Travis Voorhies ran an impressive 1:20.352 at Nashville Super Speedway last weekend 7/16/09. His S-FWD class was tough to beat with the top drivers racing pushing it to the limits.
Prepped car in the paddock:
Turn 5 at Nashville Super Speedway:
Watch out for next time as Travis plans to add a bit of boost!
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Nothing looks better than a fresh set of rotors peeking through from behind a hot set of light weight wheels. Brake rotors serve a purpose other than that racecar look.
Brake Rotors serve two main functions of the autos braking system. The rotor is responsible for converting brake pad friction into wheel torque which will halt the wheel. The second function is that of acting as a heat sink for converting kinetic energy into thermal energy.
With many choices available how can you decide on the right set up for your car?
- Rotor Sizing: By adding 30% of thermal mass to the rotor one can expect to reduce brake temperatures by 30%. So you are thinking the bigger the better right? This may not be the case. When you upgrade to a larger rotor you are adding static mass and increasing rotational inertia. This will require more energy to turn. Its a trade off. Larger brakes will run at cooler temperatures, but will hinder the vehicles acceleration.
- One Piece or Two Piece Rotors: One piece rotors are an easy one. They are constructed out of one continuous piece. This is a good thing. Simple design, low cost, and decent thermal expansion. The only downside to one piece rotors is their tendency to warp or distort at high temperatures.
Two Piece (floating) rotors are made from a friction disc and a rotor hat. These are standard equipment if you are serious about racing and brake performance. The two piece rotor allows the friction disc to expand radially during higher temperatures. This is a good thing. With the rotor “floating” you will see less brake pad taper and rotor coning. The second beneficial point is that they are much lighter than the one piece rotors. The 1 piece rotors are made from cast iron. Iron is heavy and added weight does not help your track times. The two piece rotor has a hat that is usually made from aluminum or other exotic metals. This can drastically reduce the weight of your brake system.
Vented Rotors: These are a common sight for any performance based car or even the daily commuter. A vented rotor is comprised from two friction discs joined together with a series of vents, veins, or other cooler passages. When these rotors are spun at high speeds they actually force air through the center of the disc effectively cooling the rotor from the inside out. Cooling veins can be found in every shape and form. From straight to curved and differential to kangaroo paw pick your poison!
Cross-Drilled Rotors: These are simply a blank rotor with small holes either drilled or cast along the rotor face. There has been great debates on the structural strength of a cross drilled rotor that has been cast with the holes and with the holes drilled in a second process. Initially these were developed to help vent the gas build up of ancient (1950’s) brake pad technology. While these holes look flashy and catch attention they do not provide a performance gain that justifies the material loss. The holes can bring more cool air into the rotor veins, but I do not see this benefiting your stopping power. I would rather have that mass back in the rotor to help absorb the thermal energy.
Cross drilling can be beneficial if you are looking to scrub every ounce and bit of performance out of your hot rod. Take a looks at street bikes, formula car, or carts. These all use light weight cross drilled rotors. They have less rotating inertia.
The downside to the flashy cross drilled rotors is that these holes will accelerate cracking and rotor fatigue. I have ran cross drilled rotors on my street cars for years with no significant signs of premature cracking. However, on the full fledged race car, these rotors will simply not last as long as a slotted or blank rotor. They will also chew though your pads much faster than a traditional rotor. The choice is up to you.
Slotted Rotors: Refers to a rotor face that has been machined with a hand full of shallow grooves. They come in all shapes, sizes, and patterns. Even though pad technology has surpassed the first generation there is still evidence of gassing out and brake pad dust lubrication. These slots give the gasses and brake dust particles a place to go. The last place that you want to see gas and dust is in between your pad and rotor friction surface. They will essentially lubricate the surface and hinder your cars braking performance.
Another benefit to the slotted rotor is that it can help prevent glazing. Glazing refers to the brake pad getting so hot that its chemical composition changes. Machined slots help remedy this by shaving a thin layer off the pad giving you a fresh surface to surface contact between the friction disc and pad.
Warping: Warping, in my opinion, is the most misunderstood word when it comes to your brakes. Rotors DO NOT warp, they wear inconsistently. Warping can be better described as rotor friction disc thickness variation or “TV”. This is where spots on the friction disc wear faster than others. The first step to combat “TV” is to properly torque your wheels. Improperly torques wheels can lead to devastating “TV”.
