Tick-tock, tick-tock……….. The countdown begins for the start of our 2015 DE season!! I know I am pretty excited. Last month I covered getting ready for the season so I figured this month I would return to skill development and touch on a more advanced technique, left foot braking. If you are ready for this, I suggest you plan a strategy for how and when you are going to try this out. As part of that strategy you could discuss this with one of our Chief Instructors as they can help you along the way, jump in the car with you and provide you with the necessary coaching. I am also going to cover “Understeer” this often talked about but typically misunderstood as to what is causing it and what to do about it.
LEFT FOOT BRAKING
Left foot braking is a technique used frequently in rallying, but can be equally useful on the road or track for the following:
• Reducing understeer into a corner
• Reducing drive loss through spinning wheels
• Removing the pedal transfer time between accelerator and brake
REDUCING UNDERSTEER INTO A CORNER
The theory here is that you can feather the brakes into a corner, while transitioning to increasing throttle at the apex. This can lead to a very smooth transition between braking and acceleration and is less likely to unsettle the car through unwanted weight transfer. It also keeps the weight at the front of the vehicle for as long as possible, thus providing more grip, a better turn in and reduces the possibility of understeer.
REDUCING DRIVE LOSS THROUGH SPINNING WHEELS
This technique is particularly useful for a front wheel drive car without a limited slip differential. On the exit of the corner, it is a common symptom for the unloaded front wheel to spin while applying throttle. This spinning wheel is preventing all of the power from transferring to the road and thus slowing the exit speed. By feathering the brake with the left foot, this can prevent or reduce this wheel spin and get a better exit.
REMOVING PEDEL TRANSFER TIME
Using the left foot to brake removes the pedal transition time from brake to accelerator and vice versa. This can shave fractions of a second off a lap time when done well (but who’s counting, right?), but cannot be used when it is necessary to downshift (unless you decide not to use the clutch!)
Left foot braking is an advanced technique, and should only be attempted after lots of practice. When learning to left foot brake, you will initially press the pedal far too hard as you will be used to the action of pressing a clutch all the way to the floor. It takes time to re-program the ‘muscle memory’ of your foot and leg and a bit of empty tarmac is highly recommended. Funny, as a teenager I used to left foot brake the family car all the time and my Dad used to yell at me for doing this. I now tell him how long it has taken me to re-learn how to do this once again. LOL.
I mentioned Understeer so let us touch on that as well.
When you reach the limits of grip on a corner, two scenarios can result known as understeer or oversteer.
Understeer occurs when traction is lost at the front wheels while cornering, forcing you wide on a corner despite applying the correct steering angle. If your car is understeering, you are scrubbing off speed and missing the optimum line, so it is not a quick way to take a corner.
The stages of understeer:
A. The car has turned in towards the apex
B. The driver has hit the apex but has found the car is pushing wide of the desired line.
C. Despite increasing the steering angle, the car has taken a line which is not tight enough to take the turn
D. The car has been forced off the track by understeer
Understeer is most likely to result from the following scenarios (which are more difficult to correct as you move down the list):
• Accelerating into a bend
• Braking into a corner
• Plowing into a corner too fast
• Low traction conditions in the corner such water, oil, sand
Having lost traction, understeer is actually a fairly stable state for the car to be in, and thus many manufacturers ‘engineer in’ this behavior.
UNDERSTEER – FACTORS AT WORK
PASSIVE FACTORS INVOLVED
• Weight distribution
• Drivetrain layout
• Suspension & chassis setup
• Tire type, wear and pressures
ACTIVE FACTORS INVOLVED
• Cornering speed
• Steering inputs
• Weight transfer
SYMPTOMS OF UNDERSTEER
• Light steering
• Drifting towards the outside of a bend
• Possible tire noise from the front wheels
To correct any form of traction loss, you need to consider why you have exceeded the limits of grip at the front wheels…
1. ACCELERATING THROUGH A CORNER
Picture this; you are entering a turn and start to accelerate out of the turn and find that your car has a tendency to run wide. The available grip at the front wheels is being used in equal amounts to accelerate and to steer. As you accelerate more, you have less grip to steer – simple. So, reducing either of these inputs will correct the understeer.
