What is in that subconscious mind of yours?

halfer · Nov 23, 2012

I don't have any particular thoughts on motor wattage - as many have said here, if you have a speed limiter anyway, a higher wattage won't make much difference in practice.

Now, if you were asking whether the law could be changed to permit a higher speed limit, then yes, I'd be in agreement. I frequently go above 20mph and sometimes hit over 30mph under my own steam, so whether I've achieved that with the motor is irrelevant in the event of an accident.

My primary reason for supporting this isn't my own speed, however - I'm happy as things are. But in order to encourage more people out of their cars permanently, something has to change - and as we know e-bikes haven't yet hit critical mass in the UK anyway.

Old_Dave · Nov 23, 2012

Hi mountainsport

I think I'd of built one, but not for the speed which is dictated by skinny tyres / speed limits and road conditions, but purely for the hill climb capability.

morphix · Nov 23, 2012

mountainsport said:
Hi again

No offence here to you all,but will anyone be man or woman enough to admit that if the ebike law had changed by increasing the power wattage from 250w - 1000w who would actually go for it or for the challenge,what will prevent you from doing so, will it be the fear of speed or just that overwhelming feeling powering the bike?

I'm not sure if that anyone will respond to this for various reasons

Mountainsport

Interesting post

For me, I think 350W would be the limit..especially on the sort of small-wheel bike I'm now riding with aluminium frame.. even if they changed the laws I doubt I would be inclined to get more power, because that means bigger battery = more weight. I'm quite happy with 250W, keep things light and easy to handle..and also 250W moves me along at a good respectable speed (20mph+).

I've seen 500W bike vids and they took too unwieldy to handle, borderline moped...you have to reinforce the forks etc and I wouldn't like to do that for a start.. and 1000W is definitely into moped category..I just wouldn't feel safe on those.

flecc · Nov 23, 2012

I'm not bothered about doing so, partly because my present "legal" e-bike peaks at well over 1000 watts gross.

It's all about ratings, we know our so called 250 watt bikes are nothing of the sort, so would that 1000 watts you mention be a rating meaning perhaps 2500 watts, or would it be the actual. As I've legally got the actual already, no point in the latter case. If it's the former case, I wouldn't want it since it would no longer be cycling.

GaRRy · Nov 23, 2012

1000W is easily getting into small motorcycle teritory at which point id rather have the motorcycle with better handling,wheels,tyres,seat and most of all brakes.

Jeremy · Nov 23, 2012

GaRRy said:
1000W is easily getting into small motorcycle teritory at which point id rather have the motorcycle with better handling,wheels,tyres,seat and most of all brakes.

Actually, if you measure it, you'll find that a fair few perfectly legal ebikes get to around 1000W!

Even my little alloy folding ebike, with it's small Bafang rear hub and modest 36V nominal battery peaks at around 1100W, even though the average power it uses is only around 100 to 150W.

As mentioned elsewhere, the power thing is a bit of a red herring, especially as you can easily have an ebike that's limited to 15 mph max assist speed (often by a combination of motor Kv, gear ratio and battery voltage) yet delivers 1000W or more when climbing hills.

morphix · Nov 23, 2012

mountainsport said:
Hi morphix

Have you ever ridden a 1000w ebike before? and if not, how do you know that it would feel more unsafe.Dont get me wrong here speed does increase the level of danger,but it maybe just down to the individual who is riding the bike.: I am not disagreeing with your personal opion OK.

Mountainsport.

I've never ridden one and I certainly wouldn't mind trying it for the hell of it

My only experience of 1000W is the videos on YouTube and the speeds reported (30mph+) makes me cringe! I imagine it would be a lot of fun riding at those speeds (I'm a speed freak myself, even with my 250W motor) but I just imagine the potential for accidents would be much greater and so would make this more like riding a moped than a pedelec.. you need a helmet (and I hate those!) and you would need to take your CBT every 2-3 years or whatever it is (unless you hold a full licence, which remarkably at age 40, I don't!).. and finally..what would put me off these high speed bikes is that you'd probably get stopped by cops regularly for checks etc.. blah.

103Alex1 · Nov 23, 2012

mountainsport said:
Hi again

No offence here to you all,but will anyone be man or woman enough to admit that if the ebike law had changed by increasing the power wattage from 250w - 1000w who would actually go for it or for the challenge,what will prevent you from doing so, will it be the fear of speed or just that overwhelming feeling powering the bike?

