Who is the most dangerous rider in BMX? Some would say it's Christophe Leveque, with his ethereal smoothness and ability to command a moto. Others might point to Brian Foster, simply because his well-rounded riding skills make it impossible to ever count him out during a race. A lot of the older riders I speak with feel that John Purse's incredible drive and focus makes him the most dangerous rider in cycling, period. All of these people are wrong. I met the most dangerous rider in BMX last week---at my local track.
What makes him so dangerous? Well, Alexander Pope once wrote that "a little knowledge is a dangerous thing," and that's exactly what this guy has: a little knowledge. He freely admits that he hasn't raced since the Eighties, and he isn't exactly well-versed on modern racing equipment and tactics, but that doesn't stop him from forcing advice on any kid unlucky enough to cross his path.
Some of the information this guy hands out during his impromptu one-on-one clinics is of dubious value. The rest is just plain worthless. "You ain't never gonna get no air jumping like that," he informs a kid trying to pull up and over a small roller. One of his favorite phrases is "Man, you don't got to analyze it like a science experiment---just ride FAST!" His thoughts on bike setup? "Move those bars forward to get some POWER, man!"
I know what you're thinking. "Jim, this guy may be an idiot, but why is he dangerous? And what's the difference between you and him?" Good questions. Why is he dangerous? Simply because he is an older rider who comes to the track and dispenses advice. The young racers who listen to him don't always realize that it's bad advice. After all, he's been around a while, so he must know what he's doing, right? Anybody who beat most of today's pros when they were younger (as this gentleman regularly claims to have done) probably has a lot of valuable information to share. Unfortunately, the "help" they get from this guy is going to hurt their riding.
Why am I any different from the average track know-it-all? To begin with, I don't claim to have the answers to everything. If I know anything at all about BMX, it's because I have made a conscious effort to sit down and analyze our sport in a serious fashion, aided by some other people who have been extremely successful in their riding careers. My greatest enemy in the sport is the stuff that "everybody knows", even though there,s no reasoning or proof behind it. That's what I,ve been fighting against with "BMX Basics", and it's what I'll continue to struggle against.
For instance, "everybody knows" what crank length you should ride. Your racing buddies, the guy at the bike shop, the dudes downtown who spit on your windshield and then offer to wipe it---all of them are telling you that: Short riders , whatever that means, should ride 170mm or 175mm crank arms. Taller riders are best off with 180s. Circus freaks and pros would be best served with 185s. You should use a longer crank on your cruiser---or is it a shorter one? Hmm, I can never remember.
I've always been a little suspicious of the conventional knowledge about crank length, but I've never seriously challenged it. Why not? Well, my BMX mentor, a guy named Rich Hetzel, told me "the scoop" on crank length twelve years ago, and I was afraid to disagree lest he rise from the grave (metaphorically speaking) and smack me. Looking back, I realize that he was just passing on what he'd heard when he was younger. Asking around, however, I found that nobody really knew any good reasons why a particular length of crank would be better. Has anybody actually studied this stuff?
Yes. His name is Lennard Zinn, and you can find his work on VeloNews, where he writes on a broad variety of cycling-related techincal issues. Mr. Zinn, who is 6'6", had long (pun intended) wondered about crank length, so he gathered some top-level road cyclists and performed a variety of tests on them, forcing them to ride crank lengths ranging from 100mm to 220mm. What kind of results did he have?
In Mr. Zinn's words, "The shortest and tallest riders seemed to favor the longer cranks, while the mid-height riders' trend seemed to (favor shorter cranks)." With longer cranks, the test riders were able to maintain their maximum power output longer. The exception was the 5'10" rider, who actually performed best with 100mm cranks. Crazy, huh?
Longer cranks would seem to be better. Unfortunately, the riders experienced knee pain and strain on the longer cranks, which kind of makes the higher power output irrelevant. If you could win every race you ran by using 220 mm cranks, only to have your career cut short by knee trouble, what good would it be? The final analysis? "Long cranks excel in steady-state cycling but acceleration is slower at their lower cadences. Also a higher likelihood of joint and connective tissue injuries exists with longer cranks, due to the large range of motion they require."
Well. If longer cranks hinder acceleration, why do pro BMX riders, who get paid depending on their ability to accelerate, use them? This got me so upset that I had to sit down with the calculator and Mr. Zinn's results for quite a while before coming up with the answer. It turned out to lie in a unique feature of BMX---the single-speed gearing.