Cracking: Do drilled rotors crack? Yes they do and so do slotted and blank rotors. I think that rotors crack due to the rapid heating and cooling of the disc. When you heat something up, especially metal, it expands and when you cool something down it contracts. If this is done quickly the ductile iron rotors can’t handle it. The temperatures that I am referring to is from roughly 350 degree to 1200 degrees F (glowing red rotor). Inspect your rotors frequently and looks for the early signs of cracking or micro fracturing. While you can drive you car with small surface cracks its best to change them out to prevent a catastrophic failure. If you see a crack on the edge of the rotor friction disc it comes highly recommended that you change that rotor immediately.
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Brake Fluid
Over the next few weeks I will do my best to inform you about brakes. By any means I am not an expert, but I have done quite a bit of research.Brake fluid…
Pretty interesting subject, well maybe if you are a chemical engineer. I plan to touch on the following: dry boiling point, wet boiling point, DOT rating, chemical composition, and which fluid is best for your application.
The brake fluids primary role is to transmit a force from the master cylinder to the piston(s) inside the brake calipers. The fluid inside the master cylinder is not pressurized. It it not pressurized when you apply a force to the brake pedal, its simply a reservoir.
Dry boiling point:
During mild track sessions or even “spirited” street driving it’s not uncommon for the rotors to exceed 800 degrees F. Most of this heat is dissipated to the caliper and brake fluid. Under this scenario the fluid behind the caliper piston can see temperatures of 300 degrees F. The good thing is that this is what the fluid was designed to handle, or was it? Most of the leading fluid manufactures have a dry boiling point at 400 degrees F.
Wet boiling point:
Brake fluid is hygroscopic which simple means that it likes to absorb moisture from the atmosphere. The wet boiling point refers to the boiling point of a fluid when water is present. It is crucial to keep your spare fluid sealed (unopened) until you are ready to use it. If you have a half full bottle of old fluid, toss it. Even if the lid is tightly secured the moisture will find its way into the fluid. Once the smallest amount of moisture has seeped into the brake fluid the dry boiling properties can be cut in half!
DOT ratings/ Chemical composition:
What does DOT 3, DOT 4, DOT 5, and DOT 5.1 mean? DOT 3 and DOT 4 are similar, both are made primarily from glycol ether. DOT 4 usually has a higher boiling point and is more resistant to absorbing moisture. Visually, these are dyed faint yellow or are clear. DOT 4 fluids have an enhanced chemical composition, mainly increased amounts of borate esters. DOT 4 fluids have a minimum dry boiling point of 446 degrees F and 311 wet. One thing to remember is that is you choose to run DOT 4 fluid in your car it needs to be changed more often than the DOT3.
In general, all DOT 3 DOT 4 and DOT 5.1 fluids CAN be mixed without concern. Time for a track bleed or a full service bleed? A full service bleed is replacing all of the fluid in your brake system. This should be done if there is air trapped anywhere in the system. As for the track bleed the fluid near the rotor tend to “cook” faster than the fluid in the master cylinder. At the track you can remedy this problem by throwing in a bottle or two and bleeding each corner 5-6 times. You can top it off with any of the previously mentioned fluids.
DOT 5 fluid is king, purple in color, pure silicone composition makes this fluid have a stunning 509 degree dry boiling point! These fluids should be used on race prepped cars only. Why can’t I use it in my street vehicle? First, because they cannot mix with the DOT 3 and DOT 4 fluids. Second it is chemically impossible for them to mix. It is nearly impossible for you to flush your brake system free of all glycol based fluids. Since it’s silicone there is more space in the fluid for air to fill. Air is much more compressible than any fluid leaving you with a soft pedal. Finally, this fluid can not absorb air which can in turn lead to boiling spots, freezing points, and internal corrosion.
Which fluid is best for your application:
What are you driving? If its a street car with the occasional track session, fresh DOT 4 fluid will cover all of your demands. Do you trailer your car to the track and consider yourself a certified race junky? Have a street bike or other 2 wheeled bike? Go for the DOT 5!
How do you bleed brakes? Here is a great step by step review:
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