X-drilled & Slotted Rotors CAN be cut!

[tholyoak]

You are entitled to your opinion and maybe I am wrong but I don't believe the rotor hat is going to expand appreciably when sandwiched between the hub surface and the wheel. Which are also going to expand. And even if it did, the difference in the expansion between being sandwiched with the correct 96ftlbs of torque vs say a mis-torqued wheel at where some lugs are at 120ftlbs of torque is not going to lead to appreciable distortion of the rotor hat.

Secondly on a street car you are never going to experience the types of temperatures you refer to in race cars. I would be pretty concerned if I saw someones rotors glowing red hot at night on the exit ramp as you see at night during Le Mans. The most common way people warp rotors on the street is when they run them too thin or they do some heavy braking and while the rotor is hot they still have their foot on the brake, thus the pads make contact with the rotor both melting some pad material to the disc and/or resulting in differential cooling of the disc leading to warping.

Todd

[Lil bastard]

Sorry to say you are misinformed.

I had a shop mount some tires for me and within 50 mi. all 4 rotors were warped. They readily admitted they accidentally over-torqued the bolts due to a malfunctioning air regulator in the shop and paid $850 out-of-pocket to replace them.

There are a number of articles out there on this subject. Even AutoZone warns of this in their DIY Tire Change guide - page down to the WARNING box - http://www.autozone.com/az/cds/en_us/0900823d/80/1b/d6/9f/0900823d801bd69f/repairInfoPages.htm

[tholyoak]

This is the last I will say about this, and go ahead and believe what you want.

When your tech, tells you that over tightening of wheels can warp rotors you are either not understanding him or he doesn't understand what he was originally told.

Over tightening of the wheel will not causes warping the rotor, what it can do is distort the hub flange on which the rotor sits. This distortion causes rotor runout problems, that when you measure with a dial gauge on the rotor surface will appear to be warped rotors. If left alone this problem will result in further braking issues.

There is no physical way that over torquing of the wheel to the hub will cause physical warping of the rotor. That is my opinion from working on Porsches for almost 20 years, not on what I read on the Autozone website or my local garage mechanic told me.

Todd

[Lil bastard]

@tholyoak - I'm sorry, normally I wouldn't pursue an arguement. And I don't mean to belittle or diminish your mechanical abilities in the least. I've read many of your posts and they contain valuable information, I don't think there's any question about your skill level. But in this case, you're simply wrong.

It's not a matter of what one believes, this is fact. I too have been repairing and maintaining cars of all sorts for 20 years and then some, incl. porsches, so I can assure you there was no misunderstanding of what my Tire shop told me.

The reason I'm persisting is that this is one problem which is easy to avoid, but has expensive consequences if the procedure's not done correctly ($800+ for a set of rotors). I don't want readers to get the impression that this is a matter of belief because it isn't.

Over torqueing of lug nuts and wheel bolts is a major cause of rotor warping. Full stop.

If you won't accept an article from AutoZone as proof, here are a dozen more that you can look over, and I hope, learn something new from.

• http://www.articleblast.com/Auto_and_Trucks/General/Warping_Automobile_Disk_Brake_Rotors_are_Preventab le/
  
  http://www.automedia.com/Replacement_Rotors/ccr20050201rr/2
  
  http://www.alldata.com/techtips/2001/20010430b.html
  
  http://www.thecarconnection.com/Enthusiasts/Ask_a_Mechanic/On_Site_Mechanic_for_Dec_27_1999.S209.A1474.html?p g=2
  
  http://www.mpt.org/motorweek/goss/21008.shtml
  
  http://en.wikipedia.org/wiki/Rotor_(brake)
  
  http://autorepair.about.com/library/faqs/bl815.htm
  
  http://www.ctbrakes.com/faqs.html#16
  
  http://www.thevolvosite.com/volvo-brake-rotors-and-warping.htm
  
  http://www.brakewarehouse.com/brkewrhsefaqs.asp#top61
  
  http://www.bestbrakes.com/how_to_install_brakes.shtml
  
  http://www.mpt.org/motorweek/goss/2436.shtml

[Lil bastard]

It occurs to me that there is one more worry in turning cross-drilled rotors. That is, these rotors have holes which are beveled.

These bevels are a design element that serves three important functions:

They prevent the build-up of pad material at the holes (a source of Brake pulsation).

They also prevent the holes from becoming clogged with friction material from the pad, or mud, dirt, etc.

Finally, and perhaps most important, these bevels act to eliminate, or at least delay, the onset of stress cracks which could lead to rotor failure.

This is a very real concern and probably the biggest reason that cross-drilled rotors are not widely used anymore in racing - racers use slotted discs that better prevent rotor failure and warping. Given Porsche's vast racing experience, I'm a little surprised that they decided to offer X-drilled rather than slotted rotors. I supose that it's because the aftermarket is flooded with x-drilled rotors (they're cheaper to manufacture than slotted ones) and so they enjoy a greater popularity. They also cool slightly better than slotted discs, but I'm not sure that it's a good trade-off vs reliability.

By turning these rotors, you eliminate or reduce this beveling. To do the job correctly, it would be necessary to re-establish this beveling by using a drill press and beveling out each hole in the rotor (on each side). By the time you went to all this trouble, it'd probably less expensive and more expedient to simply replace the rotors.

[CJ_Boxster]

Well i looked at the rotors before installing them and i remember seeing that there was still bevels on the drilled holes. so no worries there.