TopKart - 14 April 2008 10:20 AM

speedsense - 04 April 2008 06:10 PM

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Now hopefully understanding how important slip angle is, CAR ROTATION (the kind induced by the driver which I believe the reason this thread was started) is when the body or chassis direction is changed for a straighter exit out of the corner, and when done correctly is within the slip angle of the tires. This means to NOT induce a loose condition and slide the car (thus losing time). This is car rotation.

99% correct, but I'd add that car rotation actually involves LOOSING maximum speed from point "A" (corner entry) to point "B" (corner exit) in order to acheive a better position for maximum acceleration out of the turn. In other words, the car is not set up to acheive the maximum speed from point A to point B, but to acheive the maximum speed throughout the lap: The inevitable compromise.

So if someone says car rotation is done "within the slip angle of the tires," I think the response has to be "not exactly," because at a given corner the correct rotation might involve a slip angle that is slightly beyond the point of maximum rear traction. "Might" because not every corner is the same, so the suspension cannot be set up perfectly for every corner.

This is one point, I think, where the driver comes in. Saddled with the limits of the car's suspension settings, he has to maximize overall speed. If the 1992 Williams F1 had been allowed to continue to the logical endpoint of its evolution, we might have see a car with two-way telemetry and the ability to adjust its suspension at all 4 corners in real time, so that perfect rotation for a each corner would occur at maximum traction. Fortunately (IMHO), that was not to be.

Topkart, where ya been? Driver's who race karts understand slip angle and car rotation, only too well, as the tire IS the suspension along with a little chassis flex..... A kart racer who is very fast, knows how to rotate a kart WITHIN the slip angle of the tires without exceeding it, unless it is needed to overcome a handling problem, as Topkart points out.
It is when you add suspension that some people become confused and forget the reality or physics of the tires hasn't changed, though some seem to think it has......
Car rotation is a "learned" driving technique, practiced by many
(some by mistake) but actually understood by a few, usually the few that are running at the front..

red376 - 14 April 2008 06:26 AM

Respectfully--

I guess I just don't understand how being cognizant of slip angles vs just finding overall grip and how it translates into driver comfort and faster lap times during real world race weekend tuning would come into play. While tuning the set up during or as a result of notes compiled from practice for the race, there are many visual indicators that help teams track and log data, gauging how the chassis is reacting, how the tires are performing, and how all of that information relates with the driver feel. Where and when does slip angle need to be considered during the race weekend thrash to find speed and driver comfort?

Grip and slip angle are one of the same. If your car can achieve maximum slip angle for the full duration of a corner from turn in to exit without ever exceeding "max" for that tire you would have the fastest car on the race track (given all things somewhat equal, HP, Chassis, tires). If the driver could manage to put the car at full slip angle through the corner without exceeding max slip angle, you have a good driver or an extremely well set up car or both.
It will have max Grip as MAX GRIP=MAX SLIP ANGLE
EVERthing you do to a car (setup) has as direct result to how the slip angle (or grip) of the tire is generated, even how easy or tough the car is to drive is a direct result of how the slip angle is generated... And Strangely enough, why the car needs to be rotated and by how much depends on how well the car is generating it's slip anlge...the reason for the thread.

speedsense - 15 April 2008 03:07 AM

red376 - 14 April 2008 06:26 AM

Respectfully--

I guess I just don't understand how being cognizant of slip angles vs just finding overall grip and how it translates into driver comfort and faster lap times during real world race weekend tuning would come into play. While tuning the set up during or as a result of notes compiled from practice for the race, there are many visual indicators that help teams track and log data, gauging how the chassis is reacting, how the tires are performing, and how all of that information relates with the driver feel. Where and when does slip angle need to be considered during the race weekend thrash to find speed and driver comfort?

Grip and slip angle are one of the same. If your car can achieve maximum slip angle for the full duration of a corner from turn in to exit without ever exceeding "max" for that tire you would have the fastest car on the race track (given all things somewhat equal, HP, Chassis, tires). If the driver could manage to put the car at full slip angle through the corner without exceeding max slip angle, you have a good driver or an extremely well set up car or both.
It will have max Grip as MAX GRIP=MAX SLIP ANGLE
EVERthing you do to a car (setup) has as direct result to how the slip angle (or grip) of the tire is generated, even how easy or tough the car is to drive is a direct result of how the slip angle is generated... And Strangely enough, why the car needs to be rotated and by how much depends on how well the car is generating it's slip anlge...the reason for the thread.

I guess the most basic form of "rotating a car" that everyone here has experienced. It is like accelerating through a corner, you get that feeling about half way into a sharp corner at full throttle that you wont make it.... at this point you roll out of the throttle, weight moves forward gives the front tires bite and it almost feels as tho you are on a rail. It is that point were the grip comes back to the front tires we refer to as "rotating" and again hit the throttle. If you roll out of the thottle too hard or even tap the brake, you might even end up swapping ends..

This is the most basic example of "rotating"

If Dale jr gets his car to rotate at 130mph and is confident with the car under him, and Jeff Gordon has his car rotating at 132.7mph and is confident with the car under him... Jeff gordon will in turn have a faster lap time, he wont be braking as hard into the corner and he will power off the corner with slightly more forward momentum then jr.

speedsense - 12 April 2008 05:10 PM

I have met very experienced drivers that could not explain the difference between slip angle, drifting and sliding. Simply put, this is probably the most misunderstood topic in racing

Trying to understand all what's being said in this topic, and learning a lot! Thx for sharing!
But totally confused now: what IS the difference between drifitng, and sliding?

speedy_bob - 16 April 2008 03:03 AM

speedsense - 12 April 2008 05:10 PM

I have met very experienced drivers that could not explain the difference between slip angle, drifting and sliding. Simply put, this is probably the most misunderstood topic in racing

Trying to understand all what's being said in this topic, and learning a lot! Thx for sharing!
But totally confused now: what IS the difference between drifitng, and sliding?

