TOTW: Manage your traction quota

The riding tips on these pages are my personal opinion about matters related to motorcycle riding. They are not the official position of any organization, and are for your consideration only. They are not hard and fast rules, they should not necessarily be applied in all circumstances, and they should not be applied without thinking. Always use your judgement and take all current safety factors into account while riding. You are responsible for your riding, not anyone else (especially me). These tips were originally published by a motorcycle riding course, called “Tip of the Week” (the reason for the TOTW in the titles).

What’s the problem?

Your bike depends on traction, to move forward, stop, turn, and stay upright. Traction only comes from one place — the contact between your tires and the pavement — and there is only a certain amount of it available. Loss of traction contributes to most falls and many collisions.

Many factors consume some of your available traction, and your instincts are not always correct for preserving it. (For example, coasting does not maximize your traction, so pulling in the clutch and coasting across a slippery area does not minimize your chances of slipping.)

Solution

Understand the factors

There are a number of factors that consume some of your available traction, some that you can’t control and some that you control directly.

The factors you can’t control are surface conditions. Slick surfaces such as oil, water, or ice reduce traction. Loose surfaces such as sand and gravel can behave like slick surfaces, depending on your tires and the size and depth of the loose material. Finally, the angle of the surface affects traction. Gravity is pulling your bike straight down, and traction is maximized when the road surface is at 90 degrees to this pull, meaning perfectly level. If you are on a hill or a banked road surface, some of the force of gravity will be trying to pull you across the surface, so you are using up some traction just staying put. The greater the incline, the more traction you’re using up and the less is left for other purposes.

Of the factors you control, the following consume some of your available traction.

Braking requires traction, and many riders have experienced at least a loss of rear-wheel traction when braking hard. The harder you brake, the more of your available traction you are using up.

Accelerating also requires traction, and you have probably seen riders or drivers spinning their wheels by accelerating hard. The more you try to accelerate, the more of your available traction you are using up. (Note that accelerating means changing your speed. How fast you are going doesn’t matter — it’s how rapidly you are trying to increase your speed that affects traction.)

Turning requires traction. Whenever you are turning, the principle of inertia means your bike would rather be going in a straight line. Holding you on your curved path requires some of your available traction. The tighter the curve and greater your lean angle, the more traction you consume. Now how fast you are going matters — higher speeds consume more traction when you are turning.

Slowing down requires traction. We’ve already covered braking, but even just letting off the gas and letting your bike slow down uses up some of your traction. (The internal friction from your engine and other moving parts is slowing your wheels, just not as quickly as your brakes do.)

(Note: A physicist would tell you that we’re repeating ourselves, because all of the above are just different kinds of acceleration. This is true, but we find that most people take the word “acceleration” to mean increasing speed, and we wanted to remind you that the other factors above also consume traction. If a physicist points this out to you, just smile and nod.)

Maximum traction

So, taking all the above factors into account, when do you have the most traction available? When you’re not consuming it by doing any of the things listed above. Your available traction is maximized when you are upright, on a flat surface, traveling in a straight line at a constant speed.

The “constant speed” part is not intuitive — many people instinctively slow down in a slippery situation. But, as we discussed above, the process of slowing down is just a kind of acceleration, and costs traction. By all means slow down if you’re going too fast, but ideally do it before you hit the low-traction situation, not after you’re already on a slick surface or in a curve. Even after you’re in a low-traction situation, slowing down may be a better option than continuing at higher speed. Just be aware that it takes some of your available traction to do so.

That’s in a straight line. If you are turning, speed matters, and you have more traction at slower speeds.

This is one of the reasons why excessive speed is so dangerous — if you find yourself in an emergency situation, slowing down consumes some of your available traction. If you were already going a safe speed, this traction would be available for other uses in dealing with the emergency.

Manage your traction quota

As we’ve implied above, through the repeated use of the phrase “your available traction”, it’s very useful to think of traction as a quota. You only have so much, and the total available doesn’t change. Everything you are doing that uses traction takes some out of your quota, so if you use some up for turning, there is less available for braking.

When your quota is exhausted, you slide (and probably crash). So, if over-accelerating or over-braking causes your tires to lose traction, there is also no traction available to hold the bike in the turn you’re trying to make. Conversely, if you’re using most of your traction to hold a fast or tight turn, you may not have enough left to brake hard when that deer steps in front of you.

By thinking of your available traction as a quota, you can learn to think about managing the quota. Remember how the factors you can control affect your quota — turning hard and braking hard at the same time, for example, generally don’t mix.

For the factors you don’t control (e.g. road surface) you may be able to have some influence by looking ahead and picking a better path (e.g. around an oil slick). Essentially you’re trading off things you control (turning) for things you don’t (that slippery patch).

For factors truly beyond your control, remember that your quota has been reduced and plan to accelerate and brake more gently, turn less aggressively, and corner more slowly.

Examples

Let’s use the idea of a limited quota of traction to think through some riding situations.

Sand or Oil on the Road. A small patch of something slippery on the road is an area of very low traction, and beyond your control. If you can safely avoid the patch by changing your path, you should do so. If you can’t avoid the patch, slow down before you enter it (don’t make traction demands by braking on the patch), and position yourself to have the straightest possible path across it (to minimize the traction demands caused by leaning). If possible, get all these adjustments done before arriving at the slippery patch, then cross it at a constant speed and in a straight line. You’re making the smallest possible demands on available traction, so you should navigate the slippery patch safely.

Braking in a Curve. For normal, everyday braking, there should be plenty of traction available to allow you to slow while turning. If hard braking is necessary, however, you may exceed your traction quota when the traction for braking is combined with the traction for turning. If possible, position your bike so there is a long, straight, safe path in front of you, and allow it to straighten out as you brake. The less room you have for straightening your path, the more gently you should brake. (Because you can’t predict emergencies, it’s a good idea to always choose paths through curves that give you the option of straightening your path for braking.)

Riding Through a Tight Curve. When riding through a tight curve (such as on a twisty back road or a track) remember all the factors that take traction from your quota. Your bike will be leaned over at the tightest part of the curve so, ideally, you would like to be making no other demands on your traction quota at that time. Adjust your speed, slowing to your cornering speed, before you enter the curve, while the bike is still upright, and go through the deepest part of the curve at a constant speed if you can safely do so. The slower you go through the curve, the less traction you are using up. As you leave the curve, accelerate gradually, adding gas as the bike comes back upright.

Riding in the Rain. Wet streets are an unavoidable slick surface covering a large distance. (Note that traction is not constant. Areas that would have been slippery before the rain will be even slipperier now.) Since you can’t control the road conditions, reduce your other traction demands. Slow down so you won’t have to brake as hard later. Accelerate and decelerate more gently. Take corners more slowly, choose wider paths through the curves, when possible, and shift your body weight slightly while turning, to reduce lean angle.


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