Cross Drilled VS Slotted Rotors
by mike_sho
Over the years ive heard many debates on the actual benefits of modified or aftermarket brake discs. Many times it seems most people are confused of the better. Where in most cases its not a straight cut answer when it comes to tuning and choosing the right application for the job. Two of the most common types of ventilation on brake rotors are Cross Drilling and Slotting (see below diagram).
Diagram:
Cross Drilled Rotor (with chamfered holes)
Slotted Rotor
Which one is better? In the next section we will go over simple benefits and drawbacks of each system. To answer the question beforehand , there isnt one standard answer for all cars and environments. As well as driver. A track based car will be setup for its environment to best suit the situation at hand. One might benefit from a certain setup where as a street car with the same setup might see adverse effects.
Slotted Rotor Attributes:
- The slots on the rotor helps clean the brake pad, which improves bite.
- The slots on the rotor will slice the brake pad allowing the pad to bite harder into the disc causing an increase in disc temperatures. This will bring your brakes up to temperature faster , but might also take you too far decreasing the benefit. The slotted rotor coupled with a race pad which need to be heated would be optimum.
- Slotted rotors will also cause slightly more brake pad wear and tear giving you less miles on a pad before it needs to be replaced. Shorter maintenance schedule.
- Slotted rotors allow gas to ventilate during brake fade.
- Slotted rotors are less prone to cracking then the cross drilled rotor.
- Slotted rotors weigh more.
- Slotted rotors have more disc surface.
- Slotted rotors maintain around 96% of the friction surface
Drilled Rotor Attributes:
- Drilled Rotors offer an enhanced initial bite.
- Drilled Rotors perform better in wet weather over the slotted rotor. Due to volume of a hole vs a slot.
- Drilled Rotors are more prone to cracking than slotted.
- Drilled Rotors allow gas to ventilate during brake fade.
- Drilled Rotors offer a performance benefit since there lighter in weight.
- Drilled Rotors have more ventilation so they should cool off faster , but have less rotor material so they could get hotter than a slotted rotor. But its hard to say as the slotting also increases heat.
- Drilled rotors maintain around 85-93% of the friction surface
Drilled and Slotted Attributes:
- The slotting will increase rotor heat.
- The drilled holes will increase the cooling after braking.
- The drilled holes will increase the water braking.
- Drilled and slotted are the least reliable.
- Drilled and slotted are going to weigh less from the same manufacturer. Other designs might be lighter from company to company.
- Drilled and slotted will give the most performance benefit to acceleration due to the lighter weight.
- Drilled and slotted will also be the hardest on your brake pad (wear and tear)
- Drilled and slotted only maintain 80-91% of the friction surface.
Overview & Suggestions:
If you can stand the increased pad wear. Slotted is pretty much a great choice for stopping power and reliable both on the street and track. Good for auto-x / road course and mountain downhill racing.
Allthough if your looking for an acceleration increase as well. A drilled rotor might be the best choice. As well works well in water/rain. All good for the street or drag racing.
The Slotted and Drilled rotor could also be a good combo for someone whos into racing or ok with increased pad wear. But youll notice that it also provides the least amount of braking surface as well the least material on the rotor. Which some attribute more brake rotor material to being able to withstand heat better. Just imagine a block of metal being heated by a lighter vs a thin strip of aluminum from an intake. The thinner and or smaller amount will allow quicker and higher heating. Which will increase rotor temps which might take your brake pad out of heat range. So its a toss up on this one.
Another factor to remember is the frequency of slots or drilled holes on the rotor itself. How far they are spaced or how frequent they come. I believe a good slotted and drilled rotor combo would be that of one that has a few sets less on the holes , replaced by a small amount of slots. 3 or so. This will give more of a sharing effect rather than an overly done rotor.
Then there are the "big brake" kits. Which cost an arm and a leg, use oversized rotors and larger calipers with sometimes more pistons in use. These are indeed great braking systems. But we find this is complete and total overkill. Not only does it decimate your wallet and car budget, which isnt even the point. Maintenance is also exspensive (if the time does come), brakes are wear and tear item and sooner or later they will need replacement. As well there going to give you a big hit on performance in acceleration and unsprung weight. This is why we say stay away from these kits. With some smart choices you can have all the braking power youll ever need with the stock oem braking setup. Some aftermarket rotors and brake pads will give almost any car the ability to lock your tires. Which in the end result is what your aiming for. The ability to stop the tires from rotating from whatever speed you achieve, to a complete stop. Without much fade. As stated above its just too much of an overkill to fit a car with a large brake kit. Unless your car is running 8's and your almost hitting the wall at the end of the 1/4 mile. Then for safety reasons you might want to go this route. Otherwise your tires are what connect you to the road and those are your main bottleneck. If you want to stop faster. Tires are where that kinda money should be spent.
Now onto when shopping for a rotor , look at a few companies. Check out all your options and the different versions from each company , ask about how many holes or slots there are and dont just believe what image your being shown online is really whats in your box. Have them look at it. Also when they offer the slotted and drilled , take a look at the design. Did they decrease some drilled holes to make room for the slots or did they simply slap in some slots in between the drilled holes. This makes a difference and if you use the above guide you can also figure out the performance change and the benefit you might have as the end result driver and user. What risks your willing to take on reliability and maintinenace and where you want to see performance increases.
Another thing to remember is to find out who does the drilling and slotting for the rotors your purchasing. A lot of these places online and ebay will do in house drilling and slotting. Dont feel bad to probe these people and see how they are doing it. Some use outside manufacturers who will most likely have a better system at doing it. Some in house people might modify your holes by hand...which might end up a disaster. Be sure to get chamfered holes , this makes them smoother , more durable and less harsh on the brake pad. Beware of the ebay stores and brembo rotors. Brembo sells oem blanks to almost anyone and they are the ones doing the modifying. Usually these are not the best choice , especially drilled because they were meant to be pretty much stock replacements. There is the brembo sport rotors which brembo does themselves and is much more durable. So find out how they did it or what there seling before investing your money in your braking system and essentially your life.
The best bet is to get a good street performance pad. Some good brake fluid for starters. If this isnt enough or you still get fade , get some rotors. Then if you want better pedal effort get ss lines.
If your going to go with low cost rotors that are slotted or brembo slotted. It would probably be best to stick with slotted. Otherwise look for performance models.
Here is a list of reccomended Performance Rotors:
Brembo Sport Rotors (key word sport / gold color)
PowerSlot Cryo Rotors (these will last longer)
PowerSlot Slotted and Slotted and Dimpled
Rotora Rotors
EBC Rotors
-- Happy Tuning - mike_sho
