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'2-Second Rule'
Determined by road conditions

By: James R. Davis

A message was posted in a motorcycle conference recently which argued that we should abandon the '2-second' rule (distance between bikes in the same track - distance between each bike in the group being half that) and possibly double it to increase safety.

Yes, that will certainly increase safety, generally, but it results in a group that is spread so far out that it introduces new safety problems - like it encourages cagers to dart into the gaps between bikes.

But there are times where the '2-second' rule makes no sense whatever. To begin with, it must be realized that there is a set of implicit assumptions that goes along with adopting that rule. Most important of these is that the skills/experience level of the individual riders is about at par with each other. Additionally, but often overlooked, is the absolute assumption that you are riding on dry level pavement! (More importantly still, that you have UNOBSTRUCTED VISIBILITY.)

It has been well documented that it takes the average person almost 1 full second to recognize and then to react to an UNEXPECTED threat. (About 1/2 second if the threat is anticipated.) The '2-second Rule', in other words, provides 1 full second of distance between bikes in order to provide sufficient time for following bikers to recognize and react to unexpected threats.

If all bikers in the group have roughly equivalent skills, then no matter what the driver ahead of you does - so long as he REMAINS IN CONTROL OF HIS BIKE - you should be able to do the same without running into him. This is true whether you are on wet or dry pavement and regardless of any pavement slope you are on. (In fact, this is almost true about the bike that is only 1 second ahead of you - that is, if he, for example, begins a panic stop then in 1 second you will also be able to begin a panic stop and you will be exactly where he WAS when he did so. You will both end up in exactly the same spot - he will have stopped before you get to him but you will be traveling at about 1 MPH when you do.)

However, the bike ahead of you is not the only thing that you might have to avoid hitting. Going down hill or riding on wet surfaces dramatically increases your stopping distance and is important should you have to avoid an obstacle in the road (pothole or vehicle), or the bike ahead of you that is no longer in control (highsided, for example.)

Since your tire traction is cut by as much as TWO-THIRDS on wet roads, clearly you should increase following distances substantially over what is safe on dry level roads. Similarly, sand or gravel covered roadways should cause you to stretch out those following distances. However, that is NOT because you have less time to react - the 2-second rule is to provide REACT TIME, and is NOT a function of traction.

Since gravity either aids or detracts from the ability of your brakes to stop your bike based on whether you are on an incline or a decline, following distances must be significantly increased to maintain the safety margin if you are riding downhill - and the steeper the slope, the wider those distances should be.

When riding in a curve most motorcyclists choose their own line and certainly should not be 'required' to stay in their track (though they should stay in their lane, of course.) It follows, then, that distances between bikes should be nearly doubled when riding twisties.

If the bike ahead of you does not remain in control, then you need to be able to avoid hitting him without doing whatever got him into trouble (such as hitting something in the road.) In low traction environments (or going downhill) you need more time and distance.

The '2-second rule' means that in staggered formation there is a ONE second spacing between each bike, thus a TWO second spacing between bikes in the same track.

My intention in this discussion is to demonstrate that if you use this kind of spacing then:

  • IF your reaction time to an unexpected threat is 1 second or less (studies have shown this to be a reasonable expectation), and

  • IF your motorcycle skills are as good or better than those of the next driver ahead of you,

Then whatever the motorcyclist ahead of you does you should be able to do without running into him. (Including a panic stop, or a turn across your path, or both.)

All else being equal, the "2-second rule" should constitute your fundamental safety margin while riding in a group if you use it as a minimum spacing distance.

This does not mean it is impossible to hit the guy ahead of you if he loses control of his bike! If he T-bones a vehicle that enters an intersection, you will almost certainly run into them. If he locks his rear brake and then highsides, you might run into him.

But running into the bike ahead is not your only threat. If that bike successfully dodges an obstacle in the street, you could hit it rather than him. If a deer or another vehicle happens to run into the gap between you and the bike ahead, you need stopping/swerving ability.

Since wet surfaces or driving down a hill decreases stopping ability, it makes sense to widen the gaps between bikes when you have to deal with them. Not so that you can avoid hitting the bike ahead of you if he remains in control of his bike, but because he might not, or other panic stop conditions might arise.

Conditions which should cause you to increase following distance, then, are those that affect VISIBILITY and, as a result, reaction time.

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(James R. Davis is a recognized expert witness in the fields of Motorcycle Safety/Dynamics.)

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