Better, in terms of braking distance. I’m told that the reason they are cross drilled is because the holes reduce the amount of heat on the rotor, thus improving stopping power. So, if the aforesaid holds true, wouldn’t it make sense to cross drill all brake rotors for every vehicle?
At least to me it would. But there’s probably something I’m not getting. I mean, I know this is done in higher end sports cars, but why isn’t it done in your garden variety sedan? Does drilling holes in the rotor add a significant amount to the cost of the vehicle? I’m missing something here.
Cross drilling improves the cooling rate of the rotor. It also reduces the mechanical strength of its structure. I would tend to think that the presence of so many new “edges” on the face of the rotor would also accelerate pad wear, This is why some rotors are “vented” yet have an unbroken working surface. Cross drilling is cheaper than venting because you do not need to perform electron beam welding to fabricate the vented rotor assembly.
Due to the perforated structure of the cross drilled rotor I would venture that it is easier to warp one during extreme or prolonged use. The numerous holes can provide more initiation points for crack propagation. There is also the remote possibility that debris can lodge in the holes and scar the pads.
Overall, I’d opt for vented rotors.
I think Zenster is right on all counts. I’d add that cross-drilling reduces the effective area available for pad contact, so the braking force may actually be reduced. It also adds cost, and every penny counts on a cheap car.
I believe cross-drilled, single-thickness rotors are used primarily where size and unsprung weight are critical, as on sports cars and motorcycles. For simple durability and adequate performance on most passenger cars, the conventional vented rotor would seem to be a better choice.
Zenster, do you know if vented rotors really are EB-welded? I thought the passages were simply sand-cast - at least that’s how I’d design one if asked to.
The number one reason: cost. Your garden-variety sedan isn’t typically driven in the same manner as a high-performance sports car and doesn’t really need them.
Cost isn’t a huge issue. They really aren’t that much more expensive to buy than a regular one. If they were put as a production item from the factory they probably wouldn’t be any more money at all. Really.
It has already been touched on though, that it is mostly for cooling. Race cars that use them, use them because they are on the brakes all the time and they get seriously hot. The rotors and pads are so massive on them to begin with the surface area that is missing isn’t a big problem since they are so big.
Another problem with regular cars having them is that very few shops are equiped to resurface them.
All this equals - waste of money. These are worse than drilled brake/accelerator pedals for the person who isn’t driving a real true blue race car… or those ones who “think” they do.
One more thing- most of your modern semi-metallic, carbon metallic & ceramic pads actually need a certain level of heat to work most effectively- several hundred degrees Fahrenheit, if I’m not mistaken.
Organic pads OTOH, aren’t too good with heat, so drilled & slotted rotors might actually make a difference.
Drilled & slotted rotors on Grandma’s Buick might not let her brakes build up enough heat in a panic stop for her to stop in time, so that’s probably why they’re not on factory cars.
I think you are correct on all counts, but electron beam welding? Are you quite certain?