Welcome to the neighborhood! You'll have to join Riesentoter. A lot of great track junkies in the club. 10 of us just went down to VIR this weekend. PM me if you want any info or need to talk about anything.

 

Larry - I'm with EJ on this. I never deliberatly saw at the wheel. On the other hand in fast corners some counersteering is needed at the limit and usually a better idea than lifting I guess it comes down to how one defines "sawing". The way I see it, steering corrections are a result of trying to maintain the optimum slip angle of the tires. In other words, it is a reaction to slip angles and not the cause.
Rgds,

 

Bob, I don't either. Like E.J. said, I am providing steering corrections, when necessary, to keep the car at the limit. That is what I thought "sawing" was. So I guess that I still do not know what Fatbillybob is talking about. I do not understand why I would be "testing" the limits of adhesion of the front of the car, when I am trying to manage the back of the car. Could the initial saw of the wheel be a method to induce the type of rotation that I usually get by trailbraking?

 

Good point. Not a deliberate movement. One offbeat way to look at it in terms of "fast" as FBB posted, how is it faster, well look at 2 tennis players at service, one standing still waiting for the serve and the other "dancing" as they all do. Which is going to return the serve faster? The one dancing.

So to put it to cornering the driver is letting the wheel dance as it grips and corners enabling the driver to "offset" the wheels angle on the surface as a dirt tracker will do turning in the opposite direction as the back end swings the other. Just reduce this movement the dirt trackers do to a very small movement"sawing" we see. Better control of the steering allowing for adjustments to be made and get through the corner quicker rather than being a little fast and on the edge and having to back out of the gas even more and "hang ten" till the cars speed scrubs.
Perhaps this is what he is questioning!?

No pro here but in my case I find myself doing this when I am at 9.5/10-10/10ths. When really on the verge of .... happening.

 

Larry - Agreed. I guess we need to ask FBB to explain in more detail. One thing I have noticed is that some drivers do "saw" at the wheel - I rode with a guy who is pretty experienced (ex racer) and was surprised to see him "wiggling the wheel" through corners where I held mine steady. He wasn't going fast enough to have to make corrections. His sawing had the effect of unbalancing the car. I asked him why and he said "I've always done this".

Rgds,

 

Could the guy in the Cup car have been loose and was just playing "catch up" with the car to keep in on track?

 

Hey All;

I am not sure that anyone paid any particular notice to TonyTaylor's addition to this thread, but I find it an intriguing notion. A tire has max grip just as it starts to slip during braking. Why not cornering too, slip angles not being that much different from forward grip?

I can think of some reasons for doing the sawing thing.

- Dumb Habit.
- Correcting for loss of front or rear grip.
- Constantly sensing and managing front slip angle.

I find myself doing the latter with increasing regularity as I inexorably increase my abilities with speed on corner entry. Living on the FC forces one to manage grip to the Nth degree!

The one thing that occured to me is that it might be an attempt to swing the **** of the car and reset the suspension. There are many turns where "shaking" the car increases rotation AND a quick set of the side loading, doing so methodically through a turn might be an attempt to increase rotation and/or side bite on a recalcitrant chassis.

A Cup Car is a pretty finely tuned piece, and if it were off a tad, it would be a bitch. This driver might have had his hands full, and my guess would be understeer!

 

I'd like to chime in on this one because I've noticed this behavior on the F1 in car cameras and in the passenger seat of some very fast drivers. I'm no professional driver and would generally be full of BS, but I'd like to try out this one. Hope there are some tire experts out there.

Here goes, and I apologize in advance for trying to connect two very different sports, but I find a whole lot of commonality in dynamics in controlling anything w/ a steering wheel...

I am an offshore sailboat racing type. And when driving downwind in big winds, a sawing action on the helm is often required to turn the boat, which is what interested me about this thread. The reason for this is the force on the rudder is proportional to angle of attack (slip angle). Once the rudder stalls, it is necessary to approach the same steering force only from an increasing load directon. So you have to unwind the helm and start over. This effect would be called hysteresis. This is a fantastic word to know for all you control freaks out there. Check it out in the dictionary or the web because I find it more often than not in control systems.

I would not at all be surprised to find tires have a hysteresis effect on the slip angle vs. traction (braking, accelerating, turning). So once the maximum slip angle is exceeded by a certain amount, it cannot be re-achieved by reducing the steering angle said amount. You have to undershoot the slip angle, reattach the tire to the ground and then rebuild the force only by increasing the slip angle. Hence the sawing action.

