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I'm new on the cycling scene and I'm looking to build a bike. I'm a bit worried about my route home, since although only 5KM it's quite steep in places, with 0.25KM being at a 16% incline, and the rest floating somewhere between 3-6%.

Start altitude: 14 metres 
End altitude: 99 metres 
Maximum altitude: 99 metres 
Minimum altitude: 11 metres 
Distance: 5 km 
Total ascent: 125 metres 
Total descent: 40 metres 
Maximum gradient ascending: 16% at 2.6 km 
Maximum gradient descending: 8% at 3.4 km

I quite like the idea of an internal gear hub, but I'm wondering if that's a bad idea given the gradient and my lack of experience. Is it as simple as just using the pedal gear to vary the ratio going into the IGH, or is it a case that the IGH is simply not a sensible choice for this kind of gradient.

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  • If you're currently using a derailleur-style bike you can simply make note of what gear combos you use to do the hill, then translate those to the gears you need on the new bike. (But it's unclear why you'd want an IGH at this point in your "career".)
    – Daniel R Hicks
    Commented Mar 10, 2017 at 12:46
  • Also what wheel size are you planning as this changes the final ratio.
    – Rider_X
    Commented Mar 10, 2017 at 21:05
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    FYI there's no shame in walking the steep grades, especially if you're new/recently restarted riding.
    – Criggie ♦
    Commented Mar 11, 2017 at 5:34
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    What bike do you have at the moment? Rather than going to the expense of building a bike, ride something used and cheap. Either buy it from ebay/classifieds or ask around if friends/neighbours have a bike you can borrow. A week's riding will teach you a lot about what you want and what you don't want.
    – Criggie ♦
    Commented Mar 11, 2017 at 5:36
  • Once you have an idea of the gear tooth ratios required to climb AND descend this grade, poke numbers into sheldonbrown.com/gear-calc.html and try to get the gear-inches number. Then search for an IGH that will provide the same values/ranges
    – Criggie ♦
    Commented Mar 11, 2017 at 5:38

2 Answers 2

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By using a larger sprocket and/or smaller chainring, you can gear an internal hub to cope with just about any gradient. (There is an eventual limit where input torque can destroy the hub.)

(Edit: @Rider_X is right that the Shimano limit is more restrictive than I remembered. There are people using lower gearing and reporting no problems, but you might have to be careful. On the comparison chart below the Rohloff could be geared quite a bit lower (30:16 rather than 44:16, see Rohloff), but the Nexus is following Shimano recommendations according to this forum post))

Gear Range chart

A cheap hub will give you three gears with big gaps between them and a limited overall range, and although you can make the bottom gear low enough for a steep gradient you might find it too restrictive; a very expensive Rohloff hub will give you 14 gears with gaps and range comparable to a derailleur system (but without overlapping or duplicate gears - a 27-speed derailleur system doesn't have 27 usefully different gears). In between those, there's a range of hubs available giving you more gears, more overall range, and smaller gaps, as you pay more. See, for example:

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    I found for Shimano IGH you get to there suggested gearing limit quite quickly. 16% could be a bit a challenge to a reasonably priced hub that will give a low enough ratio.
    – Rider_X
    Commented Mar 10, 2017 at 21:04
  • And the triple has the lowest ratio! Triples are awesome despite their problems.
    – Criggie ♦
    Commented Mar 24, 2017 at 17:55
  • Anecdata: I've had a flatmate years ago who twice destroyed their Shimano hub (don't remember exactly which one, I'd guess the 7 or 8) within few years by too much torque (decision was then "wer sein Rad liebt, der schiebt" = "if you love your bike, push it [uphill]") - so I'd be carefull obeying their torque specifications.
    – cbeleites
    Commented Mar 26, 2017 at 17:44
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Can you ride your steepest incline at ~10km/h (6mph)? Apparently the Shimano Alfine 11 and 8 go down that far if you use the smallest allowed chainring/sprocket ratio of 1.9: http://www.ritzelrechner.de/?GR=SA11&KB=34&RZ=18&UF=2150&TF=70&SL=2.6&UN=KMH

The downside is that your top speed is limited to ~55km/h.

Apart from the weight an IGH should be great for mountains, especially since you don’t have to constantly change chainrings.

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