Thursday, April 28, 2011

The Nerd Report: Compact Crank vs Standard Crank

So when I first learned about a compact crank and its smaller size front rings, my ego-o-meter immediately went into biketard mode and I scoffed with, "Why would I want smaller gears? That would make me only go slower and spin more!"


Ok, yes, but! You are really only losing two top end gear ratios. How do I know? Well let's do some math!

First, what is a "standard" crank and what is a "compact crank"? A "standard" crank is usually a double ring with the big ring @ 53 teeth and the smaller ring @ 39 teeth. The "compact" crank comes out @ 50 & 34.

In the rear, I ride an 11x25 cassette. Below is a chart showing the different gearing ratios between a "standard" crank with an 11x25 rear cassette and a "compact" crank with an 11x25 rear cassette.

Holy Numbers, Batman!
What do these numbers mean? Note that the higher the ratio, the more you are using a "larger" gear. I.E. you are going downhill and need to push a bigger gear to maintain some torque on the pedals.

On the opposite end, the lower the ratio, the more you will be spinning. I.E. you are climbing a steep hill and you need a smaller gear.

Now compare the 53x11 (4.818 ratio) to the 50x11 (4.545 ratio). Yeah, if you are in your hardest gear heading down a hill, you are more likely to spin out faster using the compact than the standard, but how many times do you get into this gear and how long do you stay in it and how long does it take before you spin out where it doesn't matter what kind of gearing you are using since gravity is doing all of the work for you? By switching to a compact, consider that losing 1 to 2 top end gears is really not much of a sacrifice since you hardly ever use em anyways!

But now compare the 39x25 (1.560 ratio) to the 35x25 (1.36 ratio). Quite a difference and these are gears that you WILL use on a hilly course. With a compact, you are gaining 2 extra climbing gears.

Well, why would I want two extra climbing gears when the 39x25 is good enough? Its all about keeping your efforts steady. Yes, a 39x25 is a pretty good climbing gear, but consider the Lake Placid bike course. If you had to do only one loop of those hills, a 39x25 is fine. But since it is a two loop course, being able to spin up those hills in an easier gear will help preserve your run.

What? I am confused!

The more spikes in efforts (due to too hard of a gearing choice on hills) will come back to bite you on the run. You want your effort to to be as sustained consistently as possible. If you train with power, this is your VI, or Variable Index. Basically it takes your power profile and takes into account how all over the place your wattages are.

Here are two examples. The first is a ride with a high VI because the wattages are all over the place.

The second is a ride with a much lower VI because the wattage was much more consistent.

Generally a hilly course will have a higher VI, because of spikes of climbing to low numbers from downhills. A flatter course will generally have a lower VI because the lack of uphills and downhills will allow the rider to stay much more consistent with effort.

So, REALLY, what do all of these crazy nerdy numbers mean? Well, it depends on the terrain that you will be riding. How flat is your race course? How hilly is your race course? Think of the crank and your gearing as merely the right tool for the job at hand.

Why did I switch to a compact suddenly? Easy: Lake Placid. As described above, the hilly terrain will cause my VI to rise. By choosing gears that allow me to spin more, I will have more control over power spikes on the hills (lowering my VI), which in the LONG TERM will help save my legs for the run.

So why not just get a rear cassette with some larger gears? Like a 27 or 28? I didn't like the jump in gears. The larger gears in an 11x25 go from a 19-21-23-25. Nice and smooth. An 11x28 goes 19-21-24-28. Those are some HUGE jumps in gearing! Also! A 34x25 (1.360 ratio) is a lower gear ratio than a 39x28 (1.3928 ratio). How bout that! I think of switching to a compact as getting a more dynamic range of gearing with smoother transitions.

I just did the 70.3 down in Galveston. That bike course was as flat as a pancake. A standard crank was perfect for that course since I never needed to spin easy gears. I never got out of the big ring the whole time! In fact, I used the 53x12 and 53x11 enough to justify having them. I would have missed them had I had a compact on that day.

So when looking at your "A" race, consider the terrain, consider your cycling ability, then consider if a standard or compact crank is right for you.


  1. is this even in english? lol

    ps. im reading a Lance Armstrong book called "its not about the bike". its pretty good

  2. Ummmmmmm....... I am lost, this is why you are called the Professor

    I have a compact on Mercy and Standard on Mistress running 27-12 on each. I want a 25-11.

    Here is another debate, Roadie or Time Trial bike on hilly courses. Have you ever thought of using the Roadie for LP?

  3. BDD: Time Trial Bike all the way for Lake Placid. There are some large sections of flats on the course. Also, I don't wanna be "that guy" riding a road bike at a triathlon! LOL! ;)

  4. During training, I never leave the big ring - even on the climbs. I also climb in my saddle, I rarely stand up.
    Builds strength and eventually one day u'll be able to spin just fine on those climbs with a lower perceived exertion.
    Granny gearing it in training is not going to improve overal climbing abilities.
    Just a thought :)

    coming from a mountain bike background, on a steep climb I keep it in the middle ring no matter what - if I tried 'back it off' to a gear that reduces my percieved exertion, I'd be in the granny gear in no time, still working my butt off but now going snail pace and taking twice as long.
    Sometimes its better to muscle a bit of hill. :)

  5. And now I have a headache... haha

    Awesome post! Your spreadsheet made the gearing much easier to understand.

    One question though, was it really as simple as swapping out the crank? Did you have to change anything other than the crank itself? Change the chain length or anything?