I'm not sure if that anyone will respond to this for various reasons

Mountainsport

I feel safer on my bike than some mopeds, but a good scooter capable of 70kph+ is perfectly OK as long as you're careful with the cornering and body position. Wouldn't want to ride a scooter like that if I hadn't sat a driving test and obtained a load of experience though. Not a fan of motorbikes... at 90mph plus I prefer to be driving a car with an airbag

Am quite happy on a regular bike doing up to about 30mph. Much more than that and the bike isn't really designed for it. As far as power output ratings are concerned, it's hard to comment for the reasons above. It doesn't really seem to be the key issue ... it's whether the motor is able to deliver the necessary power when you need it that matters most to me, along with getting far more range out of batteries of the weight I currently have than is presently the case. If I could have double the present capacity (especially having ditched the car) I'd probably be quite happy with my bike as it stands even with the speed-assist limits, but I don't want the extra weight. The technology must be capable of development but it is very slow in the coming.

GaRRy · Nov 23, 2012

Jeremy said:
Actually, if you measure it, you'll find that a fair few perfectly legal ebikes get to around 1000W!

Even my little alloy folding ebike, with it's small Bafang rear hub and modest 36V nominal battery peaks at around 1100W, even though the average power it uses is only around 100 to 150W.

As mentioned elsewhere, the power thing is a bit of a red herring, especially as you can easily have an ebike that's limited to 15 mph max assist speed (often by a combination of motor Kv, gear ratio and battery voltage) yet delivers 1000W or more when climbing hills.

I think you are being a bit predantic By 1000W I was assuming this to mean 1000W contiuous not peak otherwise the OP question makes absolutely no sense as he would be just asking if we would ride what we ride now.

Jeremy · Nov 23, 2012

GaRRy said:
I think you are being a bit predantic By 1000W I was assuming this to mean 1000W contiuous not peak otherwise the OP question makes absolutely no sense as he would be just asking if we would ride what we ride now.

Not at all. What I was trying to illustrate is that there isn't a hard and fast relationship between power and speed with an ebike. Speed is usually limited by battery voltage, motor Kv and gear ratio, rather than power. Certainly you need enough power to allow the motor to turn at its maximum voltage determined rpm, but that almost certainly wouldn't be the limiting power.

For example, if you have a reasonably good hybrid ebike, with decent HP tyres, then it only needs around 130W to do 15mph on the flat with no headwind. If you want to do 25mph on the flat then it needs around 400W, provided the gearing, battery voltage and motor Kv allowed it. 1000W would get you to around 34 mph, but the slightest hill or headwind would knock that right back. If the ebike was geared to do 34mph with 1000W then it would probably be hopeless at climbing hills, even at a lower speed.

This means that a 1000W ebike would probably be similar to many currently approved "250W" ebikes in practice.

flecc · Nov 23, 2012

Indeed Jeremy, a high speed e-bike I had which powered to 22 mph using a motor that peaked at over 1000 watts was hopeless on hills on power alone, struggling even at a 6% gradient.

GaRRy · Nov 23, 2012

Jeremy said:
Not at all. What I was trying to illustrate is that there isn't a hard and fast relationship between power and speed with an ebike. Speed is usually limited by battery voltage, motor Kv and gear ratio, rather than power. Certainly you need enough power to allow the motor to turn at its maximum voltage determined rpm, but that almost certainly wouldn't be the limiting power.

For example, if you have a reasonably good hybrid ebike, with decent HP tyres, then it only needs around 130W to do 15mph on the flat with no headwind. If you want to do 25mph on the flat then it needs around 400W, provided the gearing, battery voltage and motor Kv allowed it. 1000W would get you to around 34 mph, but the slightest hill or headwind would knock that right back. If the ebike was geared to do 34mph with 1000W then it would probably be hopeless at climbing hills, even at a lower speed.

This means that a 1000W ebike would probably be similar to many currently approved "250W" ebikes in practice.

Sorry just dont see how a 1000w continous would only climb as well as a 1000w peak as its peak would then obviously be higher (eg 4000w assuming both do 4 times their continuous figure although I guess this is probably not linear). Yes it would need a bigger battery etc to allow it to do this which could be a limiting factor but again it seems to me from original question that this a given.

