OK, so THEY don't know what they're talking about... ; )
Actually, I just looked up the Moss catalog and they specifically call
them "cross-drilled brake rotors" (vents are never mentioned), so they at
least are well informed. Don't know about Vicky B.
Really, I just wanted to clarify this since my other car just happens to
have vented disks (and has no wet-weather advantage), while many
street-racer-wannabe vehicles one sees about have flagrantly exposed
cross-drilled rotors (but not vented). Porsches, I believe, are both
(maybe just the Turbo). I think nowadays the trend is, if you are going
to bother with vents, you might as well cross-drill also -- the purely
vented disk is out of fashion . Any rotor can be cross-drilled (within
metallurgical limitations), but vented rotors, as I said, require a
different (wider) caliper, so are much more expensive to retrofit (if
indeed possible). I think you can appreciate that vented rotors are
considerably more complex to cast and machine, as well, and therefore
would command a higher cost just in themselves.
Anyway, I would think it reasonable that cross drilling would help that
initial "squeeze" on the brakes in wet conditions, but after any
appreciable heat is generated (a few seconds at the most), any rotor
would be dry at the points of contact, so the difference may not be all
that dramatic. The drilling would also help with heat dissipation under
normal conditions, so there is an overall advantage. Whether it is worth
a 300% price premium is between you and your checkbook.
Tab Julius had this to say:
>
>Don't know, but Moss and Victoria mention the drilled rotors (with holes)
>but refer to them as vented or ventilated - helps the pad disperse water
>quicker. Whatever the term, that's what I'm referring to. I was wondering
>if anyone had tried them... catalogs seem to tout them as god's gift to wet
>weather breaking, but perhaps I'm just naturally cynical.
>
>
>At 06:18 PM 4/24/00 -0700, Max Heim wrote:
>>Excuse me, but why would vented rotors be of help in wet weather? I
>>believe you are thinking of cross-drilled rotors. Vented rotors consist
>>of two solid disks separated by radial vanes, which in motion direct
>>cooling air across the back of the braking surfaces (looking at the edge
>>of the disk you woud see that it is thicker than usual and has
>>rectangular openings around the circumference). This serves to reduce
>>brake fade by cooling the rotors more quickly. This extra cooling would
>>not be of any help in wet weather. Sometimes vented or solid rotors are
>>cross-drilled (round holes are drilled in a symmetrical pattern at right
>>angles to the braking surface, giving a "swiss cheese" appearance to the
>>rotor). This actually removes braking surface, but adds even more cooling
>>surface, and has the additional effect of giving any water on the disk an
>>additional outlet. I have heard that it may also give the brake shoes an
>>"edge" to bite on, leading to shorter stopping distances, but I am not
>>sure of this.
>>
>>Tab Julius had this to say:
>>
>> >
>> >I'll look servo assists - thanks. I don't expect much from the vented
>> >rotors except in wet weather, but I get plenty of that here, so I might do
>> >those. But the servo assists sound intriguing...
>> >
>> >Thanks
>> >
>> >- Tab
>> >
>> >
>> >At 06:30 PM 4/24/00 -0300, Michael P. Ohleger wrote:
>> >>Tab,
>> >>
>> >>I added a servo assist to my 67. Had great results. All the other stuff
>> >>is ok
>> >>albeit extra $$$$ and I don't think it will stop you any faster unless you
>>add
>> >>the assist. The servo gave me greater stopping power and was the closest
>> >>thing
>> >>to power brakes I could find. Cheers
>> >>
>> >>Michael
>> >>
>> >>Tab Julius wrote:
>> >>
>> >> > For a '78B
>> >> >
>> >> > All my other vehicles are '90+, and as much as I love the MG, I must
say
>> >> > that the brakes are quite a change (but of course, similar to what I
>> grew
>> >> > up with).
>> >> >
>> >> > I don't mind trying to spend a little to improve them, though I'm not
>>going
>> >> > to redo the whole system, as the car is currently in one piece and
still
>> >> > being used. Both Moss and Victoria sell Ventilated Rotors - anyone
>> tried
>> >> > them? Opinions from those who know about them?
>> >> >
>> >> > Also, VB sells a "brake kit" which includes the aforementioned rotors,
>>plus
>> >> > 4-piston calipers, carbon fiber pads, etc. Thoughts on this
>> >> > setup? Alternatives?
>> >> >
>> >> > Finally, would DOT 4 or DOT 5 be best? (never mind - just joking). But
>>the
>> >> > above questions are valid.
>> >> >
>> >> > TIA,
>> >> >
>> >> > - Tab
>> >
>> >
>>
>>
>>--
>>
>>Max Heim
>>'66 MGB GHN3L76149
>>If you're near Mountain View, CA,
>>it's the red one with the silver bootlid.
>
>
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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