How to judge the tyre traction limit?

Finding the limits is tricky, and I don't know of a way without risking going over the line.

Speed channel has been showing F1 practice sessions, and I've noticed that even Schumi will lose it in practice -- he's finding the limits before the actual race, so he pushes just so far and no further in the race, lap after lap.

There are two suggestions I might make:

1) Find a track with "safe" run-off areas to push the F-car to its limits.

In the 'States, wannabe rallye drivers tend to practice handbrake turns in empty, snow-covered parking lots -- huge empty expanses where a spin won't hit anything.

2) Practice pushing the limits in a car whose limits are far lower. The feel won't be identical to the Ferrari, but you'll start to get a handle on when things are coming loose.

A mechanic once asked me why I keep the Alfa Spider when I have the Ferrari. That's why -- the Alfa hits its limits far lower than either of my other machines, and reminds me to keep a "proper" line in turns.

And, FWIW, the Alfa's tires squeal like a banshee long before the grip runs out.

3) Don't race a car if you're worried about chipping the paint. A dive into the kitty litter hurts your pride more than the car -- other than cosmetics. If you're worried about the loss if you wrap up the Ferrari, then try racing something a tad more expendable. You won't be as worried about pushing the limits.

And learn how to work on your own race car -- racing breaks things, and you (or your mechanic) will have to put them right again.

 

Without launching into a discussion of understeer, oversteer and tire grip.... (Does the UK have driving schools like we have here in the US, where you bring your own car and are assigned an instructor for the day? Porsche, BMW and Ferrari clubs all have such days here.)

One very old and well known racing practice trick, an easy way to explore the limits of grip: in a given corner, draw a tighter line. In other words, pretend the corner is narrower than it really is; move the track out point 10 feet away from the edge of the track. Now keep increasing your speed, but in small increments. At some point, you'll reach the limit of your tire's grip, and you'll slide wider than the imaginary track-out point you've created. But that's OK, as you've still got 10 feet of track left as your margin. But dancing on the edge in this way will train you in getting a feel for how well your car will stick.

vty,

--Dennis

 

Even easier way, get on a skid pad. Pay attention and go faster and faster until you loose it. The important point is to remember what it felt like just before you did.

My driving coaches always told me, if you don't spin it every so often, you're not trying hard enough.

 

here is my take on it:

slip angle - angle between the direction a tire is pointed and the direction it travels - reason: tire deforms through torosional forces
yaw rate - angle between direction the car is pointed and car travels

you can differentiate three cases

- driving within limit of adhesion
linear behavior - cornering forces (generated by tire) are proportional to slip angle - yaw rate proportional to steering angle - car is responsive to steering; it goes where you want

- approaching limit of adhesion (transition)
non-linear behavior - slip angle will increase without increase of corresponding lateral force - yaw rate and steering angle become loosely coupled - car becomes less responsive to steering input; car floats

- driving beyond the limit of adhesion
tire slides - care will follow lateral force - steering not responsive; car spins

I don't believe that it necessary to go beyond the limit of adhesion (spin) to figure out how to sense traction limits

it is a very distinct sensation when steering angle and yaw rate become disconnect, i.e. when the car crosses from linear behavior to non-linear

the car starts to "float" while before it feels like on "rails"

the best way for me is to push the car in an appropriate turn (lots of run-off space) and do little sawing movements with the steering wheel to test if car still respondes

note that the transition phase is very narrow especially for racing tires, which makes above task hard - less so with street tires

or much simpler drive in the rain

 

Great explanation. I would only add one thing - get thee to a driving school at a track. Trying to do this on public roads will only lead to grief.

Dale

 

this is a funny thread.

the poster is trying to , basically , ask how to corner faster.

and the guys replying are trying to tell him how to do so , theoretically.

of course , the theory is just that , theory.

its track/road time that counts.

simple , just choose your corner , and try different lines and speed and
different throttle/brake applications , eventually , you'll spin the thing ,
and thats your skills limit with that car on that given corner , with those
black rubber thingys .....

 

Excellent explanation.

If the front of the car is pushing wide (thus you have understeer. Tyres squealing usually would mean that the front is pushing wide ...) and you keep on the throttle the car will keep pushing wide ... while a little understeer can be a good thing when accelerating on to a straight out of a sweeper (means you can keep on the gas a little more than if the car was oversteering), it is usually is a hated thing.

Thus if you are getting understeer entering a corner you are either entering too fast OR not setting the car up correctly for the corner via your driving (ie. the front has too much weight on it still ... maybe braking too late). Yeah do a course ... and if you can get your hands on it read an excellent book by Jackie Stewart on performance/race driving. He makes a lot of sense and helps you understand what the car is dynamically doing (ie. why entering a corner after braking too late causes understeer, etc. ... ie. the front suspension has compressed on to the bump stops and thus the effective spring rate is way too high, hence outside loaded wheel has no travel ...), and thus how to work the machine better.

Pete

 

Have to agree. Last year I was lucky enough to have Derek Bell give me few demonstration/instructional laps in a friends 996. After questioning him repeatedly about different aspects and similar concerns as our Scottish colleague, he turned round and calmly advised "It's practice , practice, practice."

Modena Scot; if the limits feel low don't be afraid to change to CS wheels and tyres as they significantly increase the grip and traction on track days.

