Ben Posted April 13, 2016 Report Share Posted April 13, 2016 Dear all, The title pretty much says it all. But as I lawyer I rarely know when to just shut the hell up so I'm going to elaborate. Here goes. I'm thinking it is time for new brakes on the 135i. I measured my rotors and I'm near/barely below minimum thickness. I can get cross-drilled or slotted for pretty close to the same price as plain. So I figure, why not go for a bit of a cooler aesthetic? Thus the question: Cross-drilled or slotted? I like the look of cross-drilled better. The supplier has written assurances (and even a warranty) that their drilling misses all internal vanes and will not result in cracking. The mere fact that they feel the need to offer such a reassurance however, leaves me something less than reassured. In addition, I have heard much spouting on the internet about the benefits of cross-drilling being mostly illusory. But Porsche and Ferrari still do it. Is it really all just for show? (Also, just to get a bit psuedo-sciencey, all things being equal, an object's rate of cooling is increased if its surface area to volume ratio increases, which is what cross-drilling accomplishes with minimal decrease in heat-absorbing mass). Also, I have heard cross-drilling offers greater bite at the cost of faster pad degradation. On the other hand, I have heard that slotting offers a nice bite. It wouldn't have the cooling advantages suggested by my psuedo-science and it wouldn't look as cool. But it also wouldn't have the risk of cracking. OK. Thoughts? BTW, I did search for a thread on this already and found some relevant stuff but nothing that tackled it head-on. If I've missed something and there is a thread already like this, feel free to keep it to yourself. Quote Link to comment Share on other sites More sharing options...
Robochan Posted April 13, 2016 Report Share Posted April 13, 2016 TL/DR: Get blanks for performance, fancy shit for looks. http://www.corvetteforum.com/forums/autocrossing-and-roadracing/3678407-does-anyone-have-any-braking-questions.html If you are not trying to solve a cooling issue or your RC CL8 Sintered brake pads dont offer enough bite just go buy the cheapest painted rotors you can find. If you want to look fly rolling into cars and coffee buy some caliper covers and some slotted, cross driller zinc coated whatevers. Quote Link to comment Share on other sites More sharing options...
Grudes Posted April 13, 2016 Report Share Posted April 13, 2016 I think cross drilled rotors look "cooler" Lol With slotted rotors they sometimes make noise when your braking. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted April 13, 2016 Report Share Posted April 13, 2016 On old motorcycles i drill rotors for weight savings, not for any performance enhancing reason. Some of those old rotors can weigh as much as a modern wheel. I'm sure this is the reason modern rotors are drilled on performance cars too. The only advantage I have heard about slotted rotors is the clear debris from the pad which for a street car makes sense. I have no idea if it is true or not, but it kinda makes sense. Point is, buy what you like, doesn't sound like it makes a difference anyway. Quote Link to comment Share on other sites More sharing options...
Smokey Posted April 13, 2016 Report Share Posted April 13, 2016 Are you going to track the car? If so get blanks as Chandler said. If not it won't matter and do whatever you want to look like. FWIW, Porsche doesn't "drill" their rotors they're cast with holes and it's done for weight savings. Quote Link to comment Share on other sites More sharing options...
Second Gen Posted April 13, 2016 Report Share Posted April 13, 2016 My M comes with slotted rotors from the factory. Assume more of the Bimmer's do the same (But also believe if not tracked it probably does not make a difference).. Quote Link to comment Share on other sites More sharing options...
miller11386 Posted April 13, 2016 Report Share Posted April 13, 2016 Slots are OK on a DD IMO. Holes have a tendency to crack over time and cause more surface area for corrosion. I would not put them on a car that sees harsh weather/salt/ohio winter. Quote Link to comment Share on other sites More sharing options...
mrntd Posted April 13, 2016 Report Share Posted April 13, 2016 Cross drilled for racing. Slotted or blank for the rest. Unless you want to pay really big bucks the holes are drilled not case in the rotors. They will crack and then you get to start over. There are a lot of different slot designs and shapes. Just straight slots tend to be noisy. I have curved slots and they are better. I only get noise under heavy braking. I understand staggered left right small slots are the best for noise. Quote Link to comment Share on other sites More sharing options...
