Is Lean Angle Irrelevant?

[Crash106]

So, I'm over at the GL1800Riders forum, and one guy says that traction is the same at all lean angles because at any lean angle, the centrifical force pushing out is balanced by gravity pushing in. Not to say you can't run off the edge of the tire, overwhelm the traction with throttle or brakes, or drag something solid and fall down, but that the traction demands at 20-degrees and 40-degrees of lean are the same. Can this be true? If true, keeping it in mind would be a comforting mindtrick when riding.

 

Here is a link on this topic:

 

http://www.msgroup.org/Tip.aspx?Num=217

[faffi]

You know better, mate. And he doesn't have a clue. He make it sound like the bike will find its own way around a set of switchbacks without a rider in attendance. And we also know that it is possible to fall off a bike even without lifting the tyres off the ground, don't we? Finally, while grip is fairly equal from upright to full lean, the direction of grip changes. The further you lean over, the more of the grip is needed to prevent you from flying off the road and the less you have left for acceleration and braking. Also, of course, grip is dependant upon friction, and the less friction, the less lean permissible before you slide off the road or fall down.

 

But nothing of this is new to us.

[DUNLOP-RTS]

So, I'm over at the GL1800Riders forum, and one guy says that traction is the same at all lean angles because at any lean angle, the centrifical force pushing out is balanced by gravity pushing in. Not to say you can't run off the edge of the tire, overwhelm the traction with throttle or brakes, or drag something solid and fall down, but that the traction demands at 20-degrees and 40-degrees of lean are the same. Can this be true? If true, keeping it in mind would be a comforting mindtrick when riding.

 

Here is a link on this topic:

 

http://www.msgroup.o...ip.aspx?Num=217

 

 

He was simply pointing out the physics of speed, radius and lean. He was not adding all the other variables.

 

Too much thinking and not enough riding. Get off the GL1800 forum and go ride.

[spgtech]

Hi Crash,

I went to the link and had a different takeaway than you did.

 

I didn't read that the traction requirements were the same at different lean angles, only that the force vectors of outward force and downward force would dictate the lean angle (of the system; the CG of you and your bike down to your contact patch). This lean angle is the outward force from cornering vector, added to the downward force (1g) vector of gravity. If your speed and radius of the corner is giving you 1g of lateral acceleration (horizontal vector of unit length 1), and you have 1g of gravity (vertical vector of unit length 1), the vectors add together to make a 45deg lean angle (of the rider/cycle system) with approximately 1.4g of force compressing the suspension.

 

In a different example, a 1.6g lateral, with 1g of vertical will cause a 60 degree lean angle to be required and will have 2gs compressing the suspension.

 

If you hang off, the bike will lean less by an amount proportional to the weight offset to the inside by body placement. If a 45 degree lean is required, the CG of the SYSTEM will be 45 degrees offset from the contact patch, even if the bike is at 40 and the rider is at 50.

 

While the example above links required system lean to lateral acceleration, is is useful to note that lateral acceleration is determined by speed and turn radius (just like in a car). If your tires and pavement conditions can maintain 1.6gs sideways, then you can run your 60 degree lean and look like Stoner, if your tires will only give you 1g sideways, then any system lean over 45 degrees will put you on your ass.

 

The author of the article you link to did make bit of a leap about it being impossible to fall down (in). Obviously, if you continue tipping in, you will alter the conditions by tightening your line, which will tighten to match the lean angle (all that stuff up above but in reverse). This will increase the lateral acceleration for the given speed (same speed/tighter line); and you can exceed the allowable traction of your tires.

 

So, YES, gravity and lateral force are balanced by lean; and NO, the lateral force is not the same for different lean angles.

 

Have fun.

-Sean

[johnnyrod]

Dreadful article, talk about a little knowledge being a dangerous thing. There's no such thing as centrifugal force for starters, and to simply state that cornering force equals gravity at 45 degrees is not only rot, but also at odds with the rest of the article that makes the point that cornering force and gravity are always equal when you're at a steady lean angle.

[bradvanhorn]

Dreadful article, talk about a little knowledge being a dangerous thing. There's no such thing as centrifugal force for starters, and to simply state that cornering force equals gravity at 45 degrees is not only rot, but also at odds with the rest of the article that makes the point that cornering force and gravity are always equal when you're at a steady lean angle.

I'm going slightly off topic here, but what leads you to say, "There's no such thing as centrifugal force..."? The term often may be misunderstood, or cited incorrectly, but still it does exist.

