Thursday, July 29, 2010

How to negotiate downhill curves.

Most of us love cornering on a motorcycle. Of course, we also prefer the curves to be on a fairly level road, gently banked in the right direction, and provide a clear line of sight all the way through. It's when any of those factors change that riders tend to start having more issues. In this post I want to concentrate on corners with elevation changes. In particular, when riding these curves downhill.



Given a choice I personally prefer to ride uphill on twisty roads rather than downhill. That's because physics does a lot of the work for me. When riding downhill I have to do that work myself. On the other hand, there are some roads I know where the curves with elevation drops are wickedly fun! Fun factor aside, we don't often have a choice. Roads turn right and roads turn left. Roads go uphill and roads go downhill. We need to know how to correctly deal with all of it.

Successfully negotiating downhill curves requires a more deliberate application of proper cornering techniques. In particular, setting a proper entry speed. Remember, a proper entry speed is one that allows the rider to roll on the throttle before leaning the bike and to maintain at least steady throttle application all the way through the corner. On the flip side, if a rider feels the need to roll off at any point in the turn, the entry speed was too fast.

I can't stress enough the importance of a proper visual lead for setting the proper entry speeds! It's what we see, or can't see, that sets up everything else.

It's the entry speed and throttle application that makes downhill cornering more difficult. Specifically, it's the fact that gravity is always working to make us go faster through the corner. Gravity is what makes going uphill so much easier. In this direction the pull is now on the back of the bike. Instead of working against us, gravity is now our friend. Have you ever found yourself able to use just the throttle for speed control on uphill corners? Hold onto that thought for a minute.

When entering a downhill turn the same requirements still apply. Slow enough before the corner to be able to maintain steady throttle. This is usually going to mean more slowing and less throttle. Notice that I used the word "slow" and not "brake". That's because braking is one way of slowing, but not the only way. The other method is engine compression.

Before we put all the pieces together it would be good to look at throttle application through a corner. Rolling on the throttle does more than accelerate us out of a curve. Judging by what I see, most riders think that's the only reason for using the throttle. This is evidenced by the fact that the majority of riders I see in our training classes want to brake late, coast into the corner, and don't roll on until the apex or later. There's so much more to it than that. Missing these other elements is a big factor in rider crashes.

Remember that rolling on the throttle lifts the bike. The reason for doing this before actually leaning the bike is to make maximum ground clearance available throughout the entire turn. Another advantage is that the bike's suspension is stable. All the bike is being asked to do is turn, not compensate between braking and throttle inputs while leaned over. Additionally, lifting the bike extends the suspension so that it can absorb mid-corner bumps. If the suspension is compressed these bumps will be more likely to throw the bike off the cornering line. Not a great thing.

In downhill turns, it also becomes very important to avoid unduly loading the front tire. We're already asking the tire to stick to the road during whatever degree of leaning we need to employ. Extra loading on the tire makes for a much smaller margin of error.

So how do we accomplish all this while still controlling speed in a downhill turn? Time to put all the pieces together.



Keep gravity in mind when setting the corner entry speed. This means braking sooner and/or more than when on level ground. Slow to a speed that allows the bike to gain a bit of momentum without putting us above the comfort threshold. Both ours and the bike's. Remember that the velocity gained due to gravity is going to be somewhat uncontrolled. Depending on the slope the entry speed will need to be greatly reduced. Always use both brakes. Apply the brakes and get off of them.

You will likely hear or read about using the rear brake in a corner to help control speed. Don't do it. Proper technique means not braking in a corner. Riding the rear brake opens the door to another kind of hazard.

When the bike is leaned over, a lot of the available traction is being used by the lean. This is true for both tires. Riding the rear brake requires traction. There is a finite amount of traction available at any given time. That traction needs to be split between side force, braking force, driving force and traction reserve. Using traction in one place takes away from the traction available for the other needs.

The particular hazard when trailing rear brake while leaned over is that any sliding of the tire will happen in a sideways direction. Usually towards the outside of the turn. Which means the chances of a low-side crash are increased. Here's another thing to be aware of. When the rear tire is near the limits of traction any side to side movement of the rider can be enough to push the tire over the edge, so to speak. Best not go there.

Be prudent when applying the throttle. Remember that the throttle only has to come back up to "steady", not "increasing" for the requirements to be met. Less throttle means less speed gained in the corner.

Ok, I know this sounds like a lot of work. Heavy braking, gain speed, brake heavily to set up for the next curve. Hey, you do what you need to do. Or else. One might wonder, though, if there is a better way. Now that you've asked, let me offer some food for thought that might help smooth things out.



