PDA

View Full Version : Need advice on rotors


brave1heart
11-08-2003, 04:53 PM
Did a lot of brakes research on the site and found tons of recommendations on pads but very little on rotors. I replaced the pads ~ 5-6K miles ago but did not replace the rotors. The front has started to vibrate under braking. I measured the rotors and they are just below the minimum thickness (17 mm for the rears and 24 for the fronts). The pads are about halfway worn out and I am keeping them till the spring but I'd like to replace the rotors. Would love to get slotted rotors but I am coming up with $380 for a set on the Tirerack. The basic plain Brembos are only $180 for a full set - about the same price as the OEM rotors. Which ones would you recommend? TIA.

http://www.tirerack.com/brakes/brakes.jsp?autoMake=BMW&autoModel=325i+Sport+Package&autoYear=2001&autoModClar=&make=Brembo&model=Replacement+Rotor

The Roadstergal
11-08-2003, 05:00 PM
A friend of mine uses ATE Powerslots on his Z3, so I just recently tried them on my 325. Standard ATE on the back, Powerslots on the front, $130 and change delivered from <a href=http://www.eap4parts.com>Eurasian</a>.

Pinecone
11-08-2003, 07:58 PM
Why do you want slotted? For street use, they look neat, but will eat your pads faster.

For track use, they don't really help that much unless you are doing a lot of other things to the car.

I suggest non-slotted rotors, but have them cryo treated (Frozen Rotors is a brand of pre-cyro treated rotors).

GSR13
11-08-2003, 08:21 PM
Why do you want slotted? For street use, they look neat, but will eat your pads faster.

For track use, they don't really help that much unless you are doing a lot of other things to the car.

I suggest non-slotted rotors, but have them cryo treated (Frozen Rotors is a brand of pre-cyro treated rotors).

Is this also true for Cross Drilled Rotors? I have always heard that they are slotted or drilled to keep the rotors cooler, but never ran any on my cars. I started reading about drilled rotors being louder and really offering no benefit. If true, why do Porsche and Ferrari use them?

Also, how do they cause the pads to wear faster? They do look nice, but if they offer no advantage, then I agree, what's the point?

brave1heart
11-08-2003, 09:03 PM
Slotted rotors help clean the pads better. Cross-drilled rotors do not work as well as plain rotors or slotted rotors because they have less material to dissipate heat over. I've no idea why they are offered on exotic sports cars except maybe because they look cool.

I am aware of the grated cheese effect that some rotors/pads produce. Here's an interesting discussion that answered most of my questions:

http://member.rivernet.com.au/btaylor/BMWText/technical/ATEPowerDiscs.html

I am pretty sure that the vibration that I've been experiencing under braking is due to my stock rotors having been warped by the Performance Friction 90 pads that I put in.

Roadstergal - thanks for the tip. I just ordered a set of Ate power disks from Eurasian.

The Roadstergal
11-08-2003, 09:25 PM
Why do you want slotted? For street use, they look neat, but will eat your pads faster.

A local told me that they have a minor advantage in inclement weather. Dunno if I believe that, but at least they look cool. :p

I hadn't heard that they eat pads. If they blaze through this set, I'll rethink the next rotor choice.

LmtdSlip
11-08-2003, 10:04 PM
Its my understanding that drilled rotors are not so much for cooling but more for additional edges for the pads to bite into...thus givving better response and more force.

Slotted rotors are similar but still maintain the rotor volume to aid in heat dissapation.

A friend of mine used to race an E36 M3 with Hawk pads and stock rotors. He eventually moved to the cryo rotors as the stock rotos would develop cracks VERY quickly from the intense heat. But this was in a race setting. Not necessary for street or even gymkana.

TeamM3
11-09-2003, 12:29 AM
slots and drilled holes are just marketing fluff, all they do is decrease swept area and reduce thermal mass capacity, get the plain Brembo OE replacement rotors but they should be quite a bit less costly than OEM rotors.

Pinecone
11-09-2003, 04:22 AM
The original idea behind cross drilling was to give pad gasses a way ot escape. But they reduce the thermal mass, and cause cracking.

Slots also give a path for the gas to escape, but give a lot of edges to remove pad material (think cheese blade carving off thin slices of pad material).

Slottted rotors can give a mariginal improvement in VERY wet conditions, as the slots allow excess water to drain off, but that is only true for the frist rotation or two of the rotor, after that the pad has swept the water from the rotor.

As for warpping, according to Carroll Smith (RIP) rotors rarely if ever actually warp. What happens is that the overheated cast iron rotor produces cementite in various areas. Cementitie is aformed when the carbon in the cast iron migrates and combines with O2 to form very hard spots on the rotor.

