Finally painted my calipers

[RUM4MO]

I haven't found any benefit to grooves over plain discs.
The groove theory is supposed to scrape the pad rather than clear water. Once your brakes are hot they won't be wet anyway.
Frankly for non track use its cosmetic anyway.

I agree with most of that, but for people living where there is a lot of salt laid down in Winter AND have front callipers mounted at the rear of the hubs, grooved discs do clear the water quicker, and when driving long distance your brake discs will not be hot between brake applications, so that thought, for most people most of the time, is simply wrong. For people who only use their cars to commute maybe 5 to 10 miles instead of using public transport, maybe their brakes remain warm due to frequent operation.

Some maybe all modern VW Group cars use frequent "brake pad-disc kissing" to keep discs clear of stuff like water, but some cars don't have that feature, in my case, VW officially advised me in writing that it was not an issue with their products, all brake friction manufacturers moved away from including asbestos in friction materials, so not a VW only issue, PLUS "you should always prepare your brakes for use before using them" - I'm not sure how that works when lots of drivers seem to be half asleep and emergency brake in traffic ahead of you causing the usual change from "free flowing" to "bunched" frequently, staying away from the M6 seems to be a way to avoid that nowadays - strange maybe.

 

[andylong]

Normal pads don't need to warm, they are made to work from cold.
Normal discs too,plain ones are great, are made to work at normal temps and as brakes get bigger they can generate more force and absorb more energy and dissipate it meaning long braking without fade. This is what vented discs are for too, not harder braking.

Things like drilled and grooved brakes are niche in thier effectiveness but you see them alot because they are pretty.

Need gas venting from your pads? You are on a track, or should be.

Spin a disc and see how long water stays on it, scrape a disc with a pad pressing on it with half a tonne of force and see how long the water stays on it.
It might be more than a half tonne, I just did a quick sum in my head, being conservative.

It does make sense that grooves and holes in your discs dissipate water, grooves that extend outside of pad boundaries should do it, but my point is the effect compared to all the other stuff there is minimal.

I did try to find some actual research on this, but failed. So all this is opinion with a few sums.

 

[SuperV8]

Normal pads don't need to warm, they are made to work from cold.
Normal discs too,plain ones are great, are made to work at normal temps and as brakes get bigger they can generate more force and absorb more energy and dissipate it meaning long braking without fade. This is what vented discs are for too, not harder braking.

Things like drilled and grooved brakes are niche in thier effectiveness but you see them alot because they are pretty.

Need gas venting from your pads? You are on a track, or should be.

Spin a disc and see how long water stays on it, scrape a disc with a pad pressing on it with half a tonne of force and see how long the water stays on it.
It might be more than a half tonne, I just did a quick sum in my head, being conservative.

It does make sense that grooves and holes in your discs dissipate water, grooves that extend outside of pad boundaries should do it, but my point is the effect compared to all the other stuff there is minimal.

I did try to find some actual research on this, but failed. So all this is opinion with a few sums.

Brake pad effectiveness when being sprayed with water is something I have tested, and I can say it is all about the friction materials, decent friction materials and the OEM friction is barely effected - very slight drop in mu vs dry brake, but unperceivable to the driver. Some of the pads we have tested however (big brand names aftermarket pads) are frankly shocking at the difference in mu from dry to wet (more than 3/4 less mu)- so holes or grooves in your disc way well help in the wet on as a sticking plaster for these poor friction materials!

Again with off gassing - this is not something I have ever seen in testing with premium friction - and the rear brakes can get upto 700-800degC! Modern rear brakes are running hotter than fronts. Again - big brand aftermarket pads I have tested have suffered with heavy fade - whether this is caused by the epoxy's gassing out - and whether holes and slots in your disc may help I don't know; haven't tested.

I do know the actual thermal fatigue of iron discs is negatively effected by drilling holes and grooves as these create stress risers when thermally cycled.
Holes and grooves may have helped with 80s/90s brake pads/systems? but with modern friction you really don't need/shouldn't have drilled or grooved discs - and they also increase the chances of brake noise.

 

[andylong]

Back in the day single make races allowed pad material changes and clearly they got hotter on a track and more likely to gas it never seemed an issue as I presume it was more about the pad working at higher temps than anything else.

Perhaps the idea is left over from racing or performance vehicles from the 50s 60s 70s when pads weren't as good as they are now.

I've had disc cracking on motorcycle discs when drilled, but it seems that this is related not to the holes per se but drilling Vs moulded holes creating stress. They are small and get hot quickly so perhaps they cycle more to higher temps.
Cast iron isn't great in tension which is created around the holes as the disc expands.

I think they are all drilled now but some used to be cast with holes so the iron crystals were aligned around the holes reducing localised stresses.

Most of the info I could find was from manufacturers who clearly want to sell Thier better than OEM discs so it's always something to bear in mind.

Racers have different issues, prolonged high temps etc etc which I will never see on the road.

What I need is the ability to stop from let's say 70 to zero with abs chattering without losing effectiveness.
I have enough brakes then.