Let's take another look at our old friends Rider A and Rider B. Today, they've brought their pal Rider C along. Rider A uses 175mm cranks. Rider B chose 180mm, while Rider C decided to go with the 185s. When all three of them go street riding, Rider A likes to pedal at a steady 100 rpm. Rider B, being Rider A's identical twin, likes to pedal with the same foot speed at Rider A. But wait! When he does that, he finds that his cranks are only turning 97rpm. Why?
Remember, your pedals turn in a circle. Longer cranks make that circle bigger, which means that your foot has farther to go. Rider B's feet, which move at the same speed as Rider A's, are pedaling through a larger circle, so they don't manage to make a complete revolution quite as often. Rider C, with his even longer cranks, finds that he is only pedaling at 94 rpm, using that same pedal speed. Hmm. In other words, Rider A is going faster than Rider B, because he is pedaling at a higher RPM, while Rider B is leaving poor Rider C in the back of the pack.
When all three of these guys sat down at the end of the ride, though, they noticed something. Rider A's legs were more tired than Rider B's and Rider C's. Why? Longer cranks give you more leverage. As you may remember from science class, when you use a longer lever to move something, you get to put in less force, but you have to move the lever farther. That's how it is with longer cranks. You pedal in a bigger circle, but you need less force. Which brings up a problem. How are our three friends ever going to ride together again, if they are all traveling at different speeds?
"You know, I'm sick of getting left behind by Rider A," Rider B said to C. "I'm going to move up a tooth on my front gear. Rider A uses 43/16, so I'll use 44/16."
"Great idea," Rider C replied. "I,ll go up to 45/16. I'm using the longest cranks, so I should have the toughest gear." What's going on? It is probably a total coincidence, but it works out that a rider with:
175mm cranks pedaling at 100 RPM with 43/16 on a 20" bike = 15.98 mph
180mm cranks pedaling at 97 RPM with 44/16 15.86 mph
185mm cranks pedaling at 94 RPM with 45/16 15.72 mph
That's close enough for government work, as my mom used to say. (Yes, my mom is out of government service now.) So Riders A, B, and C are all now giving about the same pedaling effort, but with different crank sizes and gears. And they're all going at about the same speed.
Once again, there's no free lunch. There's no way to pedal with less effort and go faster. Mr. Zinn's test, being conducted on multi-speed bikes and using riders who don't stand on the bike to race, doesn't perfectly translate to the world of BMX. We have to pick one gear, and optimize that gear/crank combination to a point where we feel comfortable.
Why pick one crank size over another? Two reasons. The first is that there is a risk of joint damage when using long cranks, just as Mr. Zinn said. For that reason, a 5'2" rider would be unwise to select a set of 185mm cranks. Similarly, a long-legged rider will find that a short crank doesn't let him use all of the strength in his legs when standing, which means that a 6'4" rider should avoid those tempting little 170mm MTB cranks.
The second reason has to do with comfortable pedaling speed. You know the feeling of being "spun out." That's when you are pedaling as fast as you safely can. If you pedal any faster, it'll throw you off your balance. I found out early in my racing career that I got squirrely at a lower pedal RPM than most. Since I didn't want to be left behind, I upped my gear and crank length. I ride a 47/16 on my 20", with 185mm cranks.
I feel more stable pedaling a cruiser, so I chose 180mm cranks and a 44/18 gearing. Because I can pedal faster and still use a gear that equates to about a 47.5/16 on a 20", I do go quite a bit faster on my cruiser than on my 20".
The final word on crank length? If you are comfortable "spinning", choose a smaller crank and a lower gear. If you aren't, consider a longer crank and a higher gear. Why do the pros tend to choose longer cranks? The answer, I think, is stability. There is a bit of bump-n-thump in the Pro class, so those gentlemen need to be stable. If they can maintain the speeds they need at a lower RPM, that's good. In general, the more physical a rider is, the longer his cranks will be, and the higher his gear will be.
The more I think about it, the more I envy my know-it-all track buddy. I mean, look at all the work we did, and it still comes down to, "use whatever,s comfortable for you, man, and RIDE!" At least we know why it has to be that way. So RIDE already, man!