On being

[Voodoo]

There has been much written on how smoother is better – Sean’s Essay #3 is a great example of this. However the one thing that I haven’t seen mentioned yet – although Sean does touch on it briefly with his reference to a “traction credit card” – is WHY smoother is better.

 

The answer is fairly simple and obvious when you consider it, but I’m always surprised to find out how few people actually do really think about it – especially when it is what you should be thinking about ALL the time when you ride a motorcycle or drive a car.

 

Now, I claim no mastery of physics and apologize for any Newtonian lapses here, but IMHO, the answer comes down to weight management. No, not that kind of weight management! I’m talking about the kind of weight management involved in controlling how the weight of a vehicle shifts from front to back and side to side.

 

Having been an instructor for the SCCA Racing Schools on and off for about ten years now, the first thing I ask my group before they go out on the track is, “What makes a race car stop?” After fighting off the barrage of silly looks and sly remarks, I select an unsuspecting racing neophyte and allow him/her to answer, “The brakes, of course.” I continue to ask the next relevant questions about what makes a car accelerate and what makes a car turn. After politely telling all of the students that their answers are wrong, I point out that the single most important thing for anyone driving a car (or riding a motorcycle in this case) needs to remember is that the Onlycolor=red> thing that makes a vehicle stop, accelerate or turn (assuming the vehicle is still rubber-side down) is the tires. The brakes don’t stop the vehicle, the tires do. The engine doesn’t accelerate the vehicle, the tires do, and the steering wheel (or handle bars) does not turn the vehicle, that’s right, the tires do. All of these “driver aids” only exert various forces on the tires. When the tires stop working, it doesn’t matter how hard you turn the wheel, stomp on the brakes or hit the gas, you are going wherever you were going before the tires stopped working.

 

As a result, understanding how to control your tires should be JOB #1, and that comes down to weight management. Since the friction coefficient of a tire – or it’s ability to change direction against the road surface - is effected by really only two things (neglecting temperature, weather and varying road surface), the composition of the tire and the force with which it’s pushed “down” against the road surface, these are the things that effect the limits of the tire and allow it to turn, slow down and speed up. The only one of these that you can continually effect while driving/riding is the force with which the tire is pushed down. Think about this because it’s really obvious when you picture it. If you hold a basketball and try slide it across the gym floor without it rolling, it offers some resistance. If your friend sits on the ball (I know, great visual) while you try and slide across the floor, it’s much harder to push since there is a much greater force pushing down on the ball then there was previously. This is a good (and visually entertaining) example of altering the friction coefficient by exerting force, and it works exactly the same way with your tires.

 

How does this apply to a motorcycle? Simple. When a motorcycle travels along a path at a constant velocity, the weight of the vehicle remains evenly distributed and as a result, the force on the tires is consistent and their ability to grip the road remains consistent. This is a where Sean’s “traction credit card” explanation is consistent. Go past your traction limit and the tire loses traction and you’re toast.

 

When you change the dynamics of the motorcycle in any way, by braking or accelerating, you’re adding another dynamic to the credit card – you’re altering it spending limit mid-course. When you alter the force on the tires by transferring the weight of the motorcycle to either the front or back, you are changing the grip abilities (or the traction limit of the credit card) on the front and rear tires accordingly.

 

It’s in the turns that this becomes increasingly important. Any abrupt change in the weight transfer of a vehicle while cornering, dramatically changes the limits of the front and rear traction credits of the tires and therefore can be disastrous for the rider. As you accelerate, the weight of the vehicle shifts towards the rear, pushing down harder on the rear tire (raising its limit) and providing more grip on the rear tire and less weight on the front tire (decreasing its limit). Remember, since you’re in a corner, if you lower the traction limit of either tire abruptly (by either jumping on the gas, or grabbing a fistful of brakes) it becomes real easy to exceed that limit and end up on the pavement. Smooth changes in traction limits are a rider’s friend and allow you to control the bike through the corner. Smooth braking/deceleration into the corner transfers the vehicle weight smoothly (which doesn’t mean slowly) to the front tire and increases the traction limit of the front tire allowing the tire to slow the vehicle and turn in to the corner. If you jump on the brakes going into the corner, you’re asking the tire to increase its grip before you have allowed the weight transfer to increase its traction limit - an easy way to exceed your credit limit and experience a nice low-side excursion. A smooth transition back to throttle after turn-in increases the traction limit of the rear tire allowing it to accelerate the vehicle through the corner while not losing grip, and provides the added bonus of making the front end slightly lighter and easier to point through the corner. Jump on the gas abruptly, and once again, you’re are asking the rear tire to provide more grip than it has available yet – since the weight transfer takes longer than the acceleration force of the engine - and the rear breaks loose. If you then jump off the throttle out of fear, you lower the traction demands of the rear tire to the point that it grips again but now it’s pointing in a different direction than the rest of the bike since it’s already slid a bit, you’re all set to go for a nice high-side ride. Weight management keeps the tires where they should be – between you and the pavement.

