Is 250w enough power for modest speed up steep hills

Electrically assisted bikes, trikes, etc.
User avatar
Cugel
Posts: 4092
Joined: 13 Nov 2017, 11:14am

Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

Jdsk wrote: 22 Sep 2022, 6:11pm The speed of the ridden machine affects other people, particularly in congested spaces.

Increasing the assisted speed limit would increase the number of machines ridden fast.

It might seem unfair to limit the assisted speed when unassisted riders can go faster but sheer numbers should come into the decision. (And I'm in favour of there being a lot more eBikes out there.)

Jonathan
My proposition isn't "to increase the assisted speed limit" but rather to recognise that it's an unnecessary and ineffective control for e-bike safe use. The thing that makes illegal e-bikes dangerous is not their lack of speed control but their excessive power. If the total power of an e-bike rider + motor is limited to something like 250 watts, this automatically limits the speed at which an e-bike can be propelled - effectively, no faster than an ordinary bike ridden by a reasonably fit cyclist without any motor.

But then the e-bike riders can, conversely, ride as fast as their fitter fellow non e-bike riders.

The notion that an increase in e-bikes that can go as fast (but no faster) than non e-bikes would be a matter for concern, such that their speed should be limited, is a peculiar argument. In that case, any increase in non e-bikes ought to attract the same response, with auto-applied brakes if any of the increased hordes of cyclists try to go above 25kph.

**********
Meanwhile, a new category of electrically-assisted personal transport could be defined (or several of them). For example, a cargo carrying two or three wheeler with a maximum rider + motor power of 500 watts but with a speed limit of 50kph, for use in urban traffic, where it could keep pace. That's not a bike, though .... is it? :-)

Cugel
Last edited by Cugel on 23 Sep 2022, 12:32pm, edited 2 times in total.
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
John Maynard Keynes
PH
Posts: 11524
Joined: 21 Jan 2007, 12:31am
Location: Derby
Contact:

Re: Is 250w enough power for modest speed up steep hills

Post by PH »

Cugel wrote: 22 Sep 2022, 5:33pm ntioning fit cyclists and consider the central point: an e-bike is meant to operate just like a non e-bike but with some extra power to enable people finding unpowered cycling of various sorts beyond their capabilities.
You really don't get it. Many people are choosing E-bikes for reasons that have absolutely nothing to do with their capabilities.
PH
Posts: 11524
Joined: 21 Jan 2007, 12:31am
Location: Derby
Contact:

Re: Is 250w enough power for modest speed up steep hills

Post by PH »

Cugel wrote: 22 Sep 2022, 10:59am Many fit cyclists able to continuously output 250 watts or more themselves are able to ride about at up to 40kph or more. This is not particularly dangerous of itself. Cyclists have been doing it for decades. 40kph is only dangerous if the cyclist is inept. I know plenty of fit cyclists riding about on non motorised bikes that are inept! (Should they be banned, perhaps)? :-)
Cugel
This is the cyclists perspective, people who are enthusiastic about cycling.
I don't know any people who don't consider themselves cyclists, who are not enthusiasts or interested in the sport, who regularly ride at 40kph.
Whatever regulation comes about will be a compromise, using these enthusiasts as the benchmark is the wrong approach, I don't care if that means you can't keep up with the chain gang you could in your twenties, I don't want to be sharing cycle space with machines assisted to 40kph.
hemo
Posts: 1302
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Is 250w enough power for modest speed up steep hills

Post by hemo »

tenbikes wrote: 22 Sep 2022, 11:38am Indeed.
My current e bike is for hauling loads off road. It needs to be more than 250w, but speed is irrelevant, in fact I have limited it down to 10mph because that's all I can manage safely off road with a load.
It sometimes gets defeated even with its generous power rating.

