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Wednesday, January 14, 2015

Gear Ratios: How to Select Touring Bike Gearing

You might have heard of the term 'granny gear' before. If you haven't, a granny gear is the smallest cog on the front crankset of your bike. If you haven't already become best friends with it, you may need to start!
Your selected gear ratios for a touring bike depend on a number of factors: where you plan to travel, the terrain, your experience, how strong you are as a rider and, of course, how much gear you're lugging around.
We recommend picking gears for all occasions, that is, having gears low enough to go up the steepest climbs, and also having gears high enough so you don't 'spin out' when the wind is on your side.
The smallest chainring, the granny gear, is often the one you should worry about most. A good guide for touring bikes is to have a granny gear so small that riding in it works out to be the same speed as you walk. You can never have a gear low enough on a touring bike!

Part 1: Gear Range and Ratios

1.1 Gear Inches: Understand Your Gear Ratios

The best way to compare chainring and cassette combinations between bikes is to check using gear inches. They are very easy to calculate: the diameter of the wheel, times the size of the front chainring, divided by the size of the rear cog. Using gear inches, you can compare bikes with different wheel sizes and drivetrain setups. On a touring-specific bike, you're looking at 15″ in the lowest gear up to 110″ in the highest.
We do our calculations with Sheldon Brown's Gear Calculator.

1.2 Gear Inch Comparisons Across Drivetrains

Given that touring triple cranksets (48-36-24) have a range of 15-110″, how does that compare to drivetrains on different bikes capable of bicycle touring?
Typical road bike gearing
  • Traditional Road – 53x39t with 11-23t = 44 to 126″
  • Semi-Compact – 52x36t with 12-25t = 38 to 114″
  • Compact – 50x34t with 12-25t = 33 to 110″
  • Road Triple – 50x39x30t with 12-27t = 29 to 110″
  • Compact w/ Long Cage – 50x34t with 11-32t = 28 to 119″
Traditional road, compact road and a road triple cranksets
 
Typical cyclocross gearing
  • Traditional CX – 46x36t with 12-30t = 32 to 104″
  • CX1 – 38t with 11-36t = 28 to 93″
Traditional CX and CX1 cranksets
 
Typical MTB gearing
  • Single – 32t with 11-40t = 22 to 79″
  • Single XX1 – 32t with 10-42t = 21 to 89″
  • Double – 38x24t with 11-36t = 19 to 96″
  • Triple – 42x32x24t with 11x36t = 19 to 106″
MTB single, double and triple cranksets
 
Internally geared hubs
  • Alfine 8s – 38t with a 20t = 27 to 84″
  • Alfine 11s – 38t with a 20t = 27 to 111″
  • Rohloff 14s – 40t with a 16t = 19 to 100″
Alfine 8, Alfine 11 and Rohloff hubs
 

1 comments:

Ἀντισθένης said...

Or the elusive 'super-compact' road double, with a 74bcd inner ring: Sugino 601/801/901, and a few others such as White VBC and Specialities TA. I am very happy with my Sugino OX801D set up 30/46, with a 12-27 cassette.

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