Inflate a balloon, tie it up, and draw a line with a marker on opposite sides of the balloon (parallel to each other). Place the balloon on a floor and line up the lines you have drawn. Place your hand on top (this will represent the wheel, the balloon is the tire). Now add a little downward pressure so that the balloon flattens against the floor (represents the tire contact patch) and the lines stay in parallel (A stationary tire with the weight of the car on it). Now with the slight pressure applied, turn the balloon,twisitng against the floor (this represents cornering force or turning force). The resistance you "feel" is the balloon attempting to return itself to round (represents the "spring rate" or construction of the tire). The two lines will no longer be aligned, (this represents slip angle ). If the balloon were rotating, the "path" the balloon would follow would be slightly different than your hand. The wheel (your hand) would be pointed slightly to the inside of the path of the tire.
Putting all four tires in this "slip" condition is a Drift.Technically your tires are at maximum grip, but watching from outside the car it would "appear" to be sliding though it isn't.
IF you keep turning the balloon (increasing the slip angle...) eventually you "break" the grip on the floor (this would represent a slide..)
So simply put, slip angle and drifting is grip and sliding is a loss of grip.
And not to be confused with the "sport" of Drifting which infact is not drifting at all, but sliding....

Hope this makes it a little more clear..

SS,
thx again!
Have been thinking about it, took my copy of Drive to Win and re-read the part about tires, slip angle and all, and FINALLY "getting" it, I think, to the bone.
Then had a little eureka moment: when I drive home, there's this fast, long 270° highway exit, an I think (front wheel driven car, I live in europe) I have already experienced "using" the slip angle; it's when my front tires start to make this "GRRR" sound, and if I then push some more (or turn the wheel even more), the front tires start to, uhm.. squeel (english is not my native language) or whistle. THAT's when I start sliding at the front.
So, before the whistling sound, there's the GRRR sound, and I always knew, I wasn't sliding just yet then. But I had no idea what caused the tires to make that sound.. now I know! Using the slip angle!Eureka! A bit wiser yet again!.

Have a nice weekend all!

speedy_bob - 18 April 2008 01:06 AM

SS,
thx again!
Have been thinking about it, took my copy of Drive to Win and re-read the part about tires, slip angle and all, and FINALLY "getting" it, I think, to the bone.
Then had a little eureka moment: when I drive home, there's this fast, long 270° highway exit, an I think (front wheel driven car, I live in europe) I have already experienced "using" the slip angle; it's when my front tires start to make this "GRRR" sound, and if I then push some more (or turn the wheel even more), the front tires start to, uhm.. squeel (english is not my native language) or whistle. THAT's when I start sliding at the front.
So, before the whistling sound, there's the GRRR sound, and I always knew, I wasn't sliding just yet then. But I had no idea what caused the tires to make that sound.. now I know! Using the slip angle!Eureka! A bit wiser yet again!.

Have a nice weekend all!

Speedy Bob,
Most street tires were not designed to spend time at a slip angle and some wheels aren't either. Unbeading a tire because of putting it through a slip angle can happen and unbeading a tire is an instant loss of pressure of your tire, just as if it exploded, and the results can put the car on it's roof... tire pressures need to be at the rated maximum, if you are going to mess around with this on the street and hopefully you are smart enough only endanger yourself and your property and nobody elses.
It is not until a driver gets involved in racing on a closed circuit that one realizes that driving fast on streets or street racing isn't even close to what is experienced on a race track. Though you may experience the "limit" a few times on the streets, a race driver experiences the limit every time they turn the wheel, touch the brake or the throttle. Something that could never be done on the street.

SS,
You're totally right!
I can assure you, I'm not racing my car daily, and I do know, that I'm far from being a racecardriver.

I'm too scared/aware of the risks, to try racing manouvres on the street anyways, nor do I want to crash the (company) car. I take care of not endangering other people, and when I take the above mentioned turn, I assure you, there's no one but me. I'm on the inner lane (of 2) and it's only 1 second or so, that I experience GRR or "WHIIEE" tire-sounds

But I did learn, that I shouldn't automatically feel scared, when a tire whiee-s: let me explain: common behaviour od most drivers, is to think, that they've lost the car, when the tires start to whistle. But as you learn more about car physics, you know that you shouldn't panic just yet, at that point.
My car, as most front wheel driven cars, will start to understeer a bit, and that's my cue to back off.

I know I shouldn't even try to induce understeer on the road, but it's a bit like ABS: try it a couple of times, with no one around, and when you actually need it, at least you'll no longer get intimidated when the knocking-back on your pedal acts up, in a real emergency braking situation.

(I've known family members, to back off the brakes, because of "the horrible sound my brakes made!")

I keep my REAL racing to sim-racing, but at that corner, a little whistling of the tires, doesn't completely offset me instantly. I still get "flown over" by the BMW's, merc's and whatever car with more then my 100 BHP engine overtaking me.

I'm not your average "I can handle it! I KNOW racing" dude, on the road I'm driving pretty defensively. Hope this gives you a clearer image, of what kind of driver I am.

Actually, It's been 3 months already since I last made a tire squeel, and my front tires last for 35.000km.

I know I shouldn't even try to induce understeer on the road .........

Brilliant.

I keep my REAL racing to sim-racing .............

What?

RobsanX - 02 April 2008 09:56 AM

I hear this term thrown around a lot, but I don't have a clear understanding of what it means...

this is a term modern drivers use, in the old days he would just say, he blew my doors off