Gearing

[IOM]

A common upgrade on this forum is to change the chain wheel to 52T. This is normally the standard big ring on a road / race bike weighing less than 10kg.
Mph can be calculated using gear inches and cadence, so in order to benefit from the large ring you must maintain at least the same cadence as you would with a smaller ring. For example a 44T ridden at 85rpm will give the same speed as a 52T ridden at 75rpm.
So, I suppose my question is are Ebike riders with 23kg+ machines, really capable of maintaining high rpm’s with the 52T chainring and therefore gain benefit from the upgrade?

 

[flecc]

I think most who make this change, like me, wish to have a high enough gearing to take full advantage of favourable circumstances, like slight downhills, to add pedalling for maximum speed then. The terrain counts of course, a large chainring might not be much use in a very flat area, but in my hilly area I get plenty of chances to spin my bikes up to 25 to 30 mph, hence this 60 tooth chainring on my 20" wheel bike:

 

[Mussels]

So, I suppose my question is are Ebike riders with 23kg+ machines, really capable of maintaining high rpm’s with the 52T chainring and therefore gain benefit from the upgrade?

For me the answer is no, I had to reduce the gearing on my 905 in order to manage a high cadence going up my local hills. I think most people who raise the gearing wouldn't be thinking about high rpm and do it to reduce the cadence rather than increase the speed.
Folders like flecc's are undergeared to start with so benefit greatly from an increase but full size bikes (with hub motors) don't suffer from that as much. Panasonic bikes are under geared to keep the chain drive below the 15.5mph speed limit but this is fixed by changing other gears rather than the chainring.

 

[allen-uk]

From my point of view, I want to change the size of the chainring to stop me COASTING so much. I pedal away, get to 14/15mph, and then I can either pedal like hell to try and keep up with the pedals, or sit and wait for a hundred yards till I slow down a bit.

Trouble is, I HAVE used my very bottom gear a couple of times on vertical(well) hills, so I don't want to lose that capability either.

Dilemma.

If it wasn't for the battery and its mountings, I'd ask my bike shop to fit 2 front rings, but so far no-one has promoted a way to do that on a Wisper.


Allen.

 

[John L]

I have a 48T front and 11T back and I have only used it by mistake! I actually fitted a 52T chainwheel but because the chain was too short I took it off. Thinking about it now I don't think I'd ever get to use a 52T except when bombing down a hill. The 48/11 set up on a 700c bike is more than adequate for that.

I'm beginning to find that I prefer higher cadence (for me 80 - 85rpm) but this means more gear changing to maintain the same cadence. But even still I usually stay within 4th, 5th and 6th cog (out of 8) on the back and 2nd or 3rd cog on the chainwheel.

John

 

[IOM]

On my Eagle, I currently have a top gear of 38T front and 14T rear. My daily commute is 10 miles each way and mostly flat. I average on full power assist 17.6 mph, which equates to an average cadence of 84RPM.

My intention is to upgrade to a 44T front, with which I am confident of still maintaining a mid eighties cadence and upping my average speed to 20.5mph, knocking 5 mins each way off my commute.

This for me is a realistic and practical benefit. I will let you know if the maths match reality.

 

[Mussels]

From my point of view, I want to change the size of the chainring to stop me COASTING so much. I pedal away, get to 14/15mph, and then I can either pedal like hell to try and keep up with the pedals, or sit and wait for a hundred yards till I slow down a bit.

Trouble is, I HAVE used my very bottom gear a couple of times on vertical(well) hills, so I don't want to lose that capability either.

Dilemma.

If it wasn't for the battery and its mountings, I'd ask my bike shop to fit 2 front rings, but so far no-one has promoted a way to do that on a Wisper.


Allen.

That's the trouble I had with the 905 especially as I got rid of the megarange freewheel, with gears low enough to get up the hills I was freewheeling up gentle hills. The Alfine hub does a great job of fixing this with bigger steps between gears.

I'm beginning to find that I prefer higher cadence (for me 80 - 85rpm) but this means more gear changing to maintain the same cadence. But even still I usually stay within 4th, 5th and 6th cog (out of 8) on the back and 2nd or 3rd cog on the chainwheel.

John

The Alfine hub isn't as good for this as the steps between gears are bigger.

I want it all!

 

[allen-uk]

Go on then, Mussels, depress me: do I take it that you DIDN'T find any practical answer to the 905 problem?


Allen.

