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OK, so you're a big smarty and can ride a bike no-handed. You steer it by tilting. Sure, you can turn a bicycle by tilting, but this is due to the design geometry of the bicycle which makes it track. It's not the kind of geometry you studied in high school, just a fancy way of saying, "we put the front wheel there because it works better there than, for instance where the seat is." So your no-handed trick is not so wonderful after all, the bike designers make it easy for you. Do you give them any credit? Probably not.

The front end has a built-in trail effect, which is convenient so you don't have to buy it separately. The wheel touches the ground behind where the angled axis of the steering tube intersects the ground, that makes trail. A bike's trail works like casters which swivel when you roll your chair in different directions. The wheels are off-center of the axle (pivot point) and swivel behind the direction of travel.

This trail effect gives you stability, the wheel tends to stay in line without having to resort to threats or whips. To demonstrate this effect stand your bicycle straight up and rotate the handlebars about 10 degrees. Push the bike forward from the saddle and the front wheel will rotate into alignment so you go straight. That's trail. Not as complicated as I make it sound, really.

The funny thing about trail is while it keeps your bike going straight it also turns it, as unlikely as it sounds. When you tilt your bike the steering tube moves in the tilting direction. Since trail makes the wheel follow the pivot point, it rotates behind the opposite way. Which doesn't make much sense the way I tell it, but it works out somehow. To see this second trail effect push your bike upright at the saddle and tilt it. The wheel rotates into the tilt and you turn. What other tricks trail has up its sleave I can't tell you. Possibly because being an effect and not a person it has no sleaves to look up.

When you tilt your bicycle riding no-handed the trail rotates the front end, turning the bicycle by tracking. When you tilt the bike back upright it straightens itself out. You can't take credit for of it, just comes with the territory, so quit bragging. In any case the bike is tracking, there's no magical turning for any other reason. To turn a bike the front end must rotate. So you CAN steer a bicycle by tilting while riding no-handed, but the bike is doing the clever bits by making itself track, you're just the lump on top keeping it balanced.

Here's where it can be confusing. It's the tilt angle of the bike which activates the trail effect, not just how the rider leans or shifts his weight around. When riding no-handed the rider leans less than the bike, in effect counter-levering the bike. So it might seem that you lean slightly the opposite way you want to turn, even though you really don't. Now I could explain all this more, but we'll get away from the main point, which is even ho-handed the bike turns by tracking.

Some claim the gyroscopic effect has a greater force to turn your front wheel than does trail. This is not true. If you recall from "Dances with gyroscopes", when I tilted my test rig to any angle with the wheel spinning the most torque I got was between 2 and 3 pounds.

I compared this to the amount of pull needed to reverse the torque I got from the trail effect on my bike with a 50 pound weight on the frame. When rolling the bike at walking speed it required about 16 to 20 pounds of pull to straighten the wheel in a 15 degree tilt. As I said, these are rough measurements, but my best guess is that trail gives you something like 5 to 10 times the turning torque as does the gyroscopic effect and so bullies it into submission. Like Napoleon said, "God is on the side of the big battalions." Though he wasn't referring to bicycles, you get the drift.

If you've ever wondered about the forward curl at the end of your forks it's not there just for show, even though it does look neat. This creates an offset that reduces the amount of trail. You don't want too much trail because the front end would over-steer and wobble from the side to side motion created by pedaling. Now, you could reduce the trail by angling the steering tube less, but bike designers have figured out the best angle for absorbing road shocks without breaking things. So don't mess with it.

Some people believe they don't rotate their handlebars in a highly tilted turn. People believe in lots of silly stuff: astrology, outlandish conspiracies, the birthday fallacy, politicians. One thing about this notion is what I would call a problem of perception, or misperception if there is such a word. What seems like a tight turn at high speed is a very leisurely turn at slow speed and needs little steering of the front wheel. What is a sharp turn at low speed is impossible or a death wish at high speed.

I stand my bicycle on the kickstand, I put a block of wood under that so it stands nearly straight up, no slouching. I clamp the brakes closed so the wheels can't revolve or bolt for the exit to avoid being exposed for the tricksters they are. I draw a line on the floor from the front to the back where the wheels touch the ground. I'll call this the baseline, you call it what you want but it'll confuse things later on if you do. The amount the handlebars are rotated I'll call the steer angle. The angle of the front wheel on the ground I'll call the turn angle. The floor I'll call "the floor."

I rotate the front wheel 30 degrees and lash it in place with wires, opting not to go the crazy glue or welding route. This effectively holds the steer angle. With the bike upright I take measurements of the front wheel on the floor. The turn angle is also 30 degrees. I then take the same measurements with my bicycle tilted 45 degrees propped up with a piece of wood. The steer angle is still 30 degrees, but I find the turn angle is now 45 degrees. It wasn't hard to find, it was right there on the floor. This means a tilted bicycle turns sharper than an upright bicycle. See, I told you wheels were tricky.

