Certainly we all know what it's like to have a term paper or project
due some time in the future. Sure, we put it off, do chores around
the house, take that extra "training" ride around the
block, settle down with a TV mini-series, but sooner or later
it has to be done, and usually at the last minute, simply because
it's got to be done. That's kind of how I've felt about writing
a gearing-oriented column. It's not my favorite topic in the world,
but it's got to be done.
The importance of gearing to the dude in the street has changed
a great deal since I first laced up my All-Stars to go riding.
Years ago, gearing was one of the most controversial topics in
BMX. Now it's kind of a snoozer as far as most riders are concerned,
but the bad advice, misconceptions, and just outright fibs about
it haven't been put to rest yet. And as the saying goes, "If
not me, who? If not now, when?"
Starting with the basics: BMX bikes have a chainwheel in front
and a freewheel in back. Chainwheels can be purchased in sizes
from 37 to 52. Freewheels are generally available in 14 to 18
tooth varieties. When a rider pushes his pedals, he turns the
chainwheel, which turns the freewheel according to the gear ratio.
The gear ratio is obtained by dividing the size of the chainwheel
by the size of the freewheel. Example:
44 tooth chainwheel/16tooth freewheel = 2.75
For every turn of the chainwheel, the freewheel, and thus the
rear wheel, will turn 2.75 times. Pretty cool, huh? Since a BMX
wheel has a circumference of 62.05 inches, or 5.17 feet, that
means that every time the rider turns the crank all the way around
he will progress 2.75 times 5.17 feet, or 14.22 feet total. To
figure out how fast we can go, we need to know how fast we can
pedal.
The easiest way to figure out how fast you can pedal is to sneak
into a health club and spin out a Lifecycle, watching the "rpm"
meter. We'll assume for a minute that you can "burst"
spin up to 180 rpm. A "burst" spin is one that you can't
maintain for any real length of time, as opposed to a steady spin,
which you could do for, say, ten minutes.
If we plug 180 rpm into our 44/16 gearing, we come up with 10,800
revs per hour, which translates to 29,700 rear wheel revs per
hour, which means that we're traveling 153,549 feet per hour,
which finally translates to 29 mph. Now that's cookin'. Twenty-nine
per would win most races, even in the Pro class.
However, most riders I watch on the track actually only realize
120-130 rpm on the straights, which takes us up to 20-21 mph with
that gearing. Now, if a rider can only spin 130 rpm, and the other
guys are walking away from him on the straights, what can he do?
Change his gear, of course.
If we take the above 44/16 gearing and change it to 46/16, we're
now pushing that rear wheel 2.87 times for each chainwheel revolution.
This translates to a four and one-half percent improvement in
top speed for the same conditions. Our 21mph guy is now a 22mph
guy.
"One measly mile per hour?" you are no doubt thinking,
"What difference could one mile per hour make?" Well,
one mph equals 1.46 fps, or foot per second. A BMX bike typically
has a three foot wheelbase, so in four or five seconds your one
mph advantage would enable you to pass a rider you were slightly
trailing before. Put another way, in a straightaway that takes
you twelve seconds to get through, you could pass up to three
riders. And all it would take would be to change that little gear
up front. Isn't that a lot easier than hitting the gym an extra
time each week, or eating tofu when you'd really rather have a
Whopper?
Now let's look at it from another angle. Just as a larger gear
ratio makes you faster, as lower one makes you quicker, in the
same way that a car accelerates faster from a starting stop in
first gear than in second. Riders who were being left behind at
the gate realized that a lower gear could enable them to reach
full power before everyone one else. Doing so could let them pull
in front and then control the race by weaving in front of any
would-be passers. So instead of practicing your start, why not
lower your gear and get the same benefits without the extra work?
Now you see the evil lure of gearing. It promised something for
nothing. In the early Eighties, gearing frenzy swept this sport.
"Gear bags" were a common sight, and most riders showed
up at a race prepared to swap between five or six different gears.
Parents huddled behind bike shops with evil-looking men who promised
to trade them the ultimate gearing secret... in exchange for their
first-born son.
"Sounds fair to me," the parents would say, "my
first-born son hasn't won since last year's Evansville National.
