Thursday, February 08, 2007

Rear wheel skids: Revisited

Last night I found myself riding in a deluge. The rain's held off for a long time. Being confined has only intensified its energy. The chance to pour upon the earth finally came. Rainfall was gleefully making up for lost time. Why is it that the idiots always pick the most adverse conditions to come out in?

Somewhere there's a driving school with a twisted curricula. Some misguided instructor is diligently preaching the gospel of "uni-directional scanning". In other words, if you're going to turn left then only look left. Any vehicles approaching from your right? Forgetta 'bout 'em!

I had the distinct misfortune to be on this driver's right as they made their left turn and pulled out in front of me. Having gone to a different driving school, my scanning was a little more effective. Another close call, but nothing serious. No harm, no foul, as I'm fond of saying.

As I passed the driver and played speed boat, I was blessing the fact that I teach riding classes so often. The constant exposure keeps me thinking about proper techniques. In this incident I had naturally accounted for the dicey traction in the equation. Believe it or not, the rear brake is relatively more effective in the rain than when it's dry. With reduced traction on the front wheel not as much weight transfer happens. This means that more weight stays on the rear wheel longer. Weight means traction. With decent tires a good rider can take advantage of the situation. Still, it would be really easy to skid the rear wheel on a wet and sloppy road.

For years and years the MSF has preached the gospel of keeping the rear wheel locked once it starts to skid. If the rider does need to let go they should make sure the front and rear wheels are aligned. We've taught the same thing here in Oregon forever. The justification is that this technique will help prevent high-siding. Since most of our students are brand new riders we've just left it at that. Even most of the so-called "experienced" riders really don't have many miles. With between 500 and 3,000 miles as a yearly average, not much deep skill learning takes place. Skill-wise, they're really still beginners. By the time the rust from long Winter lay-offs is cleaned out, there's not much riding time left. So the motorcycle safety community has taught the simple strategy of keeping the rear wheel locked if it skids. It's always felt to me like we're not really presenting the true picture.

Like me, some of you have raced or ridden on tracks. There's also been some spirited high speed cornering in other places, hasn't there? What's your experience been if you've gotten on the brakes a little too hard setting up for a corner? I suspect you've released as soon as you noticed the skid and then re-applied. That's the way it happens in the real world of experienced riders. On the other side of the coin, there's mounting evidence that riders are trying to do what they're taught and crashing anyway.

A rider who keeps the rear wheel locked may or may not end up high-siding. A rider who keeps the rear wheel locked may or may not stop in time to avoid an obstacle. A sliding rear tire adds to the stopping distance. Keeping the rear wheel locked also negates any ability to make a directional change. If the back of the bike's sliding there's absolutely no directional control available. The bike's going to keep on in whatever path it was headed for when the slide began. I also know a former instructor who found himself in a skid when a car abruptly stopped in front of him. Faithfully holding the brake pedal down, the bike started to low-side. Being a big guy, when his weight started coming off the bike the center of gravity changed. The rear tire hooked up and he high-sided anyway! He's not alone.

Being professional trainers means we need to stop and re-evaluate things once in a while. Our obligation is to serve the riders we touch in the best way possible. Real world experience shows that we need to adjust our teaching on how to handle rear wheel skids. So we're doing it. This change is only being made to our program in Oregon as far as I know. The MSF may eventually arrive here but our concern is for Oregon's riders. I'm passing it along here for what ever benefit you may derive from it.


The fact of the matter is that if a rider's bike gets into the position shown on the far right, they're pretty much screwed, to put it bluntly. So the goal is to avoid having the bike step out in the first place. The way to do this is to immediately release the brakes as soon as a skid is recognized. Then re-apply. Remember, it's firm progressive pressure on the front brake and light to lighter on the rear. Always be smooth. It's hard to do when the heart's racing and the adrenaline's pumping. Don't leave it to chance and hope it happens correctly when needed.

You knew I was coming back to this, didn't you? Practice, practice, practice, ahead of time. Practice quick stops and don't lock either brake. You're probably not going to get it right first time, every time. That's ok. There's a blessing underneath what you might consider a mistake. You might accidently lock a wheel during the practice. If you suspect you've messed up the front brake application let go RIGHT NOW!! A rear wheel skid may be harder to detect on some bikes. Pay attention to what the bike is telling you. It will give you a chance to learn to recognize what a skid feels like on your bike. What you learn will serve you well when it happens in a real situation. When it does, release quickly and apply the brakes again. Be smooth, rider, be smooth.