As you rotate the front end and tilt, the contact patch position varies relative to the steering axis. This is because you change the steering tube axis angle as you tilt. To show this, I take my bike with the front end secured at a 30 degree rotation. With the bike upright I mark the tire where it contacts the ground. Tilting the bike 45 degrees I see the contact patch is about 6 inches further forward compared to its upright position. In fact, it is in front of the steering tube axis which means reverse trail, which has its own set of consequences we won't deal with here.

To see an extreme example of this wandering contact patch, lay the bike almost on its side and rotate the front end. The contact patch varies from in line with the steering axis to a quarter way up the wheel at a 90 degree steering rotation. That would be the front of the wheel at upright

To show what this means in practice I take my bicycle with the handlebars secured rotated 30 degrees. With the bicycle tilted 45 degrees I attach a plumb bob to the frame that just touches the ground. You can also use a plumb tom or a plumb sally, but mine is a bob. This allows me to keep my bicycle at a fairly consistent tilt. I mark the starting position, push my bicycle upright around in a half turn. The rear wheel of the bicycle travelled in about a 140 inch diameter circle. I rinse and repeat the procedure with the bicycle tilted 45 degrees. This turn diameter is about 110 inches. Same bicycle, same steer angle, same travelling speed, different tilt, different turning diameter. That means the tilted bike's turn diameter is... um, 110 divided by 140 times pi minus... is smaller.

There's another way to look at this, if you like. Or even if you don't I'm tossing it in anyway. Remember from part one how where the axes of the wheels cross describes the center of the turning circle. Tilting your bike moves this intersection closer to the bike somewhere underground. Since the axles are not as long as the axes there's no problem of scraping the ground and upsetting everything. This makes a smaller circle, thus a tighter turn. This explanation is simpler, but I thought you might like to know the details first.

The more you lean the more the turn angle increases at the same steer angle. For instance, leaning 60 degrees, as motorcycle racers often do, turns a five degree steer angle into a 15 degree turn angle. This is why it often appears as though superbike racers are barely turning their front wheels. Actually they don't need to because... well. I just explained all that. Speaking of motorcycles leads us to our next section.

The tracking principles at work on bicycles apply equally to motorcycles, even though the gyroscopic torque is much stronger due to the greater mass and speed of wheel spin. There is one thing motorcycle riders use that bike riders don't use, besides a driver's license. That would be...

For those unfamiliar with counter-steering, it can be stated as, "turn left to go right." It might sound absurd, but it works.

This is pretty much the procedure for a right turn: without first leaning, rotate your handlebars left. This puts a centripetal force on the wheel's contact patch to the left. The forward momentum of the bike creates a centrifugal effect pushing the bike over to the right. The bike quickly drops down tilting you right, which is the way you wanted to go in the first place. At this point the front end must rotate right, into the turn. Or at least it'd better if you don't want to crash. Luckily trail does this more or less automatically.

Counter-steering tilts your motorcycle into a turn faster than you can lean it shifting your own weight by using the motorcycle's momentum to force itself into the desired tilting angle. Tilting doesn't really steer as such, it keeps you from falling over when turning. Counter-steering is like steering into a fall to your advantage. Neat, huh?

In a way the phrase "turn left to go right" is misleading because in the end the front wheel must rotate right to turn right. So really you "turn left to tilt right and then turn right to go right." But that's not very short and sweet and probably rather confusing.

Just to be clear, and avoid threatening emails from banged up bikers and their hostile lawyers, I must tell you this in not a tutorial of how to counter-steer a motorcycle. You should go to a motorcycle riding school as there's more technique to it than in my cursory explanation.

You can counter-steer a bicycle, but there isn't much need because, besides the speed difference, you outweigh your bike by 8 to one whereas a motorcycle outweighs you 3 to one or so. Though perhaps bike messengers darting in and out of traffic find this technique useful.

Some folks will tell you it's the gyroscopic effect of rotating the front wheel tilting your bike in counter-steering. Some folks would be wrong. Consider, one revolution of the wheel advances the bike the distance of the wheel's circumference, the same distance the wheel spins around the axle. The force from the forward momentum of 200 pounds of bike and rider moving one circumference is greater than the gyroscopic force from the 5 pound front wheel spinning one circumference. Especially since the wheel tilts from the bottom decreasing the latter's effectiveness. (See Dances With Gyroscopes.) Both forces increase at the same rate the faster you go.

To compare the differences between the gyroscopic tilting power and the momentum force we need to take gravity out of the equation. Since I can't do my experiments in space, I did the next best thing. I turned my frame from the tests in part one on end so the tilt axis is vertical and the steering axis is horizontal. This way a tilting force will rotate the frame like a swinging gate instead of tilting it where gravity would effect the motion as it starts tipping over.

First I spun the wheel and rotated it as if turning. This caused a gyroscopic force swinging the frame outward pulling on the spring scale hooked to the frame as shown. The reading was about one or two pounds.

