Slotted & drilled rotors don’t improve braking performance!

[Charles1]

Did anyone read the Grassroots article on brake upgrades this month? It highlights slotted rotors, big break kits and SS lines only improve the looks of a car not performance. Note some cars are in exception to the rule, 135 is not.
In fact most big brake kits and aftermarket calipers introduce knockback and improper balance.

[larryn]

I've always said that the decrease in surface area by drilling/slotting makes the brakes work harder, and negates any cooling benefits.

[///M ichael]

Thanks for the update!

[135-CS]

Originally Posted by Charles1

Did anyone read the Grassroots article on brake upgrades this month? It highlights slotted rotors, big break kits and SS lines only improve the looks of a car not performance. Note some cars are in exception to the rule, 135 is not.
In fact most big break kits and aftermarket calipers introduce knockback and improper balance.

Could you post the article???

Thanks Good info!!

[Red135]

I thought one of the best reasons to switch to the drilled/slotted rotor was the lighter weight.

[Charles1]

Originally Posted by Red135

I thought one of the best reasons to switch to the drilled/slotted rotor was the lighter weight.

I would not trade three lbs for braking performance. At track speeds weight in not as important as aerodynamics and power.

Most passing in road racing is done under braking, if you cant stop you lose.

In addition slotted rotors crack more often that solid rotors forcing frequent expensive replacements.

[Neo187H]

Originally Posted by Charles1

I would not trade three lbs for breaking performance. At track speeds weight in not as important as aerodynamics and power.

Most passing in road racing is done under braking, if you cant stop you lose.

In addition slotted rotors crack more often that solid rotors forcing frequent expensive replacements.

No one has said that it reduces braking performance, merely that it doesn't improve it. 3 LBS of unsprung rotating mass on each wheel is a LARGE difference if your getting down to details and for 4 years you can get those expensive rotors replaced for free under the maint program as long as you buy the first pair.

[larryn]

3lbs that close to the hubs doesn't make than much difference, a little, not a lot. If you're talking about lighter tires, or wheels.. that's way more bang for the buck in better acceleration, throttle feel.

[Charles1]

Originally Posted by Neo187H

No one has said that it reduces braking performance, .

I say it reduces braking performance. Less surface area = less performance

[Doolab]

Originally Posted by Charles1

I say it reduces braking performance. Less surface area = less performance

I second that... Furthermore, drilled rotors can and do suffer from heat stress fractures more than regular rotors, not to mention the reduced surface area, etc...

Here's a related article on this aptly named "The Truth About Brakes".

[WhiteOne]

4 years and 50K miles worth of warranty. How many free brake jobs do people expect to get? I would think the factory brakes will last longer than 50K. YOMV

[ChrisK]

Don't slot/cross drilled rotors help in rain...the ability to vent the water from between the pad and rotor?

[Charles1]

Originally Posted by ChrisK

Don't slot/cross drilled rotors help in rain...the ability to vent the water from between the pad and rotor?

Myth

[ChrisK]

Maybe an opinion. :iono:

[Mad Dragon]

Originally Posted by ChrisK

Don't slot/cross drilled rotors help in rain...the ability to vent the water from between the pad and rotor?

The brakes on BMWs clear the water while you're driving.

[ichiban]

I think weight is pretty important, and drilled are more heat resistant, so that does make up for some of the braking surface lost. If it is slotted, it will eat the pad more evenly which gives better braking, less vibration. And as for drill/slotted rotors cracking, it depends on how the rotor is made. If it is casted with holes, then it's fine, but if drilled it will lose it's integrity.

[fe1rx]

Originally Posted by larryn

3lbs that close to the hubs doesn't make than much difference, a little, not a lot. If you're talking about lighter tires, or wheels.. that's way more bang for the buck in better acceleration, throttle feel.

Steel weighs 0.3 lb per cubic inch. How drilling a rotor can remove 10 cubic inches of material from a rotor is a bit of a mystery. Any proponent of drilling want to count holes and measure them and do the math to convince us that drilling represents that much material being removed?

Also, the weight of a rotor represents thermal capacity, which is a good thing on the track.

Mass rotating at the rolling radius of a wheel appears twice as great with respect to acceleration as weight fixed on the vehicle because it has to be accelerated to both the translational speed of the vehicle and to a circumferential speed equal to the translational speed. This means that rotating mass attached to the wheel can never be credited with an effect greater than twice its actual mass.

The average radius of the rotor disc is about 5", the rolling radius is about 13", meaning the circumferential velocity of the mass lost by drilling is about 38% of the vehicle velocity, producing an effective mass loss of about 115% of the actual loss. If 3 lbs could actually be lost from the rotor this would be equivalent to about 3.4 lbs in performance terms.

As Larry points out lighter wheels or tires would have much more effect, because the weight lost would be at a larger effective radius.

Many of us that actually track our cars have learned that plain rotors are not only cheaper, they work as well or better than drilled or slotted rotors.

[ChrisK]

Originally Posted by Mad Dragon

The brakes on BMWs clear the water while you're driving.

I'm not referring to BMW's, I mean in general.

[ChrisK]

LOL The Cross Drilled Rotors vs. Normal rotors is like an oil thread. Nevertheless, I really like the BMW rotors and may install them regardless.

[Mad Dragon]

I change my brakes at 1200 miles and every 3000 miles after. I also use low-octane pads, to save a few bucks. :biggrin:

Originally Posted by ChrisK

I'm not referring to BMW's, I mean in general.

Who cares about other cars? :-P

[Charles1]

Originally Posted by ichiban

I think weight is pretty important, and drilled are more heat resistant, so that does make up for some of the braking surface lost. If it is slotted, it will eat the pad more evenly which gives better braking, less vibration. And as for drill/slotted rotors cracking, it depends on how the rotor is made. If it is casted with holes, then it's fine, but if drilled it will lose it's integrity.

Please only post facts... Some people take talk to be true...

[Charles1]

I would be OK with big brake kits and drilled/slotted rotors if we all would admit they are for LOOKS only!!!