Drilled or SLotted discs or not...

[jdening]

So, received wisdom is that:

1) Slotting reduces glaze and brake fade
2) Drilling reduced US weight and glazing, and also brake fade
3) Drilling can lead to weak points


However, Brembo say that they have seen no difference between forging and drilling holes in terms of performance or anything else.

I have used drilled brakes on bikes for years and years and have had no problems ever.

I'm inclined to think that drilling and slotting competition brakes is a good thing.

Now - I need new discs on the rear of the E30 - badly lined. Also the fronts, whilst worn evenly, are rusty and crappy inside, and that won't be good for heat dissipation. So, I can buy pattern solid rear discs for 25 quid (all inc.), or I can spend 110 quid on drilled and slotted discs for both ends...and while we're putting them on I'm going to take the calipers apart and clean them.

Thoughts? Is it worth the extra money (110 quid vs. 25 quid) to get slotted/drilled discs?

James.

[Lloyd@JRD]

As you pointed out, drilled often lead to weakness. You would be best going for something along the 40 slot lines. Hope this helps.

Lloyd :-D

[jungle-jim]

this is a grey are when it comes to drilled discs on cars vs bikes.

the wear rate of bike discs is much less than cars ( obviously ) some bikes that had drilled discs were indeed prone to warpage and cracks, namely ther early GSX-R's.

previously they used slotted/grooved.

i have read a lot of theories and studies and tests over the years and i am satisfied that drilled discs aren't really beneficial on road cars.

i would go with grooved if i was you.

i have black diamond multi grooved discs and they work well.

good pads and braided hoses make a good difference too.

with the amount of weight you have saved recently, standard discs could still be a decent option?

just upgrade the lines and pads.

[Stuart]

To be honest James, with discs that cheap, follow your ethos of avoiding unnecessary cash and run the 'cheapos' until your properly used to the E30. Once you're used to it, you will know whether the braking needs to be improved or not. My old Sierra still runs heat treated grooved discs because it is only used for trackdays so outbraking people is a no-no and she just isn't fast enough to warrant braking that hard :thumb:

[Andy916]

Hi James,

I know drilled disks work well on the bikes, but on the car it's very common to get cracks radiating out from the cross-drillings. In my case, on the scoob, the cracks stayed at a few mm then rapidly went all the way to the outer edge, needing immediate replacement - again, fairly common I gather.

I'd give the pattern parts a try, rather than go for intermediate quality slotted/drilled disks. And DS3000 pads if you can get them for those calipers. I've known a 205 with that combination to be awesome on the track, with not much less weight than your E30 - possibly as good as my scoob with its 1 grand complete kit (ally 4-pots that weigh half the originals and curved-vane slotted rotors on ally bells)

Higher quality, track-focussed disks tend to be grooved only, with curved vanes in the sandwich for better airflow eg. AP, DBA.

Andy

[jungle-jim]

dont forget, bike discs are completly exposed to aid cooling.

cars are hidden behind the wheels

anyone tried ceramic discs?

[jdening]

OK, so the prevailing wisdom seems to be that slotted brakes are probably the way to go, but for me, I might as well go stock.

OK - I've spent 23 quid on some solid Brembo rear discs (delivered!). See how that goes.