Lean Angles

1. ## Lean Angles

Here's a somewhat technical explanation of lean angles. Some of you may have already read this, but for those who haven't here it is. This is an exerpt taken from http://members.shaw.ca/bjs1/personal_tips.htm. There are more tips and techniques available at the website.

Will a little 250 lean as much as a heavy Goldwing in the corners? Does "leaning off" help traction? For that matter, why do we care about lean angles anyway?

That's what a riding buddy just asked me. Apparently he was having an armchair debate with some other riders and they couldn't agree. It's an interesting question without an obvious answer (unless you stayed awake during physics class) so here's my summary.

Very simply, all bikes will lean the same amount for a given corner and speed._ This is because the lean angle results from the balancing of two forces acting on the bike/rider's effective Center of Gravity (CG). One force acts downward due to the gravitational field, the other acts laterally due to inertial (centripetal) force. Because BOTH force equations are linear with mass, the mass effects cancel leaving no effect on lean angles.

More interesting is how lean angle depends on speed (Velocity, V) or corner sharpness. It turns out centripetal force increases with the square of V and inversely with the cornering radius (R). This means doubling your corner speed will require more lean angle than merely navigating a corner that is twice as sharp.

And perhaps most interesting, "Why does anyone care about lean angle?" Simply stated, too much lean angle and our tires will skid causing us to go "SPLAT!"._ But it's not really anything to do with lean angle._ Lean angle just happens to be a good barometer indicating the amount of lateral force being applied. How much lateral force is too much? Well, quality street tires can handle about 1.1g of force before breaking loose._ And a 45 degree lean angle is always 1g. _ So a 45 degree lean angle indicates you are right on the edge of traction. Regardless of speed, bike, corner or rider !!

Remember also that cornering force is highly dependant on speed. So if you are riding a race replica and trying to "get your knee down", then it is important to understand that if you are achieving 45 degrees at, say, 110 km/h then at 116 km/h you'll crash (1.1g). Also wiggling your handlebars or throttle at 110 km/h can crash you too...all it takes is another 10% of traction consumed and you're down. This is why world class racers put such a premium on smoothness.

For a sense of the difference between various bike types, quoted lean angles indicate that a good cruiser is in the middle 30's, good sportbikes in the high 40's and radical racers in the mid 50's. However manufacturers don't specify their test methods and the effective lean angle of the bike is probably a lot less than these figures (due to static versus dynamic loads, tire width, CG location etc).

If someone is "leaning off" then the effective lean angle is harder to see._ One has to guess at the location of the CG in order to visualize the effective lean angle._ A "leaned off" bike will appear to be at a lower lean angle than is really the case.

As an aside if you are "leaning off" thinking it is helping traction, you are mistaken. Lateral cornering forces are unchanged being based on mass, speed and corner radius._ If you had an CG at 45 degrees and then "leaned off" far enough to make the bike upright you'd still have an effective lean angle of 45 degrees and be near the limit of traction (1g).

Even non-racers make this mistake. You'll see it when riding in the rain. The rider will be contorting his/her body to keep the bike as upright as possible thinking that helps traction...but it doesn't...the forces are the same. All you can do to help is slow down (and that makes a dramatic difference because of the V^2 relationship).

Lean angles ARE important. But only as indicators of lateral forces. Given typical tire friction limits, 45 degrees is a handy number to know.

2.

3. leaning to much causes tires to skid huh?

4. For clarification, 1.1g refers to 1.1 x the acceleration of gravity (9.8 m/s2)

ie.) 1.1 x 9.8 meters per second squared or 10.78 meters per second squared.

5. Originally posted by factory_pilot
leaning to much causes tires to skid huh?
Definitely if the tire is a type tha doesn't provide a proper contact patch when leaned over, or if there are still coated areas (chicken strips) toward the edges that haven't been worn in yet.

