Why minimize lean angle?

[dylanelvis]

Dumb question. Don't understand body lean in high-speed turns. For low-speed turns, counterweighting to outside of turn results in a much tighter radius and enhanced confidence/control. But leaning body to inside of a high-speed turn (as racers do) results in bike being more upright. Outside of minimizing scrapes to frame, body, etc., how does inside body lean affect handling?

 

Moderator edit: not a dumb question at all. I split this off into a new thread because I think it is a great topic for discussion.

[JonathanE]

Racers do this to keep the tire contact patch in the tread. Riding with the contact patch reduced because you are off the tread reduces your traction, quickly. Riding on the sideways doesn't work well at all.

[EffBee]

There will be as many different answers to this as there will be answers to this. But personally, I see leaning to the inside to have several major benefits.

 

1. It does keep the bike more upright, which in turns provides a greater margin of safety should one encounter a tightening radius and need to lean the bike even further to negotiate the turn safely.

 

2. Gravity enhances traction. The more upright a motorcycle is, the greater the amount of its weight being borne directly downward into the pavement, rather than being offset by the effects of lean vs. inertia. Thus, a bike in a more upright position puts more weight on its tires downward into the pavement and uses less inertia trying to slide those tires to the outside of the turn. What happened to the inertia? It is being replaced by the rider's weight to the inside.

 

3. Because of the effects described in #2, it is possible to begin applying throttle sooner when the bike is more vertical through a turn than it might otherwise be. The sooner one can get on the throttle, the greater latitude one has in deciding when to apex and when to complete the turn. A timely sporting apex provides maximum acceleration onto the next straight. A later apex delivers greater safety in that more of the turn can be seen before committing to a given line. Either way, it is the ability to get on the throttle (partially or fully) at the earliest possible moment that offers this choice. And leaning in and keeping the bike more vertical, with more weight directly on its tires, makes getting on the throttle sooner possible.

 

4. We need not ride hanging off like a GP racer. It does not take a great deal of body weight shift to the inside of the turn to create a counterbalancing effect which in turn allows a more upright motorcycle attitude through the turn. Thus, techniques such as those branded "kiss the mirror" allow some of this to be used and while not providing all of the benefits of a full racing body position, do advance the cause of safety, control, and a broader decision-making potential than simply riding locked in one position.

[R4ND0M_AX3]

Suspensions also 'work' when the bike is upright. When in deep lean bumps in the road surface have less leverage on the normal direction of suspension travel. Some work is put into allowing side flex in some parts to account for this though.

[EffBee]

Suspensions also 'work' when the bike is upright. When in deep lean bumps in the road surface have less leverage on the normal direction of suspension travel. Some work is put into allowing side flex in some parts to account for this though.

 

Excellent point.

[Whip]

Ya look way cool......

 

[Joe Frickin' Friday]

2. Gravity enhances traction. The more upright a motorcycle is, the greater the amount of its weight being borne directly downward into the pavement, rather than being offset by the effects of lean vs. inertia. Thus, a bike in a more upright position puts more weight on its tires downward into the pavement and uses less inertia trying to slide those tires to the outside of the turn. What happened to the inertia? It is being replaced by the rider's weight to the inside.

 

Maybe I'm misunderstanding your explanation, but this doesn't make sense to me. The combined weight of rider and bike is borne through the contact patches at all times, regardless of lean angle, turn radius, or forward speed. The lateral force (the "inertia trying to slide the tires"), is a function only of forward speed and turn radius. Hanging one's body weight to one side will not affect the magnitude of either of these forces.

 

For some bikes, increased lean clearance is a good reason to shift your body weight. That includes racing bikes with tires made of glue, and fat "sport"-touring bikes like the RT, where there's enough traction to enable one to drag hard parts like footpegs and centerstands.

 

The other good reason is that the suspension does a better job of soaking up bumps if it's oriented vertically (as much as possible) to the road surface. Imagine crossing a speed bump with the bike vertical, and then with the bike heeled over 45 degrees; in the latter case the suspension has to move 40% farther to absorb the bump without upsetting the bike. Same thing with dips in the road: when leaned over, the suspension has to move a long way for the wheel to stay in contact with the road.

