MikeRJ
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| posted on 8/5/08 at 09:43 AM |
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quote:
Originally posted by 02GF74
It does increase surface area
On a solid disk there may be a small increase, but on a vented disk I suspect the difference in surface area is negligible.
Surely a disc with cross section like an I - so it presents a large front surface area, like a drum, would be more effective at cooling in the air
stream?
You mean like the shape of an old worn out disk?  It would be difficult to fit such a design under a caliper I suspect.
Everything I have read suggests that overheating brakes on a lightweight 7 type car is rarely a problem anyway.
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Hellfire
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| posted on 8/5/08 at 08:10 PM |
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Lucas Cymbran AFSAIK used to make Heavy Duty Braking Systems.
Holes in a single vain rotor - as they are known, is a safer bet and is provided for de-gassing therefore reducing the glazing effect. The same goes
for grooves.
Vented rotors are a different game as the holes and grooves nneed to be aligned - you wouldn't want to drill or groove the actual joint pad.
Any modification of the rotor surface (by drilling/grooving) is actually focusing heat to the sharpest edge - the result is thermal cracking. This
will reduce the life of the rotor and will require replacing more often.
95% of OEM brake disc's are now manufactured in China and India. They are bought; finished machined, for approximately £5 each - anything more
than that and its all profit.
To increase braking power effectively you need to increase surface area. IIRC the Bently disc's (340mm diameter) and calipers to suit (from
aluminium billet) are produced in Willenhall (Birmingham) and cost a bit more. 
So to summarise - yes drilled holes/grooves do have an effect but it reduces life by 30-50% whilst the gains are minimal - it's mainly for
aesthetics.
Steve
[Edited on 8-5-08 by Hellfire]
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Trems
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| posted on 8/5/08 at 08:42 PM |
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quote:
[I]Originally posted by saigonij[/I]
I also think that the groves don’t let the pads fully bed in as they are always being resurfaced.
I think you’re confused about 'bedding in' a pad, only the very initial few applications profile the surface of the pad to the disk, which
is why very new brakes are crap.
After that the care period whereby the brakes must be progressively heated is to do with the bonding substance that holds the pad together and the way
it bleeds back away from the braking surface, if this doesn’t happen properly (i.e the pads get too hot, too quick) then the pads will never work
properly.
As for drilling/grooving my the theory was derived as a solution to (as above) providing the boundary layer of hot gases that are produced by overly
hot pads a path to escape, they also help release dust and the additional surface area also slightly aids cooling BUT each hole also acts as a stress
riser so can be none-preferred for racing applications.
Grooves act similarly in theory but give the added bonus of de-glazing pads (which as above increases wear significantly too)
Personally on my lightweight Avon I’ll be using solid, plain discs. The open-wheeled design and that outboard disc (i.e not on the axles like some old
cars) allows good airflow around the brakes and the fact they are bolted onto the alloy wheel this acts as a very good heatsink. If I ever get
overheating problems I plan on adding ducting to air airflow but I don’t envision this being a problem.
www.tR3M5.com
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ChrisW
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| posted on 12/5/08 at 11:28 AM |
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Thanks for your replies so far everyone, and sorry for forgetting to come back and reply!
For info, this is for a tin-top project. It's running getting on for 2x standard horsepower, runs Wilwood Dynalite 4-pots on the front with
285mm discs, and Sierra rears on the back. Use is mainly what I call fast road - ie it gets taken out for a thrash and driven hard, not taken
shopping or anything like that. It does get the odd bit of track time when I feel in the mood, but it's not a regular occurance.
Not sure if that changes anyone's opinion?? 
At the moment, I'm still thinking that I'll go for the grooved ones, but mainly as an aesthetic thing. Let's face it, I spent a
fortune on fitting rear discs which do 2/3rds of nothing, so I should make the front look good too!
Chris
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britishtrident
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| posted on 12/5/08 at 07:56 PM |
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Both drilled and grooved disk have one advantage --- the improve the initial brake response in wet weather.
In for example very wet motorway running the disc picks up a coating of slime off the motorway. In these conditions on initial application of the
brake it takes heart stopping a fraction of a second for the brake pads to bite.
If the discs are drilled the holes should be properly finished --- counter sunk to soften the edges and properly de-ragged.
Grooved discs are really dodgey an open invitation for the disc to fracture.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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