quote:
Originally posted by Frank Tompson
Don't do numbers! I've read the comparison charts on the Thorn website and don't understand them.
I live in Bath and we have some big hills. My 'ideal' derailleur gearing is 26-48 on the front, 11-34 on the back (with 700mm wheels).
What I could be grateful if someone can advise if one of the Rohloff's covers that range.
Many thanks,[
]
Frank Tompson
impossible to avoids number!
To be simple, I'll only look at gear gain ratio.
If you will use same tires, cranklength, both numbers will be same.
I does not like weel inches, it cloggers too much!
weel inches are useful to compare different bikes, btw.
The gear internal ratio in the Rohloff hub are:
14: 1.467
13: 1.292
12: 1.135
11: 1.000
10: 0.881
9: 0.774
8: 0.682
7: 0.600
6: 0.528
5: 0.464
4: 0.409
3: 0.360
2: 0.316
1: 0.279
Then you must multiply with chain/cog size.
( e.g. 38:16. your chaintooth are 38 and the cog are 16tooth, getting a gain ratio at 2.375, the minium Rohloff are allowing)
your currently system is the minium gear ratio:
low gear: 26:34 = 0.765
high gear: 48:11 = 4.364
with 38:16:
Rohloff low: 0.279 * 2.375 = 0.663
Rohloff high: 1.467 * 2.375 = 3.484
What does that means?!
if you change your gearing system to Rohloff, running 38 tooth chainring front, with 16 tooth cog, it will means that you will be able to climb longer,slower and/or slower, but you will go slower downhills as you have lower gearing ratio at the 14th gear.
If you wants same low gear in Rohloff as your gearingsystem have now, use a bigger chainring:
0.279 * x = 0.765 -> x = 0.765 / 0.279 =
2.742.
(to get the same gear gain ratio, you'll need cog/chain ratio at 2.742)
(16cog * 2.742 = 43.87 => 44 tooth chainring)
then the first gear would be higher now (
using 44/16 = 2.75)) compared to 38/16
0.279 * 2.75 = 0.767
1.467 * 2.75 = 4.034 (much better?!)
still, the rohloff system would have slower maximal speed than your derallier system.
gotcha?
a side note: I have experienced myself with cadence and gearing space.
the next cog who are 15% away compared to 6% away have less smooth
transaction especially for my legs, but it easy to compensanse: higher cadence or slower speed. I found it at my racebike, much smoother transaction at 6% spaces gearing, so it would be softer at my legs, especially at sprints, but if one increases the cadence, and lowering the speed a little, nothing is lost. I have not been less effective at ~16% spacing at my commuter compared to my racebike.
Still, when I am sprinting at my city bike, I never had any issues with it's bigger gearing spaceing.
The biggest loss I have is when I am climbing, and need to change to lighter gear, and it's slow gearing and space (more then 30%?) when I change from the middle chainring to the small, and need to shift to smaller cogs to get my gearing correct.
side-side note: Funny, I who was thinking that my 1.95 tires was to thin, so I want to buy 2.35 tires...
