| Author | Message | ||
| rich (Dino2400)
Member Username: Dino2400 Post Number: 332 Registered: 10-2001 |
I don't have the motorcycle racing background of someone like Art so hopefully he'll come in and explain things. But I have crashed a motorcycle a time or two and know how/why I did it. It is very important to get off the front brake before turning in on a motorcycle. If you are not back on the throttle and get the weight off the front wheel, it won't hold traction and down you go (like I did the last time in the Santa Cruz mountains, totallying a perfect good Ducati and nearly totalling myself). A lot of situations on motorcycles require the rider to do just the opposite of what your mind/body wants to do when it panics. For example, if you get the whobbles (a tank slapper) you've got to give it gas to get weight off the front and let it settle itself. But your mind doesn't want to go faster when it feels you are in danger. Same goes for when you feel you are too hot into a corner - your mind says brake but you should just stay on it and ride it through. Even if you know logically that the bikes limits for cornering are way higher than you think at the moment, it's still hard to not panic and stay on those brakes too long and lowside it and get pitched off a cliff and down amongst the redwoods, ha! Counter-steering is a minor controversy in the world of motorcycle physics. I've always felt naturally that that's how you turn the bike: push forward on the bar that's on the side you want to turn to. In addition to the forces involved, I was told early on that the profile of the tire also causes the bike to want to fall over that direction and that causes turn in. Hard to explain that last bit but cup your hands on the desk in front of you like the shape of a motorcycle tire; create the pressure you would associate with pushing the left handlebar forward; you feel pressure on the left side and your hands want to "fall" over that direction, right? Keith Code who has written several classic books on how to ride a motorcycle at speed and has a school is firmly in the counter-steering camp. However, Reg and Jason Pridmore's schools and the Freddy Spencer school teach "body-steering" over counter steering. They say that since a bike can be turned when riding with no hands (they're right of course: i used to ride my 60s triumphs through the twisties of the ucsb campus steering with my hips and feet only all the time), that counter-steering isn't really what turns the bike. They claim it is the weighting/unweighting of the footpegs. Brakes are another funny issue. The front brake of a bike is more than enough to stop the bike. You can easily pull the back wheel completely off the ground so obviously it's not doing much braking with no weight on it. I don't think I ever used the back brake on my Ducati at anything over 10mph. On the old drum-brake Triumphs though, I used both brakes, all the time since the fronts aren't that strong and you need every once of braking power you can get just to stay alive out there! Code teaches a very aggressive turn in in which the bike spends as little time tilted over as possible and back upright and on the gas asap. He therefore says to forget about the rear brake completely (basically). The Pridmores advocate a low, tight line, the bike is more unstable and so the back brake is more needed and they use it. They also use engine braking while coming into turns while Code advocates just braking and going straight to the gear you want. I think both of these schools of thought are right for the types of lines and steering that they teach. -Rich | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 151 Registered: 4-2003 |
>>What I've been curious about is the different ways in which motorcycle racers can tweak their setups. Would you care to elaborate a little?<< Jack, I'll have to punt on this one. Most of my bike riding has been on dirt bikes or brit crap. I keep up with the sport bike guys enough to know that they are way out there when it comes to set up. You can actually make a bike too stiff! Maybe Art can help out (if I haven't ticked him off with my comment about eating democrats.) At the end of the day, though, on a motorcycle you have 4" of rubber on the front and 4" of rubber on the back. It's how you use them that counts. Smoothness counts. You simply can't get away with the things that you can in a great sports car. To survive, you have to really pay attention to what's going on. It is truly a different state of mind. Someone asked me the other day how good the stereo is in the Maranello. I didn't have a clue. I have owned the car for 3 months and haven't even tried to turn it on. I'm having too much fun trying to listen to what the car is saying. Let's just hope that it doesn't turn into too much fun, ha! | ||
| Dr. Erik Nielsen (Judge4re)
