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Hi guys. It's a simple question, but still got no reasonable answer. It's evident that rally drivers do it because it's fastest, and formula 1 drivers don't because it's not.

You can see in tarmac that sliding=less force.

Does this apply to rally? Why do rally drivers slide?


Thank you very much!


Bye bye,

Caito.-

Part of it is due to the nature of how tires grip on dirt versus asphalt.

Dealing with dirt is very different than pavement. The traction is a lot less, and the tires do not break away in the same manner as pavement. On pavement, as the car turns, the tires are achieving a greater and greater slip angle. On road race slicks, once you pass a certain slip angle, traction drops off very rapidly. On a passenger car tire, the traction drops off much more gradual, so that the average driver can usually detect it and correct it before the car swaps ends. But on the dirt, the breakaway point for slip angles is waaay out there, you have to be very sideways to find where the tires let go. So the basic nature of dirt allows you to put the car sideways in a manner that is almost impossible on pavement.

On dirt, you have to find traction, or manufacture it. Because you can achieve great slip angles in the dirt, racers have found that one fast way around the track is to use the driving wheels like vectors. You want to go fast and corner? Going fast means you want your force vector to point straight backwards. Going around a corner means you want your force vector pointing straight to the side. Do what comes hard on pavement but easy on the dirt is to combine both force vectors and the resultant force vector is pointing at a 45 degree angle to the rear and side. Like this.



The front tires aren't doing much, but in this left-hand corner if you examine the rear wheels you can see that they are pushing (the force vector) not only backwards but sideways. If you put that same car on ice and imagined that the fronts could maintain traction, the same action would be happening ........regardless of the level of traction.

+1 to Dave.

Even if you wanted to drive a F1 car like a dirt or rally racer, half sideways through turns.. it'd generally be impossible. Either you work at small sideslip angles, or you spin out - fast.

There's also some aero component between sedans/stock cars.. and open wheelers. On an open wheeler you have significant downforce, and the more sideways the car is, the more downforce and corner speed you lose.

On a vehicle with low downforce and a lot of side area, you can be sideways and not care about losing vertical aero load! There's also the advantage of picking up aerodynamic sideforce (cornering force) as you increase chassis slip. If you watch stock car racing you'll often notice the cars are set up to dogtrack.

Dirt & gravel track vehicle dynamics are really interesting given the angles involved, and how your driving forces get mixed in with cornering to a significant extent.

Jersey Tom wrote:Even if you wanted to drive a F1 car like a dirt or rally racer, half sideways through turns.. it'd generally be impossible. Either you work at small sideslip angles, or you spin out - fast.

Unless your name is Gilles Villeneuve:





Ps: I know the technical differences btween those cars and current ones, but, hey! Sorry JT, just could not hold

So we could imagine that to "twist" the rubber so it provides us with force, as the surface is loose we need to have a greater slip angle. In which case that would mean that to have greatest lateral force = sideways. Greatest longitudinale force = "spin" them, with that "spin" I mean to have wheel speed different than the speed the car is going. Which, if i'm not wrong, means a big slip ratio. So the resultant is a very entertaining sport.


More formula 1 power slide



Rally power slide
[youtube]http://www.youtube.com/watch?v=ewxrNSOKFow[/youtube]


Thank you very much for the answers!

Caito.-

twice in one day....Gilles is having a busy day...lol...

Caito wrote:Hi guys. It's a simple question, but still got no reasonable answer. It's evident that rally drivers do it because it's fastest, and formula 1 drivers don't because it's not.

You can see in tarmac that sliding=less force.

Does this apply to rally? Why do rally drivers slide?


Thank you very much!


Bye bye,

Caito.-

Modern rally cars don't drift/power slide that often anymore. The lines they take are very similar to that of road-racing cars. As it is the fastest.
On gravel they will sometimes do it, say in a hairpin, but it's not common. On snow it's far more common, probably because with the tyres they use they can carry more speed through the corner by setting the car up for the exit before they reach it.

It's why rally is now seen as "boring" compared to back in the supposed golden age. But cars are now faster than they were then

I love that video with Gigi, he's almost going backwards at one point, just amazing

It also has a lot to do with the pendulum effect.
Rally cars are designed with the weight at each end to allow controlled break away and a distinct driving style capability.
F1 cars (at least today) have the weight very close to the centre of the car which results in a sudden break away at higher speed.
Of course it is difficult to see the effect with so much DF.

The Gigi video is not a big drift, it is a handbrake turn.

drifting is not the quickest ways for rally but it is safer.

Walter röhrl was one if not the first to not drift much but try to be as precise as possible.if you loose the car then you are lost ....if the car is already in a drift this is a unstable but very controllable unstability ...if you know the game you get the car around vcorners that are effectively tighter than the turn radius of that car.

So in effect a dirttrack car has optimum grip at 40+ degrees of slip angle ,a f1 car at 2 (or whatever) degrees simple as that.

when they still used diagonals (tyre) in F1 slip angles were a lot bigger so more drifting and wheel spin was possible and necessary to get the best grip..

[youtube]http://www.youtube.com/watch?v=s1Tiodhkv7g[/youtube]

[youtube]http://www.youtube.com/watch?v=v_vwRqUF ... re=related[/youtube]
*2:29 is just...

It might not the be the fastest way for an F1 car...but it's so epic they should get points for stuff like this.

In addition to, rather than insted of the excellent reasons that have gone before, once the tyres have broken away it is much easier to 'feel' the grip levels.
On most tarmac rallies the quality and condition of the asphalt can vary quite a lot. Road camber, bumps and potholes can cause big fluctuations in grip levels.
On Gravel every corner can have different grip levels, and these can change during the day as the top layer of material is removed by the early runners.

The driver has to make a prediction (sometimes assited by pace notes) of how much grip is available on an approaching surface and therefore what braking distance, and corner entry speed is appropriate.
To help with this they can regularly break traction and update a kind of mental library of grip levels they have built up during recce runs and through the stages so far. Using wheelspin in lower gears and putting a bit of angle on the car through lower speed corners is one way of doing this.

safeaschuck wrote:In addition to, rather than insted of the excellent reasons that have gone before, once the tyres have broken away it is much easier to 'feel' the grip levels.
On most tarmac rallies the quality and condition of the asphalt can vary quite a lot. Road camber, bumps and potholes can cause big fluctuations in grip levels.
On Gravel every corner can have different grip levels, and these can change during the day as the top layer of material is removed by the early runners.

The driver has to make a prediction (sometimes assited by pace notes) of how much grip is available on an approaching surface and therefore what braking distance, and corner entry speed is appropriate.
To help with this they can regularly break traction and update a kind of mental library of grip levels they have built up during recce runs and through the stages so far. Using wheelspin in lower gears and putting a bit of angle on the car through lower speed corners is one way of doing this.

+1
It is just a shame that current F1 drivers can only enter this level of education when the car gets away from them because the DF masks it out so much.
Almost like hanging on in a manic roller coaster rather than driving.
Perhaps it is why Kimi jumped ship?
God I hate high levels of DF.

it's because the groud.
the groud for rally is soft and the ground for f1 is hard.

Caito wrote:Hi guys. It's a simple question, but still got no reasonable answer. It's evident that rally drivers do it because it's fastest, and formula 1 drivers don't because it's not.

You can see in tarmac that sliding=less force.

Does this apply to rally m3ds? Why do rally drivers slide?


Thank you very much!


Bye bye,

Caito.-