Jump to content
SAU Community

Have you ever heard that cross drilled brake rotors crack? Here's the story...


Recommended Posts

Hi all, after speaking with DBA (as I need new rotors) I thought I'd ask why cross drilled rotors are only recommended for "street use" because I know a lot of people wonder why this is the case and what will suite them. The E-mail reply was as follows...

Question -

"Just one more question. I know that cross drilled are not recommend for track use, is this because of the weakening effect on the rotors or is it more a liability thing? I have heard of cracking of the discs but realistically what sort of braking are you going to have to be doing to cause this?"

Reply -

"Adam,

the reason why we don't recommend cross drilled rotors for racing or track work is due to the following:

The disc rotor face surface area is reduced due to the holes and as a result this face heats up faster under braking.

Once you release the brakes the rotors cool very quickly due to the holes.

Due to this rapid heating and cooling of the rotor face it is possible for the rotor face to sustain what is known as heat shock.

Because the rotor is unable to heat soak and dissipate heat evenly the face of the rotor can develop cracks around the holes.

The use of slotted rotors allows the disc to heat soak and cool more evenly so the rotor is less prone to suffering from heat shock.

Heat shock can be evident in cross drilled rotors even when used by an extremely energetic driver on the street. If the drivers driving style is fast with rapid jabbing of the brakes and exallerator pedals he/she will be more likely to have problems with cross drilled rotors. Due to this reason we recommend the fitting of cross drilled rotors for looks only and improved braking performance under normal driving conditions.

I hope this answers your question, but if you have any further queries please feel free to email me.

Kind Regards,

Aaron Franklin

Technical Sales Advisor

Disc Brakes Australia Pty Ltd"

Thought this might be some helpfull info!

so is it safe to assume from that that cross drilled AND slotted discs will be less prone to this?

"The use of slotted rotors allows the disc to heat soak and cool more evenly so the rotor is less prone to suffering from heat shock"

The cracks would still form around the cross drilled holes inark beacuse the change in temp would still be significant. The only way to go on the track is slotted. Do they make 5000 series for the 34 yet adz?

I failed my RWC for the first time because I had drilled rotors with 1cm - 2cm cracks on each hole nearest the edge of the rotor... they looked sweet but the funny thing was I passed my Engineerring Cert. but not the RWC.

From what I've heard the DBA rotors were drilled after they were fabricated? While the Porsche and other high-end rotors had the holes cast from factory?

Drilling post-fabrication gives less structural integrity doesn't it?

I could be wrong though..

Because they aren't $200 rotors like DBA are...

HAHA good point.

so in other words his statement is only relative to DBA rotors... not in general

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Latest Posts

    • Yeah I've had too many issues with knock off's on the BMW's. I don't want to do a job twice or more because the parts are shit.
    • I read this and thought "ah! I will do this scissor jack on the tow point thing!" I just use my floor/low profile/costco jack and lift the car up by the tow hook itself, then slide jack stands under. Never thought about using scissor into floor jack combo :p
    • Well, my new WMI system took much longer to finalize. I actually missed my dyno appointment last Friday and lost my 150$ deposit. I'll be going back in the next week or two.  To sum it up. I only kept the AEM tank from my old setup. I replaced the AEM pump with a higher flow/pressure ProMeth 30GPH pump. I also swapped over to a 6AN low pressure feed line to the pump from the tank. There's also a pressure switch you cannot see on the pump high pressure line.    This is feeding 6x 200CC direct port nozzles and 1x 500CC Pre Throttle body nozzle. All fittings are Swagelok, because well why not. I also have a 300PSI pressure sensor up front.    I now have my Haltech ECU controlling everything. I start my pump with a basic relay at 5PSI and deadhead it. I then PWM a 3000CC methanol Injector to control flow starting around 10psi. The pressure switch in the trunk, along with my tank level are safeties before I ever get to 10PSI, and then I use my pressure sensor upfront as a secondary safety to cut the WMI and corrections in case the injector blocks or a line ruptures.  Wish me luck on the dyno!    
    • So, I'm back with bad news. There's no jack long enough on this planet that will reach the front subframe. If by some chance there is, it would weigh 200lb's.  I purchased a long reach jack... The damn thing weighted 120lb's and was massive. Didn't even come close, was still short at least a foot. It was a pain, but I brought it back. Next I decided HA! No problem, I'll get an Extra long reach jack. Well, I couldn't lift the box... It must have weighed 160LB's and luckily there was an open box in store. I took measurement and was still nowhere close.  Sadly I've lost hope and have accepted defeat. 
    • Thanks for that tip, niZmO_Man. I think the battery is OK. It's quite a new one, but I'll check. Last time I needed a new battery, everything electronic was fine, except that there wasn't enough current to turn over the starter. I decided to order one of the partial AV system translation CDs from Car Audio Workshop in NZ. That might have some effect, or help me diagnose the date problem. 🤞
×
×
  • Create New...