Rotation in Front Wheel Drive

[thomas]

Do front wheel drive vehicles benefit from corner-rotation?

[MJAmok]

Get a copy of this month's SCCA magazine. Randy Pobst wrote a good article about driving styles in FWD vs RWD vs AWD.

[dalyduo]

Do front wheel drivers benefit from corner rotation?

Absolutely. But front drivers are dynamically different from rear drive cars and tend to push rather than oversteer which is much less dramatic visually. (Unless a rear wheel handbrake is used to break loose and rotate the tail of the car.)

The first question would be what kind of rotation are you looking for? A bootleggers U-turn, power slide for a drifting show, the quick line up Pike's Peak or the fastest way through a corner on a road course?

Rotation is a function of balance, grip and momentum. You change balance with throttle, brake and steering no matter which wheels are driving.

With a car like the Mini you can make it rotate 180 degrees in its own length with a yank of the steering wheel, pull on the hand brake and stab at the throttle. This looks great as a movie stunt but you'd never see that on a road course because it wouldn't be fast.

Rally drivers used to use the rear wheel handbrake to induce rotation on dirt road switchbacks but now all the pro rally cars are all wheel drive with huge power so massive four wheeled power slides are the order of the day.

On a road course you only want enough rotation to be at the optimum slip angle through the apex of a turn, so rotation there is achieved with brake/throttle weight transfer and steering to point and balance the car properly. It isn't very dramatic and doesn't look like much with a front driver which leads me to wonder if your question assumes rotation only exists if you are hanging out the tail of the car?

Good question Thomas. We have instructors and other Mini drivers who will probably have more comprehensive answers. But until they pipe up... that's my 2 cents.

PS Michaels response was posted while I was composing mine and his is a great suggestion as well.

[J Goring]

I would not use the word "rotation" to describe what you want in a front wheel drive car. If you have a line graph that compares degrees of slip angle (horizontal) and G force (vertical) the line would look something like a mountain. It would go up to a certain point, then come crashing down very suddenly. Now, obviously we would like the most G force generated as we possibly can, so we would still want to drive the car at its maximum grip level. More "rotation" will simply be over the climax of the cars grip, generating less G force.

A better word to use would be "trail-brake." In a FWD you want to use the trail-brake technique as much as possible, but still not over rotate the car. Since FWD understeer mainly from apex out, you want to point the car as much as you can before you start to apply the throttle.

[AZRCD]

You could just throw it into a corner and snap off the gas. That would rotate it fairly well.
On a serious note, don’t forget about pendulum turns.
And, finally WRC drivers still use the hand break (a nice hydraulic one) plenty especially in tight corners like hairpins or when a very quick change of direction is needed. This is because awd can sometime push more, or be slower in a direction change.

[dalyduo]

Abe, thanks for confirming what I suspected but had no confirmation of, regarding the handbrake. Sure is fun to watch.

Originally Posted by AZRCD

You could just throw it into a corner and snap off the gas. That would rotate it fairly well.
On a serious note, don’t forget about pendulum turns.
And, finally WRC drivers still use the hand break (a nice hydraulic one) plenty especially in tight corners like hairpins or when a very quick change of direction is needed. This is because awd can sometime push more, or be slower in a direction change.

[AZRCD]

Even more fun to do. (I'm going to O'niel rally school in NH first week in Aug.)

[dalyduo]

Now your talkin'! Most excellent!

Originally Posted by AZRCD

Even more fun to do. (I'm going to O'niel rally school in NH first week in Aug.)

[Jim Pace]

The simple answer is Yes rotation can be beneficial. Under braking and corner entry they all behave very similar. However once the power is applied things change. One of the big differences w/ fwd & awd vs rwd is power induced understeer that results from exceeding the limits of the front tires. Under power while cornering (lots of weight transfer) the front tires are trying to steer and accelerate and reach the limits of traction before the rears. The result is understeer. Because of this, big rotation is frequently desired in FWD & awd because once you go to power it will push.
Ways to reduce the power understeer include taking grip away from the rear w/ less camber, toe out, changing tire pressure etc... More advanced systems split the power output so the rear axle receives more power than the front and therefore can produce power oversteer like a rwd. That is what we all love to watch and drive. Running different ring & pinion ratios F vs R is a poor mans way of doing the same thing.
JP

[thomas]

so the same brake/throttle snapping used to fling the tail at the track would benefit a fwd mid corner? (Not talking about hand braking or pendeleum, ect.)

It was more of a random thought...i was in the mini driving pretty aggressively, and found myself snapping off the brake petal trying to rotate the tail, and just wondered if the car was actually benefiting from it or not.

[Jim Pace]

Thomas,
For fun try being smoother with the brake release and rotate the car by controlling the weight transfer with the brake release. Then once it begins to rotate, use appropriate steering correction and power to exit.
True an snap release of the brake with give a quick rotation but mostly used for autocrossing or really tight hairpin turns. On the track most guys benefit more from being smoother with all the controls. This gives less drama, fewer moments, and better for tire wear.
Jim

[jlowe]

A great driver/coach once told me (about a thousand times, and counting), "Just be smooth, smooth and easy."

Works for ANY wheel drive.

[StevieDe]

Tom,
You've tapped into a very deep pool of knowledge and sparked some very inciteful responses. I concur with all that JP and Jonathan have passed along.
In a previous life I have auto-x'ed and raced front wheel drive. The big question is where this 'aggressive driving' is taking place. An organized solo-2 event is a great place to explore the limits in a relatively harmless environment. Once you have a mastered that to a certain level,track days at a local road course would be logical next step.

Bottom line, the tighter the corner the more abrupt the initial direction change needs to be. As the corner speed requirements go up ( less direction change) the more subtle the inputs need to be.

This could be from the extreme of a handbrake turn in the u-turn pit lane of the old Columbus street circuit to the subtlest throttle adjustment or dab of left foot braking to tighten your trajectory on long duration carousel type corner.

Get the most experience you can at low speed (auto-x) and step it up from there. Luckily from what limited experience I have in the new Mini it seems like a responsive but relatively forgiving platform.

Have fun, Be Safe.
SD

[sydude]

Here's Pobst's article:

[thomas]

Thanks Sydude, that helped out a lot. My goal pretty much was to find out where the Mini and a Skip Car could be driven alike in a driving style, and where they are apart. This helps out. I know also many drivers in both rallying and racing use Left foot braking to both cancel out understeer and induce oversteer.