[greenhorn]

heh, thanks Rehan and doomsday. I guess my knowledge of the technical terms regarding handling needs improvement . anyway I'm glad i was able to give you guys the correct picture. Thanks for all the advice

[sudarshansarma]

You guys are talking of skidding or sliding. Aquaplanning happens only at high speeds when the tyres ride on a thin film of water with no direct contact to the road. Symptoms of aquaplanning are the steering getting extremely light and the car not responding even to minimal inputs from the steering. The best way to avoid it is to check the threshold of speed above which your car aquaplans and stay below that. If you need to stop in an emergency when you are aquaplanning,,umm..you cant but ABS does help for sure.

[jalsa777]

nice explanation doomsday....

i will shed some light on aquaplaning...(what happened to u was not aquaplaning most probably)

the roads where we would probably encounter aquaplaning are highways where high speeds are involved.


These highways have banking on the turns to help u turn better...
so....if the surface is good...water wont accumulate on the turns..

aquaplaning will usually happen only on the straights....

when this happens.....
DO NOTHING...
thats it...absolutely do nothing..
dont lift the throttle (applies to most normal situations)
hold the steering tight and in the direction the car is moving
AND DO NOT BRAKE

suppose u are aquaplaning in a corner (highly unlikely beacuse od the reasons mentioned earlier)
first of all U R IN DEEP TROUBLE......lol

just point the steering into the slide....the direction in which the car is sliding (not the direction in which u want it to go)


dont brake....u can slowly release the throttle

Note from Mod : Please take the time to type out your posts in full words as per Team-BHP rules. Avoid the use of SMS language (u = you, u r = you are, etc), and please use proper punctuation and...not...type...like...this.

[v1p3r]

If you brake while aquaplaning in a straight line, more weight will shift onto your front wheels. This, coupled with the weight of the engine, should make sure the tyres cut through the water and bite down. I've experienced this on occasion.

Buy better tyres.

[Rehaan]

Originally Posted by doomsday

Dude, oversteer happens when the car gets nose heavy and not tail heavy (one exception which I have spoken about later)....

Weight is only one of the variables in the equation, hence the above statement is not complete - and therefore not true in all cases, as you have mentioned (the 911 example).

I would rephrase that statement to say :
Oversteer happens when the lateral forces acting on the rear of the car overcome the limits of the available traction at the rear.

The lateral forces are a function of mass/weight (momentum).
And the available traction is also a function of mass/weight (downwards force)!
(Therefore greenhorn & Doomsday are both right).

So, back to lateral force VS available traction at the rear :
Braking does increase chances of oversteer since it transfers weight to the front (doomsday's reasoning), however, if the car has an increased mass at the rear, there is more lateral force being generated by cornering - also increasing chances of oversteer (greenhorn's reasoning).

So the question is : at what point does weight at the rear stop aiding traction and start aiding oversteer?
Obviously there is no general answer, since it depends on the traction vs load curves of the tyres, and to add to that, the additional variables of speed, road surface, rate of change in direction, yada yada.

I hope that makes sense, and is not too far from the truth.
Maybe this could have also helped puffy when it came to handling JLo.

Originally Posted by doomsday

P.S. Excuse the smudgy sketch, it was the best I could manage in MS Paint.

MS Paint is the best. It is the (un)official explaination tool of Team-BHP.

Originally Posted by v1p3r

If you brake while aquaplaning in a straight line, more weight will shift onto your front wheels. This, coupled with the weight of the engine, should make sure the tyres cut through the water and bite down. I've experienced this on occasion.

True (about better chances of regaining traction AT THE FRONT), however, what that means is the rear will still not have traction, which risks having the tail come out and making the car go sideways.
That is why people have been suggesting not to make any input changes which would result in a situation like that.

See the video in this post, quite interesting : http://www.team-bhp.com/forum/modify...tml#post766056

cya
R

[rks]

Originally Posted by v1p3r

If you brake while aquaplaning in a straight line, more weight will shift onto your front wheels. This, coupled with the weight of the engine, should make sure the tyres cut through the water and bite down. I've experienced this on occasion.

Buy better tyres.

Braking could cause uneven forces that pull your car in one direction, apart from possibility of oversteer mentioned by Rehaan. And tyres will probably lock up, leading to loss of steering control. For a FWD at least, better to simply lift the foot off the pedal and try to keep steering control.

I agree on the better tyres bit. And do not upsize when an upsize is not needed, as in the case of my old Santro. Chances of aquaplaning on upsized tyres are significantly higher.

[maestro]

Could the fact that you had 3 others in the vehicle, (at least 2 behind) cause the vehicle to be more tail heavy than normal and so contribute to oversteer, especially considering it was a ramp?

[jalsa777]

Originally Posted by v1p3r

If you brake while aquaplaning in a straight line, more weight will shift onto your front wheels. This, coupled with the weight of the engine, should make sure the tyres cut through the water and bite down. I've experienced this on occasion.

Buy better tyres.

When aquaplaning, the tyres have lost surface contact.
So, if u brake, the tyres will lock up (water does not provide any grip).

Rolling tyres have more traction than locked up tyres.

Basically, there wont be any weight shift cause you wont be slowing down.

