Stopper Shopping

Not many hot rodders give much thought to what different brake pads do for the stopping of their hot rod. Oh, I'm sure the guys who race fast cars on a racetrack do assign an engineer to get the best brake pad for the particular track, but you seldom hear a discussion about brake pads.

We hope to change that at least long enough for you to read through this little test and get ever so slightly smarter about the subject, just as we did when we performed the test. The standard measure for brake efficiency is to measure stopping distance, measured in feet, from 60 mph to zero. Tests performed by vehicle manufacturers and brake makers use that measurement to compare one vehicle to another on a surface that is the same. The absolute best is the Porsche GT1 at just over 98 ft. The range for high performance sedans is 120 to 155 ft.

Our initial test using a '32 Ford highboy roadster equipped with Kugel suspension produced a stopping distance of 152 ft. The chassis, as delivered, came equipped with Wilwood brakes in the front and Corvette inboard discs in the rear. Tires (which have a profound effect on stopping distance) for this test were Toyo 800Ultra 185-60x14 fronts and 225-60x15 rears. The weight of the hot rod is 2,265 lbs with a bias of 48-percent front/52-percent rear.Wilwood sent us four sets of front pads and told us just how to seat them (see sidebar) and we did the test blind, meaning we did not know the difference between the different pads.

Overall Observations
Test 2 produced the best stopping distance on the initial stop, but repeated test produced longer distances as the pads accumulated heat.Test 4 produced the second best stopping distance, but was very consistent and predictable and produced the best numbers as the pad accumulated heat.Overall we found there were measurable differences in the stopping distances with 20 ft between the best and the worst, which can be significant in a panic stop. The driver, in every case, was able to produce the stopping without lockup. The tires only locked up occasionally and then only at the very last 10 ft of the stop. The test also showed that the roadster's combination of Wilwood front and Corvette rear brakes and the front-to-rear bias were quite good as there were no "moments" during the entire test. In each case the car came to a straight controlled stop.

While this was a magazine test, performed to provide a modicum of information needed to make an intelligent pad choice, it does not pretend to be a full-on scientific evaluation. Given that, what did we learn? Clearly there is a difference in pad compound and the test-driver, Nick Licata, was able to feel the difference in pedal pressure and modulation in each individual setup. A couple of things you should know when choosing pads: The weight of the car and driver habits affect the life of the pads. I'm told that a good rule of thumb for street rods is to change the pads when the friction material is down to one hundred thousandths. This will prevent over-extension of the piston travel.As hot rodders who spend most of our time cruisin', we would choose the pad that delivers the shortest stopping distance on the first usage. On the other hand, if we did a lot of canyon running where you can play boy racer, we'd choose the pad that gave the best pedal feel and the predictable stopping power consistently.

Hot Tip
When you are shopping for brake pads, consult the manufacturer. They have tons of experience with the compounds they produce and can give you the best advice once you tell them what you drive and what kind of driving you intend to do.Keep it safe: You should never drive faster than you can see as that's the true limitation on your brakes.

PAD & ROTOR BEDDING
If you go to many races and walk through the pits, you will eventually see a sign on the steering wheel of a race car: NEW PADS. The reason you will see this is to warn the driver that he must "bed" the new pads before he tries to use the brakes in race or qualifying conditions. If the driver ignores the sign, he might find himself in the fence.

New pads must be bedded and that means that the brakes must be subjected to a "real conditions" heat cycle. It is a fact that nearly every friction material-even OEM passenger-car compounds-improves in durability and performance after seating or bedding. The process will transfer a layer of friction material onto the disc surface and it is this layer that is essential to the performance and stopping ability of the pads and rotors.

For our test, we installed each set of pads and drove the car on the street for a few miles using the brakes as you would in normal driving. We then found a deserted street and drove up to 60 mph and leaned on the brakes relatively hard to bring the rod down to about 10 mph. We then released the pedal and repeated this procedure six or seven times. It became quickly evident that the stopping was improving with each application.

You should do this break in procedure whenever you do a brake job on your streetster. It makes things conform to one another. Once the pads and rotors reach operating temperature, you are home free.