Remember me writing previously about using the throttle as a rheostat? In other words, like a dimmer switch on a light. Bluekat will recognize the last couple of photos. I went out and rode some corners on a road she rides reqularly. I also rode some others, like in the first photo. Notice there is a huge downhill slope in the first photo. By the way, I see on her blog that she is now riding Parish Gap. Great road. In case you hadn't noticed, yet, Kari, all the blind corners go the same direction depending on which direction you ride. From Turner southbound, they all go right. You still need to be aware of limited sight distance, but it's nice to know which way the road goes!

Anyway, another key is to gear down. In the corners above I found third gear to be effective. Using engine compression to both slow for a corner and control speed during the turn makes things very smooth. I find that I have to use the actual brakes much less. The engine might make a bit more noise than you're used to. Don't worry. Here's a little secret. Bike motors like it!

As a side note, if a rider is worried about going wide on a downhill corner use a late apex. Nobody says you have to apex in the middle of a turn. If you can't see the exit of the turn, stay wide until you can see it. This means a late apex. Even if you can see the exit early, a late apex will tuck the bike back into the lane. Early apex equals a wide path of travel. A late apex tucks you back in.

Here's to many fun and safe corners in your future!

Miles and smiles,

Dan


22 comments:

Steven said...

Dan, a rider made a comment in a forum a few weeks back that made me think - she said that engine-braking is only using the rear brake, something we normally try not to do (and sometimes deride "those" riders for). Perhaps you can comment on this, especially in regard to slowing in corners.

thanks for the continued education,
Steven

Stacy said...

Dan, this is a fantastic article. I especially like the section regarding trail braking (and why it's not a good idea on the street). I've heard it's not a good idea, but yours is the best explanation I've encountered.

BTW, are you teaching the August 23rd ART?

Trobairitz said...

Dan - thank you for the most excellent and informative post. Downhill corners are the one thing I dread on the bike while learning (heck I don't like them on my bicycle).

Your explanation is helpful and I shall endeavor to put it to good use.

-Brandy

bobskoot said...

Irondad:

Curves scare me too

bob
Wet Coast Scootin

Troubadour said...

I thank you sir.

bluekat said...

(((Irondad)))
You did my downhill curves - Thank you! :)

I read your comment from the other post, and tried 3rd gear today. I'd been using 4th. 3rd is better. I didn't have to let up on the throttle, and the bike feels better. I do use engine braking (I have 1 thing right), and being in a lower gear helped that as well. Obviously, I need to start slowing sooner. I don't leave myself enough time to get all this stuff done before the corner.

Uphills - Yep, easier :)

I've picked up on the bike liking higher revs. You've done a better job of explaining it, but she handles better, feels calmer but more responsive.

So, am I ready for an ART class yet?

Ha, I hadn't noticed that about Parish Gap, but you're right they do all go the same way.

Sorry for the long comment,
But thanks much for the write up!! Great stuff to go out and practice.

Nikos said...

Dear Irondad

Nice advice and useful for me as I'm going to touring Greek mountain roads in September!

One point that I'm surprised you did not mention was where you should be looking - i.e. where you look is where you go.

Bests wishes, Nikos in England

irondad said...

Steven,

Firstly, thank you for reading and commenting.

Your question is a good one. I can totally see where you are coming from. The rider's comment is accurate. So, you're wondering, if using engine braking is actually rear wheel braking, why did I write about using compression to control speed in a corner?


Think about it as two different phases and uses of the engine.

Phase I is setting an entry speed. This means scrubbing off speed from our approach speed to a much slower corner entry speed. Here we are actively rolling off the throttle which applies braking force to the rear wheel. However, since we are doing this before the corner, the bike is straight up and down. Most of the traction is available for braking inputs since there is not yet any lean angle to worry about.

Depending on our needs, we can use engine braking by itself or in combination with applying both wheel brakes to slow for a corner.

Phase 2 is a different use of engine compression. While the bike is still straight up and down, we are bringing the throttle back to steady and holding it there through the curve until it is time to roll on near the exit. So we are not at any time actively rolling off and putting extra braking force on the rear wheel.

What we're doing is helping to prevent a speed buildup rather than scrubbing speed off by compression. The reason we shift on a bike is because we are going faster. Not to actually go faster. It's a matter of matching engine speed to actual road speed.

So we are in a corner, holding the bike in a lower gear and holding the throttle steady ( not rolling on, not rolling off )

While there is a small amount of braking force being applied to the rear wheel, most of the force is internal to the bike. The motor and transmission gears are taking the brunt of the force. The speed control is accomplished by a resistance to turning by rotating parts as opposed to a resistance to forward motion.