Epilogue
My friend was unsure of Derek's CV and only asked for his few instructional laps due to my peer pressure. Derek noted, "It will be better if I drive and you watch rather than me criticising your technique"

Nervously handing over the keys for the first time ever to someone else, my friend asked, "You are accustomed to driving Porsches?"

I burst into a heap of giggles, whilst Derek calmly replied, "I've won Le Mans 5 times in a Porsche, so I think I can handle them well enough"

 

I sense a major disappointment coming up. Sooooo.....

Before your track day, get your 360 wheel alignment not only checked, but apply front negative camber of about 1.5 degrees minimum, whilst maintaining std caster and toe in figures. Get the rear end checked to be std, but increase rear toe in to about 4-6mm total.

Get this done by a Ferrari specialist and NOT a regular tyre shop that claims to do wheel alignments. You'll need special shims for the camber anyway, and I've re aligned so many cars after being butchered by local tyre shops that it's not funny anymore.

Any road car on road tyres on the track suddenly feels like a floppy old boat with a broken rudder, and a 360 is a sensitive beast. Its' std front end alignment for track use is next to hopeless.

 

Your car will have terminal understeer if it is standard, which on the track can then cause snap oversteer.

To drive your car in such a way as to safely explore the grip limits, you'll need a better balance.

Also, you'll simply destroy your tyres trying, uness you do something to use them better... but you'll still hurt them.

 

We're just trying to break it to him gently.

Most street cars have an understeer bias, to protect the manufacturer from liability for poor driving skills -- or, more often, inattention -- behind the wheel.

Ideally, you'd like to have a dedicated track car, with the suspension retuned for each track. But for the weekend warrior, you can't go too overboard setting your street car for the track, or it might bite you when you get that cell phone call on the off ramp during the daily commute. (Plantronix noise cancelling headset - $39.95. But even with "hands-free", calls cost you concentration.)

Besides, driving your track car on the street tempts you to behaviour that gets you on the wrong side of the local gendarmes.

 

Cheers!

It matches colour of my MInardi race suit which in turn matches my speed on the track!

Even if you are going on a track day before driving school will there be instructors there? If so, the thing that let's me go quickest at at a track day is an open mind and unblocked ears.

Enjoy

 

That setting I gave you is the most basic of first steps. To make the car really good, you should lower it, change the rake, change camber all round, cornerweight it etc etc etc.

The handling is a function of the way you drive it, but the negative front camber will help save the outer edges of the front tyres, and the rear toe in will improve braking stability... the two biggest areas of problem with a roadie on the track.

The camber and toe figures I gave you are just a mild setting. You can run up to 4 degrees of camber at either end if you want, and I'd run 10mm of toe in at the rear for best braking stability and early power application, but that's extreme and only good for a qualifying type lap.

 

Well...FFixer is correct but I would leave the car stock oem settings if you are 99% street and 1% track and you most likely will set the aligment and forget it. 99% of street drivers will not take the car to the alignment shop to get set back to stock settings. While FFixer's starting alignment is not radical by any means it is not as Ferrari intended for its streetcar. You can make a Ferrari handle quite differently than "from the factory". Assuming the stock alignment is correctly set to stock I would only alter this after I had some tracktime. You will be amazed at how much driving is the driver and not the car. You could be well inside the traction range but forcing steering and braking inputs that upset the car and break traction. Instead of changing the car find a track buddy who is faster than you. Progressively build speed as you follow that person's line...and learn. At some point you will plateau your car vs. speed vs ability and then you improve either or all of the three by driving school, faster car, modified car etc...

 

Good advice fatbilly, but I guess it depends on the track you go to.

Down here for example, Phillip Island will KILL your tyres if std alignment is retained, but other tracks are less tyre hungry.

Find out what type of track you're going to first I guess, but even so, the std 360 front camber is near zero, which is just silly on the track.

 

I am with you her in general – changing camber and front toe-in will make for a nervous car on the highway - however I think doing an alignment to check for correctness is a good thing before tracking the car (and he has done it!) – furthermore I would change the rear toe-in of the Modena to the Stradale setting just to fix the twitchiness in the back (big confidence builder too)

Not sure what your concern is about oversteer – in my experience the 360 is perfectly balanced with the obvious production car bias for understeer – every car will tend to understeer into the corner and tend to oversteer out of the corner simply because of weight transfer – the only thing to watch for is the ability of the 360 as a mid-engine car to rotate very fast – so when the car looses traction things happen very fast without a lot of warning – but this again is more of an experience thing how sensitive you are for what the car does - can’t say that I have mastered it

Phil can you elaborate – I can’t figure out what situation you have in mind that is not caused by the drive
- P-car like snap-oversteer – don’t see the right rear overloaded during acceleration out of a corner – not with the 360 balance
- Suspension bind snap-oversteer – not with a sensible or the OEM setup
- Rear toe-out snap-oversteer – I could see if someone lifts in a corner but that would be a drive’s error in my books – the car goes to toe-in if the suspension is compressed; right?

 

Until you have experienced the extra grip that is available by increasing the front camber, you honestly have no idea what the balance can be like.

Just 1.5 degrees or so on the front will not make it nervous on the road, quite the opposite. It will give it bite and feel.

Snap oversteer is when the driver tries so hard to fight the understeer, that the car is provoked by either throttle application or aggressive steering input, into a tail slide. Powersliding is NOT to be confused with oversteer. Oversteer is when the tyre lateral grip limits are breached. A std car has huge scope for imrpovemnt to its' front tyre grip.