Drilled RS2 disks & ATE super racing blue

[Lee]

Drilled disks on competition cars are replaced after/during every event. Have you seen the state of them at the end of stage??

[S2Roo]

Drilled disks on competition cars are replaced after/during every event. Have you seen the state of them at the end of stage??

This to me would suggest that the discs have been working hard, and in effect "worked".

I have been informed by several differnt people who work in the industry that normal road pads i.e organic compound on older cars, semi metallic on newer cars will gas, if they are let get hot enough. Its not until the brake compound is fully metallic, or carbon that the gassing becomes minimalistic. Also if Porsche were to be making their discs drilled for "go faster" purpose, why would they bother to make them out of ceramic? When they could just as easily use steel. Given that its is also generally accepted by the general motoring press that Porsche have the best braking system fitted to a road car ever, I very much doubt that they would risk this reputation for a "gimic" IMHO.

Roo

[rotoryboy]

@Lee - See marketing does work

[SR71]

Interesting...

On my ZX12R I've got loads of holes on my rotors. Here the rotor is fully exposed to the free-stream flow with all the attendant forced convection, yet still Kawasaki persist in drilling holes in their rotors?

Wavy rotors are the new thing in the bike world but I understand these have multiple justifications: reduced gyroscopic inertia amongst others.

Reduced mass is important, whereupon the fair comparison with your brake set-up Lee, would be a even larger drilled rotor but with the equivalent mass surely?

My guess is that brake design is a compromise between mass, surface area, gyroscopic inertia and materials science.

[Lee]

Ceramic disks were created for improved performance. Those disks are drilled due to the nature of the pads used. Holes ARE stress raisers. Bike disks are never vented but drilling there does aid cooling as well as despersion of pad material/gases in this instance. Decent road pads gas to a minimum amount and grooves are adequate for their removal without compromising disk integrity/durability. Ferodo DS2500 pads are one of the best road pads ever and they do not gas to the extent that drilling is needed. Reduced reotational inertia is important on bikes but on cars, again, wheel sizes and geometry make the effect less noticable to the driver since the rim and tyre are the most significant contributors.

What do you want? Performance and durability or looks?

[Lee]

Bikes also put considerably less enegry into the brake disks. No doubt you have fully floating disks and a pair of them up front on you ZX12R. This is done to reduce overall brake temps and will reduce the tendancy to crack the disk due the reduced stresses.

[S2Roo]

Performance and durability or looks, are not necessarily the options. Either way looks don't come into the equation.

Performace rarely comes with durability, hence throwing another element into the equation, groved discs "shave off" the top layer of a pad, ensure the optimum pad material is available, but reducing pad life to a minimum. If discs are drilled, the manufacturer would/should have engineered them by various methods (heat treating etc..) to withstand the stress.

Roo

[Jamo]

Performance and durability or looks, are not necessarily the options. Either way looks don't come into the equation.

Performace rarely comes with durability, hence throwing another element into the equation, groved discs "shave off" the top layer of a pad, ensure the optimum pad material is available, but reducing pad life to a minimum. If discs are drilled, the manufacturer would/should have engineered them by various methods (heat treating etc..) to withstand the stress.

Roo

Yeh but micro fractures will occur no matter what with drilling. You can't manufacture a disc that doesn't fracture.

[Lee]

Seen too many drilled disks crazed with cracks in no time. Are you suggesting that Porsche are defying the laws of Physics by making a hole a non-stress raising feature?My 'shaved' DS2500 last 18,000+ heavily thrashed miles. My disks are always a nice shade of blue and many here know how I use them. Drilled disks wouldn't get anywhere near my car.

[S2Roo]

My friend has a GTO, obviously a much heavier car and nowhere near as good as an S2 but that was eating DS2500 pads every 2000 miles. That was with Tarox drilled and grooved discs. I was changing the pads and they were absolutely shot. Those disc lasted for a year, and it was the lip on the top edge that was the reason for changing them.

The hole may put a weakness in the disc, but its not sufficient enought to cause concern, hence why Porsche use them, and various other motorsport vehicles.

Any disc will fracture given enough abuse, drilling does not cause "microfractures". Here is a non drilled golf GTI disc, after some abuse, and I belive some fracturing can be seen.

