Physics of Cornering...and Recovering

[Motorcycle Mayor]

I'm interested in learning more about the physics behind cornering. This was sparked by a potentially fatal corner I took on CA-49 coming down (eastbound) out of Yuba Pass the other day.

Here's the setup. That stretch of 49 has beautiful, sweeping curves, a joy to ride. But -- as happens occasionally -- I entered this one particular curve wrong (nothing out of the ordinary about the curve as far as I recall, no decreasing radius or anything like that). I immediately knew I'd set up wrong, and knew I was going to go wide. Clearly, I entered the curve too fast for the degree of lean I'd taken (as is nicely explained by another forum member here).

Which wouldn't have been a problem...except an oncoming car appeared.

I don't remember exactly what I did to recover. The entire event was over in a few seconds. It reminded me of a comment made by a pilot friend of mine "Flying: boredom, punctuated by occasional moments of sheer terror" .

What I do remember, very clearly, was that it was quite a struggle to warp my curve back into my lane. I suspect I instinctively hit the brakes...which I'm positive is exactly the wrong thing to do. Too bad humans haven't evolved yet to instinctively know how to ride .

My more experienced riding buddies (I've been riding for 9.5 years) tell me what I should've done is lean harder into the turn. One of them also said I should've, after doing so, accelerated. That's consistent with "slow to enter, speed up to exit"...but it's counterintuitive when you think you're about to hit something at 60+ MPH relative.

Besides seeking additional advice here -- and getting feedback on whether what my riding buddies suggested is correct -- I'd like to understand the physics involved (introductory mathematical physics was a favorite college class of mine, many, many moons ago).

Is this just a real-world example of V^2 / R? Where if you want R -- the cornering radius -- to be smaller, you have to increase your speed (V)? Obviously limited by eventually breaking the contact patch -- gotta maintain friction! -- and going into a slide? Or is something else going on?

Thanx in advance for feedback, links, etc.

 

[RiderJoe]

Hi Mayor!

There are many videos that demonstrate cornering techniques. I like MotoJitsu’s videos on tis topic, as they make sense to me:

 

[Rocnsanman]

I met Greg( Moto.Jitsu) while attending a Torrence Police sponsored safe riding event this past February in Torrence, CA. The guy is amazing what he can do on a bike! Track stands, slight throttle and turn 180 degrees making a U turn all in a single motion. He says it's all about physics and I believe him, so do the motor officers. I've been practicing his cornering techniques and I have to say that my riding has improved tremendously.
Sometimes you have to slow down to speed up.

 

[Bionicpork]

The best advice I've heard, and in turn offer, to people asking about handling hot corners is to practice the skills before you need them. I think the struggle most people have when entering a corner hot accidentally and trying to adjust is that they aren't familiar with how their particular ride feels in those situations. This seems to be similar to what RiderJoe's linked videos say too: braking is fine, throttle off is fine, but because you're in a panic mode you're likely to upset the bike which will make you panic more.

I don't recommend intentionally entering corners too hot to practice (unless you have a practice course to use), but it is a good idea to practice increasing and decreasing your corners while still at a safe speed, and try using your brakes in a corner to see what it feels like. Practice adjusting your throttle while in the corner so you get a feel for how the inputs change the corner and stability.

The one that tends to catch new riders out is a downhill decreasing radius. They receive the advice during beginner courses to "never use the brakes in a corner, throttle-on" but when you're rolling down hill you can't really throttle-on without dangerously increasing your speed.

As far as the physics of it go, my completely unprofessional understanding is that it's mostly about the weight distribution and constant contact with the pavement to ensure maximum turning capability. Keeping your suspension working properly by being smooth on your inputs and keeping some weight on the rear tire is going to enable you to tighten the turn. Chopping at the controls will upset the weight distribution and reduce the tire contact. If you want to run an experiment grab a plastic cup and roll it across your floor (and put a rod through it if you want to "power" it. The way it curves in a circle is the way the rear tire is turning your motorcycle. You can try changing rotational speed, moving speed, and surface type.

 

[Bionicpork]

For practice I like to find an empty multi-lane road and switch lanes in the curve to practice tightening and widening mid corner.

 

[Archer]

For practice I shift off ass and onto balls of feet. And lean more.

 

[art miller]

Thanks Joe Rider for sharing the videos. What is demonstrated most of us already know but it is a very good refresher to keep one's skills tuned.

