DDD 028 – Standard vs Compact Front Rings

As summer becomes more of a reality, people start to climb more. When this happens, clients inevitably ask about 2 things: the weight of their bike and components, and what’s the biggest cassette they can fit on their bike.  On the first concern (and this is hardcore pot-kettle-black territory), I almost always suggest that one would be best to focus on the rider, not the bike.  Next time you’re climbing Cypress or Seymour, throw a 10lb bag of flour in a pack and see how it feels, then ask me about Ti bottle cage bolts.

Did I just call you fat? 

On to gearing. What’s nice about gearing is that it’s just math. Gear inches are way to determine how far one will travel in different gear combinations with all other things being equal. 

GI = DWD x (FCT/RCT), where GI is Gear Inches, DWD is Drive Wheel Diameter (in inches of course), FCT is Front Chainring Teeth and, RCT is Rear Chainring Teeth.

If you’re rocking a standard crank (53t/39t), and climbing in the 39t, changing the the rear cassette from a 26t to a 27t take you from 39.5 to 37.9 gear inches.  Multiply by pi to make it practical (that gives us inches traveled per pedal revolution), and you get 5 inches.  You’ll be travelling 5 inches less per revolution, which is noticeable, but really isn’t much.

If you change the rings in the front, and go from a 39t to 34t, the difference is enormous.  Stay in your 26t in the back and you’ll go from 39.5 to 34.5 gear inches, or 15.7 inches per revolution, which is definitely noticeable.  

The obvious downside is you only get a 50t in the big ring, and you might spin out (not have any gears left at speed) which definitely can happen descending.  My response to that is no matter how fast you think you are descending, it’s a drop in the bucket to the importance of climbing.

So, may I suggest the compact cranks to go with your weight loss program?