 

That’s why smooth=fast (and safe). If you’re real smooth, it doesn’t seem fast. Back at the track, it was always the students that took their time, followed the proper line through the corner and worked on smooth weight management of the vehicle that were real fast at the end of the day, but they didn’t seem to think they were going real fast until we looked at the lap times. The students that just tried to drive harder and faster, without real regard for smooth weight management, always thought they were going fast but, in reality, they were always much slower or crashing.

 

Anything you can do to increase your level of “smooth”, and therefore maintain even and consistent weight management of the vehicle, such as matching revs on downshifts, looking all the way through a corner to limit mid-course corrections, etc. etc. keeps the tires happy and a happy tire makes a happy rider.

 

Ride Smooth.

 

 

[David]

David, I think this is one of the best essays in Ride Well. Thanks for some really good work, here. This is the kind of discussion I'd love to see more of in Ride Well.

[ChrisNYC]

Great post vv ... it reaffirms something that I first started thinking about when I was driving automobiles (remember those?!) I started thinking that smooth really mattered, and I found myself a disciple-of-sorts of racer Jackie Stewart, who was all about smooth. He was smooth, and subsequently fast.

 

Later when I started riding motorcycles, I brought the "smooth" part over, but I'm still (over-)concerned with "now that I'm only on TWO tires instead of four, how much traction credit do I REALLY have to play with?" I think a track day for me will be quite revealing.

 

ps... I finally did meet Jackie Stewart at a book-release-siging... my signed copy sits proudly on my shelf, even though I'll never race like that ...

 

------------------

Chris (aka Tender Vittles),

Little '77 KZ400 in the Big Apple

Black '99 RT for Everywhere Else, such as...color=green>

[Voodoo]

Slight Hi-Jackcolor=red>

 

ChrisNYC said: I finally did meet Jackie Stewart at a book-release-siging... my signed copy sits proudly on my shelf, even though I'll never race like that ...

 

Good for you...I have one of the orginal prints of his book "Faster." Way back when, I worked for an Indy Lights Team and Justin Bell (Derek Bell's son) was our driver. He is personal friends w/ Jackie and had borrowed my book because he had never read it. He came back after a week off and mentioned to me that he had spent the weekend w/ Jackie but hadn't thought to ask him to sign my book for me...Nice. Let's just say his car wasn't as fast as it could have been in the next race.

 

And now back to our originally scheduled post...color=red>

[ChrisNYC]

Recourses had a post a while ago that I often think about when thinking of "smooth". It's the idea of a bike's controls being "relays". I find it interesting to contemplate this notion, and simultaneously think about "being ONE with the bike", or, NOT being "one with the bike". This mental exercise always takes me to the same interesting place: where does emotion /adrenaline / testosterone fit into this whole equation? What's the right mix? What's your mix?

 

 

------------------

Chris (aka Tender Vittles),

Little '77 KZ400 in the Big Apple

Black '99 RT for Everywhere Else, such as...color=green>

[Sean]

David,

 

I'm sorry I didn't read your post sooner! This is an excellent essay! You did such a good job of putting into words something that I subconsciously knew, but did not exactly know how to put in to words, as you have. Thanks for this post!

 

I occasionally observe other riders or drivers who try to go fast, but are clearly not smooth. Sometimes they'll even voluntarily admit that they're not smooth, dismissing smoothness as unimportant to their primary goal, which is speed. I wish I could somehow help them to understand that by focusing on speed they will not be fast, nor safe, but rather by focusing on smoothness, the product of their effort will be speed.