[steveknapp]

The other good reason is that the suspension does a better job of soaking up bumps if it's oriented vertically (as much as possible) to the road surface.

 

From everything I've learned THIS is exactly it. The lean angle of your motorcycle is a huge impact on the function of the suspension. Suspension is responsible for allowing the tires to track the road surface, which even on race tracks isn't perfectly smooth. When the bike is leaned over the suspension can't react to the vertical component without some horizontal component as well. The more vertical the bike, the better the suspension can work.

 

It's been a long time since I sat down and did the math to think this all through, show some mercy Mitch , wouldn't the angle also result in not only a change in the amount the shock must compress, but therefor also a change in the spring rate and damping? In essence a virtually changed spring and damping rate for the vertical axis? Hence some compromise is made is suspension setup for a race bike to balance suspension performance at different lean angles?

 

And the horizontal component of the force needed to compress the suspension would be taken out of your "traction budget" (ala Code). If you were really on the edge, this could be an issue.

 

I also thought this was some of the drive for engineered flex in the swingarm of some sport bikes, making the chassis more of a suspension component when leaned over.

[EffBee]

2. Gravity enhances traction. The more upright a motorcycle is, the greater the amount of its weight being borne directly downward into the pavement, rather than being offset by the effects of lean vs. inertia. Thus, a bike in a more upright position puts more weight on its tires downward into the pavement and uses less inertia trying to slide those tires to the outside of the turn. What happened to the inertia? It is being replaced by the rider's weight to the inside.

 

Maybe I'm misunderstanding your explanation, but this doesn't make sense to me. The combined weight of rider and bike is borne through the contact patches at all times, regardless of lean angle, turn radius, or forward speed. The lateral force (the "inertia trying to slide the tires"), is a function only of forward speed and turn radius. Hanging one's body weight to one side will not affect the magnitude of either of these forces.

 

Yeah, I probably didn't do a good job of explaining what I meant. As I understand it, (Mitch, you being an engineer are certainly more informed than I am), a motorcycle has less of its physical weight on its tires the further it falls from vertical (I know this goes directly against what you said, but perhaps you can help me explain this better, or tell me I'm completely wrong).

 

For example, if you were holding a 500lb. motorcycle up at 45 degrees, a scale under the bike would not show 500lbs, but less. And a scale under you, minus your weight, would show the difference to the 500lbs. When cornering, this weight you are holding in the example above, is countered in its tendency to continue to fall, by the inertial forces created by the changing of direction (i.e. a turn). So, yes, all of its weight its on its tires, but part of it is physical weight and part of it is in the form of physical weight falling but canceled by inertia, and expressed as sheering of the rubber at the contact patch. It is the sheering force that we try to reduce (or whose effect we try to reduce) by keeping the bike more upright, thus applying a greater percentage of the bike's weight (which I expressed as "gravity") straight down through the tire.

 

At least this was how it was once explained to me. I've been completely wrong several times in my life (actually several times per month if you listen to my wife), so if I'm totally upside down on this one, please let me know. I just had a birthday, but that doesn't mean I'm too old to learn something new.

[Rocket_Cowboy]

Ya look way cool......

 

My knee pucks are nicely chewed up. Unfortunately ... not in the normal direction of travel, but in every other direction from all my falls off the bike(s).

[russell_bynum]

Racers do this to keep the tire contact patch in the tread. Riding with the contact patch reduced because you are off the tread reduces your traction, quickly. Riding on the sideways doesn't work well at all.

 

 

How does this work with race tires that only have tread in the middle, or slicks that don't have tread at all?

[dylanelvis]

Many thanks for these informed, intelligent, and very helpful responses. Now it makes sense. This is a great website.

[BerryG]

Racers do this to keep the tire contact patch in the tread. Riding with the contact patch reduced because you are off the tread reduces your traction, quickly. Riding on the sideways doesn't work well at all.

