LEANING: STREET MOTOS VS. MOUNTAIN BIKES
Hi, Lee.
I just went through your book, and I have a question. I was wondering why motorcycle road racers always get off their seats to the inside (trying to keep the bike vertical) in corners, but mountain bikers do the opposite?
Cheers,
Eric
Hi Eric.
Excellent question, Grasshopper.
 Team Honda racer Jake Zemke. www.hondaredriders.com |
Why it works on a street motorcycle
Less bike lean. At any given speed and turn radius, there’s one lean angle that correctly balances gravity and turning Gs. This is the angle between the contact patch of the tires and the center of mass for the bike/rider. When you lean your body into a turn, you have to lean your motorcycle less. This is good because:
More ground clearance. Pavement traction is abundant and consistent. With all that grip, you can lean a moto far enough to scrape parts on the ground. (I’ve done it: Frequently on my Honda VFR800, and once on a BMW R1150RT touring bike in the Italian Dolomites. What a day!)
Better traction. You put more meat on the ground with a reduced lean. Also, once you get past about 45 degrees of lean, the tire starts acting like a circular scrub brush, whicis more about scrubbing than gripping.
More control. Advanced riders use their knees to sense where they are and to unweight the back end when they want the rear end to braaap around. (I’ve never done that—not on the road anyway.)
 The sun is setting, and Bobbi Watt is railing this gravel turn. Nice. |
Why it doesn’t work on a mountain bike
Sketchy traction. MTBs don’t get the kind of traction road motos do. When your tires can slip at any second, you want to stay balanced above the edges of your tires. If you lean farther than your bike (like a road racer or Bicycling Magazine reader) and your tires slip, goodbye. If you stay above the edges and your tires slip, that’s called drifting. Cool!
Less camber thrust. The more you lean your bike, the more your tires generate “camber thrust,” which is like rolling an ice cream cone—it turns on its own. This is the safe way to turn a bike, especially on dirt. The less you lean the bike, the more you have to steer. When you steer your front wheel through dirt, you plow it through all those tiny particles like a rudder. That’s so random—better hope your tire deflects where you want it to.
Summary: In most situations, lean your bike more than your body. You’ll corner faster and tighter, with more control.
But you can still say BRAAAP!
Left to right: Sketchy to sweet. It was so hard to get Bobbi to lean her body inside the turn. She knows better. |
14 Comments
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shaun palmer Says October 25, 2006 @ 8:01 pm
lee, shouldnt you mention something about the weight of a moto vs a bike? and also what about a throttle??... I am no genious, but i think these two things also have a lot to do with why you can lean a moto that way
Jason Says October 26, 2006 @ 9:18 am
“More control. Advanced riders use their knees to sense where they are and to unweight the back end when they want the rear end to braaap around.”
I come from a roadracing background, specifically the MRA here in Colorado and can tell you using your knee is a means of sensing the lean angle and a method of saving your butt when the bike starts to push. Unweighting the back end is sure means of highsiding the bike when traction snaps back….I unfortunately have tested this theory.
leelikesbikes Says October 26, 2006 @ 9:21 am
Right on. Thanks Jason.
james Says October 26, 2006 @ 9:56 am
I remember reading something about when to lean the bike more and the body less and vise versa. Whats that about lee, or am i talking rubbish
leelikesbikes Says October 26, 2006 @ 11:45 am
Shaun, the throttle and weight can indeed make a big difference, but the essential dynamics—leaning and geometry—are the same.
Throttle: Helps you braaap the rear end around, especially on dirt.
Weight: If you’re cantilevered to the inside, when your 500-lb moto slides out, it tends to take you with it—and you can maintain some control. When your 30-lb bike slides out, it tends to leave you where you are and let you fall.
leelikesbikes Says October 26, 2006 @ 11:48 am
James:
There are some exceptions to leaning your bike more. Wet skinnies and uphill switchbacks, for example. There the speed and lean are low, and the need for traction is high.
Cornering is so complex, but if you learn the basics you’re covered most of the time.
Grant Shoemaker Says October 27, 2006 @ 11:20 am
Lee – if you ever need models to take photos of for examples of what not to do – well, you have my contact info!
leelikesbikes Says October 27, 2006 @ 11:32 am
Grant! You are a bad a—mountain biking mofo. Go out and DO IT BROTHER
!
Off to the moto track right now …
BB Says October 27, 2006 @ 8:12 pm
That chick is HOT !
Phillip Says October 28, 2006 @ 5:15 pm
That “chick” is Bobbi Watt, married to Jon Watt, both of whom will school you on or off a bicycle.
Ben Says November 2, 2006 @ 7:18 pm
Hi, I have ridden a street bike on a race track before, and I can safely say that using your rear tire to “unweight” the bike is the fastest road to highsiding there is. You do not set your knee down usually if you don’t have to, because dragging your knee slows you down just a wee bit. Watch moto GP and you’ll see what I mean, the knee is about an inch above the ground, but not touching, unless if they lean too far or something. The knee can also be used as a sort of “feeler”.
Joe Says January 1, 2007 @ 9:29 pm
Sorry I’m several years late on this but it is an interesting topic.
I usually try to keep my mountain bike fairly vertical through and lean off a lot. Reason: you can keep pedalling through the corner! You can still drift this way, believe me.
Rich Says May 17, 2007 @ 4:27 pm
Joe has a good point. If traction is not an issue then leaning your body harder than the bike does allow you to keep pedalling.
The other situation I can think of is when the track is narrow and winding with trees very close to the track on both sides. By leaning my body a bit more than the bike and tucking in an elbow, I can get the maximum corner speed and just brush past the tree on the inside with my handlebar and shoulder.
Leaning the bike hard in that situation guarantees an encounter between the handlebar and the tree on the inside of the turn.
theff Says June 10, 2007 @ 2:24 pm
i have always leaned the bike and stayed straight, and thuahgt i was doing it wrong, and that you are suposed to lean with the bike, but i never seam to have the spead to do that, would i have better turns through the berms if i was going faster and leaned with the bike, or keep leaning the bike more hten me?