Whether this is a benefit would depend on averages and how well you can stay on this edge. I would imagine a rougher corner would "stall" the slip angle, requiring a whole lot of big steering to reattach the tire.

Are there any tire experts out there? Is this hysteresis thing a whole lotta hooey when it comes to tires?

While I'm at it and I still have my fireproof suit on, I remember a Physics class regarding traction coefficient. As a math exercise, there is no need for wide tires. One could in theory corner as hard on bicycle tires as a giant fat slick based on coefficient of friction alone. A tire w/ half the tire patch has twice the PSI and hence the same absolute friction.

In the real world, as the professor explains, the issue is temperature. A bicycle tire would overheat and cause the tire to melt, giving it an entirely different coefficient of friction (like none). What wide tires do is provide a larger tire patch w/ lower PSI and hence lower heating. A softer compound can then be used (stickier) to compound the advantage. I'm sure its a bit more complex than that, but what do you expect for a $30,000/yr tuition.

Anybody else got some wild *** theories? :-)

 

Bob and larry,

I am below a rookie. The sawing action best describes what I witnessed. It was just an on track observation. I still have an untrained ***-o-meter and I still look at my spedometer when nearing my limits as a way to learn to move up to the next notch. I'll enter and exit a turn as one MPH and try to enter and exit faster the next lap or for whatever corner I am working on. I just watched a really fast guy in a cup car while I was on his rear. I witnessed the sawing action and I decided to just try it. The result was that I improved my speed through this long constant radius sweeper by a full 5mph from turn in to exit. If I had some skill maybe I could have done this anyway with less steering action but the sawing action made it really easy and confidence inspiring. I felt like I had control and the improvement in speed was real per the spedometer not by my ***-o-meter. So being a rookie I post my question here and it appears that I have stumbled on a very complex topic. So while EJ makes the most sence if I knew what I was doing but...I do not. So Tony Taylor's and dnitake make the most sence to me (also I'm a science guy) at my level of trying to find my limit so that I don't loose a bunch more speed as I blow out my back end. I also noticed that this technique offered nothing in some corners. Some corners were just too short and there was no time for a succesive saw but just for minimal car corrections and the turn was over. Other turns tolerated the saw but resulted as EJ posted no time improvement or a worse yet it was slower.

 

FBB, I'm torn, because I hate to tell someone that something that is working(sawing) might not in the future. I'd still suggest getting a good driving book, and Skip Barber's is one of the best for explaining things, mostly because there are a lot of world class drivers quotedon the one theme of fast driving - be smooth. And sawing is not smooth.

dnitake, I don't see too many F1 drivers sawing the wheel - I see lots catching it as it's kicking in their hands, but that's not the same thing. BTW, your physics guy had it wrong - it's not just temperature. If it was simple physics, then any contact patch would do, but it's not simple friction that provides the traction, it's mechanical grip - think velcro. Rubber will actually interlock with the road surface in an action not unlike velcro, so the wider the tire, the more traction you get. This is a gross oversimplification, but it's not simply the coefficient of static friction that determines a tire's grip.

Cheers,
Bruce

 

brucegre,
Figures, don't it. I have a hard time believing that sawing can be fast rather than just being smooth and maxing out the grip as close as you can. The sawing I've seen and felt was also combined w/ trying to get the car to rotate, and that is definitely fast. On a rough surface, the steering input has to be much larger as there is no one smooth steering angle. I was theorizing on the need to give bigger steering input than would normally be required if you keep going over the threshold of the tire. I'll look around for some more in-car video...

Why do you separate mechanical grip and coefficient of friction? If a steel wheel were on rails and you were pulling 10G's, that wouldn't be Cf of the steel to rail as you say because they are not shear forces. But there is some other Cf that holds the rails down. Somewhere there is a molecular bond in shear holding things in place. The rubber to asphalt layer is a molecular bond in shear and I think what you're saying is there is also a vertical mating of the rubber to vertical features in rough pavement from a structural point of view. Rubber doesn't have the modulus of steel, but I bet it could contribute to some degree. Like if you were to heat the tire so it conforms and then freeze the tire solid so the Cf goes to 0, but it still holds somewhat? Scratch, scratch, well OK, now I guess I can buy that. Especially now that I know I'm way over my head on this one and I need a friggin drink...

