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Thread: Grit size of paved road surfaces

  1. #1
    Registered User WalterK75's Avatar
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    Grit size of paved road surfaces

    I've often thought that asking someone to run a belt sander over their naked body would impress upon them what road rash means. As a corollary of this, I was curious if anyone knew what the grit size of a road surface is? Excluding gravel and sand, I'm thinking in terms of paved roads; asphalt, concrete, compacted tar and gravel.
    Walter

    G. K. Chesterton wrote - "The traveller sees what he sees, the tourist sees what he came to see."

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    BMW MOV Club Director ENFOMAN's Avatar
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    Considering that the coarsest grit that I know of is a 30 grit, you may want to compare the road surface to a large file or rasp.

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    Small road corner junkie pffog's Avatar
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    Years ago one of my sons friends showed up on his motorcycle in shorts. He was talking to my son when I approached him with a big old rectangular kitchen cheese grater, and made a motion like I was going to rake it across his thigh, he jumped back, looking at me like I had gone nuts.

    I said I just wanted to save you the trouble of falling off the bike, and damaging it. He got the message.

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    Benchwrenching PGlaves's Avatar
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    All of this is in paving mix handbooks. 3/4" aggregate is a mainstay in most mixes, with an assortment of finer aggregate thrown in to fill voids and enhance adhesion. Finish courses have some course sand.

    http://www.fhwa.dot.gov/pavement/t504027.cfm
    Paul Glaves - "Big Bend", Texas U.S.A
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    Registered User arthurdent's Avatar
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    Depends

    In MN they seal oat asphalt roads with a 1/4 - 3/8 crushed basalt. Here in NE they coat them with a 1/8-1/4 crushed quartzite.

    In the end, size doesnt matter. Sliding on rock with a 250kg bike on top is going to shred your skin remarkably well regardless of rock size.

  6. #6
    Registered User AKsuited's Avatar
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    There's also friction. Locally, all our aggregates are glacial gravels that are predominantly sandstones. These provide excellent friction. They are also very similar to sandpaper. This is in contrast to polished limestone which tends to be lacking in friction, especially when wet. Pavement friction can vary quite a bit, a good reason to have ABS.

    Blacktop can vary from fine-textured mixes, "sand asphalt" to coarser top mixes and much coarser base and intermediate layers.

    Any way you look at it, you don't want to slide down the road at highway speeds without serious protection from abrasion.

    Harry
    2003 R1150RT - Silver

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    Registered User amiles's Avatar
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    At our development a shift was made from typical asphalt to a much smoother product. The original was about like what is used on the public roadways around here & the new smoother is often used for driveways, cart paths, parking lots & walkways.

    Some time ago the roadways were "sealed" by the HOA. Returning home from a rally in the rain I made a gentle right turn at a 90?? intersection on this fine, coated pavement & just about lost it. The coarser roads that I had been on getting to this stretch gave me no such problem. The storm had been on for some time.

    I suppose that the smoother pavement, while more likely to cause a skid might be more forgiving when it came to road rash.

    It might be worth comment in motorcycle training that a rider should be looking for these differences based on area pavement as he goes along.

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    In crash investigations we pull a sled that measures the friction coefficient of the roadway which basically allows us to calculate a vehicle's speed at time of accident taking into consideration length of skidmarks, etc. The same asphalt mixture or concrete gives different friction during it's lifetime and of course, whether wet or dry.

    Attempting to calculate how bad one road mix is to the naked body vs. another would be pointless. It's ALL bad so ATTGATT is the rule. I should know. At 16 yrs of age I crashed a motor scooter while trying to set the land speed record for Sears Allstate scooters, (unofficially of course) and flew off at approx 35-40 MPH, after locking the brakes because I was rather quickly nearing the end of my 'test track', sliding along the super fine gravel-covered pavement on my back wearing nothing but a t shirt for protection. The shirt was quickly disintegrated as was the skin along my back. Not fun having the nurse at the E.R. scrub my now raw back with a scrub brush and disinfectant.

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    Themason 42906's Avatar
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    You haven't lived until you have suffered an abrasion from the non-skid used on the weather decks of modern US combat ships. That stuff makes asphalt seem like a gymnastics pad.
    Experience is what you get when you don't get what you want.

  10. #10
    got, got, got no time... rguy's Avatar
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    I believe 4 grit is about 3/16" so I suppose most roads would be in the 1 - 4 grit range. Ask your tires, they should know
    Neal - '09 R1200GS / '81 R65
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  11. #11
    Back in the Saddle mcmxcivrs's Avatar
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    Quote Originally Posted by ClassicVW View Post
    Attempting to calculate how bad one road mix is to the naked body vs. another would be pointless.
    Yes, but pointless discussions usually make for the most prolific and entertaining threads here.
    Ed Miller, Calgary, AB
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    I can't wait to retire and have a fixed income. The one I have now is always broke.

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    Quote Originally Posted by 42906 View Post
    You haven't lived until you have suffered an abrasion from the non-skid used on the weather decks of modern US combat ships. That stuff makes asphalt seem like a gymnastics pad.
    I'll top that one(as to whats the grittiest!) as I'm from the generation that ran track on cinders & believe me, they are hard on your skin having had more than a few scrubbed out of my hips & knees with what I remember to be "green soap". They also used to spread them in a coarser form on some dirt roads here in KY, it was called "red dog".
    Back to road surfaces, which is in fact a worthwhile topic & not at all pointless on 2 wheels! (once you divert from personally landing on it) I always wondered how much friction you could get from the river sand they use in MO for chip/tar roads. One of the few places around with "brown" roads. I've been on quite a few & never slid but they just look slippery.

  13. #13
    angysdad
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    When I was in my late teens, a buddy, 'Super-Bike Mike' crashed his CB1000 (?) at high speeds and had his leathers shreaded. We rushed to the hospital upon hearing the news. When we arrived, we were relieved to find that his only injury was lots of gravel embedded in his buttocks.
    I will contact him to see if he remembers the grit size!

  14. #14
    Registered User amiles's Avatar
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    I seem to recall that back in the 70's Cheech & Chong, I believe, did a cut on one of their albums about a road rashed biker being treated in an ER. Lots of screaming & crying were a part of it. Might be a "think piece" for motorcycle training.

  15. #15
    Kbiker BCKRider's Avatar
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    All us ATGATT types do to so much to prevent sunburn, have a more comfortable ride, and also acknowledge there is the slight possibility we might go sliding down the pavement. Admit it, we're just pussies.

    Those guys with no gear are brave! They don't mind sunburn, don't fear skin cancer or brain damage from lack of a helmet, are tough enough to brave rain, even hail, storms. Hell, pain is what riding is about!

    They also know something we don't. THEY will not crash, so forget all that gear. And many of them will not crash in a catostrophic way.

    I suspect most of these riders will NOT die on a motorcycle ride, so in a sense, they are correct. But I bet, for whatever reason, their life insurance policy should be higher than that of geared up riders. Different attitude toward risk.
    Doug
    1992 K100RS

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