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View Full Version : why crossdrilled and slotted rotors are inferior



fataLLightning
02-22-2003, 07:36 PM
why crossdrilled and slotted rotors are inferior to full face rotors. im sure some of you wont agree with me, so ask away and ill try my best to explain.

borrowed from : http://www.teamscr.com/rotors.htm
Super Sizing

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 temperature of the brakes – which is a GREAT idea IF your temperatures are causing problems with other parts of the braking system. Take for example a F500 racecar – a small 800 pound single seat formula car. While the brakes are certainly much smaller than those found on a 3,000 pound GT1 Camaro, that does not necessarily mean that they need to be made larger. In fact, swapping on a GT1 brake package would probably do more harm than good – that’s a lot of steel hanging on the wheel that needs to accelerate each time the ‘go’ pedal is pushed. So, the motto of this story is bigger is better until your temperatures 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

Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the 40’s and 50’s, 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 friction. The holes were implemented to give the gasses ‘somewhere to go’. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads.

For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief they don’t lower temperatures (in fact, by removing weight from the rotor, the temperatures can actually increase a little), they create stress risers allowing 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 F1. 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 (look at any performance motorcycle or lighter formula car) that the rotors are drilled like Swiss cheese. 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. Remember – nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brake pad life – at the expense of higher weight. It’s all about trade-offs.

Slotting

Slotting rotors, on the other hand, might be a consideration if your sanctioning 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 reduce 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 properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)

GonePostal
02-23-2003, 10:57 AM
Bigger rotors can help stopping power if they are complimented with equally sized calipers and pads. The more surface area there is, the more friction can be created to stop the car. That is provided that your tires are adequit as well. Common sense says if it isn't broken don't fix it. So unless you have a problem with your brakes overheating, you don't need crossdrilling and slotting.

Toda Party
02-23-2003, 11:02 AM
maybe people will believe this now instead of ignoring my 130962103968 threads about this subject :)

fataLLightning
02-23-2003, 02:07 PM
" but porsches do it " :P

hondasolsi
02-23-2003, 06:18 PM
most of the time for daily driven street cars and drag racing your brakes dont heat up enough and build up as much gas as NASCAR, race bikes, or road racing cars do. sometimes brakes on NASCAR can get red hot. i have yet to witness brakes on a regular street car get like that. IMO, i think a pad upgrade with stainless steel lines would be more worth it then getting slotted or x drilled rotors.