4wd – does it offer more grip?

[monthefish]

I was always under the impression that (as well as offering more traction) 4wd offers more grip in corners etc, hence the good reputation in this respect for Audi Quattro, Scooby/Evos, Porsche 911 C4 & Turbo, etc etc

However, I’m also aware that a tyre has a finite amount of grip which I believe is shared between forward/backward motion (i.e. acceleration/braking) and directional changes, so from that respect a 4wd should have less grip (as some of the tyres’ available grip is being used to drive the car forwards).

What’s the real story and the correct physics behind it?

Cheers.

[ytrebil]

Someone knowledgeable will be around here soon but I don't think they have more grip, traction yes, but I think grip is unrelated.

[GTIR]

But its 4 wheels doing the driving and gripping, so its shared by x 4.

[jacobyte]

Not more grip, just more traction. So it' better when it's slippery (that's every road in the UK, wet or dry).

[Cupramax]

4wd will push you out of the corner better and give better traction off the line and while moving but you cant avoid the laws of physics i.e. enter a corner too quickly and you'll end up in the bushes 4wd or not.

[kambites]

As above. More traction (which can under some strange circumstances such as when you're going sideways can produce higher cornering speeds) but no more grip as such.

[John MacK]

More traction from potentially 4 sources, but just the same amount of rubber in contact with the road so same amount of grip.

[Herman Toothrot]

Traction and grip are somewhat related though. i.e. your mid corner accelerating in a rwd, the rear tyres loose forward traction and stop laterally gripping due to trying to find traction. A 4wd the effort of getting traction is spread so is less likely to over come grip whilst finding traction so lateral grip is maintained.

[xyphod]

Friction, due the weight (and down force) of the car is the same for 2wd and 4wd cars. (assuming a 50/50 weight distribution)
However with a 2wd car (say fwd) the rear wheels are effectivly being turned by the road (dragging along). So the effectivly they are just holding the car on the road and stopping it from sliding sideways.

Now consider a 4wd car.
When rotating the wheel you are applying a force downward and backward on the rear wheels, effectivily digging into the road, giving you thrust and grip on all four wheels this is in addition to the normal weight and downforce grip.

[mechsympathy]

Herman Toothrot said:

Traction and grip are somewhat related though. i.e. your mid corner accelerating in a rwd, the rear tyres loose forward traction and stop laterally gripping due to trying to find traction. A 4wd the effort of getting traction is spread so is less likely to over come grip whilst finding traction so lateral grip is maintained.

Which is why awd cars need to be driven differently. You get on the power far earlier and harder than you would in a fwd/rwd car.

[randomman]

I'm well aware I could be totally wrong on this one but bear with me.

The way I always thought of it was a tyre provides a certain amount of grip (based on size, temp, tread, style etc) and that grip is used in any of 4 directions (forward, backward, left, right)

Now lets say a tyre gives 50 daves of grip. In a front wheel drive car if you used 50 daves accelerating and 50 daves turning you would be fine (as the front wheels total 100 daves). But if you used 100 daves accelerating and 100 daves turning you skid.

Now in a RWD car you can use 100 daves turning the front wheels and 100 daves accelerating the back (the back also has to do some turning but I've ignored this for simplicities sake)

So a 4wd car, would depened on the ratio between front and back (haldex, permanent, locked diff etc) and things get a lot more complicated, but while the front tyres can still only offer 50 daves each in a turn, when you accelerate its divided by 4 instead of 2, so if you needed 100 daves for acceleration that would still leave 25 daves for each tyre to turn.

I know this could be completely wrong, but it was fun to type and my boss laughed at the description

Edited by randomman on Tuesday 6th January 16:22

[BigLepton]

monthefish said:

However, I’m also aware that a tyre has a finite amount of grip which I believe is shared between forward/backward motion (i.e. acceleration/braking) and directional changes, so from that respect a 4wd should have less grip (as some of the tyres’ available grip is being used to drive the car forwards).

Errr, no. A 2WD car shares its lateral grip and braking grip between all four wheels, but two of the wheels get all the torque, reducing the amount of the other two forces they can handle, dependent on throttle opening. A 4WD car shares all three forces (lateral grip, braking and torque) between all four wheels which means you should be able at any given point of a corner to apply more throttle without the driven end giving up gripping before the none driven end.

