Tuesday, August 14, 2007

Letters - Long Cranks

Originally posted in cyclingnews.com. (This letter addressed mountain bikes but the same holds true for road bikes).

In response to Richard Rule's crank length letter:

If you are 6'2", 35.5" inseam, there is little reason for you not to buy 180's. Long cranks give you extra leverage and allows your muscles to exert power over a greater range of motion. If you're limited in training time, don't have the aerobic capacity of a pro, and just want to enjoy 1-3 hour rides, then I think longer crank arms are great.

I'm only 5'7" with a 29" (barely) inseam. I ride a 49-50 cm seat tube frame. I have decent speed/power, terrible aerobic capacity. Conventional wisdom would put me on 170's or shorter. By working for a couple months to overcome the tendency to push, I eliminated the one significant drawback of the longer cranks. With limited training, I found a dramatic increase in performance after switching to 175's. I first learned of long crank usage when Renault Elf put their riders on long cranks. Marc Madiot, riding a 55 cm frame, used 180mm cranks with success. I "re-discovered" the theory last winter when I rode a mountain bike with 175s and found myself riding as fast on it as my road bike. I made the switch soon after that.

Some precautions. Long cranks force your feet to make bigger circles and increase the distance your various leg parts travel for each revolution. Your knees go higher, drop farther, your foot extends forward more, your Achilles is stretched a little bit more. Long legs minimize a lot of those effects. Long cranks require adaptation time, which, if skipped, give rise to some "long crank arm" myths like the inability to spin and losing efficiency. Since the cranks drop further, you'll hit them (or your pedals) more often on rocks and such.

If you allow yourself time to adapt to the new cranks, you'll be able to spin fine. Switching off season helps - you can focus on regaining pedal speed instead of keeping up with your riding friends. After my November 2001 swap, my comfortable cadence dropped to just over 70 rpm's. However, my performance increased significantly due to increased leverage/power. By March 2002, my comfortable cadence was back at 100+ rpm's. To measure cadence, buy a simple cyclometer with cadence. Mine cost less than US$60 (and it has heavy duty wires for mountain bikes). You can also count rpm's for 6 seconds and multiply by 10, but this is less accurate and immediate. To see where you ride comfortably, simply ride without paying attention to your exact cadence. I find that my cadence climbs 5-10 rpms if I ignore it. You'll find that your cadence returns to a consistent range each time you do this on a given day or week.

As pointed out in other letters, "pedaling efficiency" has more to do with having a good form and discipline rather than crank length. If you can maintain form comfortably at 100-120 rpm's, whatever the crank length, you'll be able to maintain it at lower rpm's.

Losing efficiency in specific situations is a different matter. Long cranks don't help sometimes, particularly at very low cadences. On very steep climbs at low rpm's, they seem to lose efficiency (this is my personal observation). I attribute the efficiency loss to a combination of a longer "dead spot" in the pedal stroke as well as a higher output "power stroke". Long cranks also accentuate the difference between your lowest and highest output for each revolution. This causes the pedal to "stall" in the dead spots. When pedaling at a reasonable speed (70-80+ rpm's), the dead spot issue is moot. In fact, you'll find that you have significant more power on slight and moderate uphills - you'll be able to shift up a gear or two. Your flat land cruising speed will increase as well, as much as 10%. Your top speed will decrease for a given gear due to the larger pedaling arc - you'll find yourself using bigger gears when sprinting.

If you do decide to get the longer cranks, don't forget to adjust your position on the bike. Your position is determined by the amount your cranks point forward (for seat fore-aft) and down (for seat height). Check your seat height (lower for longer cranks), seat setback (this may not be necessary because lowering your seat will move it forward), stem height and length (lower and longer, usually). If you install 5 mm longer cranks, you'll need to move your seat forward about 5 mm and down about 5 mm. Remember to first maintain the seat-pedal relationship and then worry about the seat-bar relationship. Don't adjust your seat position to fix an incorrect stem or bar - this compromises your seat-pedal position. Instead, you should fix it by changing your stem or bar. In the case of 5 mm longer cranks, your stem will need to drop 5 mm and extend 5 mm.

8 comments:

josh said...

So do you support this or more puttin it out there, i'm a bit unclear?

All that said, I am 5'8" with proportionally tooo long femurs and I'm watching a SRM on ebay w/ 175 arms....I normally ride a 172.5, but after reading this I decided to keep an eye on the SRM. So I'd be ok based on what you're advocating?

