"The limit" of cars

[raymondu999]

Hey all.

We all often hear of "the limit." "I was on the limit" "my lap was on the limit." How is it that the drivers know this? I mean, if we drive a normal road car (well if I do anyways) say I'm taking a corner fast (which I shouldn't really do ) I can kind of feel, "uh-oh. I can't turn any faster than this or I'll flip, or spin out."

But I imagine having tons of aerodynamic downforce will change this picture, and the cars will have a different limit based on their setups.

So how is it that drivers know the limit? Is it a computer calculation, more "thinking" thing? I mean, we often hear "you look for the xx meter marker and that's your braking point" meaning they have to think of what their braking distance is, or maybe, "ok. Brake until 200km/h here, cos that's the fastest I can go. Or is it more like a "feel" thing, a "seat of the pants" thing, "Ok, I can't turn any faster?" Because you obviously have drivers that are not driving on the limit, as their teammates outqualify them, and sometimes you push too hard, and you lose time then as well, indicating that perhaps they couldn't feel the limit as good as their teammates did.

Any and all explanation (from an F1 driver or open-wheel racer with odles of downforce would be great ) But I'd take any other peoples' theories as well

[mep]

Normally you never reach the limit with your road car. You don't want to do so because this can lead to a heavy crash. Well I was beyond the limit just a few weeks ago. I was leaving the autobahn on a nice bend on wet track and tried some special downshift technique (sometimes I try funny things on the road). It didn't went really good because some noise from the front appeared (no squeezing probably because the road was wet) and I feeled some understeering. Immediately after that I got snap oversteer and had quite some work to hold the car on the street in a quite big drift angle. Next time I know for what signs of the car I have to listen. When I really want the car to operate on its limit I can go until I feel the understeering but not further. On this point I should keep the car for most of the time.
I actually thought about building my own home made g-meter to see how much g's are achieved in corners. I read in a book that normal drivers don’t go beyond 0,3g’s (source: race car vehicle dynamics).
I am really a bit curious about the g's, I think that can even add some safety becasue I would keep away of the limit then.

A race car should be designed to operate on the limit. It should be predictable when it reaches the limit and don’t surprise the driver with some strange behaviour. For example the steering geometry can give some force feedback about the cornering forces. The driver feels then when he is close to the maximum force of the tire. A normal car steering wheel doesn’t give much feedback.

[shamikaze]

Your average iPhone can tell you the g-forces it is subjected to. pretty sure you can find a app to do this monitoring/reporting for you

[marcush.]

you will reach the limits of your ability quickly in low grip situations,eg.ice ,snow ,and wet ..
thats why more accidents happen when conditions change ,as nobody would drive to the limit in dry conditions as you´d feel not at ease or comfort when doing so..(all the little bits you have stored in the trays fyling around in the car when using the brakes to the max or turn in into the roundabout ,clipping the curb just enough to open the exit.. comeon.. in rain or ice conditons people lack of course common sense as they have
NO idea about the limit .,but in these conditions suddenly the limit is very very close
In no ways it is more difficult to drive on ice or on snow ,IF people would stay away from the limits of adhesion and adjust speed ,so they can do what they are used to do :drive geographically and not risk anything.

[RH1300S]

When a driver talks about 'the limit' they are not just talking about the cars. They also mean they have left NOTHING in the track. No margins to sweep up errors, any faster and they run out of road. You can see when a driver leaves nothing spare, there is a sort of inevitable momentum about a lap, the car cannot go anywhere else due to it's velocity and rate of turn at any point.

The drivers feel the grip all the time - they have plenty of experience at high 'g'. Normal mortals wouldn't know what we were feeling until we had plenty of seat time. They will feel it exactly the same way we do in normal cars at lower grip levels.

They feel it through the wheel, through the brake pedal and the throttle. It's a sort of sixth sense - when most of the top drivers say they were at the limit, I'm inclined to believe them.

I have experienced the limit of my cars/bikes several times, I have sometimes experienced the limits of a track - but seldom (possibly once ever) I have put both together at the same time. Which is why I will never be a world champion.

Separate limits are quite easy to find - matching the track and car limits is much harder and top racing drivers can do it almost at will.

[Jersey Tom]

From my limiting driving experience... you know what your racing line is and where your braking points are, etc. When you take a lap you try to hit them all perfectly, but you can tell when you've missed them or when you've blown an apex or whatever. That's part of it.

Then there's the limit of the tires. When you take a corner you can just feel when you are literally out of control. You put the car on it's path and you're pretty much along for the ride.. where at that instant your steering input does little or nothing (front tires saturated) and if you add any more throttle or brake the rear tires will give. For me it's a very "Oh --- I hope I got this line right" type feeling!

[mep]

One thing I forgot to write. I think even the top drivers have to go slightly beyond the limit to test out where it is. So on a weekend they need to get used a bit to the track the car and the tires. Some mistakes on Fridays are no problem. When it comes to the qualification they will by used to the track and get a almost perfect lap. I don't think there is a 100% perfect lap, there are always some small mistakes. These guys are humans no robots. During the race its more about being constant (~95% of possible lap time).

