Last week in Los Angeles, Dr. Christopher Thompson was convicted of six felonies, including two counts of assault with a deadly weapon, after pulling in front of two cyclists in his Lexus and slamming on the brakes. The story is tragic, if eventually positive — an LA jury actually convicted a motorist of intentionally harming cyclists.

But one small detail of the case struck me. During cross examination of one of the victims, Ron Peterson, defense attorney Peter Swarth suggested that “bicycles are inherently unstable.” It’s the sort of bicycle safety myth pedaled by the likes of Rob Anderson, who, along with attorney Mary Miles, has successfully kept the city of San Francisco from implementing traffic improvements meant to benefit cyclists for years.

Yes, a still bicycle has a tendency not to remain upright. Shocking, I know. A bicycle in motion, however, does not. Why? Physics! Namely, the angular momentum of a rotating bicycle wheel creates a gyroscope, which, combined with centrifugal force, actually make a bicycle quite stable indeed. The faster you go, the stronger the forces at play and the more stable the bike becomes — hence, it’s much easier to balance with no hands on the handlebars the faster you go. Check out how a battery-powered gyroscope build into a wheel creates a kids bike that doesn’t require training wheels, even when moving at low speeds.

Which brings me to my next point about the science of cycling and how it relates to the supposed “backlash” against cyclists. The New York Times blew the lid off the scandalous practice of coasting through stop signs by cyclists, particularly along the wiggle. As I pointed out elsewhere, not because of any demonstrable uptick in accidents or injuries, but simply because it apparently angers and annoys or something. Because of course no motorist has ever broken the speed limit, double-parked in a bicycle lane, or pulled in front of two cyclists going the speed limit and slammed on their brakes.

But there are a number of very good reasons for cyclists not to stop. Note that a cyclist who comes to a full and complete stop as required by law actually decreases their stability, making them more vulnerable to accidents, not less. Not to mention the fact that losing all that forward momentum is far more of a hardship on cyclists, who provide their own power, than motorists. If you think of traffic in terms of fluid dynamics, each stop sign is like a dam, backing up the flow of traffic. It’s a good way to slow down cars that might otherwise sail through intersections, potentially harming themselves and others, but which serves little purpose when it comes to cyclists moving at lower speed who have better visibility, maneuverability and a shorter braking distance than cars.

A cyclist who comes to a full and complete stop as required by law actually decreases their stability, making them more vulnerable to accidents, not lessIt’s part of the larger struggle of cyclists to change two generations of automobile-centric traffic planning. Amusingly enough, the first group of San Franciscans to lobby for paved roadways were, actually, cyclists, decades before automobiles were widely available. Why? Because paved roadways significantly increase the efficiency of bicycle travel by decreasing the amount of rolling resistance. The friction between cycling advocates and car drivers aside, the friction where the rubber meets the road is where a significant amount of forward force is both gained and lost.

It’s the reason why road bikes have skinnier wheels, and higher tire pressures, than off-road bikes. For the most efficient ride on paved streets, you’ll want to keep your tire pressure topped off to the level indicated on the tire — a higher-pressure tire means the wheel surface holds it shape better, meaning less contact between tire and surface. For off-road cycling, you might want to let some air out — by adding more rolling resistance, you improve traction. Hence, mountain bikers might have half the pressure in a tire compared to a road racer.

And energy efficiency is really where cycles outshine cars. The human body is far more efficient at converting energy fixed in calories (or, more accurately, kilocalories) than automobiles. Thanks to biochemistry, the human metabolism can turn 30-40 calories — 4 grams of fat or 7 grams of carbohydrates — into a mile of forward motion on a bicycle. How many calories worth of gasoline does it take to move a car one mile? Over 1,000 if the car gets 30 miles per gallon, which few do. That’s because an internal combustion engine is not nearly as efficient at converting chemical energy into kinetic energy, with most of the former wasted as heat.

There is a physical force that both cyclists and motorists have to overcome, and can create an advantage for themselves — aerodynamics. The movement of air against a body in motion creates friction just like rolling resistance. And both bikes and cars can reduce this friction by drafting. Compare the “Shake and Bake” in The Ballad of Ricky Bobby with the sprint on the final leg of this year’s Tour de France by Mark Crenshaw and Mark “The Missile” Cavendish of the Columbia-HTC Team. In both cases, the lead vehicle expends more power per foot second by breaking the wind for the tailing vehicle, allowing the “pulled” party to conserve enough energy to pass even faster.

Though like with cars, where in normal situations drafting would be considered “tailgating,” the same goes for riding down market street — don’t draft strangers, because one of them might actually brake for a stop sign, causing a rear-end collision and sending you hurtling through the air at the same speed you were going on your bike. Momentum: She is an indifferent mistress.

Photo of Tour de France cyclists drafting during a stage-ending sprint by Mike Knell.

Jackson West has ridden a bike around the San Juan Islands, up and down the Cascades, in Vancouver, Seattle, Brooklyn, Austin and all over the Bay Area. He likes to keep things light. Have any bike-related questions? Send an email!

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  • Alex Zepeda

    Sounds like a great reason to *not* build bicycle lanes to me. If you can’t manage to keep your bicycle upright at a stop sign, or red light, perhaps you shouldn’t use a bicycle to get around. The entire problem with Mister West’s logic is that he ignores the accidents that come with people coming from intersecting directions, and not stopping, not yielding, and not looking.

    By Mister West’s logic, we should do away with stop signs and traffic signals for cars too. Cause, dontcha know, cars are more efficient when they don’t have to stop all the time too. Hell, you’re more likely to stall at a stop than coasting down the street in gear. So maybe we REALLY SHOULD just not require cars to stop either.


