C. F. = F / P
What Does It Mean to Me?
What you see above is the formula for the coefficient of friction. It says the value of the coefficient of friction is equal to the force needed to move an object divided by the force pressing two surfaces together. I’m not going to get into the math behind various types of surfaces but whatever that number, when it comes to keeping your bike from sliding down the road, it is vitally important to you.
The engineers designing road surfaces, tire composition and tread design, and bike suspension are intimately familiar with this law of physics. For the most part, they do a good job. Their work translates into how much traction your bike has under various road and tire wear conditions. When all is normal, (clean dry road surfaces and good tires with adequate tread, properly inflated,) most motorcycles can handle forces in excess of our willingness to test them. I know I get a little nervous when my kickstand or foot peg scrapes the pavement in a curve even though my traction is still good.
Any condition that lowers that mystical C. F. is what we riders have to look for as we travel down the road. There are many of them. I’ll mention a few here but I’m sure there are some I’ll miss.
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Water acts as a lubricant on the road. Depending on the pavement type, it can significantly lower your traction. Tire designers do a pretty good job here; motorcycle tires are made to have good traction in the rain but there are limits.
Slow down when it is raining because you cannot predict exactly when you loose traction if you’re pushing it. Be particularly careful when you have to ride on those lane markings and at intersections with stop and crosswalk markings. That material is a first cousin of latex paint and can be really slick. At one such intersection my foot slipped out as I came to a stop and I nearly dropped the bike. Carol hates it when that happens. If possible, avoid riding on them by stopping a few feet back from the lines at an intersection and avoid lane markings in a curve.
Rain after a dry spell will spread a slick of fresh oil over larger areas, lubricating the road until enough rain has thoroughly rinsed the surface. Extra caution is needed when it begins to rain.
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Why care about C.F.? It’s the science behind the friction or traction that keeps you and you motorcycle in stable contact with the road on those two little tire footprints, each about the size of a man’s shoe not including the heel area. Any force such as hard acceleration or braking, centrifugal force or any alteration of the surfaces, either tire or road, lowers the C.F. |
How low you can go before “losing it” is something we face every time we ride. I, for one, prefer not to push it too close to the limit, whatever the conditions. I prefer to use vigilance and caution to avoid traction problems.
And we haven’t even touched on skidding during a panic stop. There are different considerations to discuss when skidding occurs. We’ll save that discussion for another time.
Submitted by Tom Scully
NC-E Chapter Educator
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You’ve seen it. You will find it just off the travel lanes, near the shoulder, in the middle of the road, in the middle of your lane, at intersections.
It’s the leftover traces of nearby construction, winter road treatments for ice and snow, and wear and tear of the surface over time. It’s the loose stuff and it needs to be avoided.Sand grains will act as little ball bearings between your tires and the road surface. Generally, dirt can be found on the roads all year long but it is always the worst in the spring until road cleaning crews or Mother Nature clear it away, or at least get it next to the curb or on the shoulder.
The stain you see in the middle of a travel lane is caused by fresh oil but over time ultra violet light, evaporation and rain degrade the oil to just a stain. But it was fresh at some point.
If you are unfortunate enough to run through fresh oil you can assume you have no traction at all. The lubricating properties of oil work as well on the road as in an engine. If you realize the problem and can steer straight, just throttle back slowly and coast to a stop with minimal braking. If you can, clean the oil off the tread surface. Proceed slowly for a few miles until the oil wears off the tires. Change pants if necessary.
Co-Rider loses life -
Oil Slick - double click on the "Recollection,," tab
By itself, gasoline or diesel fuel will rapidly evaporate and not cause too much of a problem. But if you are close to the source or it is also raining, traction can be much reduced. At higher speeds even sudden throttle rollback is enough to loose traction. If you smell gas or diesel fuel coming from the pavement, there may be a dangerous condition present. Again, slow down and stop with minimal brake until you can determine the exact nature of the problem.
By itself, gasoline or diesel fuel will rapidly evaporate and not cause too much of a problem. But if you are close to the source or it is also raining, traction can be much reduced. At higher speeds even sudden throttle rollback is enough to loose traction. If you smell gas or diesel fuel coming from the pavement, there may be a dangerous condition present. Again, slow down and stop with minimal brake until you can determine the exact nature of the problem.
On the highway it’s likely to be a shredded truck tire. On the country road it could be anything from common litter to an aluminum ladder off a truck. It’s definitely difficult to maintain traction when you’re bouncing over junk in the road.
Once you see an object in the road, plan an escape route, slow down and execute. Remember to look at the escape path and not the hazard.
Looking at the hazard is one sure way of running over it in your attempt to avoid it.
Just sit by the fire and tell stories about past riding adventures. That’s where I’ll be.
Use them at your own risk. You might get away with marginal tires on your car but when only two tires are in contact with the ground, they need to have enough tread depth and be inflated to the recommended air pressure. Anything less will give you poor traction even under the best of conditions. Add some water or junk on the pavement and you’re really behind the eight ball.