Regarding ice:
I feel more comfort to drive on the limit on ice than on dry road just because the speed is much lower and you actually touch the limit almost all the time. Therefore you get a feeling for it quite soon. I rather want to know where the limit is than getting surprises by it because it can be to late then. Whenever there is snow I jump into the car and search for some empty parking areas to train some low grip driving.

When it comes to low grip surfaces I think of rally cars. Where actually is the limit for a race car on low grip surface? Driving technique is totally different for them because they get the car into a drift and overplay limits of tire grip by this.
They put a car that would understeer trough a corner into a stable power-oversteer condition.
I think rally cars are regarding to driver and car technique a quite interesting topic. Sad we don't care much about it here.

[marcush.]

I happened to have a real amateur driver having a go for me in Hockenheim .He had done some laps in Hockenheim already in trackdays and was not doing silly things...As it happened he was dead slow.We discussed about where he could find time and he told me :no ways the car is at the limit ,braking later is impossible ,and earlier throttle as well ,it is optimum from my side... and the car is just wonderful.
My answer was:look at the time this is at least 2 seconds slower than expected ,where do you think the time might be? He shrugged complete clueless,and I asked him if he used the entire track.
what do you mean? I could see you did not use all the curb and plastic grass on the exit to the main straight ,and you are not going all the way to the edge of the track in approach to Nordkurve.
I want to keep the margin as safety..I never drove so far out....maybe its dangerous...
I told him to go slow for once and go where he thinks the car would go when he drove faster...just to see how it felt...he tried .2 laps later he was not even pushing but was already going quicker than before,another five laps to build cnfidence and he did it everywhere and had found:2 seconds.He did not put a foot wrong still ,no risk involved ,but using the whole track made such a difference.(small circuit Hockenheim 73sec in that car)
ah btw he now drives a Norma and has won the championship in the first attempt..

of course f1 drivers know where to go ..

[747heavy]

there is another limiting factor to mention -> power (engine)
If the driver is flat through a given corner, that´s it, he can´t go faster.
The same would be true for top speed.

Therefore we could say, we have:

power limit´s -> as how fast we can go
traction limit´s -> tire,grip (often the main limiting factor)
human limit´s -> ability, skill, fear, physical limits (e.g. black out due to high g`s)

@ mep

you will need a decent amount of downforce to corner at 3g lateral acceleration.
a non/little downforce road/race car will normally top out at around 1.5g max under normal track conditions.

[marcush.]

this nicely shows . a low power car needs to keep momentum at all cost ,you just cannot afford to slow down ...so very little steering input is very high on the agenda .
with high power cars you still can be quick with that aproach but in reality you will likely find time shortcutting and relying on acceleration .so it opens new options until you again run out of grunt .
but the key to quick laptime is less finding the limit but never exceeding it.You could be fighting to save your life in each corner approach but still be seconds off the pace.
But you could deliberately brake early and still post a decent time.
a lot of drivers don ot understand that you need to release the car to be quick so you give a steeering input to change direction but then let the car find its way to the exit not steering ....every input is indeed slowing you down.. very apparent when indoor karting .I d say the limiting factor usually is the driver and I loved it being asked how quick our racecar was around a circuit....

[raymondu999]

Exactly.. but with each new lap, with track evolution, changing conditions, wind etc, this is a set of moving goalposts. If I ever saw one.

[mep]

@ mep

you will need a decent amount of downforce to corner at 3g lateral acceleration.
a non/little downforce road/race car will normally top out at around 1.5g max under normal track conditions.

ups I wanted to writte 0,3g sorry.
(Hm I start wondering again if anybody reads my messages)


1,5g for a non/little downforce road/race car...
I think even that is to much at least for non aero road car.
You can get short peak when you have very very light non aero race car.

[747heavy]

the simple underlying equation for the complete car is.

Ff = µ x W (= m x g)

Ff = friction force (needs to be equal to F=m*a, to support the car in lateral accel.)
µ = coefficient of friction
W = weight of the car ( mass x gravitation) or vertical load

so µ becomes your limiting factor, as W is given (mass of car x gravitation)
for racing tires on a rubbered in race track it is possible to have µ>1.

For a road car on normal tires on a normal road I would think the limit is around 0.8-1 g lateral accl.
Race cars (Touring Car/GT) with low to moderate downforce corner in the 1.3-1.5 g range.
Again tires are the important factor

[marcush.]

ah ..you have to make the best out of what you have ..

[mep]

Yes I agree to all but what you want to say by this?

The only important think I would add is that µ is also a function of load µ=f(W).
The more force you put on your tires the more µ drops.
So its Ff=µ(w)*W
Thats why I said you can only get 1,5g with a very light car or by aero.
If that's the sentence you are answering to.