Going Compact: Standard vs. Compact Cranks

May 28, 2008 at 8:22 am 2 comments

If one were to take a tally of standard cranks vs. compact cranks at any T1 transition area at any triathlon in the country, standard cranks would be the runaway winner.  The reason for this is obvious: many top triathlon bike companies stock their bikes with standard cranks.

My Pinarello FT1, on the other hand, came stock with a compact crank which may be a reflection of fact that compact cranks are much more dominant in Europe than in the U.S.  The question is what, if any, advantages does one type of crank have over the other?

I’ve seen a few articles and many online forum advice givers try to answer this question.  Those in favor of standard cranks typically denounce compact cranks as for “weaker” riders or that one “will lose speed.”  Even an article by Triathlete Magazine entitled The Pros and Cons of Going Compact does little more than explain the physical differences and changes that may occur on your bike.  The article completely fails to address any differences in top-end speed (other than saying you’ll lose some) and likens going to a compact as a halfway house to a triple crank.

Of all the articles I’ve seen, the only one backed up by actual testing  is an article by Slowtwitch.com.  The Slowtwich article lists a few general benefits of going compact, including:

  • Easier climbing.  The smaller gear ratios make it easier to climb.
  • Reduced weight.  The compact crank weighs less than the standard crank and you can get maintain similar climbing with a smaller, lighter cassette (e.g. an 11-23) versus needing to carry a 12-25 or a 12-27 with a standard crank.
  • Closer gear ratios.  Closely related to the previous two items, the larger your cassette span is the more your gears are spaced out.  A standard 12-25, for instance, has a gear ratio of: 12-13-14-15-16-17-19-21-23-25.  A 12-23, on the other hand, has a gear ratio of 12-13-14-15-16-17-18-19-21-23.  On the 12-25 cassette you are skipping the 18 cog in exchange for the 25 with the result that the biggest 5 cogs in the cassette all skip at least one tooth.  Not that big of a deal except when you’re looking for a very minor change in gearing.
  • Reduced knee stress.  Pushing the big crank is hard on knees, but the compact crank reduces this stress a bit.  This was one of the biggest reasons I chose the Pinarello over the Cervelo P3: my knees (old football/wrestling injuries) hurt on the P3 from about two minutes into the ride whereas they rarely hurt on my compact.
All this is great (read: boring), but where this article separates itself is in the actual testing it did to try to find out the true difference in top-end speed.  The tests were performed based on 700c wheels and 90 RPMs for the cadence.  Here’s the first result:
  • With the smallest cassette (11-21) on both the compact and the standard, the top end speed on the standard crank was higher: 33.2 MPH vs. 31.3.
Here’s where the arguments for the standard go down the tubes.  First off, there probably isn’t even a elite professional athlete (let alone an age grouper) pushing these types of speeds so the difference in top-end speed is meaningless.  You would have to be physically capable of pushing faster than 31.3 MPH on a compact crank for a standard crank to benefit you in any way in terms of top-end speed.  Sure, if you’re pushing the same tooth ring in the back on both a standard crank and a compact crank at the same RPMs the standard will go faster as this proves, but you can always use a smaller cog on the compact because it is easier to push.
A more interesting result occurs when we look a a more traditional standard vs. compact set-up:
  • With a 12-25 on the standard crank (very common stock setup) and a 11-23 on the compact crank, the top-end speed on the compact is actually faster: 31.3 MPH vs. 30.42.
In other words, with this setup, not only do the top-end speed arguments fail, but you get all the benefits mentioned above (easier climbing, lower weight, closer gear ratios, etc.) and you’ll go faster!
Even with this difference, I’d like to point out again that there is NO DIFFERENCE IN SPEED unless you’re pushing over the top-end speed which, based on the event results I’ve seen, doesn’t happen.
I encourage you to take a look at the article and judge for yourself.  If you can stand the hit to your ego before your group ride or race starts, you’ll be fine because you’ll be passing those who laughed on the hills and running faster than them afterwards because your knees and legs still feel fresh.
[UPDATE: See my recent thoughts on this topic]
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2 Comments Add your own

  • 1. nicholasjmills  |  June 4, 2009 at 12:38 pm

    Useful post, thanks! I happened to find it via a google search and have been looking for some definitive testing on this question.
    I recently switched from a standard to a compact – the only time I find a downside is on decents where I can run out of gears. It’s rare though, and hey it makes me rest more.

    Good luck with the road to Ironman! I’m doing the same: looking at Florida 2010 for a flat bike course. Any recommendations Stateside?

    Reply
  • 2. Going Compact (Revisited) « Why Not Tri?  |  June 1, 2011 at 11:48 am

    […] an earlier post, I discussed the virtues of going compact.  At the time, I had primarily ridden compact cranks  and hadn’t spent any significant […]

    Reply

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