 

 

How does this work with race tires that only have tread in the middle, or slicks that don't have tread at all?

 

Tread actually reduces traction..(on a smooth dry surface.) Tread is there to give water someplace to go.

 

Most preformance tires have a profile that puts more rubber ( and sometimes softer rubber ) in contact with the pavement when the bike is leaned over than when it is upright.

 

While I understand weight transfer, contact patches and slip angles for four wheeled devices I have yet to fully grasp the math involved in explaning how a motorcycle tire works in a corner. I do know that I can corner faster and feel a lot less tire slippage when I shift weight to the inside of the corner reguardless of the lean abgle.

[ShovelStrokeEd]

The dynamics of suspension action/reaction coupled with fork and chassis flex and swingarm flex are sufficient to make a really fast, powerful computer's head spin.

 

It is difficult to model the various parameters and even measure what is going on. I certainly can't do either.

 

Some things I have noticed though, mid corner bumps tend to want to twist the front end and the effect is much more noticeable when lean angle increased. Now I ride a bike with basically 10 year old suspension and chassis technology and I ain't all that fast to begin with. Leaning my upper body to the inside of a corner and even "sneaking a cheek" off the seat allows me to corner at the same speed with a reduced lean angle and makes the suspension behave much better. Couple this with the application of power through the turn to allow the suspension to move up in its operating range rather than compressing in response to the load induced by the turning forces also eases the unsettled feeling.

 

I'll leave the why and wherefore to the suspension engineers. Something else to think about though is how tire choices effect all this. One of the reasons I haven't gone to Pilot Powers or M1's on my Blackbird (besides tire life) is that I don't think the suspension on my bike is up to coping with the increased loads a stickier tire might put into the system.

[MotorinLA]

For example, if you were holding a 500lb. motorcycle up at 45 degrees, a scale under the bike would not show 500lbs, but less. And a scale under you, minus your weight, would show the difference to the 500lbs. When cornering, this weight you are holding in the example above, is countered in its tendency to continue to fall, by the inertial forces created by the changing of direction (i.e. a turn). So, yes, all of its weight its on its tires, but part of it is physical weight and part of it is in the form of physical weight falling but canceled by inertia, and expressed as sheering of the rubber at the contact patch. It is the sheering force that we try to reduce (or whose effect we try to reduce) by keeping the bike more upright, thus applying a greater percentage of the bike's weight (which I expressed as "gravity") straight down through the tire.

 

Thanks for the flashback to my college physics classes, I can picture the chalk drawings on the blackboard now....

 

Unfortunately the flashbacks are too fuzzy to help me remember all the formulas and explanations about centrifugal force, inertia and how things are affected by a change in the center of gravity. I do remember two things:

1. The bigger the contact patch, the grater the amount of friction.

2. Moving the center of gravity toward the center of the turn (leaning in), reduces the amount of centrifugal force exerted on the moving body (thus reducing the amount of force that is pushing you toward the outside of the turn).

 

The real question is this:

 

If you go thru a turn and the bike loses traction, which crash will hurt more? If you are on top of the bike it is a longer fall to the ground, but if you are hanging off to the inside you’re probably going faster…

 

Inquiring minds would like to know.

[David]

2. Moving the center of gravity toward the center of the turn (leaning in), reduces the amount of centrifugal force exerted on the moving body (thus reducing the amount of force that is pushing you toward the outside of the turn).

 

That doesn't sound right to me, but I never even had those classes you speak of!

[MotorinLA]

2. Moving the center of gravity toward the center of the turn (leaning in), reduces the amount of centrifugal force exerted on the moving body (thus reducing the amount of force that is pushing you toward the outside of the turn).

 

That doesn't sound right to me, but I never even had those classes you speak of!

 

Like I said, it has been too long since I was in school for me to remember the exact formulas (or is that formulae ). If I remember correctly, the amount of force is related to the radius of the turn.

 

If you want to test it out personally, I've found that the little metal carousels they used to have at the kiddie parks made for a good demonstration. If you stand at the center of the spinning carousel you will feel a small amount of force away from the center. The further you move from the center, the greater the amount of force you will experience.

