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!"

WRONG!!!!

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.