More powerful motor = more power provided the power to use it is available and even on the flat at 30 mph I still would prefer the advantages a moped/motorcycle give in terms of safety.

Please note I am not anti 1000w ebikes. I am anti 1000w ebikes that are still counted as bicycles rather than mopeds/motor cycles with all the rules and restictions that follow (or to be fair we should scrap those as well and thats never going to happen).

Jeremy · Nov 23, 2012

GaRRy said:
Sorry just dont see how a 1000w continous would only climb as well as a 1000w peak as its peak would then obviously be higher (eg 4000w assuming both do 4 times their continuous figure although I guess this is probably not linear). Yes it would need a bigger battery etc to allow it to do this which could be a limiting factor but again it seems to me from original question that this a given.

More powerful motor = more power provided the power to use it is available and even on the flat at 30 mph I still would prefer the advantages a moped/motorcycle give in terms of safety.

Please note I am not anti 1000w ebikes. I am anti 1000w ebikes that are still counted as bicycles rather than mopeds/motor cycles with all the rules and restictions that follow (or to be fair we should scrap those as well and thats never going to happen).

The explanation isn't that easy, but has to do with the fixed relationship between motor rpm (and hence bike speed) and applied voltage. Motor rpm is determined not by power, primarily, but by the applied voltage and a motor constant, Kv. For example, the motor on one of my ebikes has a Kv (measured as wheel rpm) of about 10 rpm per volt. On a 36V nominal battery, no matter how much power I put through the motor, it is still only ever going to turn at 360 rpm maximum. On a 20" wheel this gives a maximum speed (with no real load) of just over 21 mph. I can double the power, by just increasing the current limit by a factor of 2, but the bike still isn't going to go any faster at all as the speed is limited by the maximum rpm that the motor will spin at.

This is a characteristic of permanent magnet electric motors. It means that, in practice, there needs to be a fairly big difference between the maximum power point (which is usually around half maximum motor rpm) and the maximum speed point.

morphix · Nov 23, 2012

Jeremy said:
The explanation isn't that easy, but has to do with the fixed relationship between motor rpm (and hence bike speed) and applied voltage. Motor rpm is determined not by power, primarily, but by the applied voltage and a motor constant, Kv. For example, the motor on one of my ebikes has a Kv (measured as wheel rpm) of about 10 rpm per volt. On a 36V nominal battery, no matter how much power I put through the motor, it is still only ever going to turn at 360 rpm maximum. On a 20" wheel this gives a maximum speed (with no real load) of just over 21 mph. I can double the power, by just increasing the current limit by a factor of 2, but the bike still isn't going to go any faster at all as the speed is limited by the maximum rpm that the motor will spin at.

This is a characteristic of permanent magnet electric motors. It means that, in practice, there needs to be a fairly big difference between the maximum power point (which is usually around half maximum motor rpm) and the maximum speed point.

you sometimes have people talking about 'over-volting' motors, i.e putting 48r into a 36V motor. Does that mean the motor has latent RPM potential?

flecc · Nov 23, 2012

morphix said:
you sometimes have people talking about 'over-volting' motors, i.e putting 48r into a 36V motor. Does that mean the motor has latent RPM potential?

Yes, it's pro rata, changing from 36 to 48 volts increases the rpm by the same one third increase as the voltage.

Geebee · Nov 23, 2012

I enjoy cycling, having had a 1kw rated 2kw peak bike for a short time, it is much more a low powered motor bike feel than cycling.
If you have stupidly steep hills get a crank drive and the higher power is no longer required.
A moped class would make more sense.

103Alex1 · Nov 24, 2012

Geebee said:
If you have stupidly steep hills get a crank drive and the higher power is no longer required.

I have both a crank drive and a decent gear range and it's still an exhausting effort to climb prolonged hills (a 1:7.5 is hardly an Alpine trail !) unless you drop down to pretty much a walking pace. Quite happy to do the pedalling but it would be nice when you're knackered after a 15-mile stretch to be able to push up the power output when you hit a long hill to avoid having to drop your gears so far and lose so much momentum. Surely it shouldn't involve buying a moped to cover those circumstances ?

What is in that subconscious mind of yours?

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