Steve49841

I'm trying to come up with a way of figuring out what my brake point should be at the end of a straight. I have an 02 Z06 with Hawk HPS pads. Say for example, I was able to get to 130 MPH on the straight and I wanted to make my turn in at 60 MPH how many feet of braking distance would it take to bleed off 70 MPH. Is there some rule of thumb, I realize there are a ton of variables like tires and driver skill. I also realize it's really all about practice and experience but I'm trying to come up with a starting point. I am interested in hearing which marker you guys lift and brake at.

AU N EGL

HPS are STREET pads not track pads. So really about the same as your stock Z06 Pads.

Here is a StopTech White paper on Brakeing Systems ( PDF) This should get you started.

Gordy M

At a minimum I would switch to HP+ and preferably DCT70's. If you are talking about Grattan you have 100 ft increments on the left side at the end of the straight. With HP+ I would brake as I passed the first marker with the DCT70's I would wait to just before the second. After several runs the HP+ would start to need longer brake points or my speed was getting faster.

Bill Dearborn

There are a lot of variables besides brake pads. You have to contend with increased heat during the run, track layout, track conditions, tires, etc.

With near stock pads you will notice some loss of brake effectiveness as you get them really hot. If you braking going down hill you need more brake. The example you give is close to Turn 1 (The Ninety) at the Glen except the at the Glen you are on a pretty good down hill slope in the braking zone. Most people (with race pads) are on the brakes just before the 300 ft mark.

Bill

Steve49841

I made a mistake, I have the Hawk HP+ pads not the HPS. So the thinking is 300-400 feet to bleed off 70 MPH?

yakisoba

1) Stay in the gas until you see your Deity of choice.
2) Count three,
3) Brake.

Rough guideline.

linutux

I've seen this as:
"Flat out until you see God, count to three, then brake." - Anonymous

Anyone know the source of this quote?

AU N EGL

Here is another good one:

"when the fear of death outweighs the thrill of speed, brake." LG

1ED1

hp+ pads will overpower any street tire, and a good choice for street and track. choose a brake pad that will work with the tires that you use.

yakisoba

I don't know the source, but should make clear that I didn't come up with it

I like LG's version.

This has nothing to do with the OP's question of course. However, to that point, I think you have to experiment. Measure how long it takes you to brake, know what that is both in feet and in how it feels in your butt when the ABS kicks in. It'll be different for each pad you get too.

John Shiels

when your eyes go like this brake!

MungoZ06

From the Au N Egl link ... under Kinematics " ... Note that this equation assumes a step-input deceleration from a fixed speed followed by
a linear and constant rate of deceleration until the vehicle comes to rest. In practical application, deceleration cannot be achieved instantaneously, nor can deceleration be assumed to be constant for the duration of a stopping event."
Stopping distance (or deceleration distance from speed X to speed Y) increases geometrically with speed.
I spent a whole session (about 12 laps) at Summit Pt practicing my braking points on HP + pads and stock tires going into Turn 1. Varied max speed into braking zone ... ranged from 120 - 130 ... and after the session ... thinking about it ... figured out that I really wasn't optimizing my deceleration rate ... so my braking points would need to be adjusted again once I improved my threshold braking technique ... so it's an iterative, learning process ... FWIW

Steve49841

The mathamatical approach is WAY to complicated, I scaned the "white paper" and got a head ache. I think I will just start to experiment, using the "later, deeper, harder" method.

The Spark

TedDBere

FOTFALMAO

davidfarmer

x=vt+1/2at*t where v is drop in velocity, and t is time, and a is acceleration. you need to use v=at to determine the time it takes to declerate at the given braking load (say -1.2g), then substitute a and t back into the original equation.

Everything must be converted to like units, it f/s, f/s/s (32.2f/s/s = 1 g), etc

Freshman physics, but whether it's worth breaking out your calculator is up to you.

If it is important, build a spreadsheet that you simply input velocity change, and maximum decleration, and it does all of the conversion and calculations for you.

davidfarmer

quickly, at -1.2g's and 70mph of decel (102f/s), I came up with 2.65 secs of decel, or roughly 150'

davidfarmer

I was travelling out of state for a funeral when I did my calcs, and realize I made a mistake. The V in the x= equation must be the initial velocity (130) not the change in velocity (70)

Therefore, the time is still the same, but the distance changes to 369feet.

The distance is based on take the initial velocity component and subtracting the acceleration component, and I blew it.

Hope you didn't try this in the field, or you are probably in the tire wall right about now.

96GS#007

Info like David Farmer provided gives you a good 1st lap starting point to adjust from assuming you know some of the general info required.

After that you have to experiment. The variables change every lap...pads heat up (and maybe get too hot), tires gain and then lose grip as they heat up/wear/age, track elevations affect where the weight is and the elevation/camber of the track may be slightly different if you're off-line, etc. Therefore you have to be able to make constant adjustments based on practical knowledge and feel.

JMO.

davidfarmer

JMO, I totally agree with you...and it only takes me about 3 laps to get my braking points dialed in.

HOWEVER, as an engineer, when somebody asks, I can't help but try and answer. The math is simple, and while there are too many variable in the real world for it to be especially usefull, just knowing that braking distance is related to speed and speed squared (time squared, which you get from the v=at equation), it helps you realize how the energy dissipated and hardware damage goes up exponentially when you go faster.

btw, if you combine the 2 equations, you get

x= Vi * Vd/a - Vd*Vd/a/2

where Vi equals starting speed in f/s
Vd equals change in speed in f/s
a=accel in f/s/s

f/s =mph *5280/3600
f/s/s=g*32.2