blondejay;20861 wrote@ashdvs your brembo's in comps reason to factory 7/9 series what's the size/set up?
Mine are stock dia and thickness for 740 Turbo and 760 Turbo models only, up to 1990.
11.25" dia. 22mm thick.

The difference between a standard rotor and these, simply is that they're slotted and made by Brembo.
Spac;21089 wroteDrilled rotors always crack - even in moderate use. It may be possible to drive softly enough to avoid it, but what's the point in that?

As best as I can tell, it's caused by the outer surface being much cooler at the holes.
Drilled rotors are rarely used in race cars, but when they are, they have a LOT more holes than the drilled rotors you can buy for road cars. IIRC, it's about the ratio of surface area in the walls of the hole vs surface area removed.
Also, they only seem to be used on endurance racing cars, where the rotors aren't expected to endure many heat cycles.
As above, they fatigue and crack between the drilled holes, the dramatic/rapid temperature change is the cause.
Throw some puddles/standing water into the mix and its even worse.

On endurance cars and even may other types of race cars, rotors are a throw-away item, like a tyre set and are simply not intended to have any sort of long service life and go through an infinite number of heat cycles.

See that's where I would personally beg to differ. Take my expert background MTB (mountainbikes) particularly downhill. We see steel rotors glow in alpine environments on a 3minute run.
Most of the time they cool and end up bluing a touch, in extreme cases I've exploded some (mostly carbonfiber during expe demonstration and prototypes) but often warping.
Then the introduction of full floating rotors. And it doesn't happen.
Bikes use thin, light steel rotors.
Cars use thick, internally vented cast iron.




I remember standing at the Cheddar Challenge one year, and there were a load of bikes coming in from the elite class; they pulled over the line, and stopped... BANG.... tyres were popping as the rims had heated up so much from the V-Brakes on the course (it had something like 1000m of climbing and descending over a 6 lap race for the elites)

The common mod in the UK is to use Police brakes on the P80 cars; the problem is that one type of 16" wheel fits, whilst another doesn't... Perfo and something else ring a bell, but I can't remember exactly...
Spac;21122 wroteBikes use thin, light steel rotors.
Cars use thick, internally vented cast iron.
This is the key point. We regularly see fatigue cracking on cross drilled cast kart rotors too.
that said, it is often curb impact that brings an end to their life before they fail.
That's why I was saying we see warping more so than breaking. I've exploded many. But that's because I removed to much material. And they couldn't handle the heat. Carbon rotors were the most fun though!!!!! Getting carbonfiber to glow redhot is a wicked bit of fun
Cast iron is the material for car rotors correct? That's why the crack. So so brittle.
Depends on the qualities of the cast , many different grades .
Even the control V8SC and Development Series car rotors will typically see fatigue cracking after minimal use.
Components are given a 'service life' and then thrown away.

And we are talking about really good quality hardware - I cant remember who the current rotor supplier is at the moment. (Actually not sure that manufacturer is control now with the COTF regulations, dimensions obviously are).
It may be Alcon.

9 days later
Can't help but wonder what Mercedes Benz does with thier rotors as they have drilled holes on most models. Maybe in the casting process?
Though they may be dimpled only.
Vee_Que;21727 wroteCan't help but wonder what Mercedes Benz does with thier rotors as they have drilled holes on most models. Maybe in the casting process?
Vee_Que;21728 wroteThough they may be dimpled only.
No need to wonder. They could very well be drilled. Take a look at them after 10k of general road use.
They'll, without doubt, have fatigue cracking.
The interesting part would be to know what the intended rotor replacement intervals are.
And that's the big thing right there.
What material are they made from? I could speculate a softer more pliable material.
Understanding amg/barbus (think that's how you spell it) are hundreds of thousand $ vehicles. It would suggest the operator has a wage to keep up with these massive service needs
Even on c class 2 litre models they have them. I can't imagine them only lasting 10, 000km I'll ask at work though from ex merc mechanics.
Vee_Que;21760 wroteEven on c class 2 litre models they have them. I can't imagine them only lasting 10, 000km I'll ask at work though from ex merc mechanics.
Have a re-read. I didn't say they'd 'only last 10k' - I did say I would think them to have fatigue cracking by this point.
How bad? Dunno. It'd likely depend on factors including internal layout of the vanes, thickness of each side/plane, material used (we're talking about steel here), shape of the hat part of the rotor (if one piece), wheel design (promoting or hindering cooling), environmental factors (Do they live in NT where it never rains or is the thing enduring life in Victoria), driving style (stop-start commuting to work vs long freeway runs)

One of the purposes of a drilled rotor is to accelerate bringing brake temps down.
Steel, as a material, if you heat it and cool it at rapid rate and repeat this over a defined number of cycles is going to suffer fatigue. On a drilled brake rotor, the easiest path for this to happen is between the drilled holes.

Simples! (in the words of my favourite meerkat)
Good discussion but we're probably well OT of @blondejay 's original post.
It's it still brake related. I can see it being an advantage in Europe where people do regularly drive at and over 130km/h with people then jumping in front of them doing 100 or less, or faster speeds even. It makes sense the soft pads over there!
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