But wait, there's more... Hot tires are slicker than snot, i.e. the velcro don't stick when it's hot and the softer hot compound would conform more to the unchanging road surfaces mechanically speaking. I'll stick w/ the Cf thing if only for a bit just to have something to ponder... Boy, do I ever need to get back on the track...

 

dnitake -

Were you sawing at the wheel a tad when your avatar pic was taken?

I think your sailing analogy was a very good one. To regain grip you need to retreat slightly under center on the slip angle to then reapproach the max. Invariably, the car will tend to slip over it again, and so the cycle continues. Also, hysteresis is indeed a term universally applied to tire dynamics.

I think it is important to make a distinction between proactive and reactive inputs. It is also necessary to seperate cars that are approaching, at, or beyond the FC. All initial steering inputs are proactive. A car that is not responding well mid corner would need more proactive input. A car that is at or over the FC and past the optimal slip angle would likely be in a reactionary mode as grip came and went, slip angle was exceeded and restored. The experience, skill, and speed with which one assesses and reacts to this is the key. Finely tuned ****-o-meters in full use here!

There is an over-under aspect to this phenominon, and what is smooth for one side of the equation will not work for the other. Once they learn the line, anyone can drive a car like "it is on rails" when they are inside the FC and have not exceeded the slip angle of the tires. This is where the vast majority of DE drivers reside. If they do so with stillness and serenity at the wheel, this is smooth and proper for the speed they are traveling. They also will by default be inside the FC and not achieving max slip angles. If they are sawing at this same speed, they are indeed lacking in smoothness and should break this bad habit they picked up on TV post haste.

If someone is on the FC and the brink of the slip angle, then "sawing" will become a necessary tactic to maintain chassis balance and try to optimize grip, but only in general if it in a reactionary sense. I don't think that proactively and continuously sawing the wheel is a tactic that has a lot of application.

If the car appears to "be on rails" in this max FC/slip angle scenario, this is a very talented driver getting the most from his equipment.

We start students off with a little white lie. At a certain point we need to make the student aware that what is smooth is very relative to the speed which one is travelling. Below max velocity, smooth is anything that accomplishes the goal without upsetting the car. At or above max velocity, it is anything that RESTORES balance and therefore smoothness.

FBB - I think the sawing you felt was effective was simply making your mind more comfortable with the extra speed you manufactured elsewise in the turn, and may be obscuring the true reason you were quicker.

 

Vehicle dynamics geek weighing in here. No hysteresis to worry about here, in these cases. As the tire develops slip or slip angle, if you were able to bring it right back to the peak force generation point after exceeding that peak (essentially a peak point on the mu-slip curve) you would not need to go further beyond, only return to the peak. Whether or not you realistically could is another question. Doable, if you're really in touch with the car (highly calibrated a$$elerometer, as we say in the biz), for lateral grip/turning situations. Extremely difficult to do during braking, even for braking system controllers to do.

It's all about the tire's mu-slip curve, and John H, you are correct, perhaps more than you know - the tire will not generate any lateral/cornering force until it has a side slip angle. Basic tire dynamics. Just as in braking or acceleration. Likewise, there is a certain peak to that mu-slip curve, which is what we're always trying to ride (you know, that stupid friction circle thing?) while driving hard.

So it's hard to draw conclusions about what the driver was doing without being in the car or seeing a data trace after the fact (anyone have his email? Get a copy of his data? ) but if he was turning in excessively, to a point of understeer, then releasing and reestablishing his corner - he was just getting to the limit quickly without finesse (or smoothness). Seems pretty much the same anyway if he was driving it to oversteer and sliding it through the corner. I agree, I think he could have likely achieved the same if not better results by better steering input, trailbraking, whatever.

Ok, if we're gonna talk about F1 steering technique - anyone care to comment about that crazy Spaniard's (Alonso) go-kart snap steer and how it applies to an F1 car? I've always wondered how he could get away with such a binary corner entry, but he's generally in the game if the car's on...

 

Yeah, I've seen him do that and I am amazed that the car doesn't plow like a pig. Could be that he likes to play pitch and catch with it. Turn the wheel hard to make the back step out, and then catch it with the gas.

 

Maybe he's doing something like "playing the skip" - playing the transient turn-in response of the tires.

I wouldn't mind the chance to drive those tires myself and eval...