 

[Mussels]

Go on then, Mussels, depress me: do I take it that you DIDN'T find any practical answer to the 905 problem?


Allen.

No practical solution, the best solution seemed to be the gears within the bottom bracket but these are expensive and inefficient.
That's not quite true, I did find a solution. I sold it and bought a 906.

 

[flecc]

That's the trouble I had with the 905 especially as I got rid of the megarange freewheel, with gears low enough to get up the hills I was freewheeling up gentle hills. The Alfine hub does a great job of fixing this with bigger steps between gears.

The Alfine hub isn't as good for this as the steps between gears are bigger.

I want it all!

The NuVinci continuous gear transmission solves that problem, and the latest one just launched is now as light as some conventional hub gears and has an increased 360% range. Any gears you want and as close ratio as you like.

Fecn has the previous model and it's worked well on a Kalkhoff.
.

 

[allen-uk]

This is only a guess, of course, but my best one would be that it'd be cheaper to buy that 906 than to upgrade to a NuVinci.


A

 

[Mussels]

This is only a guess, of course, but my best one would be that it'd be cheaper to buy that 906 than to upgrade to a NuVinci.


A

The NuVinci won't go on the 905, I think it was a solution for my Alfine gears being too wide apart. As replacement Alfine hubs aren't cheap so it would be a reasonable replacement when the Alfine has worn out.

 

[IOM]

The posts on this thread confirm my belief, that gearing like most other things is a matter of personal preference.

I opened the thread questioning the practicality of a 52T chainwheel!

With this set up, the higher gear will rarely be used, unless you are an extremely fit cyclist or you prefer to ride within the speed the motor outputs at low cadence. The problem then is, if you are a low cadence rider you really need the low gear inches you have just sacrificed by fitting a 52T.
If you fit it purely to hurtle down hills, then don’t forget what goes down must go up!

So in summary, I still believe, on a 23kg+ full size Ebike with single chainweel, 52T is not practical.

 

[Mussels]

So in summary, I still believe, on a 23kg+ full size Ebike with single chainweel, 52T is not practical.

I'd generally agree but it depends what you have on the back.

 

[flecc]

If you fit it purely to hurtle down hills, then don’t forget what goes down must go up!

So in summary, I still believe, on a 23kg+ full size Ebike with single chainweel, 52T is not practical.

Not necessarily so, it depends on the motor power available, the rear gear range available and the overall climb ability in consequence. Since mid 2006 I've used a 52 teeth chainring with a 25 kilo full size e-bike in my very hilly North Downs area, eZee's very powerful SB motor version and a 34 tooth largest rear sprocket making that entirely practical even for my over 70 years.
.

 

[IOM]

Hi Flecc,

I recollect from an earlier post you made, that you are familiar with the following calculation and would appreciate if you could answer for me:

‘Riding a reasonably powered bike on the flat at full assist (Wisper 905) at 15-17.5mph, what would be the combined watt output of bike and rider?’

 

[flecc]

Hi Flecc,

‘Riding a reasonably powered bike on the flat at full assist (Wisper 905) at 15-17.5mph, what would be the combined watt output of bike and rider?’

This means major guesswork at that speed, since I don't have the precise power output curve for that motor. It's peak power of about 550 Watts is at about 10 mph, but falls off thereafter and will be quite a lot lower at 15 mph, maybe 250 watts, still plenty enough to maintain that speed on the flat. A maintained output from a fit male rider in their middle years can be around 100 watts for around five hours, 200 watts for an hour. Therefore around 350 watts combined for continuous riding on the flat, more than what is needed in still air conditions.

Of course that's not a very useful figure to know since it is an excess. More useful is the absolute maximum for climbing hills, and then torque comes into it.

At around 9/10 mph the 905se will have the coincidence of maximum power with torque still very high before it falls away with speed. The power then will be about 550 watts, plus the rider at what is needed for the hill length. For a five minute climb they might manage 300 watts to add to the 550, for a 15 minute climb maybe 230 watts from the rider; for a very long 10% gradient Alpine pass, 100 watts from the rider to add to the 550 watts from the motor.

If the climb speed is allowed to drop lower than the optimum 9/10 mph, the motor power also falls with speed reduction, though the torque remains high.
.

 

[IOM]

Thanks Flecc,

It is the second part of your answer, I am really interested in, and realised that shortly after posting my initial question. Unfortunately I had to leave and didn't have time to edit my post.
However you have anticipated well and given me the information I require.