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

[adznight]

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!

[inark]

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"

[adznight]

I doubt it because you still have the reduced face surface...

[Abo Bob]

I wouldn't think that would be safe. It's cross drilled parts that cause the problem.

[R32Big_boy]

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?

[inark]

oh well thats great to know for the track car im building up

will stick to slotteds

[benm]

If you want cross-drilled just bite the bullet and buy some Porsche rotors, how can you go wrong

[inark]

how do they explain that?? if theyre so bad for track work why do all hardcore racecars have em?

[Abo Bob]

I know I'm a different Adz but I thought that I was told the 5000's are available now but since I was going for the 4000's I didn't pay much attention sorry.

[adznight]

I checked last year and found the 5000's for GT-T's were in development but was told they were canned as the demand would be too low. It's not "cost effective"....Im sick of hearing that this week

[Downforce]

Do they make 5000 series for the 34 yet adz?

DBA5000 rotors are available for R34 GTR... not GTT (unless you have R34 GTR brakes )

[Downforce]

Do they make 5000 series for the 34 yet adz?

Direct replacement DBA5000 rotors are available for R34 GTR... not GTT (unless you have R34 GTR brakes )

[benm]

how do they explain that?? if theyre so bad for track work why do all hardcore racecars have em?

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

[adznight]

What he said

Hardcore setup - no holes

[RTFGTR]

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.

[Downforce]

if they were heat treated during/after fabrication...problem solved.

DBA cross drilled rotors are claimed to be heat-treated but they still crack..

[adznight]

There is no way your could machine a kangaroo paw design!

[prae]

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..

[adznight]

I had the same idea. Don't know though.

[inark]

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