Singlespeed

[Richardab]

Is a singlespeed bike a viable option for ebike conversion.

I was wondering about how the pedal assist sensor would think you were just riding slowly when you were grinding up a hill needing some help.

Is it much more efficient to just stick with a geared bike

 

[Deleted member 4366]

A hub-motor doesn't know or care whether you have power or not. If you're already able to ride a single-speed bike, a motor will only make it better.

 

[Richardab]

But isn't the PAS what tells the motor how fast to spin, if you are grinding slowly up a hill needing lots of help will it just think you are pottering along slowly...or is that where thumb controllers are a benefit and can over ride the PAS

 

[DynatechFan]

sort of - I think there are power/speed graphs floating about - my own experience is that as I slow to work harder the PAS helps more, as road speed goes up it helps less - this is on a geared hub wheel

Single speed ebike sounds intriguing - I built a single speed MTB for fun and have been totally hooked with the whole SS vibe

 

[Richardab]

Me too, I mostly ride SS, both MTB and commute bikes, so it seemed the obvious start point on my learning curve, just trying to understand if it compromises the ebike

 

[DynatechFan]

One question would be how you get the hub in the frame - my SS conversion is on a "normal" MTB frame - its my Avatar actually. But most ebike rear hub kits I have seen are most definitely 130mm or wider

A SS frame would be narrower?

If frame width isnt an issue then getting the freewheel in is the next challenge - again on my SS I had to use a set of spacers to convert a cassette hub wheel

 

[Richardab]

I have two options for conversions, one is a carbon SS commuter with 135mm rear (not sure if its a bit too fragile and fancy to mess with?!), the other an old hybrid with 135mm shimano hub gear, I could make this SS or put a front motor in and keep the hub gear

 

[DynatechFan]

sounds doable then

The only "proper" single speed I have is an old Archie Wilkinson which is much too narrow, no brakes either . . .

FWIW the folks on here talked me out of a front hub conversion and I have been very happy with the decision to fit a rear hub

 

[Richardab]

I have a vintage SS too, you are right its much narrower, more like 120mm.

Yes from my initial research it does seem rear hub is preferable. It would be slightly easier on the carbon SS as its disc braked already. The hub geared hybrid has a drum brake in the rear hub which would leave me with trying to solve a replacement back brake.

Any reason not to use the carbon framed bike, I keep thinking I will compromise it but maybe it would be the making of it!!

 

[anotherkiwi]

But isn't the PAS what tells the motor how fast to spin, if you are grinding slowly up a hill needing lots of help will it just think you are pottering along slowly...or is that where thumb controllers are a benefit and can over ride the PAS

The PAS from a Chinese kit only tells the controller that the pedals are moving forward. The controller gives more or less current to the motor and you set that amount with the buttons to change assistance level.

Some ready made bikes have more elaborate controllers which also get pedal rotation speed from the PAS magnet disk.

 

[Richardab]

Ah OK that is less sophisticated than I thought

 

[Deleted member 4366]

Ah OK that is less sophisticated than I thought

More sophisticated than you thought! Trust me, you don't want a bike that gives power according to how fast you pedal. I've had one, and it was absolutely diabolical. It sounds sort of logical, but when you think about it, it's the exact opposite of what you need. You need extra power on hills when you're pedalling slowly. The last thing you want is for the power to start dropping off as you struggle up the hill.

 

[DynatechFan]

The last thing you want is for the power to start dropping off as you struggle up the hill.

Is that what the ungeared/direct drive hubs can feel like?

 

[Woosh]

Is that what the ungeared/direct drive hubs can feel like?

no, the direct drive hub feels like riding with two bricks attached to the back wheel.

 

[Deleted member 4366]

Is that what the ungeared/direct drive hubs can feel like?

No. That's a different type of loss of power. What I'm talking about is a power algorithm based on cadence.
It works like this: You set off from a standstill with little power to help you because your pedal speed is too low. You build up speed, and as you pedal faster the motor gives more power, so you start to accelerate faster until you run out of pedal speed and have to change up a gear, but when you change up, your pedal speed goes down and so does the power, so you don't have enough power for that speed. Therefore, you have to shift down a gear to get your pedal speed up to get more power, which makes you run out of pedal speed again. The end result is that you're shifting up and down all the time and can never set into a nice pedal rhythm.