Cross-drillled or slot brake rotor
02-25-02, 08:47 PM
#27
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Re: MUST READ brake article
Originally posted by DamonB
GRM wrote a great article on braking systems. I found it reprinted here: GRM brake primer
This is a MUST read; very informative yet easy to understand. Allow me to quote a small portion pertaining to discs:
Let’s look at some common rotor “modification” and “performance” upgrades that you may have been ex- posed to. We’ll try to separate the marketing from the engineering: Bigger rotors will make your friends think you are cool, bigger rotors look sexy, but bigger rotors do not stop the car. What a bigger rotor will do is lower the overall operating tempera- ture of the brakes—which is a GREAT idea IF your temperatures are caus- ing problems with other parts of the braking system. Take, for example, a Formula 500 racer, a small 800-pound, single-seat formula car. While the brakes are cer- tainly much smaller than those found on a 3000-pound GT1 Camaro, that does not necessarily mean that they need to be made larger. In fact, in- stalling a GT1 brake package onto our formula car would probably do more harm than good. That’s a lot of steel hanging on the wheel that needs to accelerate each time the gas pedal is pushed. So the motto of this story is bigger is better until your tempera- tures are under control. After that point, you are doing more harm than good, unless you really like the look. (And hey, some of us do.) Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the ‘40s and ‘50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as “gassing out.” These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of fric- tion. The holes were implemented to give the gasses somewhere to go. It was an effective solution, but today’s friction ma- terials do not exhibit the same gassing out phenomenon as the early pads. For this reason, the holes have car- ried over more as a design feature than a performance feature. Contrary to popular belief, they don’t lower tem- peratures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads—sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or Fl. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it. The one glaring exception here is in the rare situation where the rotors are so oversized that they need to be drilled like Swiss cheese. (Look at any performance motorcycle or lighter formula car, for an example.) While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remem- ber that nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operat- ing temperatures and longer brake pad life, at the expense of higher weight. It’s all about tradeoffs. Slotting rotors, on the other hand, might be a consideration if your sanc- tioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to re- duce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut prop- erly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)
3
GRM wrote a great article on braking systems. I found it reprinted here: GRM brake primer
This is a MUST read; very informative yet easy to understand. Allow me to quote a small portion pertaining to discs:
Let’s look at some common rotor “modification” and “performance” upgrades that you may have been ex- posed to. We’ll try to separate the marketing from the engineering: Bigger rotors will make your friends think you are cool, bigger rotors look sexy, but bigger rotors do not stop the car. What a bigger rotor will do is lower the overall operating tempera- ture of the brakes—which is a GREAT idea IF your temperatures are caus- ing problems with other parts of the braking system. Take, for example, a Formula 500 racer, a small 800-pound, single-seat formula car. While the brakes are cer- tainly much smaller than those found on a 3000-pound GT1 Camaro, that does not necessarily mean that they need to be made larger. In fact, in- stalling a GT1 brake package onto our formula car would probably do more harm than good. That’s a lot of steel hanging on the wheel that needs to accelerate each time the gas pedal is pushed. So the motto of this story is bigger is better until your tempera- tures are under control. After that point, you are doing more harm than good, unless you really like the look. (And hey, some of us do.) Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the ‘40s and ‘50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as “gassing out.” These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of fric- tion. The holes were implemented to give the gasses somewhere to go. It was an effective solution, but today’s friction ma- terials do not exhibit the same gassing out phenomenon as the early pads. For this reason, the holes have car- ried over more as a design feature than a performance feature. Contrary to popular belief, they don’t lower tem- peratures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads—sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or Fl. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it. The one glaring exception here is in the rare situation where the rotors are so oversized that they need to be drilled like Swiss cheese. (Look at any performance motorcycle or lighter formula car, for an example.) While the issues of stress risers and brake pad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remem- ber that nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operat- ing temperatures and longer brake pad life, at the expense of higher weight. It’s all about tradeoffs. Slotting rotors, on the other hand, might be a consideration if your sanc- tioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to re- duce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut prop- erly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)
3
02-25-02, 09:52 PM
#28
Originally posted by rswst8
i'm just putting the rotors on now and will be coming to MADS with them in a month, maybe i'll crack them and only get a month of enjoyment out of them, but at least max will have to think twice the next time he sees a car with drilled rotors
if these crack, i guess i'll stick with slotted ones
i'm just putting the rotors on now and will be coming to MADS with them in a month, maybe i'll crack them and only get a month of enjoyment out of them, but at least max will have to think twice the next time he sees a car with drilled rotors
if these crack, i guess i'll stick with slotted ones
Also, it is the combination of the stock disc's size and drilling that makes them crack. I am quite sure that there are cars with bigger "cross-drilled" discs that can take the abuse. On the other hand, you can crack just about any rotors in the stock size. I've cracked up several sets of solid-face ones. Cryo treating has helped tremendously, but my cryo set is starting to show some cracking on the surface now.
Drilled and slotted rotors work fine for the street. If that is where you drive your car, get whatever rotors you want. Drilled and slotted rotors do look much nicer than the stock ones.
-Max