When we suddenly encounter something that makes us want to pucker we're going to fall back on habits. Practice until our habits work for us, not against us. Keep your skills sharp for the unexpected!

This strategy allows us a chance to make the most of our braking. It's going to give us a better chance of stopping short of the obstacle. Releasing and re-applying will extend the time we're actually able to brake as opposed to sliding the rear wheel. We're also going to have a better chance of maneuvering around something since both tires are rotating.

Miles and smiles,

Dan

8 comments:

Tinker said...

People need to be aware how rain affects brakes, especially as it can effect them differently. The front brakes are commonly disks, nowadays, though I did have one that had dual drums. Anyway disks usually are wet in rain, and actually can have a thin film of water on them. This is GOOD, since it reduces efectiveness and you are likely to have reduced traction. It's bad because there is a moments delay and then rather suddenly the rakes regain there normal effectiveness.

The rear brakes are more variable, in that older bikes very rarely have rear disks, while bikes with sporting natures/pretensions and higher prices have another disk. But in rain, a drum is usually just as effective as always, and right from the start it works.

I remember about 30 years ago a motrorcycle write described the government method for testing brakes. The let them sit in tubs of water, thus ensuring that water seaped into the drums, where normally in actual operatio they were dry, and forthe front brake the first applied the disk brakes briefly, and THEN took a stopping distance measurement. He concluded that the government was wet testing normally dry brakes and dry testing normally wet brakes.

Anyway, unless you know when you will want your brakes at maximum effectiveness, you will not be able to follow the government practice.

Be aware, and be careful.

gary said...

Great piece, Dan. It pretty much confirmed most of what I think I know about braking. I have only one question: Is it wise to tell folks that they are pretty much screwed if they get into situation #3?

I've been in that situation many a time, and rarely has it resulted in a crash. A lot of the time, it is how I set up my entry into a tight corner, and it's the "sweet spot" in the torque curve on the way out.

I realize that, as a safety instructor, you can't really teach this stuff with a clear conscience. It requires many hours on the racetrack to learn properly.

But please don't tell folks they are always screwed in that situation, or they might believe you. That's usually when you hear the phrase "...then I had to lay `er down.".

Just my two-cents.

Ride well,
=gc=

balisada said...

Braking is serious business, and I have pondered the topic that you have talked about.

I should get out and practice this weekend!

Balisada

Combatscoot said...

I always did feel like keeping the brakes on in a skid was screwy.
John

irondad said...

tinker,
I am really grateful for vented disc rotors on the front of bikes. My old 900 Honda has solid disc rotors. Exactly what you described happens. In the rain I apply the brakes. For a while there's very little braking until the rotors dry. All of a sudden there's too much! Vented rotors cut down on that a lot.

Pays to get to know your bike well, huh?

balisada,
I know you took our course and were taught to hold the skid. Disconnect that and remember to let go as soon as you notice it. Then re-apply. Your approach is great. Practice quick stops without sliding either wheel.

combatscoot,
It was ( and still is ) the prevailing wisdom among rider education folks. I guess the thought is that it will serve the most riders. I still shudder when I think back to the MSF course we used to teach.

We had an exercise where we encouraged the students to skid the rear wheel on purpose and then taught them how to control the skid. It always felt wrong to teach a new riding student how to skid.

gary,
See the next post, bro'!

Dan

Steve Williams said...

I can confirm that in Pennsylvania the MSF instructors preach the keep it locked rear wheel approach for both the beginning and experienced rider course.

The Vespa stops well and aside from snow I have never locked either wheel intentionally or not intentionally. I have worried about what would happen if I did lock a rear wheel up. I am glad to be reading your post in this area and it pretty much matches what I think I would do and does match what I do in a car when the wheels lock---release and reapply to get control back.

I used to practice quick stops a lot on my LX150 but have not done it at all on the new GTS. Time to hit a big parking lot and practice!

Thanks Dan.

Bryce said...

I have often had a rear wheel skid,
mostly when traveling a mite too fast
for conditions.
I ride a 26 year old Goldwing (only thing big enough to take my size and weight).
Your description of braking, sliding, then releasing the brakes is similar
to ABS brakes on automobiles when the
brake pedal is pushed from inside the vehicle and held in place. On, off on
off in rapid succession.

irondad said...

bryce,
It is sort of like ABS. Although I would hope that after a couple of tries I would finally get the braking right and be able to stay on it and get stopped!

Dan