How To Use Braking and Turn-in

Posted on March 29, 2013

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How To Use Braking and Turn In

By: Rob Oakman

Audi R10 at Le Mans

As you rumble down the straightaway, building up energy as you go, it’s a bit boring to be honest, happily though you eventually find yourself approaching a corner and that’s when the fun begins. Being a race of course you want to get around that corner as fast as possible, keeping up as much of the energy you’ve built up as you can get away with while still making the corner. This is where your brakes come in…obviously. But your brakes can be used for more than just turning momentum into heat, they can help turn your chassis in the corner, and be an active chassis adjustment if you combine them with turn-in. How? This is how.

Plan Ahead

If you recall in another article when I said that Projection is the art of Racing, then Braking and Turn-in are two of its brushes. Together and separately they are how you choose the way your chassis is going to act in the corner instead of letting it be a jerk and choose for you. Remember that Braking and Turn-in set the speed, arc and rotation for the corner. This determines where you land your apex, if you do, and where you are going to end up on the track at exit. These are things that need to be precise. To do this you need to know where and when you are going to brake and turn into the corner.

The Active Chassis

A chassis doesn’t drive a perfect arch in most corners. Turn-in and exit are actually a bit sharper than the center because of the dynamic forces involved. When you turn-in you want the chassis to rotate freely enough that you can point the nose to the apex quickly, but not so quickly that the rear tires can’t keep up. This is why ideally the weight on the front end is lighter than the rear; so the front can change direction quickly on turn in and set the rotation for the corner. The heavier weight on the rear will then jack (Or leaver) onto the outside front tire to plant it into the track so you don’t push. But what if your balance is off? What can you do to fix the imbalance on track?  Let’s see.

Pier-luc ouellette Trail Braking hard at ICAR ( courtsey psl karting )

Pier-luc ouellette Trail Braking hard at ICAR    ( courtesy psl karting )

How to Compensate

A: Trailbraking – Say you reach that corner and the chassis pushes like a dump truck. What can you do? Pit? Deal with it? Or just hope the chassis will come in later? Those all cost time. What you can do that isn’t defeatist is trail-brake. Trail-braking is when you brake later as you approach the corner, keep braking after turn-in and, sometimes, all the way to the apex. By keeping your foot on the brakes as you turn-in you push more weight on the front tires while taking the same amount from the rear. You artificially jack (Leaver) weight from the rear and plant the outside front tire into the track. What this does is add grip to the front end by taking it from the rear and improve, if not fix, your push. This is generally how you drive anything front wheel or all wheel drive all the time.

BMW Trail braking at Turn-in

BMW Trail braking at Turn-in
( courtesy speedsportlife.com )

B: Get Snappy on the Wheel – If you have a particularly aggressive push you can delay your turn-in a bit longer and then turn faster and sharper while still hard on the brakes. This is rather aggressive and puts a lot of pressure on your front outside tire, but if wear isn’t a major concern this can improve a stubborn push. By moderating your brake pressure at different points from your turn-in to the apex you can actively adjust your chassis all the way in.

BMW still Trail Braking to apex

BMW still Trail Braking to apex
( courtesy speedsportlife.com )

 

C: Brake Bias – If you drive something with a bias adjustment (Changes braking pressure of the front and rear wheels) you can crank more rear brake into the chassis. This will free up the rear quite a bit on entry and it will really speed up the rotation on Turn-in. Obviously you need to be more careful on the brakes if you have to dial in a lot of rear bias as locking up the rear wheels is easy to do. Looks awesome though.

Pulling brake bias out of the rear will help a lot if you are loose on entry and have the adjustment, but you can loose a lot of braking force if you take out too much, this increases the length of your braking zone. You also put a lot more load on the front brakes and can easily overheat, overwork and wear them out.

D: Power Through the Corner – What if you have the opposite problem? What if you are loose on turn-in? Now you have to change a few things. Instead of trail-braking what you want to do is get all your braking done before you reach turn-in and actually get back to the throttle immediately. This is called “powering through the corner”. This does the exact opposite of trail braking. As you get on the throttle you shift weight from the front tires to the rear. You add grip to the rear tires while stealing it from the front. Most rear wheel drive cars respond well to this technique. You want to be very easy with the steering wheel on turn-in and, obviously, don’t stand on the gas as that would have the opposite effect you’re after. You might make a highlight reel though.

https://i1.wp.com/www.audiworld.com/news/12/lemans-12/audiworld-lemans-45.jpg

Running the curves at Le Mans
( courtesy audiwourld.com )

Not every corner has a braking zone. Some are full throttle, some you coast through, some you decelerate through, and some accelerate. So what can you do to change your handling then? Lots.

E: Get agressive with the Wheel – How aggressive you are with the steering wheel makes a big difference to your chassis. In sections where you are pushing you can arch the chassis into the corner by entering from a wider line and then turn the wheel sharply at a later entry point. This shifts the weight of the chassis aggressively and takes advantage of the pendulum effect. Because the rear tires are following the fronts they change direction after the front end. By being aggressive with the wheel you increase the force of the direction change that the rears have to deal with. This is however hard on the outside rear tire.

F: Use a Different Gear – Grabbing a higher gear in the corner can help too. If you usually run the corner in second, try third. I don’t know why but it helps. If you don’t have gears you can try moving your body to shift weight. You want to be careful though. Don’t move too much or you just make things worse.

If you’re loose and accelerating you can stay on a regular line and turn the wheel slow and steady in your hands to apex. The same applies in partial throttle and off throttle sections. Dropping a gear might help but it is not always possible because of rpm. Just be smooth on both the wheel and the throttle so the chassis is stable. Don’t jump on and off the throttle. This upsets the chassis and will make the condition worse. Again, if you don’t have gears try moving your body, but be careful.

The Rules

The basic rules for Braking at turn in are: trail if tight and add rear bias, off if loose and add front bias.

For Turn-in its: sharp and aggressive if tight, smooth and easy for loose.

There is far more to Braking than just this, so next time I will get into a bit more detail before we move on to the Apex and Exit.

As a bonus here is a great video of Leh Keen driving the Circuit of the Americas in a very Tight Brumas Porsche from the youtube channel Drive. Note the lock up he suffers from having too much rear brake bias.

If you have any questions or comments feel free to send them along below and follow OakmanOnRacing.

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Leh Keen at COTA
( courtesy Drive )

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Posted in: How to Race