Compact / Alfine Gear Inches Comparison

[threebikesmcginty]

I did try tacking this onto an older thread but no-one has taken pity on me so I'm now appealing directly on this thread...

Right, object of exercise is to see if my back-of-fag-packet-scribblings are anywhere near the mark, bare with me I've never bothered with anything bike related in this sort of detail before.

Current road bike gears are 50/34 compact with 12/27 cassette. On 24mm tyres I make this a range of 30.22 to 100"

I quite fancy trying an Alfine 8 hub with 32mm tyres, putting this through the 'Sheldon Gear Calculator' using 170mm cranks 20t rear and 42t front it comes up with a range of 29.9 - 91.6".

So it seems the same at the low end and not far off the top end although it loses the 12t and works out about right to the 13t (which is 92.31"). One cog off the high gear seems ok to me, that's if my calculations are correct - it could all be bollocks mind!

Can anyone mark me please?

Be ever so grateful

 

[Moodyman]

Nearly there McGinty.

You don't use tyre width, but rim diameter - 27" or 26".

For 27" wheels your bottom gear is 34" whilst your top is 112.5".

I went from a triple to an Alfine and only noticed a shortcoming at the very top end, which is fine as I can freewheel.

Alfine is one smooth piece of work. Only downside (with 8-speed) is the large jumps between gears, but you get used to that and only change when you get a significant gradient change.

The 11-speed Alfine has addressed this by creating shorter gaps, but it's pricey. For commuting and utility riding (99% of my riding) I'd never get another derailleur bike.

Though I still have two and love v. much.

 

[P.H]

You're pretty much spot on.  Think of a gearing system giving a range, your compact has a range of 330% (The top gear is 3.3 time higher than the lowest)  The Alfine has a range of 309%.  If you were to set them with the same bottom gear you would loose a bit less than one gear at the top end compared to the compact.  Of course with a derailleur it's easy to increase or decrease the range, with a hub gear you can set it at whatever you choose but the relationship between the bottom and top gears is fixed.  

 

[threebikesmcginty]

Thanks gents - I now see where the gear range % comes from too!

Gotta get me one of them Alfines...