Think tractor v sports car. I have no need or interest in a sports car.
What load weights are you hauling and distance over the terrain ?
Is very hilly ?
Nearholmer
Posts: 1029
Joined: 26 Mar 2022, 7:13am

Re: Is 250w enough power for modest speed up steep hills

Post by Nearholmer »

I don't want to be sharing cycle space with machines assisted to 40kph.
That’s the key issue. ‘Cycle space’, and even more so ‘shared-use path space’ is for humans, human-powered things, horses in the case of bridleways, and anything powered that is allowed in absolutely has to be of a speed and capability that is similar to HPVs, otherwise it has the capacity drive the current users out of those spaces, just as cars drove cyclists and horse-riders off the roads.

There are several possible algorithms that could emulate human power, which could be applied to things allowed into such spaces, but the present crude algorithm, while not a brilliant emulation, isn’t too bad, and changing it would require a great deal of international collaboration to build a consensus, unless we want to create a “UK special”, which would involve s lot of extra cost.

What form of EAV/EV people use on roads bothers me less. It would be nice to see a class of light-weight, low-speed thing for sustainability reasons, provided it doesn’t sneak into the places mentioned above, but that’s a different question - the key question here is what should be allowed to ‘mix it’ with people, horses, and HPVs?
tenbikes
Posts: 317
Joined: 11 Jan 2009, 6:41pm

Re: Is 250w enough power for modest speed up steep hills

Post by tenbikes »

^^^ I have no idea of the weight but it is much more than I can lift......logs and wood chippings, loaded in small units to two massive panniers and a trailer.

Off road. Very steep. Distances up to 2km.

Mid drive. 34 front, 46 rear.

Personally I have no issue with power, it is speed that seems to be the issue for people.

It is clear from this thread that policing power output is next to impossible: you need an electronics lab to measure the motor.
Police cannot do this on the beat.
They can check maximum assist speed though, and put a speed gun on bikes which appear to be going excessive speeds.
Sure, we know that that is unlikely too but it is more attainable as a control measure that wattage.

If a bike at 250w passes you at 30mph and one passes you at 15mph but with a wattage of 500w, what will you notice? Speed or power? Which of the two would you prefer to experience?

Cargo bikes like mine should have a generous power allowance but still be speed restricted in the same way as a fast/light road ebike.

Consider mum with two toddlers and the week's groceries, in a hilly city like Sheffield on her cargo bike. She isn't interested in speed, but she needs grunt power in spadefuls.
Nearholmer
Posts: 1029
Joined: 26 Mar 2022, 7:13am

Re: Is 250w enough power for modest speed up steep hills

Post by Nearholmer »

I’m half-persuaded* by your point about speed being the real issue, but feel compelled (yes, really, it’s a bit obsessive!) to point out that your view that speed and power aren’t related ignores the laws of physics, which say that they are intimately connected.

Power is the rate of doing work, it tells you how fast work is done, in this context how fast a given mass is lifted through a given height.

You don’t need a bike of power greater than 250W to lift a heavy load up a steep hill, you just need time, and the patience to go very slowly.

Touring cyclists, and those guys you see in films of developing countries, have been doing it for donkeys years, and I’d be surprised if even the hardiest of them can sustain 250W all day, then the next day, and the day after.

So, when you say you need more power, you will only ever need it to go faster than you otherwise would.

When you talk about “grunt power”, what you possibly mean is torque, and the way to get more torque is to gear-down and go slower.

Power = torque x angular velocity, the latter classically converted to linear velocity by the action of wheel on road.

* Only half-persuaded, because a speed-only limit on what is allowed on shared-use paths would permit humongous great HGVs, provided that they were suitably speed-limited, which probably isn’t what you intended.
tenbikes
Posts: 317
Joined: 11 Jan 2009, 6:41pm

Re: Is 250w enough power for modest speed up steep hills

Post by tenbikes »

What about motor longevity? If a 250 can just about cope with the load would it wear out faster than a 500 doing exactly the same task?
How would battery range be effected?
Nearholmer
Posts: 1029
Joined: 26 Mar 2022, 7:13am

Re: Is 250w enough power for modest speed up steep hills

Post by Nearholmer »

Depends upon the design of the motor. It’s perfectly possible to build one that’s exceedingly robust, and has the thermal characteristics that allow it to genuinely deliver its stated rating continuously, or to build one that has poor bearings, and thermal characteristics such that it barely manages to deliver its stated rating for an hour or two before getting uncomfortably warm, and a service life a quarter that of the more robust one. The latter one will be cheaper in first cost, of course. The former one will probably be German.

Batteries store energy, and lifting a given mass through a given height slowly usually uses less energy than doing so more quickly, partly because a less powerful motor is less heavy (although a robust one will be heavier than a fragile one), partly because some of the losses involved are proportional to speed, or speed squared etc, but at bike speeds the difference may not be great. At car speeds the difference becomes really clear - petrol is an energy store, like a battery, and you will get far better mpg if you drive slower, all other things being equal. In a battery car, a given Wh battery will take you further at low speed than at high speed.

All this does need to be thought about carefully at design stage though, because the design needs to be optimised for the speed at which the vehicle will spend most of its time (getting the gearing right for the duty in a petrol car, vs a petrol tractor, vs a petrol Land Rover is the classic example, they each have different typical operating speeds) - get that wrong, and it will be operating for a high proportion of time at sub-optimal efficiency, which can negate all the benefits of going slowly.

Unless you have perfect regen braking (impossible) going faster will also cause significantly more energy to be wasted in braking, because the energy possessed by a moving body is proportional to the square of its speed, and when coming to rest all (friction braking) or some (imperfect regen braking) of that energy is wasted as heat.
User avatar
Cugel
Posts: 4092
Joined: 13 Nov 2017, 11:14am

Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

PH wrote: 22 Sep 2022, 7:24pm
Cugel wrote: 22 Sep 2022, 5:33pm ntioning fit cyclists and consider the central point: an e-bike is meant to operate just like a non e-bike but with some extra power to enable people finding unpowered cycling of various sorts beyond their capabilities.
You really don't get it. Many people are choosing E-bikes for reasons that have absolutely nothing to do with their capabilities.
Please list the other reasons.

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
John Maynard Keynes
User avatar
Cugel
Posts: 4092
Joined: 13 Nov 2017, 11:14am

Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

PH wrote: 22 Sep 2022, 7:37pm
Cugel wrote: 22 Sep 2022, 10:59am Many fit cyclists able to continuously output 250 watts or more themselves are able to ride about at up to 40kph or more. This is not particularly dangerous of itself. Cyclists have been doing it for decades. 40kph is only dangerous if the cyclist is inept. I know plenty of fit cyclists riding about on non motorised bikes that are inept! (Should they be banned, perhaps)? :-)
Cugel
This is the cyclists perspective, people who are enthusiastic about cycling.
I don't know any people who don't consider themselves cyclists, who are not enthusiasts or interested in the sport, who regularly ride at 40kph.
Whatever regulation comes about will be a compromise, using these enthusiasts as the benchmark is the wrong approach, I don't care if that means you can't keep up with the chain gang you could in your twenties, I don't want to be sharing cycle space with machines assisted to 40kph.
Yes, I take the cyclists' perspective since we're talking about people riding bikes. The "fit cyclist" power benchmark is just a benchmark. Select another if you like. How about using the typical leg power of those who ride bikes to commute, who I regularly see going at 40kph and faster. For confirmation, stand on a London road during the commuting hours.

You seem to be obsessed with dangerous cycling behaviour on shared paths. This is a result of inconsiderate mindsets, not motors. Plenty of non-motored cyclists on shared paths go about idiotically. Personally, I'm pretty much against shared paths for cyclists and pedestrians as they don't really mix well unless all involved are considerate ... which they ain't.

And if you're bothered about cyclists going at 40kph on the road, well .... perhaps you shouldn't be cycling yourself? Such cyclists are a miniscule danger to other cyclists compared to the hundreds of loon car drivers per fast cyclist you'll count on most roads. If you can manage them car l;oons, you can certainly manage another cyclist or three going at 40kph.

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
John Maynard Keynes
User avatar
Cugel
Posts: 4092
Joined: 13 Nov 2017, 11:14am

Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

Nearholmer wrote: 22 Sep 2022, 8:05pm
There are several possible algorithms that could emulate human power, which could be applied to things allowed into such spaces, but the present crude algorithm, while not a brilliant emulation, isn’t too bad, and changing it would require a great deal of international collaboration to build a consensus, unless we want to create a “UK special”, which would involve s lot of extra cost.

- the key question here is what should be allowed to ‘mix it’ with people, horses, and HPVs?
It would be a very easy thing to change the motor-controlling firmware of many e-bikes to make them detect (as they do now) the rider's leg power and scale the e-motor power to match, such that the total power never exceeds X watts. It might be a more difficult matter to change the legislation but so what? Are you saying we can't or shouldn't improve "not a brilliant emulation" as that we have now? Are all things to remain the same forever because change involves some effort? I feel history is agin' you! :-)

As to the "mixing" question .... my now long experience of mixing cyclists with pedestrians provides me with the opinion that they shouldn't be mixed other than in unavoidable circumstances, when the control of the mixing should be much greater than it is now - particularly the control of ALL bicycle speeds, not just those with a rather feeble e-motor. 10mph maximum seems appropriate. (Maybe just 6mph).

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
John Maynard Keynes
Nearholmer
Posts: 1029
Joined: 26 Mar 2022, 7:13am

Re: Is 250w enough power for modest speed up steep hills

Post by Nearholmer »

One of the reasons I asked about uK participation in CEN and IEC is that they are the places where the conversation about a possible ‘next gen’ algorithm needs to take place. It would be really interesting to know whether other countries perceive there to be a problem to be solved, for instance.
my now long experience of mixing cyclists with pedestrians provides me with the opinion that they shouldn't be mixed other than in unavoidable circumstances
My now long experience suggests something different altogether. If you fancy a day out in Milton Keynes any time, come on over, and we can spend all day riding about on shared used paths with a promiscuous mix of cyclists, e-scooterists, people walking, dogs, delivery robots etc, and I’d wager that you will have cause to review your conclusions. It works, and one of the reasons I’m so passionate about controlling EAPC performance is so that it continues to work. Density of traffic of all permitted kinds is clearly a major factor, because the same promiscuity would probably lead to trouble if density was very high.
Carlton green
Posts: 1875
Joined: 22 Jun 2019, 12:27pm

Re: Is 250w enough power for modest speed up steep hills

Post by Carlton green »

A day or two ago CJ made what I thought to be three rather good posts, thank you Chris .. some really constructive posts from the Electrical Engineering chap in Milton Keynes too.

A point in one of them was basically that some folk are, or act like, idiots, and that only a lack of electric assisted power stops them doing stupid things or, in some cases, even more stupid things than they currently do. As such, and as in much of life, the majority of folk are limited by what the mindless or unthinking minority will do; in this case that results in limiting e-bike power and capping assist speed.

To be honest I think that 250 Watts sounds to be plenty to at least keep people mobile and active, and particularly so when transmitted to thrust at the wheel / road interface through appropriate gearing. An assisted speed cap doesn’t seem unreasonable to me, an an unassisted cyclist I just hope to average around 12 mph and the assisted speed cap is the right (top) side of that lowly figure.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
User avatar
Vantage
Posts: 2952
Joined: 24 Jan 2012, 1:44pm
Location: somewhere in Bolton
Contact:

Re: Is 250w enough power for modest speed up steep hills

Post by Vantage »

250w is a staggering amount of power. So much that when I stood in front of my bike and pressed the throttle it near ran me over. I couldn't hold it back. That same power dragged me at 66kg, the bike at 35kg and the loaded panniers & rack at I'm guessing roughly 50kg up a 20%+ hill in Wales not too long ago. It still gave my legs a good workout but I doubt a non powered rider and bike could have done it. And it has to said, my perfectly legal mid motor at 250w could peak at over 630w when pushed.
Bill


“Ride as much or as little, or as long or as short as you feel. But ride.” ~ Eddy Merckx
It's a rich man whos children run to him when his pockets are empty.
Post Reply