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Lean And Cornering G's

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So hanging off the bike moves the center of gravity a bit giving us a little more clearance before we start scraping parts. My question is, what other advantages does this give?

 

Things I suspect are affected by hanging off:

1. suspension compliance due to the forces down the bike to the track being a little out of line

2. contact patch shape

3. steering head angle slightly less

 

1. would seem to be a disadvantage?

2. does its shape add more or less cornering g's? Perhaps it doesn't matter since friction is a component of the coefficient and the normal force?

3. reduces the slip angle so seems a positive but i'm sure this is a seriously slight amount..

 

When talking street riding where we always have more clearance (if your not an idiot) perhaps hanging off/leaning the upper body helps in no way? Or perhaps the sudden need to go to max lean angle would be a help having that max be a little more. Thoughts?

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If you are top heavy, it helps more if you hang off top only imho.

 

Rider weight also affects lean angle clearance on stock untuned bikes; a heavier rider is gonna have less lean angle and vice versa.

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Good body position reduces the lean angle of the bike for a given speed and radius, and using less lean angle has lots of benefits from more traction to reduced tire wear, or most importantly the potential for increased speed

 

as for your 3 points

 

1: suspension works best in the vertical plane, doesn't work at all in the horizontal, so the more upright the suspension the more its able to work. so the less lean angle the bike has the better the suspension can do its job, not sure how thats a disadvantage

 

2: Not entirely sure I understand what you're saying but the size of the contact patch doesn't create G force, unless you are trying to say that a larger contact patch = more grip = higher attainable cornering force, regardless the more upright the bike , the more the "Fat Part" of the tire is in contact with the road, the greater the available traction, which is why the pickup technique is taught at the school and regularly seen in professional racing world wide

 

3: well beyond my knowledge to comment on

 

 

Tyler

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Thanks for the replies !

 

I am curious as to the nuts and bolts of what your saying T-McKeen

1. This is interesting. Because gravity combined with centripetal force will always act directly down the lean, wouldn't that mean the forks would be getting side pressure on any kind of rider lean? Imagine a 600 pound person leaning off so much that the bike didn't need to lean and imagine the side pressure on the forks. Without rider lean it seems from the perspective of the bike the force is always straight down its lean, as if you were riding vertical with a seriously cambered road under you and getting pushed on from the top, in which case the suspension would react normally? However I can also imagine a theoretical bike that could achieve an 80 degree lean angle, then a non rounded absolutely vertical bump in the road the suspension couldn't move with.. the two scenarios seem to conflict a bit.

 

2. Doesn't the contact patch elongate and actually have a bit more surface area cornering than straight up? Taken to the extreme, where the wheel lying on the ground and just slightly lifted on one side, has a lot of rubber down. So why is it the "Fat Part" when standing up? Just the tire profile on big liter bikes we are talking maybe?

 

As to the other benefits you mentioned, does it actually reduce tire wear or just wear more evenly but same overall amount of wear? Also why more traction?

 

Thanks !

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>> Because gravity combined with centripetal force will always act directly down the lean

 

Well, no, I don't think that's quite right. Centripetal force would actually be trying to stand the bike up, and hanging off simply counters that force thus pushing the bike (rather the tires) 'into' the ground and thus stabilizing the bike even more. Gravity will help the hanger (?? ;-) by pulling his weight down and forward momentum will provide a bit of a force multiplier the farther to the inside the hanger hangs.

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Thanks for the replies !

 

I am curious as to the nuts and bolts of what your saying T-McKeen

1. This is interesting. Because gravity combined with centripetal force will always act directly down the lean, wouldn't that mean the forks would be getting side pressure on any kind of rider lean? Imagine a 600 pound person leaning off so much that the bike didn't need to lean and imagine the side pressure on the forks. Without rider lean it seems from the perspective of the bike the force is always straight down its lean, as if you were riding vertical with a seriously cambered road under you and getting pushed on from the top, in which case the suspension would react normally? However I can also imagine a theoretical bike that could achieve an 80 degree lean angle, then a non rounded absolutely vertical bump in the road the suspension couldn't move with.. the two scenarios seem to conflict a bit.

 

 

 

Ok so, the purpose of suspension is to keep the tires in contact with the road, and absorb all the little bumps and ripples and imperfections that asphalt and tarmac have, Imagine for a moment you have a bike in a wheel chock, stand on the pegs and bounce up and down, the suspension works quite well absorbing the force and keeps the tires on the ground, basically the same thing as riding over some really rough pavement, now get off the bike and shove it sideways, the suspension does nothing as the force applied is perpendicular to its direction of travel. this is what I mean by "Works best in the vertical, doesnt work at all in the horizontal" and for simplification assume vertical to always be perpendicular to the surface of the road, not the horizon.