This is the easiest form of understeer to correct, and a slight, smooth reduction in power will free up more grip (with the added benefit of a forward weight transfer) and a small corrective input to the steering will get you back on line. BTW, if you do decide to accelerate aggressively mid corner you are likely to cause oversteer.
2. BRAKING INTO A CORNER
When you apply the brakes, most of the braking effort is exerted on the front wheels due to the forward weight transfer. So if you are braking into the corner you are already using most of your available grip trying to scrub off speed. If you then apply some steering, the addition of these lateral forces on the tire can cause the limits of grip to be exceeded. So, correcting understeer seems simple – stop trying to turn the corner. However, if you happen to be in the middle of a corner as your car starts to understeer, continuing straight might not seem like the best plan. An alternative strategy could be to reduce your braking effort, trailing off, freeing up more grip for steering and hopefully allowing you to take the corner successfully. More on trail braking later.
3. PLOWING INTO A CORNER TOO FAST
If you have attempted to take a corner too fast, have turned the steering wheel, and find yourself running wide, you are now recognizing “I am probably going to go off.” But before you close your eyes and hope for the best, all may not be lost. You have exceeded all of the available grip, yes, but it may be possible to actually increase the level of grip by the slightest, smoothest touch of the brakes. “The brakes?” I hear you shout, “but isn’t that adding to the demands of the tires, not reducing them?” This is very true, but if you are not totally out of control, by gently pressing the brakes you are causing the weight to transfer to the front and thus artificially increasing the levels of adhesion at the wheels. This may however not work. The idea is to enter the corner at a slower speed, then get on the power early on the way out.
4. LOW TRACTION CONDITIONS
If you have entered a corner at speed and notice a sudden reduction in traction due to oil, water, sand, etc., the best course of action is to consider how lucky you are that life has been good to you so far. If life has not been good to you, consider how lucky you are that it will not be bothering you much longer. Just kidding! There usually not all that much you can do but to adjust to what happens to your car as you slide. Understanding how your car is sliding and what is on the other side of the slide will dictate what to do. Whatever you do, if you begin to go off, do not try to yank the car back onto the track as you will surely sling shot across the track and into a wall as your car once again regains traction.
AVOIDING UNDERSTEER – RULES OF THUMB
• Be as smooth as you can
• Do not enter corners too fast, and accelerate as you exit
• Do not brake in a corner unless you are going to be using trail braking…
On some corners of a track, it may be possible to better navigate the corner by maintaining braking into the turn. If this is the case, ensure most of the braking effort has been carried out in a straight line and progressively release the brakes as you approach the apex. The resulting forward weight transfer can reduce understeer and improve ‘turn in,’ however, it can also make the car more prone to oversteer. This is an advanced technique and should only be used once you are very confident with your car, the track and the conditions. Take an Instructor out with you as they will surely be able to help.
SIMPLE MODIFICATIONS TO MAKE A CAR LESS PRONE TO UNDERSTEER
If you find understeering a problem, you can make some relatively easy modifications which can make the handling more neutral. These include:
• Reducing the front tire pressure
• Softening front springs or anti-roll bar
• Use softer front tires
• Increase front down force (larger splitter)
Might be worth consulting an expert before doing anything too dramatic, but if you are feeling adventurous, the chart below can help
ADVANCED UNDERSTEER DIAGNOSIS AND MODIFICATIONS
Below is a flowchart which can help diagnose and treat the symptoms of understeer.
Credit to ‘Competition Car Suspension’ by Greg Simmons for the original chart.
Well, that is all for now gang. Looks like I will need to cover Oversteer next month. Remember, registration for Lime Rock opens on February 11 and for all you Instructed Drivers, be sure to sign up very early (12:01am if you are ambitious). Not to worry if you are noted as “Wait Listed” as this is a normal occurrence until enough Instructors sign up for the event.
See you all soon and remember to keep the shiny side up.
Tom Iervolino, NNJR – Track Chair