Understanding Braking Issues
The brakes and braking are so critical to a good lap and you must understand how all the parts in the brake system have an impact on everything that happens after you hit the brake pedal.
Just telling the engineer that the brakes “don’t work” doesn’t tell him anything about the problem you’re having. The drivers feel and feedback has a large impact on how the brakes work out on the track, and should be considered when setting up a brake system, and then again when diagnosing braking issues.
The brakes should work just how the driver likes, so then out on track, their operation should all be in the background…. almost seamless……. you hit the brakes at the right place, but then you’re thinking about the apex and getting off the brakes…..hit the right line, and then get off the brakes. The brake power and feel are what allow you to do this.
Brake feelings and reactions are personal. Some drivers like a super hard pedal and don’t care about the feel; some like a softer pedal with a lot of feedback; some like a very linear increase in braking grip, and some like a ‘very immediate’ reaction. And different tracks require a different kind of reaction; at one extreme we have a street track where we need a very quick reaction, which will almost stand the car on its nose and stop the car. But at the other extreme, we have an oval or very fast corners, and the last thing you need is an ‘Urgent reaction’; you don’t want to upset the platform too much; and you want a gentle, steading effect instead of stopping.
Many things influence this… pad compound, type of brake fluid, braided stainless steel versus solid steel brake lines, master-cylinder size, pedal height and ratio, brake bleeding, AND HOW YOU USE THE BRAKE PEDAL.
Brake Bleeding Procedure
I know there are several different methods used, but I have found this process to consistently give a hard pedal.
If you change to new pads after this bleeding, it’s quite possible that you may have to bleed the brakes
again after bedding.
Bleeding is usually best done with 3 people : one in the car ( or at the front BUT with good access to pull the brake pedal for FULL travel ), then 2 other people; one each on the front and rear axles.
Always start on the INNER bleed nipple, then OUTER, then go to the wheel on other side of car and start with the INNER nipple again, followed by OUTER nipple.
If the system has been opened ( new seals or cylinders ) it may be necessary to go across the car two or
sometimes three times.
The pedal should be depressed over its FULL TRAVEL with BOTH the front and rear bleed nipples open at the same time.
On the final stroke when the nipple is ready to be closed, let the pedal return to the top and then push down half way and hold and then close the nipples. This will give a firmer pedal.
And after we have considered all of the above, then we must make sure we have the right pads to suit the drivers style and feel; different pads have different characteristics.
Brakes and their related problems are possibly one of the most under-estimated, and “taken for granted” ( that they will work ) causes of “LACK of PERFORMANCE”.
On almost every corner that requires slowing, the way the driver enters, dictates how the car is in the whole turn, and consequently the exit speed onto the next straight.
Although it can be a real pain sometimes, we must make a big effort to ensure that the operation of this very simple brake system is optimized.
Finally, we need to consider the brake bias or balance between front and rear. This bias number can be very different for different types of cars….sedans V’s open wheel; front or rear engine; front or rear wheel drive; slicks or DOT grooved; experienced or novice driver. All these and more need to be considered, and then the whole system can be optimized for that combination of variables.
As a last note on the Bias subject, if your bias is 50% or 55% or 60%, or whatever it is, this is just a reference number for right now, for this driver in these conditions, on this track. If you get rain, or a track with more/less grip, or for many other reasons, that Bias number will change, for an optimized system, and you will have a new reference for this new particular set-up. Experienced drivers are in tune with their brake bias, and treat it as a moving number, meaning they are adjusting their bias as the tires degrade, and the track grip changes, and as they use fuel (in a big tank).
A typical Indy car fuel tank is about 32 gallons (almost 200# weight), and when they start a race stint, they have new tires and full fuel, but as the laps go by, the tires wear (usually the rears go quicker) and the fuel level goes down, changing the front/rear weight %. So, over that stint, they adjust the bias to retain the optimized system….maybe as much as 3-4%. But then after a pit stop, they are back on new tires and full fuel, so as they are going through the pits, they are already adjusting the bias back. They are very active with the bias, just as they are with the sway bars.
By the way, if the track is wet, you will have lost a huge amount of grip, so you will not be able to generate the same stopping power, which normally transfers a lot of weight onto the front axle. So you need to reduce your Bias number and typically we will start by turning the brake bias knob 2 full turns towards the rear brakes, which is usually about 4%, so your bias # will go from something like 56% to 52%. These 2 turns may not be exactly what you need, but it is a good starting point.
