SPEED STRATEGY: Rule 1
Rule 1: Maintain speed that allows you to see the roadway at least 4 seconds ahead.
Speed, Space, and Time
If you're going to ride a motorcycle fast and want to do it in relative safety, you have to understand the importance of space and time.
You need space to decelerate or to change direction--more speed, more space. As you go faster, you need greater distance to brake to a stop, greater distance to swerve around an obstacle, and greater distance to lean the motorcycle into a curve. And it's not simply a proportional increase. For example, if you can brake to a stop from 60mph in 160 feet, the same braking force will stop you from 120mph in 640 feet. Because of that, the rule is modified for higher speeds (see below).
Time goes along with space, of course: you need space to make an evasive maneuver, and you need time to execute it. But time gives you something else too: the opportunity to track a moving threat so you can avert the intrusion altogether. For example, a careless driver merging onto the freeway may force you to brake to avoid rear-ending him. But if you spot him before he reaches you, when he cuts off someone in the next lane, you can gently accelerate or roll-off to eliminate the threat completely. The earlier you identify a potential problem, the less severe the action needed to avoid it.
This rule dictates a speed consistent with the environment and ensures that you have enough time and space to respond to a hazard that suddenly appears. Make it the cornerstone of your speed management strategy and follow it as if your life depends on it. Because it does.
Application of the Rule
The 4-second sightline interval is what MSF calls your "immediate path of travel." If an obstacle appears 4 seconds ahead, you'll have just enough road to brake to a stop before you reach it. But if you fly into a blind turn with less sight distance and the road is blocked by a pile of crashed motorcycles, you're probably going to join it.
Note that this isn't the same as the 2-second following distance rule taught by MSF. The 2-second rule gives you time to react to when a vehicle ahead moving at the same speed as you brakes unexpectedly. The 4-second rule applies to the road itself, and it gives you the distance you need to avoid an obstacle that comes into view.
You probably know how to count a time interval from MSF: Spot a point in the road ahead and count out loud, "one one-thousand, two one-thousand,..." until you reach that point. But it isn't necessary to continually count out the sightline interval. With practice, you will quickly develop a sense for it so you can see the interval at a glance. On a straight, vacant stretch of road, take a guess at a 4-second interval and count it out. Adjust your guess and repeat until you've got it right. I've found that once acquired, the sense of it sticks permanently, though it's reassuring to calibrate it occasionally.
A few notes on the use of the rule:
- While 4 seconds is a good rule of thumb, it's not enough at higher speeds. Over 80mph add 1 second. Over 100mph, you're on your own.
- At speeds below 40mph, a 3-second interval gives you adequate braking distance. This would apply to many blind turns on the Bay Area's paved goat trails.
- The 4-second interval is valid if you're good on the brakes and the surface is clean and dry. If you're new, if you don't regularly practice hard braking, or if the road is wet, add 1 second. If you're a riding god capable of MotoGP-caliber braking even in an emergency, you can subtract a half-second.
- The rule tells you not only when to slow down, it also helps you identify spots where higher speed may be possible. Other considerations will limit speed, but at least the sightline interval will tell you if you have enough braking distance.
- The rule is usually easy to follow because you'll often have much more than 4 seconds. Coming on to a quarter-mile straight at 60mph you'll have 15 seconds of sight distance. Where the rule can save you is in a situation like cresting a hill or approaching a blind curve. When the sightline shortens to 4 seconds, it's telling you that you don't have enough information to continue at that speed. It helps you to distinguish between the yin and the yang--where the environment's inherent limits dictate restraint and where you can open it up and have some fun.
Background
This rule is derived from the "safe stopping distance rule" taught to riders in the UK:
Maintain speed that allows you to stop in the distance you can see to be clear. Stated that way, it's harder to put into practice because of uncertainty about stopping distance and the difficulty of estimating distance. Counting out seconds of travel is much easier, and it works just as well.
David Hough also recommends a time-based rule in
Proficient Motorcycling, but I think his times are unrealistically high. If you're interested in my reasoning for the 4-second rule, send me a PM.
edit, 1/31/10: revised interval at 80+ to 5sec, lowering braking performance requirement