Now how about that gearing secret?" One company went so far
as to produce a kit that enabled the rider to swap gears without
tools. The only caveat was that the rider not pedal backwards,
because doing so would pitch the currently installed gear right
off the bike.
I couldn't tell you exactly what it was that killed the gearing
controversy, but if I had to place my bet it would be on the one-piece
polished aluminum chainwheels that became available for Profiles
and similar cranks in 1988 or so. Faced with a choice between
a great-looking chainwheel and having five bolts that loosened
continually and got lost at the worst moments, riders were willing
to forego any supposed benefits of gearing changes and take the
former.
Most of the riders I meet today have never changed their gear.
If they have, it was probably to pick up a better-looking chainwheel.
That's something I'm happy to see, because obsession with gearing
made BMX a lot less fun than it could have been for quite a few
people, particularly young riders. On the other hand, this means
that some riders are simply not extracting the best from their
bikes and themselves.
I hate to bring it up for fear of clouding the matter further,
but crank length also affects your gearing. The longer your cranks
are, the more leverage you are exerting on the chainwheel, which
will make pedaling easier. When I was younger, I ran 45/16 gearing
with 180mm cranks. Today, I'm using a 47/16 with 185mm, and the
pedal pressure is approximately the same as it was with the previous
setup.
The downside of this is that longer cranks require longer legs.
They also increase the diameter of your pedaling circle, meaning
that you are pedaling farther to get the same results. Most riders
will lose nearly ten maximum rpm for every five mm they add to
their cranks. For that reason, if you are 5'4", don't listen
to the bike shop guy who tells you to run 180mm cranks. Run 175mm,
or even 170mm if you like to spin. Some very famous riders used
to use short cranks and low gears to achieve incredible spin rates.
By 1988 nearly everyone who was anyone was using short cranks
and a low gear. Then a guy named David Milham came along, ran
a 52/14 gear, and killed people, forcing everyone to rethink their
philosophy.
Speaking of David Milham... Most riders will fare best with a
16 tooth freewheel and a chainwheel between 42 and 47 teeth, but
that doesn't mean that you will. Don't be afraid to blow twenty
bucks on a huge chainwheel if you're happy with the regular stuff.
Most riders, though, will do best with a 44/16 or 43/16 gearing.
44/16 was the acknowledged standard for a long time in this sport,
and most complete bikes came with 44/16 until, say, 1986, when
Kuwahara and a couple others started shipping their bikes with
a 43/16 setup. Today, complete bikes seem to show up with whatever
the manufacturer had on hand. Chances are that you either got
into BMX by buying a complete bike new or picking up a variety
of used stuff, so you probably didn't have any say about your
gearing when you started riding. And since any gear becomes second
nature after a while, you may not have given it much further thought.
Despite the apathy most riders feel concerning gearing today,
there remains a chance that you can moderately benefit from consciously
choosing the right gear. Our friend in this effort will be the
elapsed-time method of measuring performance from
two months ago.
Go to your home track with the gear you're using and time yourself
three times. Average the result. Throw out the wrecks and obvious
miscalculations. Then go home and change your gear one tooth up
or down-your choice. Ride on the street with it until you're comfortable,
and then return to the track. Don't change your riding style.
It other words, don't clip a turn you've been railing around,
or vice versa. Ride it the same way you rode with the previous
gear. Check your times. If you got faster, that gear is worthwhile,
and you should go up (or down) another tooth to see what happens.
If you did not improve, go to a gear on the other side of what
you had before, i.e. if changing from a 44 to a 45 up front slowed
you down, try a 43. Keep changing until you get your best time.
Then stick with it.
When you visit a track with longer straightaways, you might want
to consider going up a tooth. If you have a small, indoor-type
track on your agenda, try dropping down one tooth. Don't make
any changes more drastic than that, and you should do very well.
I hope that we've put the gearing bugaboo to rest a little bit
here. Changing your gear with an intelligent goal in mind can
sometimes make just the little difference you need to do your
best. If you don't expect anything more, you'll be okay. But it
you find yourself reaching for that gear bag in the morning before
the street ride... don't blame me!