New member Username: Judge4re Post Number: 20 Registered: 4-2003 |
This is the best way I ever heard it explained: Oversteer is when you see the wall you are about to hit in the rear view mirror. Understeer is when you see the wall you are about to hit through the front window. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5498 Registered: 12-2000 |
LOL Psk, no offense taken either way. It was 100% drivers mistake. I can give you a million excuses like it's hard to know your brakes are locked up in the rain or that the tow truck shouldn't of been there in the first place, however, in the end it just comes down to bad driving on my part. | ||
| Jack (Gilles27)
Intermediate Member Username: Gilles27 Post Number: 1092 Registered: 3-2002 |
Dale, you are right with your thoughts on weight transfer. "Throttle steering" is essentially weight modulation. More throttle will lighten the front end, less throttle does the opposite. What I've been curious about is the different ways in which motorcycle racers can tweak their setups. Would you care to elaborate a little? | ||
| PSk (Psk)
Member Username: Psk Post Number: 645 Registered: 11-2002 |
That is the stupidist thing I have ever read ... BTW I am not saying that it is not true! Manufacturers do dial in understeer as it is easier for Joe Average driver to handle ... but it is a real pain and time waster on the race track. Pete BTW: Rob, my BAD! comment was refering to understeer not to your driving ...  | ||
| Todd (Tkrefeld)
Junior Member Username: Tkrefeld Post Number: 197 Registered: 11-2001 |
Its something the lawyers in US spec cars came up with so the maker would not be sued. It is dialed in specifically in US spec cars for this reason. AS a liability issue if the car leaves the road tail first it is the manufactures fault and they are therefore liable. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5491 Registered: 12-2000 |
umm, I locked the brakes, that's my excuse and I'm sticking to it. | ||
| PSk (Psk)
Member Username: Psk Post Number: 641 Registered: 11-2002 |
BAD! Pete | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 137 Registered: 4-2003 |
Rob, watched your vid clip. Thought the purpose of racing was to stay on the track, ha! Wouldn't you know it, Bubba just had to park the truck where you would hit it <sigh>. At least you stayed in the car. This gave Bubba II a chance to get away! Seriously though... why were the other cars able to make the turn and yours didn't? Plus, is it fair to say that understeer in a car is similar to what bike riders call "pushing the front tire?" And yes, Terry, I'll get the book cause I don't even have a clue as to what toe and chamber mean or why I should even care. Of course in the Maranello just about all of this is moot. Coming in too hot? Just brake harder. Need to pick it up? Just push harder on that thing on the right. This is probably the most forgiving car that I have ever driven, which is scary. I figure that one of these days, this pony is gonna reach around and bite me. But so far, so good. Keep those cards and letters coming folks. thx | ||
| Terry Springer (Tspringer)
Member Username: Tspringer Post Number: 653 Registered: 4-2002 |
Buy and read/study "Tune to Win" by Carroll Smith. It has excellent technical sections on suspension design and setup that go into great detail about understeer / oversteer and how to tune your suspension for each. While the book will give you all the techinicals.... its still a "black art". Everything is a tradeoff. Like tire pressure. Technically, less pressure (to a point) will yield more grip. Higher pressures decrease the size of the contact patch. However lower pressures may decrease the sidewall strength thus allowing the tire to deform under stress and decrease the contact patch during hard cornering... precisly when you need it most. This is why race tires have such stiff sidewalls... and why they ride like crap on the road. If you really want to tweak your tire temps, an autocross is a good place. Get a buddy with a tire pyrometer and take reading across the tread pattern immedialty after your run. It will not only tell you good info about pressures, but can point you in the right direction for camber and toe changes. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5489 Registered: 12-2000 |
Understeer... http://www.spec7.org/videos/hallett_crash2002.mpg 7 mb | ||
| Hubert Otlik (Hugh)
Member Username: Hugh Post Number: 983 Registered: 1-2002 |
Okay next track event you all can ride along with me, and you'll get your fill of understeer, I promise. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5486 Registered: 12-2000 |
Dale, actually, some movement of weight to the front tires is good. Too much is understeer. ;) Learned that autocrossing as it's more noticable. Just by lifting, the weight shift will give you some much needed traction for steering input. | ||
