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.
We decided that the test would be performed as follows:
First test:
1. Install pads.
2. Make one stop to seat the pads in the calipers.
3. Make three consecutive stops, recording driver comments as well as stopping distance from 60 and 30 mph to 0.
Second Test:
1. Remove pads.
2. Deglaze discs with abrasive wheel.
3. Install next set of pads.
4. Repeat test procedure.
Third and fourth test:
A repeat of test one and two with different pads.
Test 1 with pad number 15Q 6824-7112Q:
60 to 0 mph @ 151.42 ft and 30 to 0 mph @ 35.32 ft
Driver comment: good feel; same pedal pressure throughout each test.
Description of pad compound:
The PolyMatrix Q pad compound has the following characteristics:
Enhanced friction ceramic formula features lowest noise and dust properties.Improved friction over OE replacement pad compounds with smooth engagement, increased fade resistance with quick recovery time.Compatible with all vented iron rotors.
Applications:
Disc brake conversions on street rods and other performance street vehicles where low noise and dust are important.
Test 2 with pad number 15E 6096-7112E:
60 to 0 mph @ 133.41 ft and 30 to 0 mph @ 30.97 ft
Driver comment: As pads heated in subsequent tests, the pedal became more sensitive.
Description of pad compound:
The PolyMatrix E pad compound has the following characteristics:
Medium friction compound with highest effective range in medium temperature pad group. Smooth engagement with consistent response from a flat torque curve throughout its entire effective temperature range. Pads bed quickly and provide fast response without excessive abrasion on iron or steel rotors.
Applications:
Light to medium duty road racing and track day events. Drag racing with iron or steel rotors. Performance street category competition.
Test 3 with pad number 15T 5911-8405:
60 to 0 mph @ 153.81 ft and 30 to 0 mph @ 34.57 ft
Driver comment: soft pedal, needed more pedal pressure--more consistent throughout stops compared to others.
Description of pad compound:
The PolyMatrix T pad compound has the following characteristics:
This pad is known as the "cold stopper" pad with higher friction levels over a wise temperature range. Improved stopping power while retaining low noise and dust properties. The T is standard equipment on many of Wilwood's brake conversion packages. Economically priced and long wear and low rotor abrasion.
Applications:
Considered a high-performance street pad. Excellent break-in pad for bedding new rotors.
Test 4 with pad number 15O 8850-89354-MR:
60 to 0 mph @ 144.37 ft and 30 to 0 mph @ 33.81 ft
Driver comment: Best pedal feel of any test and very predictable stopping.
Description of pad compound:
The BP-10 (Smart Pad), compound has the following characteristics:
Medium friction compound with low noise and dust properties of a street performance compound. Smooth engagement with consistent response from a flat torque curve throughout its entire effective temperature range. Good low to medium temperature wear rates. Beds quickly and provides fast response without excessive abrasion on vented iron rotors.
Applications:
High-performance street/strip, drag race, and track day categories using vented iron rotors. Disc brake conversions on street rods and musclecars.