 

Of course, you may want to try this when there are no kids around. Parents always get weird when grown men play on the children's exercise equipment by themselves...

 

If you can’t find a carousel nearby, the Alice in Wonderland Teacup Ride will also work.

 

Field trip anyone?

[David]

I see what you are saying, now, but I think the effect would be so little that it would be difficult to measure. The average radius of the turn doesn't change with less lean angle that is induced specifically from splitting the center of gravity (mass, really) by leaning off. It changes a little for the rider, but that's so little that I can't see it making any practical difference.

[Quinn]

Okay, now I'm confused. I thought it was the lean angle that determined the contact patches that determined the radius of the curve. What y'all are saying is that if I held the bike upright and stood on the footpeg off on one side, the bike would turn in a fairly tight radius? What if I leaned the bike over but moved my arse to the high side; would I go straight?

I just don't understand how an unbalanced bike turns more except by pulling the bike into a steeper lean angle. What have I missed?

[David]

What you're missing is that it's the combined lean that determines radius (speed is the other factor). When you lean your body off to the inside, you can raise the bike more toward vertical...without changing the radius.

[ShovelStrokeEd]

'Zactly! At speed, if it ain't leanin' it ain't turnin'. (Pissed my spell checker off with that one. ) Again, I can't 'splain the math but shifting a significant portion of the weight of the combined machine/rider towards the inside of the turn allows one of a couple of things to happen. More speed around the same radius/lean angle, a tighter radius for the same lean angle/speed or less lean angle for the same speed/radius. On re-read, all of them mean the same thing.

 

A little more thought tells me the centrifugal force is acting on a lever that has a pivot on the tire contact patch at one end and the center of mass of the bike/rider on the other. Shifting the center of mass down and inside will tend to lessen the lever arm trying to mousetrap the bike/rider over the outside of the point of contact with the road.

[Wooster]

Ya look way cool......

 

 

After reading all erudite remarks and explainations, I think Whip got it rite.

It's cool looking and is cool, balancing bike w/throttle thru the turn, cool.

 

Wooster leaning left

[steveknapp]

I did take those classes, but it's been a long time.

 

You can take a large and complex body and once you know it's center of mass, you can treat it like a dot, but a dot with mass. So leaning the bike, or leaning off, your "Center of mass" would be in the same place. But you change the bikes lean angle to the road and the suspension action.

 

I'm not seeing where anything else changes.

 

Fernando's example of leaning the bike over puts less weight on the tires, also not true. The downward gravitational force needs the also vertical force of the tires. Physics says the X and Y forces must equal out. You can have a force on the Y axis act upon the X via a moment. But the pivot point, in this case the contact patch, needs to counteract both the forces on both the axis (I'm thinking 2D here).

 

It's the moment, the torque, of the fact that the bike pivots on the contact patch, not around the center of mass. Something needs to keep it from falling over.

[kuyaed33]

Racers do this to keep the tire contact patch in the tread. Riding with the contact patch reduced because you are off the tread reduces your traction, quickly. Riding on the sideways doesn't work well at all.

 

 

How does this work with race tires that only have tread in the middle, or slicks that don't have tread at all?

 

I thought tread was only there for water?

[kuyaed33]

Ya look way cool......

 

 

plus like whip says " ya look way cool..."

[MotorinLA]

I did take those classes, but it's been a long time.

 

You can take a large and complex body and once you know it's center of mass, you can treat it like a dot, but a dot with mass. So leaning the bike, or leaning off, your "Center of mass" would be in the same place. But you change the bikes lean angle to the road and the suspension action.

 

I'm not seeing where anything else changes.

 

I may be wrong, but although the location of the center of mass within the body may remain in the same place (thus you can treat it as a dot), the location of the center of mass in relation to position in the roadway arguably changes (i.e. leaning in moves the center of mass closer to the center of the curve).

 

Am I confusing everybody else as much as I am confusing myself???