[spgtech]

Dreadful article, talk about a little knowledge being a dangerous thing. There's no such thing as centrifugal force for starters, and to simply state that cornering force equals gravity at 45 degrees is not only rot, but also at odds with the rest of the article that makes the point that cornering force and gravity are always equal when you're at a steady lean angle.

I'm going slightly off topic here, but what leads you to say, "There's no such thing as centrifugal force..."? The term often may be misunderstood, or cited incorrectly, but still it does exist.

 

 

Hi Brad,

Not the OP here, but centrigugal force is really a convenient way of describing centripital acceleration. An object travels in a straight line unless acted upon by another force. In this case, the motorcycle is not pulling outwards, it is being pushed inwards. This centripital acceleration is what is constantly pushing the motorcycle inwards from the straight line it would take otherwise (like if it crashes). As an example, as I'm sure you have noted, a motorcycle that hits ice in a corner doesn't go straight outward, it goes in a straight line tangential to the circle; so the morotcycle goes forward in a straight line from the moment it lost traction, it's just the road which curves away from the track of the bike.

 

It boils down to semantics, but this is what is meant when somebody says that there is "no such thing" as centrifugal force. Centrifugal force is a common way of describing an apparent "outward" pull, when it is really the object trying to go in a straight line.

 

-Sean

[bradvanhorn]

Thanks Sean. I was aware of what you posted; I was just asking Johnny to confirm this was his perspective, as I assumed that would be the case (although I suppose it remains unconfirmed since Johnny has not replied). As you said, it is semantics and from my experience it usually takes a true physics geek to argue force vs. inertia, etc., when everyone usually understands the point being made regardless of the "correctness" of the physics terms.

[Hotfoot]

So, I'm over at the GL1800Riders forum, and one guy says that traction is the same at all lean angles because at any lean angle, the centrifical force pushing out is balanced by gravity pushing in. Not to say you can't run off the edge of the tire, overwhelm the traction with throttle or brakes, or drag something solid and fall down, but that the traction demands at 20-degrees and 40-degrees of lean are the same. Can this be true? If true, keeping it in mind would be a comforting mindtrick when riding.

 

Here is a link on this topic:

 

http://www.msgroup.org/Tip.aspx?Num=217

 

Eek. I assume your common sense has already told you that this article is misleading, and probably won't help you with your riding. Something that is really important to know about lean angle, is that the more the bike is leaned over, the harder it is for your suspension to do its job. (Refer to Sean's post, above.) So when you get leaned over really far, it isn't so much the grip capability of the tire you are concerned about (assuming you aren't riding off the edge of the tire's intended traction surface), as the ability of the suspension to keep that tire solidly in contact with the pavement. Which I guess is why the author says "so long as you keep your tires on the ground, you cannot fall down".

 

In horseback riding, the equivalent statement is "as long as you keep your feet in the stirrups, you can't fall off". There is a grain of truth in the statement (I suppose) but does this REALLY help you in real-life application? When the horse bucks, your feet fly out of the stirrups, and you fall off. Knowing that you should keep your feet in the stirrups is not enough to actually keep you from falling off! And telling you that "as long as your tires are in contact with the ground, you cannot fall down" is not helpful if your tires are already sliding, or if you are running so wide in a turn that you are over the center line or going off the edge of the road. Education about how to properly judge entry speed, steer the bike effectively, or use good throttle control would be much more useful!

 

I think what the guy is trying to address in the article is fear of lean angle. Some riders feel a little panicky when leaning over a lot, because at some point your brain tells you that you are falling. I think the author is trying to say that the bike will automatically balance itself in a turn, and (unless you are going REALLY slow) will not just tip over and fall into the inside of the turn.

[johnnyrod]

Hi Brad, yep as Sean says, it's a bit like saying gravity pushes your feet upwards, it doesn't, that happens because it's trying to pull you downwards.

 

I think Hotfoot's right, it could well be trying to say "don't fear the lean angle" but the way it's worded is somewhat over the top and makes rather grand claims, plus the odd bit of pure rubbish. I think my main beef is that there is an assumption that cornering force (centripetal) and gravity (falling in when leaned over) will always be in balance, an that just isn't true. If you hang a weight on a bit of string, the tensions in the string (force upwards) balances the weight (force downwards) and unless you swing it around, will always be - because they're linked, one is the product of the other. When you're going around a bend, leaning makes the centripetal force, but the radius and speed of the turn you're trying to make determine the amount of force you need. As we all know, it's quite possible to require more cornering force than you're generating and then you slide off.