Tuesday, May 29, 2007

the middle pedal

let's keep some driving dialog going. i had a request to write a little about braking. now i left foot brake and that may be another writeup altogether but braking is braking. let's just talk basics here.

in most autox courses (and even more so in roadcourses), you may encounter a corner that requires heavy braking. here's a perfect example from this saturday:



above is a plot including longitudinal G (accel and decel) in light blue.

at this point on course (the crosshairs), looking at the numbers in the upper left, you can see i'm pulling .93 g's at peak (on a not so grippy surface on 'street' tires). the intensity of the red color in that short distance, indicates this hard deceleration. in this case, the car is going from 53mph to about 18mph in a very short distance.

now here's the deal. when you have to really put the brakes on, don't be a wimp. STAND on that pedal. i've read that most of the initial braking force is not used to slow down the car, but to slow down the inertia of those heavy tires and wheels. randy pobst had covered it in sportscar mag and it makes a lot of sense. now it all depends on the braking ability of your car but with abs and grippy tires these days, it's not so likely that you'll lock them up. if you do, get used to finding that limit.

our resident alien rode along with me a while back and he gave me a nice little piece of advice, "it's all about lengthening your acceleration zones." now it's something i try to envision whenever i take a run. how late can i brake? how soon can i get back on the gas?

brake hard when the situation warrants it. lengthen the time you're carrying speed up to corner entry. of course, the sooner you get it over and done with, the sooner you're back on the gas. simple yet sometimes we don't really think about it. i know i didn't until he made me aware.

get your braking done quickly and effectively. maintain maximum momentum midcorner. (this is where data aq is super useful to see if you're maximizing lateral g's) and get right back on that go pedal.

now of course you have to time it all precisely.. if you overshoot your turn-in point. kiss that run goodbye. understeer city.



if you brake too early, well let's just say that's the better option because the car will be settled and willing to turn in. i'd much rather undershoot than overshoot any day.

find that edge! guess what.. looking ahead is the key to determining when and where. so look ahead. and envision the most possible time on the gas pedal.

try it. let me know how it works for you.

-dan

1 comment:

Rich said...

Good write up, I had a hard time with giving up speed into a hard corner so I could carry more out. But there is a noticeably faster result when you do.