[Slyder_Steve]

I have to start with my head hurts from grinding back to my college physics days (daze).

 

Anyway, the total force on the tires has to remain the same whether shifting weight or not. It is a matter of weight and speed versus turn--gosh, sounds a lot like inertia to me.

 

Bottom line for me is you've given yourself more flexibility by allow more angle on the bike. The fact that the bike is standing straighter in the turn allows for more contact patch from the tire (at least at extremes), and more suspension travel.

 

Besides you look really cool hangin' a knee

[russell_bynum]

The fact that the bike is standing straighter in the turn allows for more contact patch from the tire (at least at extremes), and more suspension travel.

 

About the contact patch: Assuming you haven't reached the edge of the tire, is the contact patch bigger or smaller with the bike upright than it is when it is leaned?

 

We are often told that the contact patch is bigger when the bike is upright. But is that true? Logically...it would seem that you tax the tires much more when you're leaned than when you are upright, so it would be a benefit if the tire manufacturers shaped the tires so that they actually had a bigger contact patch while leaned.

 

So which is it?

[Slyder_Steve]

I guess the answer is...is depends.

 

My hypothetical point was at extreme angles, you'll start losing contact area. Granted on the RT you'll lose pegs, and a few other things before you get near the extreme of the tire.

[russell_bynum]

I guess the answer is...is depends.

 

My hypothetical point was at extreme angles, you'll start losing contact area. Granted on the RT you'll lose pegs, and a few other things before you get near the extreme of the tire.

 

Gotcha. Definitely, once you get to the edge of the tire and keep leaning, then you're definitely decreasing contact patch. That's why chicken strips = good.

[RFW]

The more upright a motorcycle is, the greater the amount of its weight being borne directly downward into the pavement, rather than being offset by the effects of lean vs. inertia. Thus, a bike in a more upright position puts more weight on its tires downward into the pavement [sNIP]

That is not correct. The angle that the force acts through in contact with the tire-pavement contact is exactly the same, no matter whether you do not hang off the inside (and hence the bike itself is at a greater angle), or if you DO hang off the inside (and hence the bike itself is more vertical).

 

Whether you hang off or not, the center of gravity of you-plus-the-bike does not substantially change. Your CG moves more inward, and the bike's CG moves more outward, but the combined CG does not significantly change. And, all that matters here is the total (combined bike and rider) CG. The bike may be more vertical, but all that serves to do is allow the a more optimal contact patch. The side force is totally unchanged.

[ShovelStrokeEd]

On modern, sporting tires, the contact patch is increased with the bike leaned over, not decreased. It is actually at the minimum with the bike upright. That is why it is critical to follow the guidelines for wheel width vs tire section provided by the tire manufacturer. This was not true in the old days when many motorcycle rear tires were nearly square in section. Racing tires from that time tended to be nearly triangular in section for this very reason.

 

Today, sections tend to be fairly complex curves to maximize contact patch with the bike leaned over. This is one of the reasons why tire pressure is so very critical to obtaining maximum traction as well. The deformation of the tread under load is taken into account by the tire engineers in order to allow maximum surface area with the bike leaned over. It is also why, when headed for the track, you generally run a lower pressure than you would on the street although I tend to maintain those relatively low pressures all the time at the expense of some earlier wear. An example, my Blackbird calls for 42/42 for tire pressure which is fine if I was going to operate it at the very high speeds of which it is capable all the time. I do not. Therefore, I tend to run 36/38 most of the time, gaining both comfort and traction. If I am off to attack some twisties, when I get there, I'll drop the tire pressure a little more as I am looking for more compliance over surface irregularities. Now, I certainly would not want to do a sustained top speed run (ca 175 mph in my case) with that low a tire pressure and would make an adjustment prior to the attempt.

[Bud]

Read More Proficient Motorcycling by David Hough.

 

Page 167

 

"In a nutshell, hanging off in turns can help stabilize the bike, reduce steering effort, and increase lean over clearance."

 

Another author, I can not recall who, talked about having 100 "traction points" available. When your bike leans over, some of the traction points are being used to keep the bike from sliding sideways which leaves fewer traction points available for braking and steering.