Aki said...

I support it for those that are willing to put in the time to adapt to the long cranks and understand the +'s and -'s.

With longer cranks I think you'll lose a touch of speed and some of the snap in short, hard accelerations which require a big rpm gain.

You'll gain torque so you'll be better on moderate (big-ring) hills, slightly lower cadence, and for sustained efforts.

Although I haven't tried arch cleats, it might have a similar effect to that - takes the edge off the top but really fills in the middle.

When I made the change I had been training very little, even less than I normally do, getting out for 45 minutes every week to two weeks. I was open minded to bike changes as I had nothing to lose. I found the cranks made a huge difference in my overall riding at that time and stayed with them.

I eventually made sure the four bikes I ride even semi regularly have 175s on them (two road bikes, my tandem, and the mountain bike that got me started on this whole crank thing).

However, I've noticed my top speed has dropped. Not critical perhaps as my aerobic base is more an issue but I love going fast and longer cranks took 40+ rpm out of my top rpm speed (286 -> 244).

Your change will be less dramatic. I went from 170s to 175s and I have very short femurs. If you watch one of the clips I've posted (the Nutmeg State Games) you can see my decidedly slower cadence and big circles.

Mike Starr said...

I have used 170, 172.5, 175, 177.5 and 180's. Can't say that I rode any better, or any worse with any one of them. I think I liked the 170's best, only because my mind kept thinking I could bridge gaps at 130+rpms easier, but I don't seem to have a problem with the 175's my bike came with now and I'm 6'2". I guess it comes down to the fact that the body adapts to most anything and since most peoples riding rarely goes into the 130+, or less than 60 rpms ranges, just about any crank will work just fine. Best to not overanalyze, otherwise you'll have yourself believing in the hype.

gewilli said...

180s on every damn bike...

but then...

i'm 6'6"

Aki said...

I found that when I was in shape I could use shorter cranks effectively - fit enough to get to the finish and the shorter cranks let me sprint faster. But as I got heavier (and stronger I suppose) the long cranks work better.

6'6"! 180s end up expensive. At least my 175s are reasonably common. Two of my close friends, both a bit over 6', use 180s.

Of course now I'm thinking if I get really fit I could put some 170s on. haha. Prob not.

gewilli said...

yeah, you get to choose from Dura Ace or Record. Rumor has it there are a some others out there... for Mt Bikes i've got mostly XTR with a few XT and sugino and an old set of NOS Suntor XC Pro...

Ethan said...

Hi Aki,

First I wanted to mention that I enjoy your blog and have been reading for a while without ever commenting. I am the "guy in blue" dragging Adler to the front in the March 25 Bethel race that you helmet-cammed..

Anyway, I just wanted to mention that I have had the same experience as you with the longer cranks. I bought a cheap bike for racing this spring that I wouldn't worry about crashing and inadvertantly got 175 cranks instead of my normal 172.5. I've been riding that bike exclusively for the last two months and I immediately noticed I felt more efficient on 5 minute type climbs, the difference wasn't as noticeable on longer climbs.

On the other hand, my sprinting seemed noticeably less snappy at first. I really struggled to turn the pedals over and lost about 50 watts off my top-end power. Sprinting is my favorite part of riding though so I have been sprinting a lot with it and have seen a dramatic improvement. I believe some of the increase would have happened on any cranks, but I have added 250 watts to my top power output (on the 175 bike, 200 compared to the 170 bike) , that I think has to be partially attributed to getting used to the longer cranks. It seems to me that neuromuscular adaptations are most important for sprinting so it may take longer to adjust your sprinting to different crank lengths than adjusting to other riding efforts. I am very curious to see how I perform on 172.5s when I get that bike back in a couple of weeks.

Aki said...

ethan - thanks for reading the blog, comments or not. I always wondered who the "guy in blue" was because he seemed willing to do a lot of work and seemed strong.

I'm contemplating trying shorter cranks again (which I hinted at in an above comment). I realized that my top speed is really my only strength. Someone said something about "I can't believe how many people Aki passed in that sprint". And the sprint in question was horrible for me - soooo sloooow. I want to amplify my strengths, not flatten them out.

I don't do any hilly races (though that might change with my move) so I was thinking focusing on sprinting might be good. I don't know though - it would involve buying a lot of cranks if I move back to 170s. For now, no changes.

I'm curious to see what you find with the shorter cranks. I may take your lead there.