New Brakes!

[kaanage]

1) Cross drilled. ......weaken the rotor (have a close look at an old drilled rotor and notice the cracks around the holes...)

There is a simple way to prevent this - you put a large ball bearing in the hole, with solid backing for the rotor, and belt it with a hammer to peen the edges of the hole (repeat for each hole and on both sides). The compression of the material greatly reduces the tendency to crack from the thermal expansion and compression cycles. Obviously, you can't to this to the interior of a ventilated rotor but the heat is greatest at the pad surfaces.

I never had cracks with my racing disc rotors when prepped this way.

tech info about crack propagation and the peening technique from Engineer To Win - Carrol Smith (RIP)

3) Now, as a designer, I have spoken with a few engineers and fellow designers in the automotive field in my time. The reason they give me for cross drilling/slotting rotors? It's a simple one, looks. Cross drilled rotors and slotted rotors look cool, it's as simple as that. One designer who works for the VW group said that when he was working on the 977 lineup of Porsche GT series 911s, the engineers designed the carbon ceramic brakes for them, but they looked hideous, so the decision was made to cross drill them, so they looked cool, like they were actually worth the $25,000 premium.

Maybe that's true now and if you can afford carbon ceramic brakes (and put up with the poor cold performance and noise) but for cast iron rotors, slotting and crossdrilling not only reduce the "trapped air" effect (which I agree is negligible) and help cooling but also helps the pad dust clear while braking. All this is really only relevent at racing speeds.

[gavs]

I'll be ordering through Greg, he is a forum sponser too. Will wait for GTI JOE and see if he also wants in...

[kaanage]

Also note that larger rotors => greater rotating and unsprung mass (unless going for a carbon/ceramic setup which is $$$$).

This is why the Top Gear experiment with bigger brakes on the people mover made it lap slower.

[GTI JOE]

I'll be ordering through Greg, he is a forum sponser too. Will wait for GTI JOE and see if he also wants in...

Thanks Gav, I've sent you a PM. Great posts, lots of useful information as usual man.

[gavs]

Also note that larger rotors => greater rotating and unsprung mass (unless going for a carbon/ceramic setup which is $$$$).

This is why the Top Gear experiment with bigger brakes on the people mover made it lap slower.

Exactly, another good point kaanage What you posted by Carrol Smith is right too, but how many people can afford the rotors that are of the correct steel grade for this to work, I can see so many people going out to their cars now, fitted with the cheap DBA drilled discs and shattereing the discs doing this!

[kaanage]

Steel and cast iron rotors are stronger than that!! Otherwise, they'd shatter from braking stresses if drilled or grooved.

The one disc that I had which hadn't been peened as described (the holes were chamfered, though) was no problem for me to do - it just took a bit of time and was pretty noisy, even using a sand bag to back the rotor. The other rotors that I bought had all been peened but I did buy them from race suppliers, not normal aftermarket sources.

[Allegiance]

I get a **** load of brake dust on the front wheels.

[gavs]

In case anyone else want's it for reference.... From Go Auto...

Brakes are discs all round – 288mm vented up front and 232mm solid items out back – assisted by ABS with EBD and brake assist, along with the ESC, traction control and electronic limited slip differential devices.

[gavs]

Another bit of info RE brake fluid Boiling Temps, best ot top, generic at bottom: (Info from another site courtesy of Greg at GSL Rallysport)

Martini GS610 Race Fluid
Dry - Min 330
Wet - Min 214

Castrol SRF (Not really viable at $165 per Litre!!)
Dry - 310
Wet - 270

TRW GP600 Dot 4 Racing Brake Fluid ($65 per Litre yet same dry boil as Castrol SRF)
Dry - Min 310
Wet - Min 204

Motul Dot 5.1
Dry - 270
Wet - 185

Castrol Response Super Dot 4
Dry - 286
Wet - 184