AudiOn19s Posted April 13, 2016 Report Share Posted April 13, 2016 TL/DR: Get blanks for performance, fancy shit for looks. http://www.corvetteforum.com/forums/autocrossing-and-roadracing/3678407-does-anyone-have-any-braking-questions.html If you are not trying to solve a cooling issue or your RC CL8 Sintered brake pads dont offer enough bite just go buy the cheapest painted rotors you can find. If you want to look fly rolling into cars and coffee buy some caliper covers and some slotted, cross driller zinc coated whatevers. says the guy with weird looking J-Hook's carved into his rotors Quote Link to comment Share on other sites More sharing options...
justinwebb Posted April 13, 2016 Report Share Posted April 13, 2016 I always drag both my pads and rotors across the concrete before installing, added performance. Quote Link to comment Share on other sites More sharing options...
dsm_sleeper Posted April 13, 2016 Report Share Posted April 13, 2016 says the guy with weird looking J-Hook's carved into his rotors Fancy. Quote Link to comment Share on other sites More sharing options...
Cordell Posted April 13, 2016 Report Share Posted April 13, 2016 IMHO there is no reason to run anything other then quality blanks. I have never seen a cross drilled rotor with any real mileage on it that wasn't cracked, that includes factory Mercedes, BMW, and GM'S factory parts. Slotted rotors are nothing special either. Just because someone makes cheap drilled or slotted rotors doesn't mean you need to buy them. Quote Link to comment Share on other sites More sharing options...
SpaceGhost Posted April 13, 2016 Report Share Posted April 13, 2016 I always drag both my pads and rotors across the concrete before installing, added performance. Winner! Beat me to it. Quote Link to comment Share on other sites More sharing options...
Robochan Posted April 13, 2016 Report Share Posted April 13, 2016 says the guy with weird looking J-Hook's carved into his rotors Only in the front! I run super cheapo blanks in the rear. I'll never run a drilled rotor. Quote Link to comment Share on other sites More sharing options...
zeitgeist57 Posted April 13, 2016 Report Share Posted April 13, 2016 I ran eBay cross-drilled/slotted rotors on my Corvette and Passat, never had a cracking issue but in both cases I used higher-quality, ceramic pads. IMO you can get great rotors, but if your pads suck it's going to create a lot of heat/dust and cracking. 99% of rotors are all cast in China anyway: you're paying either for truly high-performance rotors, or someone is machining Chinese blanks. And I did take my Corvette to BeaveRun back in the day, for a private event with only about 12 cars. I did a ton of laps and stayed on the ass of my friends' Ford GT in the turns. Rotors/pads were always fine. Quote Link to comment Share on other sites More sharing options...
99StockGT Posted April 14, 2016 Report Share Posted April 14, 2016 Unless you are doing lots of high speed breaking with it, go with quality blanks. To continue your pseudo-science mode of thought, taking the same size rotor and drilling/slotting it reduces the contact/friction patch between the pad and rotor. I've always lived by slow speed breaking better with blanks, repeated high speed breaking better with drilled/slotted. Quote Link to comment Share on other sites More sharing options...
Littleguy Posted April 14, 2016 Report Share Posted April 14, 2016 I don't know much about BMW brakes, but one of the modifications that I thought helped braking was upgrading my brake booster. Quote Link to comment Share on other sites More sharing options...
BIGGU Posted April 14, 2016 Report Share Posted April 14, 2016 agreed with what everyone else says, if your doing street / DD go for blanks. if you wish to see track time, do the slotted. The slotted will help remove glazing off brake pads at the track, that is really their only real purpose. Quote Link to comment Share on other sites More sharing options...
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