[Biturbos4] Zimmerman brake discs in the UK?

Quincy Chiang b5quattro at shaw.ca
Sat Oct 23 16:23:34 EDT 2004

First to answer Andy's question:

I read that the gas issues you described is caused by abestos pads used in the old days.  Under harding braking (heat from friction), asbestos releases gas that can get trapped between pads and discs, hence they came up with drilling holes into the discs to vent the gas.  This issue no longer exists as asbestos has been outlawed since the late 80s (or early 90s?) due to health problems (lung diseases, a carcinogen..)

Now to address jy's question:

Here's a description of x-drilled discs taken from Stoptech's website:

Drilled or cross-drilled rotors: Disks that have been drilled through with a non-intersecting pattern of radial holes. The objects are to provide a number of paths to get rid of the boundary layer of out gassed volatiles and incandescent particles of friction material and to increase "bite" through the provision of many leading edges. The advent of carbon metallic friction materials with their increased temperatures and thermal shock characteristics ended the day of the drilled disc in professional racing. They are still seen (mainly as cosmetic items) on motorbikes and some road going sports cars. Typically in original equipment road car applications these holes are cast then finished machined to provide the best possible conditions by which to resist cracking in use. But they will crack eventually under the circumstances described in another section (see Cracking). Properly designed, drilled discs tend to operate cooler than non-drilled ventilated discs of the same design 
due the higher flow rates through the vents from the supplemental inlets and increased surface area in the hole. That's right, inlets, the flow is into the hole and out through the vent to the OD of the disc. If discs are to be drilled, the external edges of the holes must be chamfered (or, better yet, radiused) and should also be peened. 


Now I don'w know how Stoptech and Alcon make their wx-drilled discs, but Stoptech seems to agree that even when the x-drilling is properly designed from the factory, cranks can/will eventually occur.  I've seen lots pictures of OE x-drilled discs crack, specifically I recall seeing a bunch of pictures of a Porsche 959, all 4 discs (x-drilled from factory) have smalls cracks all over them, propagating from every holes.

Unless you go racing, I think blank or at most slotted discs (help shed dust and water off the discs) should be enough.

Btw, how do you guys get brake fade?  Are you standing on the brakes continuously on long downhill highway stretches or at track events?  I haven't tracked my S4 yet, but on long trips (even on very steep decent heading west towards Vancouver) I find the stock brakes work very well.  But in your case, I agree that you should upgrade your brakes due the siginficant increase in power.


----- Original Message -----
From: j y <jimnetpa at yahoo.com>
Date: Saturday, October 23, 2004 8:58 am
Subject: Re: [Biturbos4] Zimmerman brake discs in the UK?

> Would u include StopTechs or Alcons in your generalization - both 
> fit the scenarios you highlight - but most S4ers (on AudiWorld) 
> swear by them.
> Quincy Chiang <b5quattro at shaw.ca> wrote:Just curious, why do 
> people like cross-drilled discs so much? Most x-drilled discs you 
> buy out there are basically blank discs with a bunch of holes 
> drilled. Even if they treat the drilled discs somewhat, they're 
> still more prone to stress cracking around the holes and 
> subsequently warpping the discs. Also by removing material, you're 
> lower the thermal mass capacity of the discs which makes them the 
> brakes fade easier (although there may be extra cooling due to the 
> holes, not sure how much of an advantage that is). Lastly the x-
> drilled discs eat brank pads up much faster.
> You may say that Porsches have drilled discs, but AFAIK their 
> discs are casted with holes in them and they are treated 
> afterwards to strengthen the structure, very different than some 
> vendors going at a bunch of blank discs on a drill press.
> No bashing here, just stating what I know and curious of what 
> others think on this subject.
> Quincy
> ----- Original Message -----
> From: Andy Turner 
> Date: Friday, October 22, 2004 7:47 am
> Subject: [Biturbos4] Zimmerman brake discs in the UK?
> > 
> > Anyone know of any stockists in the UK for Zimmerman cross-drilled
> > discs (rotors!) in the UK? GSF Car Parts get mentioned a lot, 
> but they
> > don't have any. I've got a 2000 S4, and I believe my discs are 
> 321x30> on the front and 256x22 on the back - is that right or am 
> I asking for
> > the wrong thing? (which might explain them not having any!)
> > 
> > Cheers
> > 
> > 
> > andyt
> > 
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