Picture a guy holding the reins behind two fast moving horses. He can control the horses' speed by digging in his heels. That's what's going on when we are scrubbing off speed by engine braking as we set up for the corner.

Now picture the guy using the reins connected to the bits in the horses' mouths. Instead of the horses moving quickly and him providing drag, he's preventing the horses from moving quickly in the first place. Much less pressure on his heels. That's what we're doing with the bike in the corner itself.

Great question! Hope this helps.

Take care,

Dan

irondad said...

Stacy,

I'm honored by your comment. Especially by the fact that you put a reference to this post on your site. When I provide something helpful to a rider like you who is intelligent and takes riding seriously I feel good about it.

Yes, I'm teaching. Track only, not classroom. I will be there all day, though.

Take care,

Dan

irondad said...

Trobairitz,

My pleasure and thank you for the positive feedback. It's amazing how many riders struggle with the same thing. Only a few are secure enough to say so. Have fun practicing!

Bobskoot,

Photoshop curves scare me. I can handle pavement curves ok. I have used that LED rechargeable light. What an awesome present! Thank you so much.

Troubadour,

You are welcome.

Take care,

Dan

irondad said...

Bluekat,

I consider you a friend. I made a promise. Promise kept. Besides, the "research" was so fun!

I'm glad to see you trying the lower gear. The goal is to use a gear that allows you big control with small wrist movements.

Your comment about having to allow more time to get it all done is very astute. I salute you.

Comment all you want. I have plenty of space left!

Take care,

Dan

irondad said...

Nikos,

I sort of covered that by talking about visual lead. Didn't want to dilute the content of the post.

However, you make an awesome point. Head turns for directional control should never be left out of the equation. Thank you for adding that fact back in!

Hope you enjoy your ride. May all your surprises be pleasant ones.

Take care,


Dan

Richard Machida said...

Downhill curves almost always make me anxious, for some reason left turns more than right. We have quite a few roads where there are steep dropoffs, no shoulders, and plenty of gravel. Thank you for the excellent post as it addresses issues I'm working on. Or at least starting to work on again.

It was great to finally meet you a few weeks back. I am finally back from the road trip.

Keith said...

Great post. Thank you. Most of my riding is on the flat. I need get out more and be intentional about practicing these skills so that they are there if/when I need them. Thanks again.

Lucky said...

I'm going to have to go find a curvy, downhill road and try this out. Downhill curves are not my strong suit right now...

Hooray for excuses to go "practice"!

Orin said...

Does your rider training curriculum include the Friction Circle? This is one of the major concepts Skip Barber Racing School imparts in their 3-day Racing course.

Since I can't draw it, I'll try to describe it: draw a circle, then a vertical arrow from the bottom, through the circle, pointing to the top of the page. Last, draw a horizontal line from outside the circle on the left, intersecting the vertical arrow.

The circle represents 100% traction. The top of the arrow, braking; the bottom, acceleration; the horizontal line, turning left or right.

The point is, a tire only has 100% traction to give. If that 100% is braking (i.e., the wheel is locked up), there's nothing left for steering. That's the scientific explanation of why your car slides off a curve if its wheels are locked up.

I'm not so brave (or maybe it's dumb) to ride my Vespa at a speed that would make this an issue, but it is something I keep in mind when riding on twisty roads like Chuckanut Drive...

__Orin
Scootin' Old Skool

Jack Riepe said...

Dear IronDad (Dan):

I read this three times so I wouldn't miss anything. Great post.

Fondest regards,
Jack • reep • Toad
Twisted Roads

irondad said...

Richard,

Great to meet you, too. It's been interesting to see how many folks say they have trouble with downhill curves of various kinds. Glad this helped.

Keith,

Not only for practice, but you need to find some curves to even out your tire wear!

Lucky,

Don't forget the Viking Warrior yell as you hurtle down the hill!

Take care,

Dan

irondad said...

Orin,

Your description is a good one. We call it the Friction Pie. Either way, as you so rightly point out, there is no provision for deficit spending.

Therefore, that makes traction management critical.

Hope you're settling in up there and prospering.

Take care,

Dan

irondad said...

Jack,

You honor me by reading. Hope I give you some value in return!

Take care,

Dan

Charlie6 said...

good clear writeup and reminders Irondad....in downhill curves, Mr Gravity is not your friend!

BeemerGirl said...

Thank you for breaking this down and making it so clear. I keep practicing and getting better all of the time. Just trying to remember so many things at once, on approaching...sometimes one or two drop away. As I perfect some I pick back up the others. Thanks for sticking this in my brain. I'll be working on it next weekend! -Lori