Advantages of drilled/grooved discs

[tom g]

I'm generally really impressed with the standard brakes on my E46 330ci. Except that they're awful in the wet, unless dried regularly.
I know that's normal, but I've never had a car so bad - applied brakes in the wet = nothing for 100 meters!

I wondered if grooved or drilled (or both) would help clear the water faster when very wet?

Has anyone had any experience of using these discs? Last time I had grooved discs on my mk1 MR2 and my nova, years ago, and they were rubbish: warped very easily

[tom g]

Patrick1964 said:

Warping is usually a sign that the discs have got too hot, too quickly, usually as a result of abuse.

Patrick1964 said:

In short, try a better pad first (Ferodo DS2000 is a good place to start). If this doesn't work for you try a grooved disc. IMO drilled and grooved together is only for the track.

Would a different pad compound really help the wet brakes problem though? I thought the compounds just differed for friction vs temp.
If I replaced the discs after bedding in new pads, would that require another set pads? (my discs have approx 1mm lip)

EFS

Edited by tom g on Tuesday 17th February 10:36

[tom g]

Cheers Patrick. The problem is definitely not caused by temperature; the pads work fine when stone cold. I have no problem with fade either. The problem only occurs in heavy rain (the manual recommends periodically applying the brakes to dry them out).

After doing a google, it seems the discs are due a renewal, as a max lip of 0.8mm is allowed (total 1.6mm reduction in thickness). It's normal for discs to last one set of pads.

So I have to change the discs anyway. The question is to stick with OEM, or give some groovy discs a try!

[tom g]

I came across this article when googling.
http://www.stoptech.com/tech_info/wp_warped_braked...

warped brake discs are very uncommon; the typical cause of brake judder is unevenly deposited pad compound

[tom g]

Shropshiremike said:

tom g said:

I'm generally really impressed with the standard brakes on my E46 330ci. Except that they're awful in the wet, unless dried regularly.
I know that's normal, but I've never had a car so bad - applied brakes in the wet = nothing for 100 meters!

I wondered if grooved or drilled (or both) would help clear the water faster when very wet?

Just out of interest, you do know that BMW do a drilled type disc for the front of the 330 as a factory part? I'm not sure if it's a proper type cast with holes ( like Porsche ) or just cross-drilled.
Had them on our 330 but I can't say they seemed any better than the standard ones on my cousin's car.
Didn't have the problems in the wet of "nothing for 100 metres" though!

Mine's got quite big brake cooling ducts which I think channel road spray onto the discs.
I imagine BMW "motorsport" discs would cost a small fortune!

These look good value link

[tom g]

lee182 said:

BMW performance brakes cost around £1000, that's for the 130i. So shouldn't think that they'll be any dearer than that. The kit consists of a new set of disks and calibers, and some pads. And if you really want to spend some money get a bbk, Stoptech are what I have on the M5.

£1000??
I just bought a set of 4 grooved discs AND mintex redbox pads for £230 delivered! (per previous link)
after reading reviews, it seems these discs fare better than OEM, so thought I'd give 'em a try.

[tom g]

Hehe no, I didn't spot that, but I doubt bmw can offer upgraded calipers discs and pads for £1k!!! I should think it's just the discs, or an option price

[tom g]

but shirley that's an upgrade price when buying a new car? If not then £900 is chuffing good value.

Well I've bought grooved discs now - no more expensive than OEM - I'll see if they help. Logic tells me they will, as the water can escape quickly through the grooves.

[tom g]

update - in case anyone is interested - I fitted the "cheapo" £230 set of 40-groove discs and mintex pads, and the wet braking problem is completely gone even after driving in near monsoon conditions with cold brakes.
In normal conditions, they seem to be as good as or better than OEM.