Friction Can Be A Drag

[gfloyd2002]

How fast can you take that corner? How quick can you stop? It depends on the road surface, and one riding skill to develop is the ability to judge the road surface as we approach a corner or come through an intersection where we may need to stop quickly. Following are some measurements of coefficients of friction for various surfaces to guide our thoughts. These first friction coefficient estimates are motorcycle-specific from the Master Strategy Group:

Concrete 0.55-1.2
Concrete (wet) 0.44-0.9
Asphalt 0.5-0.9
Asphalt (wet) 0.4-0.7
Gravel 0.4-0.8
Ice 0.1-0.25
Snow 0.1-0.55

Here is another estimate, taken from an engineering text on rubber/asphalt and rubber/concrete coefficients:

Asphalt 0.5 - 0.8
Asphalt (wet) 0.25 - 0.75
Concrete 0.6 - 0.85
Concrete (wet) 0.45 - 0.75

Not like we are going to do calculations on the road, but it is useful to see how friction varies on different surfaces. We can see that wet surfaces lose roughly 20% of their grip, and that concrete is about 20% stickier than asphalt. We can see that wet surfaces have pretty wide variations, and roughly the same grip as gravel. For a more practical application, and a cool little utility that shows other variables in motorcycle stopping distances, take a look at the Motorcycle Stopping Distance Calculator.

[Alex]

Nice pun.

I was surprised that concrete ranged higher than asphalt. I would have thought top quality asphalt would have more friction than top quality concrete.

[gfloyd2002]

Originally Posted by Alex

Nice pun.

I was surprised that concrete ranged higher than asphalt. I would have thought top quality asphalt would have more friction than top quality concrete.

I was surprised also. That is why I checked the numbers from the Master Strategy Group with an engineering text. Frankly a bit shocked they held up. So I did some follow up research, and apparently the issue is the petroleum in the asphalt, which can get greasy. Also, concrete holds up better in areas that get stress (like corners), and while asphalt wears and breaks into gravelly bits under heavy use, scuffing up the concrete depolishes it and improves the surface for grip. Given the ranges in friction coefficient, there can be grippy asphalt and slick concrete, but it appears that concrete is generally the grippier surface.

[Rexbo]

Originally Posted by gfloyd2002

Frankly a bit shocked they held up. So I did some follow up research, and apparently the issue is the petroleum in the asphalt, which can get greasy. Also, concrete holds up better in areas that get stress (like corners), and while asphalt wears and breaks into gravelly bits under heavy use, scuffing up the concrete depolishes it and improves the surface for grip.

Don't forget about heat! When they first re-paved laguna seca about 5 years ago with asphalt, they hosted motogp about a month after on a 100 degree july day, and all the bikes started leaving grooves in turns 1 and 2! Even then, the riders were still complaining how slick some of the turns were because all the tar was oozing up.

[Misti]

So knowing just how slick certain surfaces can be in the wet, how do you alter or adjust your riding to deal with it? How might you brake for a corner in wet slippery conditions and how might you adjust your throttle control?

Misti

[gfloyd2002]

Originally Posted by Misti

So knowing just how slick certain surfaces can be in the wet, how do you alter or adjust your riding to deal with it? How might you brake for a corner in wet slippery conditions and how might you adjust your throttle control?

Misti

Go slower and be smooth on the throttle. I slow more for corners to keep bike a bit more upright, brake earlier, and wait later in the corner before I roll on anything beyond maintenance throttle. Best to make difference between braking, cornering and throttle more pronounced than usual to make sure limited grip isn't used up by multitasking.

I also repeat to myself - "do not roll off the throttle if your back wheel starts to go, you wuss" over and over.

[coondog]

I can't believe they included snow and ice. At least not with tire talk. I'm in the tropics and road tires vary amongst people I think due mostly to what's hep at the moment. I wear way different treads during rain season than dry, and I'm sure tis would skew the stats. (you love that **** bro?) How about you man, do you ride the same tread year round, is it just hot all the time or do you have monsoon, do you use the most "in general" full coverage tire?

[tjkamper]

Great post.

[gfloyd2002]

Originally Posted by coondog

I can't believe they included snow and ice. At least not with tire talk. I'm in the tropics and road tires vary amongst people I think due mostly to what's hep at the moment. I wear way different treads during rain season than dry, and I'm sure tis would skew the stats. (you love that **** bro?) How about you man, do you ride the same tread year round, is it just hot all the time or do you have monsoon, do you use the most "in general" full coverage tire?

Tires would definately make a difference with the friction coefficients, and the idea of swapping out tires for wet and dry season sounds like a good one if you have pronounced seasons where you are. Particularly if you are a nut like Spooph and ride in the snow and ice regularly, you'd need a specialty winter tire. (If you look at Spooph's snow pics, you'll see he 's running almost a knobby tire.)

For me, the wet season is in the afternoons and the dry season is in mornings. . It comes and goes too much year round to make changing tires useful. I'm still running the stock IRCs, which I can't wait to change - I've been disappointed with performance. (Despite my best efforts abusing them on rough roads, they just wont wear down, and I'm not waiting for 10k miles to switch to a good tire.) I'm planning on getting Pirelli Sport Demons, which have a good reputation for wet weather and are reasonably priced, but I need to wait for a friend/relative to visit who is willing to transport them down for me. (Cheap tires are $300/each if you buy them down here.)

