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Thread: the physics of cornering on gravel roads

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    Flirting With The Redline dpwell's Avatar
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    the physics of cornering on gravel roads

    Hi - I've been making forays lately off-pavement. Nothing too rough, just gravel roads.

    I've read/been told that the way to corner is to lean the bike but, instead of leaning with the bike as we would do on pavement, one should keep the body upright. I'm curious as to why. Presumably there will be centrifugal force outwards as the bike leans, and traction can be lost pretty easily on gravel. Does the upright body position provide a down force that helps maintain traction?

    I've also read stuff about spinning the rear wheel as one goes around a corner. Is this a skill that someone who putzes along a gravel road at a modest speed is going to need? It sounds pretty challenging to me. Am I going to need this skill heading up the Dempster highway?

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    Flirting With The Redline 8000 Posts! Trials's Avatar
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    Big part of that is in using the terrain, berms or other features allow the bike to be horizontal at times, centrifugal force can be used to gain incredible traction and acceleration coming out of a corner and it's fun.


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    Flirting With The Redline 8000 Posts! Trials's Avatar
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    Oh and no you probably won't be blasting around corners with a heavy loaded motorcycle,
    take the corners sane and easy and blast ahead in straight lines

  4. #4
    Do not lean with the bike like on the street, let the bike move under you. How fast I go depends on how deep the gravel is. Deeper means faster for me. I have ridden my ST1300 2-up over some really deep gravel in new road construction and my biggest gripe was how slow the Follow-Me truck was going. (Two Harleys riders duck walked their bikes most of that 8 miles and described it as the "road from hell".) Steering becomes "mushy" the slower I go. Peg steer the bike (weight the footpegs). We just do not have the traction in gravel or offroad to lean with the bike, your front tire will washout.

    As far as drifting the rear wheel to corner. No on the ST ... sometimes on my GS ... often on my 500 EXC. On my old GS without traction control there was a gravel road in AZ that I rode often that I would drift the rear tire .. a little. On my newer GS it's too much trouble to turn off the Traction Control. On my KTM it's great fun but it's a very throttle controlled effort. It would not be worth the risk/effort on a heavy street bike. In really deep gravel like in some stream beds .. no .. but a little extra speed does wonders. For me it's similar to riding in sand and I am just "suggesting" direction to the bike ...
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  5. #5
    Flirting With The Redline dpwell's Avatar
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    I originally read about skidding the rear wheel as a means of steering the bike in David Hough's Proficient Motorcycling. Here's the quote:

    "... the trick is to use more body English, keep the machine vertical, and steer more with the throttle. After all, sliding the rear end sideways is another way of pointing the front end in a different direction. You can make the rear tire slide by rolling on the throttle, snapping it closed, or by dabbing the rear brake..."

    Keep it vertical? This is making me think of speedway dirt racing technique. Is that what he has in mind?
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  6. #6
    RiderCoach 5000 Posts! NORTY's Avatar
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    Quote Originally Posted by dpwell View Post
    Keep it vertical? This is making me think of speedway dirt racing technique. Is that what he has in mind?
    Don't forget, the main goal of speedway racing is to change direction upon a slippery surface as quickly as possible. So, what Hough's goal is, and the speedway racer's goal, are 2 different things. Hough wants to convey a strategy of rotating the motorcycle by not only the front tire, but also by sliding the rear wheel. Because of the great reduction of tire friction on dirt (compared to street) sliding can be accomplished by very little "lean." It also increases stability by not needing the extra friction for leaning, thus offering more friction for accel/deceleration.
    Take note when you watch speedway racers next time. As they approach a turn, they ARE leaning and the rear wheel begins to drift to the outside. At the apex, the rear wheel should be at it's utmost "sideways" position Also, it's most vertical. As the racer leaves the apex, the rear wheel becomes more inline with the chassis, and the lean increases as the rider moves thru a larger arc.
    So, with speed, we lean to change directions, even when the rear is sliding to the side. When the speed slows, we don't need to lean as much to accomplish the desired rate of turn. Racers use the rear wheel to help turn the chassis in many forms of racing. Drifting is a prime example of this. You'll also notice that to the extreme, it's a very slow way to get around a turn, but it looks dramatic.
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    Flirting With The Redline 3000 Posts! Galaxieman's Avatar
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    It’s been a couple of years since I lived about 3 miles off the paved road down a mostly gravel, but often sand-washed road, so my skills are probably pretty dusty. That said, the biggest thing I remember from adjusting to that road was learning to get more comfortable with the bike moving around underneath me. Momentum and gyroscopic forces help keep the bike more upright, so once I got comfortable carrying a little more speed, the ride actually became easier. Not that I’m suggesting you go flying down a dirt road initially. But understand that you might not be going quite as fast as it feels like because the bike ‘wanders’ more, and that movement is normal... you just have to get used to it.

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    Moderator/RiderCoach We've stopped counting... Missy B's Avatar
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    Quote Originally Posted by Galaxieman View Post
    It’s been a couple of years since I lived about 3 miles off the paved road down a mostly gravel, but often sand-washed road, so my skills are probably pretty dusty. That said, the biggest thing I remember from adjusting to that road was learning to get more comfortable with the bike moving around underneath me. Momentum and gyroscopic forces help keep the bike more upright, so once I got comfortable carrying a little more speed, the ride actually became easier. Not that I’m suggesting you go flying down a dirt road initially. But understand that you might not be going quite as fast as it feels like because the bike ‘wanders’ more, and that movement is normal... you just have to get used to it.
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