.

Don't take too much notice of watt ratings, all motors peak much higher and the markings on some motors may be 'marks of convenience' to make them appear legal.

Which bikes or kit motors are you thinking of?

 

[CerIs]

Which bikes or kit motors are you thinking of?

Was originally thinking about a cyclotricity but they have a wait time till after xmas.

Now im thinking a front wheel drive kit off ebay (cant face RWD complexity) / 10ah bottle battery / and cheap(ish) mountain bike from halfords. Looking at around £500 so far which seems like a bargain, or too good to be true lol!

 

[JohnCade]

If it was me I would buy a kit from one of the dealers who are on this forum. You will get a proper warranty and they stand by their products. Woosh and others sell good kits and Woosh will even fit it for little money if you are near them. Not all kits are equal and though nominally rated at 250W some motors are much more powerful.

A CD kit is easy to fit and perhaps the best for keeping up a good speed. Look back up the forum for some threads.

 

[acm2000]

My Krieger would do 25 if you derestricted it easy

 

[RobF]

Was originally thinking about a cyclotricity but they have a wait time till after xmas.

Now im thinking a front wheel drive kit off ebay (cant face RWD complexity) / 10ah bottle battery / and cheap(ish) mountain bike from halfords. Looking at around £500 so far which seems like a bargain, or too good to be true lol!

The 250w BPM motor has plenty of poke and should do a reasonable job for you derestricted.

It's not safe to put anything much more powerful in the front, unless you engineer it well, and even then you can not be sure of the strength of the drop outs.

 

[CerIs]

It's not safe to put anything much more powerful in the front, unless you engineer it well, and even then you can not be sure of the strength of the drop outs.

Was thinking that myself, there are 1000w FWD kits on ebay, surely the front wheel will be mostly spinning on the ground with that kind of power?

 

[RobF]

Was thinking that myself, there are 1000w FWD kits on ebay, surely the front wheel will be mostly spinning on the ground with that kind of power?

More likely to be spinning out of the disintegrating drop outs.

 

[trex]

Was thinking that myself, there are 1000w FWD kits on ebay, surely the front wheel will be mostly spinning on the ground with that kind of power?

DD motors are not as torquey as geared hub motors, so you will be OK. The main advantage of DD kits are cheapness and reliability. DD motors are cheaper than geared hub motors because they don't have a gearbox. To get the most of your 1000W DD kit, you will also need at least a 48V 12AH battery with 30A BMS. DD motors remain the best choice for high power, high speed, high mileage systems but you'd need 1500W and above to beat the BPM geared hub kits running at 48V. Even then, DD motors burn about 30% more energy on average compared to geared hub motors at the same speed, so that will negate the cheapness attribute. On reliability, DD motors will remain forever kings of the jungle.
Here is a quick comparison between geared and DD motors:
http://www.ebikekit.com/knowledge-base/E-Bike-Motors

 

[CerIs]

Yes I think ill be getting a DD. The bpm 250 looks out of my price range tbh.

Was looking at this on ebay http://www.ebay.co.uk/itm/26-Ebike-Cycling-Electric-Bicycle-Conversion-Kit-250W-36V-Hub-Motor-Front-Wheel-/400504711080?hash=item5d3ff0e7a8:g:YxUAAOSwd4tT8c3i . Good price at £130 but says max speed is 25 km/h - doesn't mention if its limited or that really is max (there is no LCD comp). C

 

[trex]

you'll have to upgrade your present battery - otherwise, your new DD kit will produce 30% less power than your present hub kit. If you don't throw enough money at it, this project is not going to fly. DD e-bikes aren't exactly cheap by the time you kit it out with a suitable battery.

 

[CerIs]

you'll have to upgrade your present battery

Haven't bought a battery yet, but standard 36v - 10ah should do the job?

 

[trex]

no. The controller for those 1000W kits have 12 Mosfets, they are usually fitted with 30A fuse. Your current controller has 6 FETs and no fuse. Your current battery is normally fused at 20A. It'll blow every time you hit a steep hill. You will need a minimum 36V 15AH battery with high discharge Samsung 29E cells, best fit is 48V 12AH Samsung cells.

 

[CerIs]

The controller for those 1000W

oh right, was just posting 1000w as example - im only going for 250w (or maybe 500) . Think id be in a ditch within a week on a 1000w lol

 

[trex]

that 250W kit on ebay that you linked to is gutless. They quoted 15NM torque, not even good enough for the Netherlands.

 

[soundwave]

5000w each wheel woof

HPC "Thunderbolt" - Cross Country Complete Kit
$4,299.00

http://www.hi-powercycles.com/

 

[CerIs]

that 250W kit on ebay that you linked to is gutless. They quoted 15NM torque, not even good enough for the Netherlands.

hmm wasnt aware I needed to be looking at torque, what should I be looking for? (not all items list it). Is it a big deal?

 

[JohnCade]

hmm wasnt aware I needed to be looking at torque, what should I be looking for? (not all items list it). Is it a big deal?

It is if you want to go uphill or fast on the flat. That’s what I meant above about not all kits and motors being equal. They might all be rated nominally at 250W but some will peak at 700W or so and some will struggle to actually give you 250W. The cheap eBay kits are not very powerful usually.

You should read up about it more before you commit yourself. Just this last week there was a thread here where someone bought a kit from eBay and it wouldn’t pull the skin off a rice pudding. But he bought it and it works so he’s stuck with it.

 

[Nealh]

You still haven't given a budget.
For your needs I would consider the GSM 18a 250w Crank drive from Woosh with a 13 or 15 ah battery from them or Eclipse, that set up will give about 45mile range be very good for hills and achieve 20mph + esp if you like to pedal. No wheels to build or fiddly messing about if you have a puncture. Don't forget you will need a pair of torque arms for front forks if they are ali other wise eventually the drops will snap due to the rotation torque.