    PS: If you'd like to borrow my roadie with a triple, just let me know ;) haha

  6. Hey John,

    For the Ironman distance, "muscling" it up a hill is basically the WORST thing you can do. For a sprint or olympic and even a few times at a Half Ironman, muscling it is fine.

    Do you ever wonder why a lot of folks can't run very well during the run @ an Ironman? Beyond poor conditioning, going too hard on the bike, especially up the hills, is what bit them hard into walking too much during the run. Going too hard up the hills creates a ticking time bomb that goes off when you don't want it to.

    Something to consider!

  7. Your knowledge just amazes me. I know that I am new to this sport but I have taken leaps by just reading your blog about things like this and also with swimming.

    Thank you.

  8. You just saved me from having to write a "tech post" to my blog.
    I'm already compact but am planning on trying a new cassette this weekend. I find myself wanting the missing gears in my current cassette. So I've now got a 50-34/12-23 to try out. I should be fine with the climbing. I was on a 53-39/12-26 last year, so the easiest gear is the same ratio.
    The part about the VI is cool. I knew that I wanted smoother changes. I never thought about how nicely a power meter graph would show that.
    Are you swapping the cranks out yourself?

  9. Oh, in case you and others are unaware of this resource. If you are interested in all things BIKE!
    That website is the encyclopedia of biking.

  10. i have a compact on both my road and tri bike. Cozumel is totally flat but has a nasty wind (so Ive been told) so I am hoping that the compact will do me good!

    awesome post!

  11. I've gone through this whole math exercise (stay tuned to my blog for the results) and there is a whole section on this in the USA cycling L3 manual. Net result for me I mix it up a lot. For IMFL I'm going 53x39 w/11x28. I rode Rev3 Quassy with that setup and am probably going compact for that race with the climbing. BDD, I'm also going roadie for it.

    I'm not racing Placid but am doing one of the camps and am bringing 50x34,11x28. High VI makes running afterwards more challenging.

  12. I've gone through this myself quite a bit. I had a 53/19 w/11-28 but hated some of the jumps - but not the one's you mentioned. It was the jump from 15 to 17 that is the biggest percentage gap but becomes necessary with wide range cassettes. I determined a 50/34 w/11-23 would be best but didn't want to buy a new crank so in the end I got a 12-26 to pair with my 53-39. I drop 1 top gear and 1 bottom gear and am much happier with the gear spacing. For a really hilly course I can do a mix 'n match keeping the 12-19 cogs from the 12-26 and grab the 3 climbing cogs from the old 11-28. How's that for crazy?

  13. great post. One of the first bloggers to go and tackle this mystery too. LOVE your response to JP too. I agree with you 100%, why? Because I am a hammer fest hill attacker. I get on the bike and HAMMER. Well, that was last year. Oly distance I can handle that... HIM distance, NO WAY.

    Smart training man, it's not about winning the bike leg, its about surviving the race.

    Cedar Point is a flat course, my road bike in my ironman distance race will be JUST FINE! Because I AM THAT GUY!

  14. Excellent post Jon! I understand the basics of the ratios between compact and standard but you explained it so well that I now feel proficient in this knowledge

    JohnP is right - if you don't have to run after the ride. Sometimes in training I intentionally muscle it up the climbs in the big ring for conditioning purposes. However, on race day you are no longer training and your gearing decision needs to be made based upon the course elevation and what is going to give you the best chance of success on the marathon.

    Wise choice Jon!

  15. I think Jeff & Matty got the jist of my post...

    FOR TRAINING muscle away. Stop drinking the 'wussy' kool-aid on babying it up the hills. You wont get stronger if you dont engage the muscles. By the time race day comes around the gear that you used to 'muscle' will now be the gear you are 'cruising' in.
    That means, REMOVE your small chainring and force yourself to work hard. If your goal is to just finish, that advice isn't for you. If your goal is to improve and make it to the 'next level' then granny-gearing it ain't gonna work.

    I agree you need to pace yourself throughout a race to a point, but we're talking about training here.

    Everyone has their own training regiment obviously, to each there own. :)

  16. John - HUGE sigh of relief! You had us all worried that that was your race strategy! LOL!

  17. Believe me as confusing as it all sounds, IT ALL MATTERS.
    I run a compact Dura ace 50/34 and have 2 rear cassettes.But lately have run an 11/28.Yes that is one large pizza pie back there at 28. Unfortunately have had some leg issues lately so I can't tell you how trully wonerful that 28 is or will be.

  18. Very educational, I love nerdy posts! What about *gasp* a triple? Does that accomplish some of the same things that a compact setup does?

  19. Uhhh...what?


    I get the don't mash thing in an IM for sure though.

  20. I should probably figure out how to change a flat before changing a cassette ???!!! wouldnt even know where to start!

  21. I can't tell you how many times I've had this argument in my head, I'm constantly going back and forth. I'm currently on a full size crank. This season my group is doing a TON of climbing, I mean a ton! It's good stuff, but I'm usually wishing for the compact on Saturdays.....

  22. Hi little bro,
    I took a little break from the whole blogging thing but wanted to stop by and see what is going on with you. The Nerd Report totally cracks me up:) I love it that you are so technical and analyze everything! Miss you! Have a great weekend!

  23. Thanks for all the information. I "think" I understood some of it! :)

  24. I should go talk to someone at my local bike shop... I'm currently running a 54/42 up front, and a 23/11 in the back. Made for speed? Yes. Made for hills? Not as much...

    I don't know if it's better to go with a different cassette or compact cranks though... I'm headed up there over Memorial Day weekend and I'm going to try out the set up I have on now to see how it works out.


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