[Lee]

Sorry dude, not according to Engineering fundamentals. Holes, drilled or cast, are stress raisers and microfractures are pretty much a certainty (all depends on temperature cycling during use...if you don't use them they won't crack).

That problem with the golf disk is more likely a material flaw. If your mate was getting through DS2500 that quicly then he has a serious issue with component selection. Sounds like his disks were far too small for the kind of abuse he was giving them. The drilling on those Tarox disks are quite large reducing the mass of the disk and their effectiveness as a heatsink. Every pad has a temperature limit and you must select the other components to ensure successful thermal management. If he was getting through pads that quickly I suspect he probably had a very spongy pedal from boiled brake fluid too.

[dan_b]

I'll stick my oar in again if I may with three little tales from three contacts of mine:

My cousin works at Jaguar in their "Thermal management" department - ie. he designs and tests braking systems and cooling systems. They did tests on drilled discs vs. non-drilled discs to see if they would improve braking performance. Jaguar have fairly stringent braking testing -repeated high speed stops, fade resistance tests, yadda yadda yadda.

He said to me that x-drilled discs made not one inch of improvement to the braking potential of the test cars, and in fact served to increase the temperature of the pad-disc interface. This didn't cause problems on those tests, but you can imagine it would lead ultimately to increased risk of brake fade as you're keeping the brake temperatures up. He said his department recommended that x-drilled discs should not be used on Jaguar road cars on performance and cost grounds - they're more expensive, but don't improve performance. Their recommendations were overruled by the marketing gurus who said it helped the "sporty image" of the marque and would help sell cars.

I had a very long conversation with the race engineer at EBC - the brake pad manufacturer - when I was discussing with them getting a refund for my cracked EBC Reds recently. We talked about disc types, and he said (and you'd think he should know) that (I'm paraphrasing here) "holes in discs on road cars are for show - they don't help to imrprove braking performance. You don't see them on many competition cars unless they're specifically trying to get heat in to the disc/pad. You sometimes see this on the REARS of Touring cars on the shorter races in order to get temps in to the disc/pad to get the hard race compounds up to operating temperature."

A friend of mine who works at Williams F1 has a Passat 1.8T in a fairly high state of tune. He recently "upgraded" his front discs from solid (vented) to an x-drilled type, but same overall dimensions, and EBC Greens. Since then he has suffered very significant brake fade issues which weren't there before. I suggested to him that it might be the discs overheating the pads for exactly the reasons Lee's talked about - the drilling has reduced the heat-sink capacity of the disk, and has increased the pad temperature, putting too much heat back in to the fluid causing rapid fade...


F1 doesn't use cast-iron discs (they're never steel) as much for the reasons of saving weight vs. cast iron than for ultimate braking potential. F1 carbon-carbon discs actually operate at relatively similar temperatures as the cast-iron discs used in Indycar and CART racing, which is 7-900C. Yes in theory carbon-carbon should be able to work up to about 2000C but in practice this doesn't happen as you get evil oxidation issues causing immense fade problems after only a few minutes. There was an article about F1 braking technology in this weeks Autosport.

I personally will stick with non-drilled discs, use a big multi-pot caliper, a decent lot of brake fluid and a high performance pad.

[S2Roo]

[QUOTE=Lee]Sorry dude, not according to Engineering fundamentals. Holes, drilled or cast, are stress raisers and microfractures are pretty much a certainty (all depends on temperature cycling during use...if you don't use them they won't crack). -

If they are designed correctly/appropriate material selected , the stress/microfractures, will not effect the functioning of the disc. Hence why they are used in various fields of motorsport.

As for the GTO set-up, it worked very effectively, with no fade. The brake fluid would not have boiled, it being silicone based. As I am sure you are aware the brakes on formula 1 cars do not function effectively, untill they are at extreme temperatures due to pad/disc material. I doubt the brake fluid they use would boil.

The point of the Golf disc is that any disc can crack, drilled or not, given enought abuse, unless the right material is not selected, as you suggested.

[S2Roo]

I don't think it would be feasable to suggest that the carbon discs pictured, are running at an operating temperature any where near that of a castiron disc would function effectively at. Also a more likey cause to cracking is sudden change of temperature, rather than drilling holes.

[charlie]

Can you also supply the original RS2, 332 x 32 mm disks? And what would the price be....
Cheers

Jeffer you have a PM :mischeif: