Who needs more than 250W?

Electrically assisted bikes, trikes, etc.
ChrisF
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Who needs more than 250W?

Post by ChrisF »

I have recently added an e-kit to my old Galaxy, and an enjoying using it. (You may have seen my post yesterday about etiquette on hills).
Apart from a couple of tests, I've not yet used it above level 2 (out of 5), so I assume 40% of max assistance.
The other day I rode up a 25% hill, still on level 2, and still in the big ring (so 46/34). I didn't need to put in much effort. If I had changed down, to turn the pedals faster, I would have needed less effort (using the same level of assistance).
Now, I'm a light rider (60kg) so can imagine a heavier one needing twice as much help for the same hill. But who needs any more power than that? Why do some riders crave 500 or even 1000W (which are illegal on roads)?
Chris F, Cornwall
markjohnobrien
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Re: Who needs more than 250W?

Post by markjohnobrien »

Probably because the battery lasts longer, especially on longer, hilly, rides, and even more so if carrying a load of stuff in panniers.

I’m a lot heavier than you and the battery wouldn’t last as long with me on the bike.

N.B- talking about 500W.
Raleigh Randonneur 708 (Magura hydraulic brakes); Blue Raleigh Randonneur 708 dynamo; Pearson Compass 631 tourer; Dawes One Down 631 dynamo winter bike; Litespeed Blue Ridge Ultegra light tourer;Raleigh Travelogue 708 tourer dynamo; Kona Sutra.
stodd
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Re: Who needs more than 250W?

Post by stodd »

markjohnobrien wrote: 3 May 2021, 3:29pm N.B- talking about 500W.
I think you were talking about 500Wh (battery capacity), which is what makes the battery range greater.
OP was talking about 500W; a more powerful motor, which will generally make the battery range less
Jdsk
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Re: Who needs more than 250W?

Post by Jdsk »

ChrisF wrote: 3 May 2021, 3:07pmWhy do some riders crave 500 or even 1000W (which are illegal on roads)?
I'd guess that it's because they want to go faster...

Jonathan
yakdiver
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Re: Who needs more than 250W?

Post by yakdiver »

I ride an etrike and it weights in at 42LB +, I'm 83Kg most of the time I'm in at 2 to 3 level out of 5 and I only have 250 w motor, but I do feel I'm pushing a small motor too far, bit like a 850cc mini against a Ford V8 on a very long drive
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markjohnobrien
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Re: Who needs more than 250W?

Post by markjohnobrien »

stodd wrote: 3 May 2021, 4:18pm
markjohnobrien wrote: 3 May 2021, 3:29pm N.B- talking about 500W.
I think you were talking about 500Wh (battery capacity), which is what makes the battery range greater.
OP was talking about 500W; a more powerful motor, which will generally make the battery range less
Oops - my bad.
Raleigh Randonneur 708 (Magura hydraulic brakes); Blue Raleigh Randonneur 708 dynamo; Pearson Compass 631 tourer; Dawes One Down 631 dynamo winter bike; Litespeed Blue Ridge Ultegra light tourer;Raleigh Travelogue 708 tourer dynamo; Kona Sutra.
stodd
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Re: Who needs more than 250W?

Post by stodd »

yakdiver wrote: 3 May 2021, 4:23pm I ride an etrike and it weights in at 42LB +, I'm 83Kg most of the time I'm in at 2 to 3 level out of 5 and I only have 250 w motor, but I do feel I'm pushing a small motor too far, bit like a 850cc mini against a Ford V8 on a very long drive
There's a huge range of motors nominally rated 250w (legal requirement). They can almost all generate much more for short periods, 700w is not uncommon; 400-450w is typical. It's also common for the same motor to be rated 250w for UK/EU and 350w for US. Finally, there is a big difference depending whether the motor and gearing are designed for high toque at low speeds (eg for hill climbing, cargo bikes) or for maximum speed.
Red Kite
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Re: Who needs more than 250W?

Post by Red Kite »

Motors are commonly given a torque rating - e.g. the Bosch ALP on my bike claims 50Nm.

Something I have seen little reference to is that, assuming the motor is more or less torque-limited and that the motor can produce its rated torque or something close to it over a reasonable rpm range, is that more power will be available for a given torque if the cadence is kept up to an optimal level. I can't find it right now but I'm sure I have seen something from Bosch that recommends 50 or more.

Conversely, a very low cadence could mean that a 250W motor can't even produce its full power anyway.

It took me a few miles to get the hang of it but I soon overcame the temptation to bump up the assistance level for hills while not using a low enough gear. I now change gear pretty much as I would on an unassisted bike and consciously keep my cadence up around 50/60. Playing with cadence on the Bosch simulator also suggest that range increases if cadence is kept up, perhaps because the human is also somewhat torque limited so tends to contribute more when pedalling a bit faster.

To anyone who thinks their available assistance is too puny, I'd suggest checking that they aren't trying to use too low a cadence/high a gear.

Lower cadence/higher gears will also punish the transmission - bigger sprockets mean lower chain tension, and lower force on the teeth of both sprockets and chainring.

Apology if the above is just a statement of the bleeping obvious, this is a voyage of discovery for me at the moment (I'm up to 113 miles on my first e-bike).

I appreciate there might be riders who for one reason or another can't spin quickly - perhaps they are the most likely to benefit from more power.
Cube Touring Hybrid One e-bike, Brompton P6R (Swytch kit on order)
stodd
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Re: Who needs more than 250W?

Post by stodd »

Red Kite wrote: 4 May 2021, 12:13pm Motors are commonly given a torque rating - e.g. the Bosch ALP on my bike claims 50Nm.

Something I have seen little reference to is that, assuming the motor is more or less torque-limited and that the motor can produce its rated torque or something close to it over a reasonable rpm range, is that more power will be available for a given torque if the cadence is kept up to an optimal level. I can't find it right now but I'm sure I have seen something from Bosch that recommends 50 or more.

Conversely, a very low cadence could mean that a 250W motor can't even produce its full power anyway.

It took me a few miles to get the hang of it but I soon overcame the temptation to bump up the assistance level for hills while not using a low enough gear. I now change gear pretty much as I would on an unassisted bike and consciously keep my cadence up around 50/60. Playing with cadence on the Bosch simulator also suggest that range increases if cadence is kept up, perhaps because the human is also somewhat torque limited so tends to contribute more when pedalling a bit faster.

To anyone who thinks their available assistance is too puny, I'd suggest checking that they aren't trying to use too low a cadence/high a gear.

Lower cadence/higher gears will also punish the transmission - bigger sprockets mean lower chain tension, and lower force on the teeth of both sprockets and chainring.

Apology if the above is just a statement of the bleeping obvious, this is a voyage of discovery for me at the moment (I'm up to 113 miles on my first e-bike).

I appreciate there might be riders who for one reason or another can't spin quickly - perhaps they are the most likely to benefit from more power.
Yes. The torque rating is pretty confusing because it is quoted in so many different ways; in particular it is very difficult to compare between crank drive and hub drive based on the quoted values.

I absolutely agree with what you say about gears. Also lower gears/higher cadence (within reason) means less pressure and is better for the knees. The gearing is less important on a hub motor as the motor can't take advantage of it, but valuable because you still can.
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simonineaston
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Re: Who needs more than 250W?

Post by simonineaston »

I've always taken the view that the best way forward for me would be a setup that changes the nature of the original bike as little as possible, so that I have a 'normal' bike to ride, but one that can get up hills a bit more readily than usual. I just wanted a bike that would nudge me gently back towards cycling after a long break. One way and another, less watts = less weight.
(rides: Brompton nano & ever-changing Moultons)
Red Kite
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Re: Who needs more than 250W?

Post by Red Kite »

simonineaston wrote: 4 May 2021, 1:36pm I've always taken the view that the best way forward for me would be a setup that changes the nature of the original bike as little as possible, so that I have a 'normal' bike to ride, but one that can get up hills a bit more readily than usual. I just wanted a bike that would nudge me gently back towards cycling after a long break.
My position exactly. I have nothing to compare it with except unassisted bikes but I'm astonished at how realistic the Bosch system is. It never feels like a motor bike, I just have better legs and don't overstress my heart. For me it's the difference between enjoying riding and struggling so much that I just wouldn't do it. The 250W is enough for now, and I ride mostly in Eco.
Cube Touring Hybrid One e-bike, Brompton P6R (Swytch kit on order)
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mjr
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Re: Who needs more than 250W?

Post by mjr »

Is the bigger use case for higher power speed pedelecs, where doing 28mph sooner would make some no-protection roads more manageable (in a cyclecraft style)?
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Red Kite
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Re: Who needs more than 250W?

Post by Red Kite »

mjr wrote: 4 May 2021, 2:39pm Is the bigger use case for higher power speed pedelecs, where doing 28mph sooner would make some no-protection roads more manageable (in a cyclecraft style)?
It's hard to see why anyone could object to a 28mph machine per se when a 50kW+ motorcycle is legal - the issue becomes one of rider licensing, possibly training, vehicle safety and type approval, and registration, and where they could be used.

It's possible I'm missing the point, I'm not totally sure what a "cyclecraft style" means. I assume it relates to riding responsibly and according to the rules of the road?

I wonder how EAPC's over/under 250W are seen to relate to mobility scooters, if at all? The type of mobility scooter that is allowed to do up to 8mph on a road hasto be registered with DVLA although they don't have to display their registration numbers or be insured. The registration requirement seems anomalous when there is no vehicle speed limit for EAPCs that don't need to be registered.
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Marcus Aurelius
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Re: Who needs more than 250W?

Post by Marcus Aurelius »

Blatting up a hill at 800 Watts is fun. When you get a really steep bit, you can be into 4 figures.
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Re: Who needs more than 250W?

Post by Cyril Haearn »

Marcus Aurelius wrote: 4 May 2021, 6:30pm Blatting up a hill at 800 Watts is fun. When you get a really steep bit, you can be into 4 figures.
If you are referring to illegally modifying you €bike, I hope the police catch up with you
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