Gearing finally sorted

[RobF]

Regular readers may recall I found first gear on my Alfine 11 Rose/Bosch bike too high.

Spinning at a reasonable cadence gave more than 7mph - too fast for steep climbs.

My first mod was to change the rear sprocket from 20t to 23t.

This improved things, but not enough.

I have now changed the front chain ring from, I think 48t, to 36t.

Result - spinning first now gives just over 5mph.

The reason this matters is there's no throttle on the Bosch system and it demands reasonable cadence before it will give you full grunt from the motor.

Of course, I've lost some top end.

Spinning 11th is about 23mph - plenty fast enough for me.

Cracking on in my parlance is anywhere between 15 and 20mph.

Well pleased with my new first gear.

I don't want to attack every hill, so use it to trundle up less steep banks I could go faster on if I wanted to.

 

[Streethawk]

With that gearing it should be capable of climbing walls!

 

[Artstu]

Ultra low. When I'm putting a lot of power in on my bike chasing segment times high power input and a nice cadence gives me less power, so I end up in 8th gear pushing a less than ideal low cadence, and that's on some uphill bits!

 

[RobF]

First gear is still not that low in push bike terms.

For example, a tourer will have a bottom gear which the rider can winch the bike up hill at 2/3mph.

Lots of stuff online about the Alfine 11 having a first gear which is too high.

Dawes withdrew one of their Alfine 11 bikes because they couldn't make first low enough while at the same time giving the customer a high enough top end.

Fortunately, I don't want a 30mph top gear, but plenty of push bike riders do.

I believe my problem is exacerbated by the 29er wheels and near balloon tyres - that's a lot of circumference.

Moral of the story is if you are considering an Alfine 11 bike of any sort, make sure you are happy with the gearing before buying.

 

[Artstu]

More than ever this highlights the need to try before you buy. Also goes to show the wide range of requirements of e-bike users.

 

[103Alex1]

Interesting. Glad you've found a solution. I don't think you'd have the same issues if you wanted such low speed climbing with a bike that operated on speed sensor / constant 'stepped' assist rather than the Bosch assist profile. Isn't it as much the assist profile as the hub that's at the root of the issues you came across for the riding style you're looking to accommodate ?

The Alfine 11 has the lowest 1st gear of any IGH bar the Rohloff and a higher top gear than the latter.

http://www.moustachebikes.com/ch/fr/dl/GearInchChart_N360.pdf

But MTBs intended for low speed steep climbs (for example) will predominantly have a derailleur. Not least for the low gear / low speed climbing functionality !.

 

[RobF]

Thanks Alex.

I think you are right about my riding style clashing with the Bosch software.

The de-tuned Bosch drive for hubs must also play a part.

I doubt I would have had any bother with a derailleur, extra grunt and first would have been lower anyway.

 

[103Alex1]

Not so sure how much real difference the extra grunt from derailleur version on a 250W Bosch system would make longer term, when you'd got used to any initial marginal benefit.

Main thing is, though - at least you didn't get a bike with a hub motor ! Very low speed climbing + hub motor = disaster for battery consumption / efficiency and high stress on motor with risk of 'labouring it'. With a high powered hub motor, very low speeds on steep climbs don't tend to be seen ( ) so motor stress is easily manageable, but if that's what you are actually looking for then crank drive is still the sensible way to go.