These hard spots wear much slower than the rest of the rotor, leading to high and low spots. BUT the high and low spots are not directly relaed to high and low spots on the other side of the rotor, which would happen if the rotor actually warped.

For maximum performance go with plain rotors, cryo treated.

For maximum look, go with cross drilled.

GSR13
11-09-2003, 12:00 PM
The original idea behind cross drilling was to give pad gasses a way ot escape. But they reduce the thermal mass, and cause cracking.

Slots also give a path for the gas to escape, but give a lot of edges to remove pad material (think cheese blade carving off thin slices of pad material).

Slottted rotors can give a mariginal improvement in VERY wet conditions, as the slots allow excess water to drain off, but that is only true for the frist rotation or two of the rotor, after that the pad has swept the water from the rotor.

As for warpping, according to Carroll Smith (RIP) rotors rarely if ever actually warp. What happens is that the overheated cast iron rotor produces cementite in various areas. Cementitie is aformed when the carbon in the cast iron migrates and combines with O2 to form very hard spots on the rotor.

These hard spots wear much slower than the rest of the rotor, leading to high and low spots. BUT the high and low spots are not directly relaed to high and low spots on the other side of the rotor, which would happen if the rotor actually warped.

For maximum performance go with plain rotors, cryo treated.

For maximum look, go with cross drilled.

Thanks for the info!

Honestly, I always thought the rotors were drilled to allow air to flow through them, thus cooling the rotor faster. I assumed the slots did the same thing, just not as effectively. I suppose that is what I get for thinking. :tsk: :D

rockfish66
11-09-2003, 01:00 PM
Did a lot of brakes research on the site and found tons of recommendations on pads but very little on rotors. I replaced the pads ~ 5-6K miles ago but did not replace the rotors. The front has started to vibrate under braking. I measured the rotors and they are just below the minimum thickness (17 mm for the rears and 24 for the fronts). The pads are about halfway worn out and I am keeping them till the spring but I'd like to replace the rotors. Would love to get slotted rotors but I am coming up with $380 for a set on the Tirerack. The basic plain Brembos are only $180 for a full set - about the same price as the OEM rotors. Which ones would you recommend? TIA.

http://www.tirerack.com/brakes/brakes.jsp?autoMake=BMW&autoModel=325i+Sport+Package&autoYear=2001&autoModClar=&make=Brembo&model=Replacement+Rotor


Have you actually measured the runout? It sounds like your rotors are worn enough to warrant replacing them anyway, but may not be your problem.

Worn LCA bushings can cause a similar vibration under braking that is often confused with warped rotors. Check those, too.

brave1heart
11-09-2003, 06:57 PM
Have you actually measured the runout? It sounds like your rotors are worn enough to warrant replacing them anyway, but may not be your problem.

Worn LCA bushings can cause a similar vibration under braking that is often confused with warped rotors. Check those, too.

I had the LCAs replaced 2 months ago.

Chris330Ci
11-09-2003, 08:09 PM
Just a thought... I assume your car is still under warranty, no? Why not bring it in and have the OEM rotors replaced? Once you get it home, swap out the new OEMs for the ATEs when they arrive. Then put the OEMs in a box somewhere so when the ones you ordered wear out, you'll have a brand new set to put on.

SARAFIL
11-09-2003, 08:14 PM
Just a thought... I assume your car is still under warranty, no? Why not bring it in and have the OEM rotors replaced? Once you get it home, swap out the new OEMs for the ATEs when they arrive. Then put the OEMs in a box somewhere so when the ones you ordered wear out, you'll have a brand new set to put on.

They won't cover rotor warpage if they see his aftermarket pads, that's why...

:angel:

Chris330Ci
11-09-2003, 08:58 PM
They won't cover rotor warpage if they see his aftermarket pads, that's why...

:angel:

:eeps: :eeps: :eeps:

Pinecone
11-10-2003, 04:42 AM
They won't cover rotor warpage if they see his aftermarket pads, that's why...

:angel:

So next time you put in aftermarket pads BEFORE the stock ones wear out. Then swap in the stock to get new rotors. :)

brave1heart
11-10-2003, 06:07 PM
Just a thought... I assume your car is still under warranty, no? Why not bring it in and have the OEM rotors replaced? Once you get it home, swap out the new OEMs for the ATEs when they arrive. Then put the OEMs in a box somewhere so when the ones you ordered wear out, you'll have a brand new set to put on.

Good thought but not an option for me. The car has 56K miles on it (barely 30 months old :D).