6. i dunno about that, can anyone back it up somehow? I lowsided on tradex, when it had just started to rain lightly. I was down very low into the sweeper and the bike just layed down under constant throttle (no speed increase/decrease) and im fairly certain there were no steering input changes doing so.
at the end of the day it was a sheet of water over the track. i was hanging like a monkey, lowered my center of gravity as much as possible beside the bike, stood it up. and was for certain taking the sweeper much faster.

i cant see myself being the single exception to what is being said, so what is going on?

and then there are the real racers you see on tv, who are dragging knee toe and elbow . there are people who routinly drag bike parts, pegs etc.

reg pridmore on his vfr800 on laguna will drag pegs with a passanger on the back (and one of this boards member was a passnger while he did so)

maybe im missing something?

7. Are you missing years of professional experience, very spensive race slicks and a pro-tuned suspension? hehe

8. i ment maybe im missing part of the story. about leaning off.
why was i able to go faster and harder under worse circumstances by leaning off like a mother. if it doesnt help your traction.
Wont your bike have more of a contact patch the more upright it is? contact patch = grip. Your tires are not a half spheracle profile

many race tires have a very exagerated side profile , does this not also change the 45 degree factor? more lean = potentially more contact patch in that situation?

i just want to understand it all :P

9. ## Re: Lean Angles

Originally posted by Brumos
Here's a somewhat technical explanation of lean angles. Some of you may have already read this, but for those who haven't here it is. This is an exerpt taken from http://members.shaw.ca/bjs1/personal_tips.htm. There are more tips and techniques available at the website.
Hmm... you can't believe everything you read.

Or can you?
I agree Jayson, personally this makes more sense to me.

10. yeah, usually at low lean angles, a tire will 'let go' slide across the surface, and then at some point 'hook up' again.

the word skid sounds to me like, brakes & tires locked, tires sliding across the surface,

anyone else?

11. Originally posted by factory_pilot
yeah, usually at low lean angles, a tire will 'let go' slide across the surface, and then at some point 'hook up' again.
You mean high lean angles. A low angle would be 15 degrees where as a high angle would be 45 degrees.

12. if your bike is at 15 degrees to the ground, you are dragging through your frame and engine, let along the knee and leg that was sticking out

13. The higher the speed, the lower the lean angle needed to succesfully complete the turn. The lower the lean angle, the higher the lateral force (the force acting to pull the bike out from under you) acting on the bike and rider. The greater the force, the more likely the chance of losing traction.

If travelling at the same given speed while keeping the bike upright will cause the bike to travel in a straighter path thereby causing the bike to overshoot the turn. It's similar to applying the front brake while leaned over... causing the bike to stand up and travel straight.

14. Originally posted by Jayson
if your bike is at 15 degrees to the ground, you are dragging through your frame and engine, let along the knee and leg that was sticking out
Yes, you are absolutely correct. I misunderstood factory pilot.

15. Originally posted by Brumos

If travelling at the same given speed while keeping the bike upright will cause the bike to travel in a straighter path thereby causing the bike to overshoot the turn. It's similar to applying the front brake while leaned over... causing the bike to stand up and travel straight.
take 2 bikes same corner same speed
(these are imaginary angles but display a point)
one rider sits on the seat and take a 45 degree angle, completing the turn

the other rider heangs of the side of the bike and pushes his body down. said rider stands the bike up to a 80 degree angle and takes the same line as the first rider

did the line change with lean angle?

lets assume you are taking a corner now using 70% of the bikes grip, you apply the front brakes enough to stay withing the given traction for your tires, slowing you down considerably without causingyou to tuck the front end. when you apply the front brake, and slow down, can you not work with the effects and lean your bike more into the turn as you slow, keeping you balanced, and on line?

have you ever trail braked into a decreasing radius turn?

enter faster than you exit. as it tightens up you slow down drop the bike in and lean over...

because you are on the brake does not meen you have to shoot wide, is the point im getting at, because you change lean angle does not meen the bike will shoot wide either.

you balance the forces.

no?

16. Originally posted by Brumos
You mean high lean angles. A low angle would be 15 degrees where as a high angle would be 45 degrees.

High lean angles is correct. Because lean angle is relative to perfectly vertical, which is 0 deg lean angle.

You don't usually start measuring lean angle from horizontal (i.e. 0 deg lean angle would mean lying flat on the ground).

Manufacturers will typically speaking of increasing the available lean angle, meaning higher # = more lean available.

http://www.mcnews.com.au/NewBikeCata...2003_Page1.htm

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