 

[SkooterG]

I can't recommend highly enough the Lee Parks Total Control clinic. A one day riding school done in a parking lot. It changed my life back in 2007 or so. After riding for many years, my skills finally quickly improved greatly after taking his class.

 

[waynevb]

You shouldn't expect that leaning is the way to take a corner. Learn about counter steering, test it out and you will understand that counter steering causes the bike to lean. The race boys pull so hard on their bars to get around corners.

I had been riding for 50+ years and didn't know about counter steering. There was a doctor in the Bay Area, Doc Wong ran bike clinics and he taught that skill. Once mastered, it was a revelation.

It also applies to bicycles and works on my Segway Ninebot electric scooter.

 

[RiderJoe]

I can't recommend highly enough the Lee Parks Total Control clinic. A one day riding school done in a parking lot. It changed my life back in 2007 or so. After riding for many years, my skills finally quickly improved greatly after taking his class.

Same here. I took a class from Lee Parks (in 2004?), and that course gave me a lot more confidence. Highly recommend it.

 

[vzhq16]

There's no one right answer that covers every situation. I think the most important thing to keep in mind is not to panic. If you're over cooking a curve, remain calm, get you weight further into the turn and don't make any drastic changes to the throttle application or brakes. A bike generally likes to be under power in a turn. But if you're already too fast, does it make sense to apply more power? No. Remember that you have those two contact patches giving you 100% of the traction they have to offer. It's up to you how that traction gets used. If you're over cooking a curve, you want as much of that available traction to get used getting you around that curve. If you start applying brakes or throttle, some of the available traction is then going to be used for braking or accelerating. That's not what you want! You want to turn. Remain calm, no drastic changes to throttle application or braking, get your weight to the inside and steer the bike around the curve.

As much as there's a whole lot of physics going on to explain what makes a bike move the way it does, the more important aspect of the journey is that you're in control and thinking your way to a safe and successful journey.

 

[RossKean]

You shouldn't expect that leaning is the way to take a corner. Learn about counter steering, test it out and you will understand that counter steering causes the bike to lean. The race boys pull so hard on their bars to get around corners.

I had been riding for 50+ years and didn't know about counter steering. There was a doctor in the Bay Area, Doc Wong ran bike clinics and he taught that skill. Once mastered, it was a revelation.

It also applies to bicycles and works on my Segway Ninebot electric scooter.

Whether you are aware of it or not, you always counter-steer if you are riding at more than 10 mph or so. Push left - go left is the way it works. This induces the lean and allows the bike to turn. KNOWING about counter-steer allows you to think about what you are doing and how your actions affect the bike's trajectory so you can consciously push harder to get you through an extreme turn. Reduce speed before entry and power out.

 

[Coachpilot]

And... panic = a tighter grip on the bars and bracing with your shoulders. This prevents the bike from both leaning and turning. Once turn is initiated (counter steer) more lean angle is needed, rider MUST relax grip... just ask Marc Marquez and Pecco. They grip with their legs and the arms are relaxed but functionally deliberate to guide the bike.

 

[RossKean]

And... panic = a tighter grip on the bars and bracing with your shoulders.

Somewhat related to panic - look where you want to go, not at what you want to avoid. Target fixation is real.

 

[MotoMike]

"Is this just a real-world example of V^2 / R? Where if you want R -- the cornering radius -- to be smaller, you have to increase your speed (V)?"

Nope. Turn radius = MPH. The faster your speed, the larger your turn radius. Watch the video below, produced by the Yamaha Champions Riding school for an excellent explanation.

 

[GoldFJR]

RossKings right. I came into a corner, not really focusing, and did exactly what you did. I immediately looked up the road and focused on the outside lanes white line. Got me out of there quickly, but I’m still not sure how I made it .
Focus, focus, focus!
I’ll leave out the technical stuff for someone else.

 

[dafish]

My key thoughts for recreational sport riding:

1) Come in soft so you can come out harder.
2) Don't play hard unless you can see around the curve.
3) Look where you need to go, not where you're headed.
4) Push the bike down from the bar on the inside curve side. This is sorta like mountain sledding and slalom skiing, and it’s indeed counter steer, but it's a good memory mnemonic.
5) Always wear brown pants when you ride.

 

[Bionicpork]

5) Always wear brown pants when you ride.

Others may call them adult diapers, but I call them Padded Underwear

 

[HilltownDave]

Others may call them adult diapers, but I call them Padded Underwear

And to think I’ve been devoting all this energy into having the debate about what aftermarket seat is best when all I really need is Depends.
Two birds with one stone!