| Nick Berry (Nickb)
Junior Member Username: Nickb Post Number: 113 Registered: 8-2002 |
Enough of the theoretical explanations. Here is an easy way to understand and remember understeer and oversteer. Understeer means your front end hits the wall and oversteer means your backend hits the wall.  | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 832 Registered: 4-2002 |
ACW got it right! its about the slip angles on the tires. "Tune to win" Carrol Smith (may he rest in peace) has an excellent disertation of undeersteer and oversteer, and what a driver can and cannot do when these things arise in a corner. | ||
| ScottMellor (Scottmellor)
New member Username: Scottmellor Post Number: 2 Registered: 6-2003 |
Might I suggest the book "Going Faster" by Carl Lopez. It is the companion book to the Skip Barber School. It talks about this and more in a very readable way. It also explains the Heel and Toe question posted earlier. | ||
| acw (Acw)
Junior Member Username: Acw Post Number: 151 Registered: 2-2002 |
Understeer: the slip angle of the front tires is greater than the slip angle of the rear. In other words, the front tires are sliding more than the rear. In understeer situations, steering more into the corner won't get the car to turn more. Best way to proceed is to lift the gas slightly and possibly reduce steering as well. Note that lifting will likely cause oversteer so be ready to get back on the gas when you do that. If you break during understeer at the limit, you will probably spin from oversteer. Lifting and reducing steering should be sufficient. ACW | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 135 Registered: 4-2003 |
Getting back to understeer... If you brake to reduce understeer, wouldn't that cause more understeer? That is, what about weight shifting back and forth between the front and rear? I thought that this is how you steer with the throttle to go from understeer to oversteer. Thoughts? | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 134 Registered: 4-2003 |
James, you are correct in that a motorcycle countersteering is very much like a car that is crossed up, just in reverse. WM does a great job in explaining this. I really like the rudder analogy. (Thanks Bill) Understanding countersteering and being able to do it is perhaps the second most important thing to learn about riding a motorcycle (knowing how to panic brake is the first). Sadly most of the newbie riders, particulary the Rubbies on Harleys, don't have a clue. The trick is to practice at slow speeds and work your way up to where you have the nerve to do a sharp countersteer at, say, 80 MPH. Try it at 30 MPH first. For example, imagine a concrete block falling off a truck to your right. Push hard on the left handlebar. You'll be amazed at how fast you will turn. Of course, at speed, you really have to push. You'd be amazed at how much bike racers are really man handling their bikes. They may look smooth. But underneath, they're working. Dale | ||
| ScottMellor (Scottmellor)
New member Username: Scottmellor Post Number: 1 Registered: 6-2003 |
From my Laverda days, I remember being told that the counter steering push on the handlebars caused a gyroscopic effect that caused the chassis to tilt in the opposite direction. | ||
| John Millard (Jmillard308)
New member Username: Jmillard308 Post Number: 25 Registered: 5-2003 |
What exactly do people mean when they say understeer? Understeer is when the slip angle of the front wheels is greater than the slip angle of the rear. Oversteer is the opposite. The slip angle is the difference between the direction the wheel is actually travelling and the direction the wheel is pointing. | ||
| James Glickenhaus (Napolis)
Intermediate Member Username: Napolis Post Number: 1917 Registered: 10-2002 |
WM Thanks; that does make sense. I love pics of bike racers countersteering. | ||
| wm hart (Whart)
Intermediate Member Username: Whart Post Number: 1379 Registered: 12-2001 |
That's a pretty metaphysical Question, Jim. Here's what i know about countersteering, having had to employ it, and having read alot about it which only seems to confuse the issue. On a bike, you wanna turn right, you press down on the right handlebar,the bike sort of leans right and you go right. (I am not talking about a sharp slow turn, where you actually turn the handlebars in the direction of the turn). So, when you are pressing down right, the front tire is actually deflecting left,if you picture it, the rear wheel is driving you forward and the front wheel is acting almost like a rudder. Its almost impossible to think about this when riding (for me), its just lean down on the bar in the direction you want to go; but as you are going thru a turn, you can actually change your line by deflecting the front wheel in the opposite direction of the turn; ie not so much leaning down on the right bar, but pulling on the left bar (which is what is happening to the left bar anyway when you are leaning on the right one). There, i've made it thoroughly confusing.... But, in steering into a skid in a car (let's say the backend is swinging out to the right and if you continued turning to the left, the rear would come around), you are in a sense straightening the car, briefly, before continuing.) I'm not articulating what the difference is, but i think the behavior of the two wheeled critters is different. | ||