Then I replaced the wheel with a 50 pound weight. I made a pivot point (turn axis) at the far end of my armature seven feet from the vertical tilt axis. When I swing the entire rig from this axis the frame turns in a 14 foot diameter circle which creates a centrifugal effect swinging the frame outward pulling on the spring scale. The reading in this case was about 12 to 15 pounds. (This would be even greater if my rig were robust enough to have carried 200 lbs.)

Now I admit my methods and equipment were crude. I don't know how fast the wheel was spinning or how fast I was walking and pushing through the turn. Plus my rig was a lot messier looking than shown with braces and little casters on a platform attached under the rig in step two. But the point is the momentum creating the centrifugal effect is much greater than the gyroscopic force, and that is what tilts the bike in counter-steering.

You might be wondering why I bothered with all that since most people don't counter-steer their bikes. It all has to do with stability, why it's easier to stay balanced at speed as opposed to at a standstill. It isn't because of a gyroscopic effect, it's forward momentum doing the trick. Just as by counter-steering you can tilt your bike by steering you can keep it upright by steering, too.

If you're standing still on your bike the only way to stop falling over is shifting your weight to maintain balance. Or you could put your feet on the ground, but that's cheating. However when rolling along singing a song you can correct slight tilting by steering, using momentum to maintain your balance. If you start falling to the left, a slight turn to the left creates a centrifugal effect to the right pushing you back upright.

The truth is, at speed you don't need to shift your weight at all to stay balanced, you do it simply by steering. The faster you go, the more effective it is. In fact, this is happening all the time, the trail effect does it automatically. Every time the front wheel turns your momentum creates a centrifugal effect the opposite way. Standing still you have no momentum to help you balance this way. That's really all there is to it.

The following is from Exploratarium:

"British scientist David Jones... pioneered project URB, a study in which he tried to construct an unridable bicycle. He intended to cancel out the gyroscopic action of the front wheel of a bicycle by mounting a wheel next to it that rotated in the opposite direction. Jones's findings were that canceling out the gyroscopic action did not affect the ability to steer the bicycle and that the overall stability of the bike wasn't affected. In another experiment, this time using a bicycle without a rider, Jones found that gyroscopic action did make the bicycle more stable. This indicates that the center of gravity (which changes with the addition or subtraction of a rider) may play a significant role in stability. Project URB was a powerful demonstration because it seemingly dispelled a popular conception that the gyroscopic effect of the wheels results in stable motion."

I did the following experiment. I pushed my bike upright and released it. It travelled a short way, started tilting, the trail effect rotated the front wheel, it made a turn and flopped over after about 10 feet or so. I then attached the spare tire from my car, which weighed about 50 pounds, on top of the saddle. I repeated the test as before. This time the biked travelled about 12 feet or so. I repeated the test several times and the weighted bike always went a little farther. (Not the most controlled test, but the best I could do with the tools at hand.)

I don't know what tests were performed by Professor Smith, but I suggest it isn't simply center of gravity but forward momentum and the centrifugal effect that goes with it which is the prime reason a riderless bike is less stable. The rider's extra mass creates more centrifugal effect countering the tilting. This is also why a riderless bike stays up a longer time the faster it goes, more momentum means more centrifugal effect as the bike turns from the trail effect. And that's a bike with the same center of gravity.

Still, a lot of folks are enamoured of the exotic sounding idea of wheels as gyroscopes helping you turn and maintain stability. Unfortunately it doesn't work that way. Remember "Real world crash testing you can do" from part one where you secure the front wheel with wires so the bike can't turn? Probably not. But if you do, and you actually do the test you'll discover a bike which doesn't turn falls over just as quickly rolling as at a standstill. Gravity's pull is the same whether the wheels are spinning or not.

A single, unattached rolling wheel is another matter altogether. You can get a wheel on its own to roll quite a ways. But as we saw in Part One a bike isn't a wheel and behaves very differently because of the constraints from the frame and other wheel.

There you have it. A bicycle does not turn by cone or gyroscopic effects it turns by tracking. A tilting bicycle turns sharper than an upright bicycle. You can steer a bicycle no-handed by tilting because the trail effect makes it track. Bicycle stability at speed comes from forward momentum. So, even though the cone and gyroscopic forces are there, it's the much more powerful tracking forces that steer a bike. And this time no stupid jokes.

Thankfully, when riding a bike we don't have to think about any of these things, calculating the various effects, making countless adjustments distracting us so much we are oblivious to the passing scenery, not to mention the odd bus in our path. Most of these things happen below the radar. Otherwise the expression, "it's like riding a bicycle" would have an entirely different meaning. These effects are more like autopilot or power steering. So, hats off to physics and bicycle designers, we thank you.

If at this point you are still unconvinced I invite you to try these experiments for yourself. Or build a bicycle without a steerable wheel and try riding it. If you don't kill yourself get back to me.

As for me, I'm moving on to other vehicular puzzles. Such as, how does Fred Flintstone turn his car when it's just a pair of oversized, stone rolling pins in a log frame with open ended axle slots? Wouldn't that thing just fall apart? Does he steer it with his feet? Curious, no?