 

The combination of force your alluding to is called Load Factor, its the resulting G force felt in the Z axis of a vehicle that is under the effect of 2 gravities. the math for this stuff is mostly all for airplanes and its not quite 100% totally the same, cause bike have tires with width and the CoG is moved off center with body position and lots of other little differences, but they are very similar so it basically applies it just not absolute because real world application and physics math world are VERY different.

 

Basically a vehicle at 45° of effective lean, or bank angle, will generate 1 G of horizontal acceleration, and have the constant normal 1 G of atmospheric gravity, this results in 1.41 G load factor applied in the Z axis, at 60° this becomes 2 G's and skyrockets from there, your 80° lean results in like 5.8 G of load factor.

 

However none of this really matters, because no matter how much you lean the bike over, the bumps and ripples in the pavement are still on the pavement and basically in the "vertical" plane, yes the suspension will always be absorbing the load factor thats applied in its plane, but its ability to absorb imperfections in the road surface becomes less and less effective the greater your lean angle. This is why frame stiffness is a finely tuned aspect of a race bike as it provides some of the actual "suspension movement" at high lean angles. Too stiff and the bike can't absorb anything, not stiff enough and it wont keep the rubber on the road so to speak

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So hanging off the bike moves the center of gravity a bit giving us a little more clearance before we start scraping parts. My question is, what other advantages does this give?

 

Things I suspect are affected by hanging off:

1. suspension compliance due to the forces down the bike to the track being a little out of line

2. contact patch shape

3. steering head angle slightly less

 

1. would seem to be a disadvantage?

2. does its shape add more or less cornering g's? Perhaps it doesn't matter since friction is a component of the coefficient and the normal force?

3. reduces the slip angle so seems a positive but i'm sure this is a seriously slight amount..

 

When talking street riding where we always have more clearance (if your not an idiot) perhaps hanging off/leaning the upper body helps in no way? Or perhaps the sudden need to go to max lean angle would be a help having that max be a little more. Thoughts?

 

In order to have a more realistic perspective, you could see that the dimensional changes and therefore things affected by hanging off are not dramatic:

 

http://forums.superbikeschool.com/index.php?showtopic=3324&page=3

 

Being motorcycling racing an extreme sport in which 0.01 seconds make a difference, a couple of degrees of less lean are worth the trouble of hanging off.

However, for street riding, with its safety margins, hanging off should be reserved only for unforeseen emergencies.

 

As lean angle increases, the divergence between the lines of suspension and bump forces increases as well.

There is also increasingly more weight applied along the line of the suspension, which moves both suspensions from their sweet spot settings.

As you explained, the elastic property of the forks and rear swingarm acts as a spring for side forces, and helps alleviate the bad situation some; however, there is no dampening effect and some undesirable oscillations follows each bump.

 

Steer1.gif

 

The more you lean, the higher is the force that translates into steering torque transferred from the bumps (vertical force) to the handlebar (which could induce tank slappers):

 

http://www.dinamoto.it/dinamoto/8_on-line_papers/Avancorsa/avancorsa_eng.htm

 

f9_eng.jpg

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Going off on some engineering points which is fine, but I didn't exactly follow how it related to the original subject.

 

One bit of data I can add is modern sport tires have more rubber on the ground when leaned over, than upright, due to shape.

 

CF

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Here's a chart on the Dunlop site for their contact patch at lean angles that shows what Cobie mentioned about how the patch gets bigger as you lean it over - to a point. I'm not following the original poster's point about suspension being at a disadvantage hanging off. The bike's more upright hanging off for a given corner speed than if you don't so the suspension able to better do it's job. Where's the disadvantage? At some point you're going to go fast enough through the turn to be scraping hard parts. When that happens, what can you do to go faster?

 

 

 

ROADSMART-II_IRP_chart.jpg

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That is a very cool chart! I would be interested to see how full race slicks compare - I wonder if they are designed to have the max contact patch at even higher lean angles?

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Very cool chart !!!

 

Dont forget however that the increased contact patch size at ~40° of lean angle is also the result of the increased cornering load deforming the tires carcass and the resulting lateral acceleration is consuming a considerable amount of the traction thats available, it doesn't change the fact that the more upright the bike the harder you can accelerate.

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