| James Glickenhaus (Napolis)
Intermediate Member Username: Napolis Post Number: 1913 Registered: 10-2002 |
Is motorcycle countersteer similar to car opposite lock to control oversteer? | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 714 Registered: 11-2002 |
In a car with limited adjustments available to influence vehicle dynamics, tire pressure is by far the most influential. Increasing front tire pressures from manufacturer recommended street pressure, can aid grip on the front by increasing the 'stiffness' of the tire's sidewall (improving response), and reducing tread squirm, so the tire can bite into the surface of the road better than at lower pressure. This is a GENERALITY. Every tire and every car/ driver is a bit different, but in general, this will work, especially for front wheel drive, but even Ferrari's respond well to more front than rear tire pressure (on street tires, sometimes on DOT race tires). OTOH, in general, decreasing tire pressures may improve grip. Pressure reduction from manufacturer recommended may aid a tires compliance with the road surface, increasing overall grip. So now that we may still be confused, what we can take away from this discussion is that different changes must be tried and proven. There are general trends, but few fast and hard rules for improving grip (and balance, a different quality). It's easier to make recommendations with much more given data (specific car, track, weather, driver, tire, etc.), then we can say increase front pressures to 38 psi from 32 psi, etc. | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 132 Registered: 4-2003 |
Crap, I meant Rob... or is it bob? Night, night. | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 131 Registered: 4-2003 |
This is all helpful because I'm trying to translate from the 2-wheel world. On a motorcycle, you brake hard, which overloads the front tire. You then release the brakes, which, of course, unloads them. Then you pitch the bike into the corner, which again overloads the front tire. Now, this is the non-intuituive part. You slowly gas it because this actually transfers weight to the rear and slighly unloads the front, i.e., oversteer. In a car, understeer is what makes the car seem stable. A car with high oversteer, e.g., an older 911, will seem twitchy. Another way to say it is turn in. In a RWD monster like the Maranello you get the sensation that the car is reacting slowly. Which for most of us is a good thing because we tend to overdo it. Thus, because it feels like the car is not turning fast enough, we get on the brakes to slow it down. Which, again, is probably a good thing. But, here's where I get confused. If I brake harder, that puts more load on the front tires, yes/no/maybe? Wouldn't that tend to make the car understeer more, not less? What keeps running through my mind is watching the F1 cars at Montreal trying to make the chicane in the wet. Sometimes, they just couldn't do it. It looked like the driver completely lost the front end and the car wouldn't turn at all. Thus, they ended up going straight onto the grass. Finally, I don't end whata think about FWD cars. Time for bed. Dale ps Rod, I don't doubt you, but pls explain why more tire pressure reduces understeer. Does more tire pressure change the profile and, thus, create more traction? | ||
| Hubert Otlik (Hugh)
Member Username: Hugh Post Number: 981 Registered: 1-2002 |
rob- yah. realtime et. al. are doing well with the new rsx, and foo with mazdas, among the rest of the FF field. not a bad platform to start with -- it's inherant limitations not withstanding-- and much safer, IMO. anyway, back on topic. so, dale, what's your question in light of the definitions given? | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5480 Registered: 12-2000 |
I put 100k miles on a fwd Toyota Tercel. All my racing has been rwd though. Some fwd cars are kicking butt in World Challenge. | ||
| Hubert Otlik (Hugh)
Member Username: Hugh Post Number: 980 Registered: 1-2002 |
rob- ouch. ugh. i'm going to go cry in fwd heap. sniff. sniff. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5479 Registered: 12-2000 |
Some cars have front wheel drive?  | ||
| Hubert Otlik (Hugh)
Member Username: Hugh Post Number: 978 Registered: 1-2002 |