 

Unfortunately, driving a BMW car as well, it seems that everyone on the road wants to race me. I am really not in favor of street racing, I think for obvious reasons to those here. But, I get the occasional souped up Acura Integra that tries to provoke me by tailgating me and weaving back and forth. So my trick, and a dirty little trick it is, is I make no motion that indicates I'm going to engage them. Rather, I just calmly maintain my current speed, and wait for the next curve in the road. As I approach the curve, instead of braking for the turn, I maintain my speed, slowly and smoothly make my way to my selected entry point, smoothly turn in towards my apex, smoothly roll on the power, out to my exit point. I do it in such a graceful manner that it doesn't even look like I'm pushing it at all. The agressor on my tail sees this smooth execution, and interprets this as an easy turn ahead. So, they follow me into the turn at the same speed I entered at, right on my tail, but quickly they realize that they've misjudged the situation. Very quickly you see their Acura's nose dive, the front end oversteers, their tires wailing like dying elephants, and their whole chassis is generally upset and unstable. I smoothly motor away, leaving them to disappear in my rear view mirror. Hopefully they learn a lesson from the experience, but sadly, I doubt they ever really do. They should be careful what they ask for because they might just get it. They wanted to engage in a speed contest, and then without realizing it initially, they then find themselves right smack dab in the middle of such an engagement, but by then it's a little too late.

 

To further reinforce this topic of smoothness and its importance in traction management, I think of an experiment in gradeschool on inertial forces. The experiment was simple. Take a piece of kite string, tie it to a bar suspended above the ground, and place a weight on the bottom end of the string. Continue to slowly add weight to it. What's incredible is how much weight the string will hold when the weight is slowly and smoothly applied, something like 40 pounds! But then in the second experiment, only a 5 pound weight was tied to the end of the string. The weight was lifted up, level with the bar, and then dropped. As the weight fell, it rapidly tugged on the string and snapped, leaving the weight to fall to the ground. The idea is that inertial resistance is a huge component. You can try this experiment with a paper towel, sheet of paper, tissue, etc. Slowly pull on the ends of a piece of paper, and it will take most of your strength to pull it apart. Then, rapidly jerk on the ends of the paper and it tear in two, almost effortlessly. This same idea of inertial reisistance, and the inability of the stressed material to absorb the force fast enough, is why smoothness is so critical in traction management. In your car, if you smoothly apply the brakes, you can bring the car to a quick, effective stop. Nail the brakes hard, and the tires will instantly lock and skid, increasing stopping distance. When cornering, enter the turn smoothly, and you'll be able to sustain my higher speeds and lateral forces. But if you try to rapidly jerk the car into a turn, you'll quickly break traction, losing control.

[Voodoo]

Sean said: I do it in such a graceful manner that it doesn't even look like I'm pushing it at all.

 

That's the real ticket, Sean! Nothing feels better on the road and nothing makes the vehicle happier. That's the best way to experience the "Whoosh" of speed rather than the "Whoa!" of speed...

[DanC]

Nice work Dave. Your post makes me ache for warmer weather!

[Mjames]

David,

 

Now that you've explained the WHY, the HOW becomes more of meaningful quest. Great post! Now get out of your heated house and go teach me a thing or two.

[freebird6]

Interesting reading. I distinctly remember Jackie Stewart talking about racing, actually as a commentator, sometime when I was in High School and learning to drive. He said...."neayver strrrrress the caaar, you can't finish if you break it and you won't be fast if you are strrrressing the caaar" in his best brogue. I often repeated that sentiment to my sons as I was teaching them to brake early and plan their lines through corners and accelerating away and decelerating to stops. Great stuff, thanks for this section.

[Downs]

I did a track day on a FJR about a year ago and it really opened my eyes to what the bike was capable of. I mean I knew it could go faster than I push it on the road but at least on the track you know that you generally aren't going to encouter gravel or a deer mid turn.

[Peter Parts]

In shifting, there is no smooth except through slipping clutches unless you know the bike really well (years?) and can synchronize the engine speed (really through sound) and the gear train. Good reason to keep dry-clutch machines a long time because they aren't made for slipping.