  • Richmondsfblog

    Ah, this totally explains why the Critical Mass riders are so rude every time. They’re afraid of falling down! Thanks for clarifying!!!

    Why do bikers run stop signs? Because it saves them time and they can get away with it. Let’s just admit it. It will be ok.

  • UCBlindside

    Obviously, Mr. Zepeda and Richmondsfblog do not ride bikes, and that is okay, they don

  • Muni Diaries

    I ride my bike to and from work in San Francisco every day. My rule is: Assume the worst from cars. I’ll let others spend time educating the driving class on how to behave around bicyclists on the streets of San Francisco. Until the day when all cars magically see half-painted bicycle lanes and observe the fact that it’s easier to die while riding a bike than if you’re in the car that hits the bike, until that day, I ride defensively. I do not give a single car the benefit of the doubt. When drivers do see me, when they yield while turning right and thus crossing a bike line, I thank them.

    But as it relates to this post, my point is this: Cyclists need to balance their selfish intent to ride totally efficiently at all times with a respect for the rules of traffic. Flaunting the rules only pisses drivers off, and exacerbates a situation of total disrespect and distrust. And that will just keep the situation humming along at a dangerous status quo.

    I’ve been in cars where cyclists come flying through an intersection, almost to get hit by me or another car. It’s not cool being in the car in that situation. You put your life in danger, at my hands.

    My advice to cyclists is to chill out, observe basic rules, only roll through stop signs slowly and after making triple-fucking-sure that no cars are coming. That, and seriously, give us all a break: Stopping at a red light and putting one foot on the ground for 10 seconds isn’t going to expend too much of your energy.

  • Alex Zepeda

    So, if I don’t see anyone at an intersection and I’m in a car, I should just roll through? The defense that nobody was in danger wouldn’t fly in traffic court with a car, why should it with a bicycle? If you can’t keep from falling over at a stop sign, walk — don’t ride.

  • Jackson West

    Some additional points. First, California drivers aren’t really in a position to complain about cyclists who don’t make full stops, since we are notorious for the “California roll.”

    Second, I would actually suggest taking a look at whether stop signs are the best solution for traffic control at many intersections. I grew up in Seattle, where traffic circles are used extensively to control traffic speeds and intersection navigation, with no stop signs. And traffic safety studies have long suggested that roundabouts, as used widely in Europe, are safer than intersections controlled by traffic lights.

    Thirdly, the issue of instability is not that cyclists will fall over at intersections. It’s that a cyclist at a full stop is much less able to avoid oncoming hazards from any direction because it puts them in the least maneuverable and most awkward position compared to being on the move.

    I would support a change to traffic regulations like Idaho’s, which allows cyclists to treat stop signs as yield signs. And, again, this debate seems to hinge on the perceived “lawlessness” of cyclists ignoring stop signs (when wanton disregard for traffic laws is not unique to any class of vehicle), not any actual consequences. If anything, cyclists going through stop signs, along with “careless” pedestrians, may actually force motorists to be more careful and aware when driving, providing a net benefit to traffic safety.

  • Alex Zepeda

    The difficulty of overcoming inertia could be said for any mode of transportation. Feet, automobiles, roller skates, skateboard, sledding, etc. By that logic we should replace all stop signs with yield signs for everyone.

    Stop signs serve a few useful purposes. First, if followed, they prevent people from colliding (be they on bicycles, sled dogs, driver’s seat, or what have you). Second, they slow down traffic. This is particularly desirable in residential areas where the goal is not necessarily to have the most efficient roads possible (see also speed bumps and traffic calming).

    It’s a far less daunting task to cross a street like Moraga than it is to cross, for instance, Lincoln. This would be true even if all of the automobiles were replaced with bicycles. Even if it won’t kill you, it will still hurt, and potentially injure you quite seriously if a bicycle and pedestrian collide at speed.

    Are roundabouts a good idea? Perhaps. Is allowing bicycles to ignore traffic safety laws? No.

  • SF94122

    Apparently you haven’t been to the Sunset, or the Richmond; we LOVE to roll through stop signs!

  • SF94122

    Thanks for calling out the reverse situation. Whether on a bike or in a car, you’re going to encounter someone pulling stupid moves – sf drivers aren’t the best, and there are just so many cyclists..

  • sagitta100

    Many cyclist have figured out that by riding on the sidewalk, they can avoid those pesky stop signs.

  • Greg Dewar

    I have had plenty of near misses with bicyclists, and find them to be the biggest assholes about pedestrian safety. They ride their bikes on the sidewalk, and crash through stop signs, without a care for us, the walker, who is most likely to get hurt by both cars and bikes.

    I realize San Franciscans have a reflexive tendency to embrace a selfish, “me first” philosophy, instead of trying to operate in an urban environment the way those in other cities do – common courtesy, respect, and following a few basic rules so everyone can get where they want safely. But that would never fly here – people’s self righteousness and self centeredness trump any real cooperation.

  • John Murphy

    “I have had plenty of near misses with bicyclists, and find them to be the biggest assholes about pedestrian safety.”

    Pretty bold statement in light of this…


    The biggest assholes about pedestrian safety, in order
    1) MTA
    2) Motorists
    3) Cyclists
    4) Pedestrians

  • johnny

    “I think [the bicycle] has done more to emancipate women than anything else in the world,” feminist pioneer Susan B. Anthony said in 1896. “It gives a woman a feeling of freedom and self-reliance. The moment she takes her seat she knows she can’t get into harm unless she gets off her bicycle, and away she goes, the picture of free, untrammeled womanhood.”

    This is what the bike does for me, too, bitches.