Wednesday, March 9, 2011

Crankset Conundrum

Triple Crankset
A simple question is all it takes to start a spirited and polarizing discussion.  Ask a group of people whether Van Halen was better with David Lee Roth or Sammy Hagar as lead singer - usually the group splits down the middle with each being convinced it is right.  Ask a group of cyclist whether a triple or double crankset is superior and you are likely to start a riot.

 Every day we are asked whether we recommend a road bike with triple or compact front gearing and we always answer with "It depends".  The factors for consideration include: where, how and what you ride.  Before advances with 10 speed cassettes and compact gearing  you had to choose between a double (usually a 40, 52 tooth combination) or triple setup.  Of the two, the most versatile combination was a triple crankset setup up in front with a 7, 8, or 9 speed cassette in the rear.  This combination provided a low ratio for climbing and a high ratio for hauling on the flats or down-hill.  The drawback is that you end-up doing a lot of shifting, the front response can be slow; gear ratio redundancy and more metal means more weight.

Compact Double Crankset

Most often the recommendation is to use a Compact Double combination (more about what that entails later.)  The one exception where a triple is always indicated is when the cyclist is planning to use the bike for touring with panniers or a trailer.  The additional weight of a loaded bike up long grades requires some pretty low gearing to be usable.

Since the introduction of the 10 speed rear cassette in 1997 the gearing choices became a little more complex.  Compact double chainring combinations of 50/ 34 tooth rings started showing up on production bikes in the early-to-mid 2000s.  This combined with a 10 speed rear range of 11 to 28 provides a wide range of gear ratios without the drawbacks of the triple chainring listed above.  But, customers appear to have anxiety at the thought of losing their granny or bail-out gear ratio for very steep/long climbs on the bike.  Bikes have also become lighter as a general rule which allows the rider to push a slightly higher gear up hill. Usually a compact double provides adequate low-end for most cyclist.

A great way to prove this for yourself is to use a gearing calculation program to compare different configurations of the respective systems.  This particular site has been around since 1996 and provides a lot of useful information.

A Trek Madone 4.5 Triple comes standard with a 50/39/30 chainrings and an 11-28, 10 speed cassette for a total of 30 ratio combinations.  This provides a low of 88 inches traveled per pedal rotation to a high of 375 inches traveled.  Unfortunately there are 7 ratios that are so similar they are considered duplicate ratios. Also, it requires using all three chainrings to complete a sequential shift pattern for the 1st 8 ratios - that is a lot of shifting up front.

By comparison, a Trek Madone 4.5 Compact comes standard with a 50/34 chainrings and an 11-28, 10 speed cassette for a total of 20 ratio combinations.  This provides a low of 100 inches traveled per pedal rotation (a difference of (13%) to the same high of 375 inches traveled.  This combination has only  two ratios that are close enough to be duplicates.

The difference in low speed between the compact and the triple is less than 1 mph at 80 rpm for these bikes.  In the end it comes down to personal preference and what you are most comfortable with using.  If you are considering an new bike or changing your gearing then test ride two bikes in the same day to compare.  Then you can experience the difference and decide which is for you.

1 comment:

  1. My buddy Alex has a great post on compact doubles. Worth a read. Basically, that for non-racing and off-road scenarios, more moderate double chainrings (say 44/28) paired with a wide range cassette gives you the best of all worlds. The bummer is that until recently, you had to find some older 94 or 86 bcd cranksets to make this work with a reasonable/low tread.
    What's interesting is that he wrote this nearly 6 years ago. Now SRAM is shipping a mountain double that is essentially the same thing.
    Typical bike "technology": what's old is new again.