[Shaun]

Another author, I can not recall who, talked about having 100 "traction points" available. When your bike leans over, some of the traction points are being used to keep the bike from sliding sideways which leaves fewer traction points available for braking and steering.

Replace "leans over" with "travels in an arc", doesn't matter if it's leaned over or not.

 

I favour giving the suspension a better chance to do what it's designed to do. Chassis flex can't beat springs/shocks. A nasty wallow in a tight corner can unload a well heeled bike and convert 100 traction points to 50 in a blink.

[steveknapp]

 

Saw this on badweb. Thought it might help some folks.

[chrisolson]

might also give this Article_ by_David_Hough a try . Even has a picture of an RT

[pmdave]

One of the big advantages of moving weight in the saddle is adjusting steering feedback. The position of the contact rings (in relation to bike centerline) is a function of tire profile and lean angle. A wide profile tire leaned way over moves the contact ring way over to the "lean" side, and that means that drag on the tire has more leverage to steer the front wheel toward the direction of turn.

 

Since bikes steer "backwards," a wheel that's steering itself toward the turn tends to countersteer the bike back toward vertical. IOW, the rider must maintain some pressure on the low grip to keep the bike leaned.

 

Hanging off toward the curve helps keep the tire contact ring closer to the bike centerline, which can help neutralize steering input. And the less steering input the rider must apply, the less traction is being consumed.

 

Bikes with narrow (or triangular) tire profiles may actually corner with more neutral feedback with the rider counterleaning toward the outside of the turn, but of course that also eats up leanover clearance.

 

pmdave

[pmdave]

Let's also note that the motorcycle doesn't lean around the tire contact patches. When the bike "leans", its a result of the front wheel steering wider ("out tracking")and forcing the bike/rider to roll the other way.

 

The bike/rider mass tends to roll more around the combined CoG. That's not quite accurate, since a bike in a curve rolls in complex movements where the actual center of lean moves all over the place. The center of roll can be feet above the ground or even feet below the ground. But it's more true to understand the bike/rider rolling around the CoG than around the Contact patch. The diagrams often used dto depict gravity vs centrifugal force are misleading.

 

The point of this is that in discussing the merits of hanging off or counterleaning, the combined CoG doesn't "lean over". Rather, the bike/rider rolls around the CoG--which more-or-less maintains a constant arc and distance from the turn center.

 

You can actually see this for yourself when watching race videos where the bikes are coming at you out of a turn and entering the next turn. At first, it seems that the bike leans around the CP, but as you mentally plot the position of the CoG of the bike, you'll realize the contact patches out-track farther than the CoG, then quickly cross to the other side of the CoG as the rider forces the bike to lean the other way.

 

The position of the bike CoG is typically at about rider knee location fore-aft, and at an elevation of the top of the wheel rims. Once you imagine this position of the CoG, you'll be able to visualize the bike rolling around that center. Obviously, as the rider moves laterally in the saddle (hangs off or switches sides) the combined CoG will move laterally.

 

One of the other interesting points about hanging off is that the CoG changes elevation as the bike rolls over. Its easy to get the bike leaned because gravity is pulling the CoG downward. But to get the bike rolled up out of the lean, the CoG must be lifted up, and that requires a bit of steering traction. If the bike can be held more vertical, there is less fall/rise in the CoG, and therefore less traction consumed getting the bike rolled from side to side.

 

pmdave

[David]

One of the other interesting points about hanging off is that the CoG changes elevation as the bike rolls over. Its easy to get the bike leaned because gravity is pulling the CoG downward. But to get the bike rolled up out of the lean, the CoG must be lifted up, and that requires a bit of steering traction. If the bike can be held more vertical, there is less fall/rise in the CoG, and therefore less traction consumed getting the bike rolled from side to side.

 

This is why you'll see some racers lean the very most AS THEY PULL ONTO A STRAIGHT UNDER POWER. By hanging off/leaning off further, they can make the bike more upright without a steering input.