 

Funny, riding home this morning, I realized another bad consequence of BMW's marketing-driven urge for published HP figures.... which means less torquey engines and more high-rev power. Since first gear has to be tall in proportion to engine inertia (for compelling safety reasons), you really want a bike with low-end torque for easy take-off in first-gear. Not a screamer. If smooth (and clutch longevity) means anything to you.

 

Ben

[racer7]

The two major post here are on target and sound a lot like the classroom stuff I taught at various tracks when I still did a lot of that.

 

Many times student riding with me expressed surprise that my hands moved so little while we ripped off teaching laps. Apparently many believe that it takes sawing at the wheel to be fast- something learned from movies or TV- when exactly the opposite is true. I used to show in car video clips of offs in class sessions and have students analyze the errors and while they could see how a bad line in a wet corner resulted in an off, they usually missed the video showing a jerky steering input as the primary event. Or the data log on the screen showing an abrupt jump off the throttle causing a snap spin. I always started the class on brake system design and maintenance with the reminder that tires do it all and understanding the math of how that balance works is the key to being able to set up a car for maximum performance in the braking zone- where most passes in racing (except Nascar) get made.

 

Re how it feels- at ones very fastest on a track there is no adrenalin present, at least for me. The feeling reminds me a lot of my time as a competitive shooter and is a zen like state of complete focus with zero emotion in it. It also takes almost no physical effort though the concentration is tiring. There is also a phenom one cannot teach and I can't really explain- that is the automatic work done by fingers and forearms as though they had by themselves the ability to detect small tire slips and correct. This happens so fast that there is no way nerve impulse could travel to the brain, be analyzed, and conscious choices fed back to the hands and folks who don't have this "fast hands" ability never get truly fast in 4 wheels. Its fast hands that allow driving a loose car well and it takes a loose car to be really fast- if its always rock solid control you're seeking, slow is the result. Dancing on the edge is what's needed. Newbies often feel the adrenaline effects of unaccustomed speed but the experienced instead say something like "that was an interesting race". Stewart's comment is well understood by racers - you've got to finish to win and any idiot can be quick for a short while be beating crap out of the car- but will typically crash out or have a mechanical problem in anything except the shortest races.

 

[Bud]

It seems to me, and I'm sure I'm wrong, that when I accelerate, both the front and rear suspension "lifts" and then I brake, both of the compress.

 

Can someone with knowledge explain why it just "seems" that way and really isn't?

[mneblett]

Which bike? The answer is different for early airheads vs. oil/hexheads.

[Bud]

R 1100 r

[NCStephen]

In very my very simpletons and not engineering nor physics understanding: Normally when under throttle, the rear gears try to climb each other and without the paralever will do a a fair job of jacking up. The paralever does a nice job, but not 100% job of doing lessening that. Even with a chain drive there is some hardening of rear suspension even if not lengthing of the spring. Hence when in twisties and there is limited clearance, being on the throttle just a bit helps keep the rear spring at a more optimal height.

 

Upon braking, the rear wheel is dragging against the suspension and pulling at it so attempts to go as far behind the bike as possible. Without other forces acting upon it and the bike, that would tend to be somewhere in its travel other than fully extended. At that fully extended point the arch of travel for the rear wheel is moving forward some. So the brake is trying to move it rearward and lower the bike as a result.

 

The front compresses simply due to the momentum of the mass of the bike having the greatest affect on the front suspension. If there wasn't sufficient distances and mass involved the bike would easily rotate around the front wheel so it is in front of the slowing wheel and wheel dragging it stop. So what we experience is our bodies shoved forward, the bike pressing down on the front forks and the front dives (not so much on the telelever bikes but the forces are still acting upon it. In extreme braking and skills riding, this is what causes a stoppie.

 

In one school I know they teach joint braking but applying the rear fractionally quicker than the front. The thing you have noticed is the very reason why. The rear squats a little when the brake is applied. If you hit the front brake first, the rear extends and rises and then the rear brake trys to pull the wheel back down and thus you loose a small, yes small, amount of braking potential. Thus what they teach is to let the rear brake go on 1/4 sec faster than front. It settles then the front brake will do its job and you might retain a little bit more of the rear brake.

 

For an exaggeration of this rear brake squatting, try pulling on your hand brake on your car while going a city speed on an empty smooth street. Don't lock things up, just slow the car a bit with the hand brake on only and see if you don't feel the rear lower just a little.

 

NCS