[Misti]

Originally Posted by gfloyd2002

Go slower and be smooth on the throttle. I slow more for corners to keep bike a bit more upright, brake earlier, and wait later in the corner before I roll on anything beyond maintenance throttle. Best to make difference between braking, cornering and throttle more pronounced than usual to make sure limited grip isn't used up by multitasking.

I also repeat to myself - "do not roll off the throttle if your back wheel starts to go, you wuss" over and over.

Good points. It is important in wet or slippery conditions to be very very smooth with all the control actions you make. You still want to roll on the gas but you want to do it smoothly, evenly and less aggressively than you would in the dry. Braking while upright is key as most crashes in the wet or on slippery conditions happen when riders try to brake while leaned over.

What about your body position when riding in wet/slippery conditions? Should you change your body position at all and how might it effect the bike and its stability?

Misti

[gfloyd2002]

Originally Posted by Misti

What about your body position when riding in wet/slippery conditions? Should you change your body position at all and how might it effect the bike and its stability?

[Animal78]

Well I for one find it interesting.

I think that the friction between each surface and the differences can be compromised easily. I have ridden on lots of different roads as I am sure many have and sometimes concrete is the worst! Sometimes Asphalt is the best. I think the mixture and science behind the mixtures is what makes a great roadway.

Most asphalt roads around here in the summer are very sticky until it rains. Then they break up and come apart in big chunks. Concrete is better in the winter. Cause no matter how cold the surface is the grip stays. Rain tend to effect the concrete less. All bets are off though if the surface is oily and it has just started to rain. Then asphalt might as well be a ice skating rink. Once again in the real world concrete wins this test too. The concrete absorbs the oil and holds it while asphalt just has a layer on the top that starts to wash off in the rain and spread.

It's as much as where you live, the amount of traffic on the surface and how well the surface was layed as to how much traction is available. I am always cautious on unknown roadways especially if the conditions are not ideal.

[Domagoj]

Originally Posted by Animal78

It's as much as where you live, the amount of traffic on the surface and how well the surface was layed as to how much traction is available. I am always cautious on unknown roadways especially if the conditions are not ideal.

I can't say for the concrete, but in my opinion the quality and type of layer is the most important factor. I have been on "rough" and kind of porous asphalt roads where rain makes almost no difference at all (of course after a certain quantity of water it makes a difference). Then again there are many cases of asphalt where even a little bit of rain makes the road look like a mirror, and you can tell just by looking at the surface that there is not a lot of grip there.

Amount of traffic is also very important, as continuous rubbing of the surface polishes it and in time makes it more smooth and more slippy. There are a few two-lane highway ramps here which are an obvious example of it - cars prefer the right lane and left one is almost unused. After 2 years of rubbing the difference in roughness is easily visible. But on the other hand, the left lane is way more dirty, so it doesn't really matter in this particular case.

Dirt by itself is also important factor. This is easily visible on a bit wider twisty roads, where the line which most cars make is clean, and edges of the road are full of sand and dust and whatnot. This may be very important if you are trying to turn a bit later, as it puts your turn point in the dirty part of the road.

Last but not the least that I can remember are the lines on the road. Painted stripes showing middle and those big arrows on the road indicating that the lane is about to end and similar painted markings. Those are simply terrible in the wet.

All in all, the table is a nice general guidance.

[coondog]

Originally Posted by gfloyd2002

Tires would definately make a difference with the friction coefficients, and the idea of swapping out tires for wet and dry season sounds like a good one if you have pronounced seasons where you are. Particularly if you are a nut like Spooph and ride in the snow and ice regularly, you'd need a specialty winter tire. (If you look at Spooph's snow pics, you'll see he 's running almost a knobby tire.)

For me, the wet season is in the afternoons and the dry season is in mornings. . It comes and goes too much year round to make changing tires useful. I'm still running the stock IRCs, which I can't wait to change - I've been disappointed with performance. (Despite my best efforts abusing them on rough roads, they just wont wear down, and I'm not waiting for 10k miles to switch to a good tire.) I'm planning on getting Pirelli Sport Demons, which have a good reputation for wet weather and are reasonably priced, but I need to wait for a friend/relative to visit who is willing to transport them down for me. (Cheap tires are $300/each if you buy them down here.)

Sorry about hearing you've got to ride on those rim protecters, and they don't wear down, I gave up waiting, went to a new conti road tire for rain and they discontinued my size. Now I stick with MT75's after the GT501 experiment was great for riding but harsh on wallet. I wish I could deliver them, been in the tropics as least with home address if not physically most of my life and would like to see your island. Happy Trails Man.

[Sailariel]

Floyd, When you get the Pirelli Tyres you will think that you got a new bike. "Dramatic" is the closest word I can find for the difference you will feel. The only downside of the Pirelli tyres is that they wear rather quickly for the average road rider. I like the Bridgestone radials. That's what my new bike came with. For handling, the Pirellis are great. I use Pirelli tyres on all three of my racing bicycles. I have experienced a lot less road rash since I made that change.

[Misti]

Originally Posted by Animal78

It's as much as where you live, the amount of traffic on the surface and how well the surface was layed as to how much traction is available. I am always cautious on unknown roadways especially if the conditions are not ideal.

When you say you ride more "cautious" on unknown roadways what exactly does this mean? Do you just slow down or do you change things with your body position, your throttle control, how you turn the bike etc???

Misti