[driverrob]

mechsympathy said:

Herman Toothrot said:

Traction and grip are somewhat related though. i.e. your mid corner accelerating in a rwd, the rear tyres loose forward traction and stop laterally gripping due to trying to find traction. A 4wd the effort of getting traction is spread so is less likely to over come grip whilst finding traction so lateral grip is maintained.

Which is why awd cars need tocan be driven differently. You can get on the power far earlier and harder than you would in a fwd/rwd car.

I'd have to drive vary carelessly to lose grip in my GTO. In over 4 years I've only managed it on snow and on loose gravel.

[garycat]

The biggest advantage I've found with my scoob is that when you are accellerating it is unaffected by different road surfaces, e.g. if there is an iron drain cover a 2wd car will slip the wheel that goes over it.

Also there is a difficult T junction near where I live, that is quite steep uphill and joins a NSL so you need to do a hill start, turn, and be up to speed quickly. When it is wet, lots of 2wd cars just spin their wheels as the diff transfers power to the least loaded wheel, or the TC cuts power.

It is also noticeable that when slowing down using engine compression, this acts on 4 wheels rather than 2, so it can make a difference if you are turning on a trailing throttle.

When it is very slippery 4wd can give you a false sense of security as traction is still good, but braking & turning is as bad as with a 2wd car.

[ewenm]

4wd has the same amount of grip as 2wd (assuming identical weight, tyres and weight distribution) but can use it more effectively in some circumstances giving better traction.

[mechsympathy]

driverrob said:

mechsympathy said:

Which is why awd cars need tocan be driven differently. You can get on the power far earlier and harder than you would in a fwd/rwd car.

I'd have to drive vary carelessly to lose grip in my GTO. In over 4 years I've only managed it on snow and on loose gravel.

Picky picky.

[matt uk]

4wd – does it offer more grip?

So answer to the question, would a fair summary be, 'no' on the way into the corner (off the throttle) but 'yes' on the way out (on the throttle)?

[ytrebil]

matt uk said:

4wd – does it offer more grip?

So answer to the question, would a fair summary be, 'no' on the way into the corner (off the throttle) but 'yes' on the way out (on the throttle)?

Grip is to do with weight and tyre contact with the road surface. So having FWD, RWD or 4WD won’t affect your grip. For example, a 4WD empty Ford Cosworth with wide, summer tyres on will have less grip than a RWD Ford Cosworth with slim winter tyres on in the snow. However, the 4WD will give you better traction as the front wheels will be affected by engine torque. Which leads me to believe that in the snow and ice, having better grip is much more important than having more traction.

[Maverick_JDL]

most of us I think are all touching on the right things, I think it gets confusing and complex when you think about what "grip" means and what "traction" means. 4wd only makes a difference when power is being applied in the same way there is only a dynamic difference in fwd and rwd when power is being applied or as it is removed during cornering (ish), lift off in a car mid corner regardless of what it is and you will kick the back end.

4wd in my eyes is like this... (assume all TC aids off), enter a bend off the power to hot in either 4wd or 2wd and you will understeer (momentum and inertia (i think)), now in the 4wd car the chances are if you get back on the gas in a controlled fashion the system will move the power around between the wheels ensuring each wheel is using its maximum available amount of grip, this will pull the car back in line and away you go... now in a rwd if you get back on the power you can turn the car on a bit of power induced oversteer and get the car back on track that way... in a fwd car you need to stay off the gas until the car has found its own grip and then get back on your way..

4wd more effectively distributes power between the available grip of each wheel.... but however can "bog" you down in many conditions.

In grippy dry conditions say I would rather have rwd on wet or gravel then 4wd.

[Maverick_JDL]

matt uk said:

4wd – does it offer more grip?

So answer to the question, would a fair summary be, 'no' on the way into the corner (off the throttle) but 'yes' on the way out (on the throttle)?

Yes depending on the road conditions.

Same car i.e Porsche 997 in the dry you would want 2wd in the wet you would want 4wd.