rob- what layout of car are you referring to? b/c increasing front tire pressure in a fwd car will do nothing but make you slide around more. | ||
| Hubert Otlik (Hugh)
Member Username: Hugh Post Number: 977 Registered: 1-2002 |
terry: >>Actually front wheel drive cars scare me somewhat because I have no clue at all how you would drive them quickly!<< actually, a well set-up FF is very, very quick around a track. when it starts to really understeer i lift a touch to get the rear to step, unwind the wheel a touch, and get back to modulating the throttle. an FF car's got to be handled like a woman; quickly and smoothly. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5476 Registered: 12-2000 |
A quick way to reduce understeer is adding pressure to the front tires. Most European cars come to America recomending lower pressures in the front because they don't think we can drive (well, it's true). | ||
| Kds (Kds)
New member Username: Kds Post Number: 37 Registered: 5-2003 |
Understeer:It's what can happen when you go off road near a texas cattle ranch. | ||
| Terry Springer (Tspringer)
Member Username: Tspringer Post Number: 652 Registered: 4-2002 |
Understeer is when you go into a corner too fast, turn the wheel in the direction you wish to go and the car continues to go straight. The front wheels lose traction before the rear. You go off the road travelling straight. Oversteer is when the back wheels loose traction first in the corner and thus the rear end tries to swap position with the front. You go off the road backwards, or spin. Porsche 911s are notorious for this if you lift on the throttle mid corner. Understeer is correctly by simply slowing down. You may lift on the throttle or even apply gentle brakes in order to slow to the point where the front wheels gain grip. Oversteer is controlled more with the throttle. Generally, (and more importantly in a rear wheel drive car) apply brakes or lifting off the throttle completly is a bad idea and will make the oversteer worse. Driven wheels have more traction. The oversteer can be corrected or managed with opposite lock in the steering and with throttle modulation. One of the really fun things about driving a 911 quickly is this process. A 911 on the edge is steered in a corner as much with the throttle pedal as the steering wheel. Note: I have no idea how you correct or manage oversteer in a front wheel drive car. Actually front wheel drive cars scare me somewhat because I have no clue at all how you would drive them quickly! | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 5475 Registered: 12-2000 |
Best example of understeer is you hit a patch of ice and try to turn. The car won't turn. Well, the same on dry pavement, but not as exaggerated. It's not that a car won't turn in at all, it's the car isn't turning as nimble as you want. The car is "pushing" through the turn. Now oversteer is the car is too "nervous" and steers too much. Most fast drivers would rather have a car that oversteers. It's hard to do anything with understeer except go slower. Oversteer can be managed by a skilled driver. | ||
| Hubert Otlik (Hugh)
Member Username: Hugh Post Number: 976 Registered: 1-2002 |
understeer: your outside front gets overloaded and breaks traction sooner then the rear. if you're tyring to get rid of understeer a larger rear swaybar will help, because it puts more transitional weight onto the outside rear, basically doubling the spring rate of the rear suspension under corning, reducing the traciton of the outside rear tire, helping it to break traction faster then the front; inducing rotation. stiffer rear springs will accomplish the same goal, and are usually used in conjunction with lager sway bars. then again, the issue of weight transfer (and it's dynamic behavior) are what you've got to keep in mind if you're dialing in/out given chartaristics, and a major component in that is the layout of the car; i.e., FF, FR, MR , RR. | ||
| Dale W Spradling (Drtax)
Junior Member Username: Drtax Post Number: 130 Registered: 4-2003 |
Okay, now that we have solved DES's love life... Let's talk about driving F-Cars again. What exactly do people mean when they say understeer? Note that I'm not trying to be silly here. As some of you know, I have riden motorcycles for more years than I care to admit. And one subject that constantly confuses riders is counter-steering. Because the physics of turning a motorcycle are very different from a car, counter-steering is not an issue in the car world. However, we do throw term like understeer and oversteer around. I'm guessing that there is actually a lot of confusion on the subject. So what's your definition of understeer? (We can take up oversteer on another thread.) So come on, all you guys (and a few gals) who paid good money to go to driving school. Speak up! |