It will just make regaining steering control a longer process.

(you have tons more experience than me.
just adding my 2 cents)

Originally Posted by jalsa777

When aquaplaning, the tyres have lost surface contact.
So, if u brake, the tyres will lock up (water does not provide any grip).

Rolling tyres have more traction than locked up tyres.

Basically, there wont be any weight shift cause you wont be slowing down.

It will just make regaining steering control a longer process.

(you have tons more experience than me.
just adding my 2 cents)

that makes sense. I've never tried braking while sliding or aquaplaning , and i dont think its the right thing to do anyway. the reason has been explained very clearly in the quoted post.

also
I may be wong here,but I recall from physics class in school(12 yrs ago) the weight of a body has surprisingly little to do with the frictional force it exerts on the surface it's resting on. the main effect comes from the coefficient of friction which on turn depends on the molecular forces between the 2 materials.

stability of the car will depend on
1. suspension tuning
2. aerodynamics/downforce
3. centre of gravity in relation to its footprint
4. weight distribution around its centre of mass
a heavy car is not necessarily more stable.
How heavy is an F1 car? or a lotus elise?

a heavier car also suffers from greater inertia, which means quick directional changes will cause it more grief than a lighter car.

a heavier car will however be more stable than a lighter car in the presence of crosswinds.

[v1p3r]

Originally Posted by rks

Chances of aquaplaning on upsized tyres are significantly higher.

Please explain.

Originally Posted by jalsa777

When aquaplaning, the tyres have lost surface contact.
So, if u brake, the tyres will lock up (water does not provide any grip).

Rolling tyres have more traction than locked up tyres.

Basically, there wont be any weight shift cause you wont be slowing down.

It will just make regaining steering control a longer process.

(you have tons more experience than me.
just adding my 2 cents)

Theoretically, you are right. Practically, I'm not too sure. What I've written comes after deliberate trial and observation.

[rks]

Originally Posted by v1p3r

Please explain.

Here is a website that explains:

Cruise Control and Aquaplaning: the facts – Car Reviews, News & Advice – carsales.com.au - Carsales Editorial

Modern cars, even small, lightweight models, have much wider tyres than ever before. Coupled with smoother roads that can hold an even film of water without high dry spots, the chances of water getting trapped between the tyre and road surface are higher.

It is similar to the difference between a stiletto heel and a wide flat heel on a shoe. Where a stiletto can punch through a film of water to contact the ground, a wide heel can slip. The tread pattern on a wider tyre assumes critical importance when a vehicle's weight alone is not enough to punch today's wider tyres through a film of water.
[...]
Braking and steering actions can be totally lost as the forces of nature dictate where you go next. Scared? You should be when in most cases it is caused by sloppy maintenance, not cruise control.

The mindset that doesn't replace tyres until they are bald is the real killer. Modern tyres have to be replaced long before the tread disappears.
[...]
Poor wheel alignment is a primary factor when it causes uneven tyre wear and robs the tyre of its grip in the main area where it contacts the road. Worn shock absorbers will also encourage aquaplaning if they cause the wheels to leave the ground after they hit road surface variation, and allow a film of water to collect between the tyre and road.

The point is that when you have wider-than-stock tyres, the chances are that "the vehicle's weight alone is not enough to punch today's wider tyres through a film of water". So one has to be even more vigilant in replacing oversized tyres before the tread pattern wears out. In my case I have wider-than-stock wheels, but stock size tyres. Still, in so much as I get a wider contact patch, chances of aquaplaning shoiuld increase, although I am not 100% sure of this.

[jalsa777]

Originally Posted by rippergeo

I may be wong here,but I recall from physics class in school(12 yrs ago) the weight of a body has surprisingly little to do with the frictional force it exerts on the surface it's resting on. the main effect comes from the coefficient of friction which on turn depends on the molecular forces between the 2 materials.

How heavy is an F1 car? or a lotus elise?

well,
more weight means more pressure on the tyres,
that means more foot-print (contact patch)
and that gives more grip.

of-course that adds more inertia.

hence, its a delicate balance,
lot of extra weight and inertia will be more than foot-print advantages,
and that spells trouble.

About F1 cars,
they generate tons of down-force (literally speaking)
no point getting them into this discussion

[v1p3r]

Originally Posted by rks

... although I am not 100% sure of this.

And that is the crux of the matter.

[jalsa777]

also, i have this theory (i may sound funny)

i have never tried this, just a theory.

When it aquaplanes,
just jump in ur seat. make others do that too.
you'll have a sudden downward force,

maybe that'll help the tyres punch through the water.

(lightning fast reactions are necessary over here. lol)

[vabs78]

Originally Posted by jalsa777

When aquaplaning, the tyres have lost surface contact.
So, if u brake, the tyres will lock up (water does not provide any grip).

Rolling tyres have more traction than locked up tyres.

Basically, there wont be any weight shift cause you wont be slowing down.

It will just make regaining steering control a longer process.

(you have tons more experience than me.
just adding my 2 cents)

All this is true if all 4 tyres are aquaplaning. It will be a rare case.
Generally only one or two tyres are aquaplaning at a time. So, v1P3r's observation makes sense.