Anorak facts on drilled discs.

[8Tech]

stevesingo said:

8Tech said:

Each front disc is 485g lighter and each rear disc is 250g lighter, giving a total unsprung weight loss of 1470g or 3 1/4 Lbs. Not to be sniffed at!

You can't add up all the saved unsprung mass. Any saving in unsprung mass is specific to the suspension/brake/wheel assembly as the spring/damper assembly controls that mass. Also to a lesser extent the axle from which the mass was saved, factoring in the ARB's.

From AP's web site

http://www.apracing.com/info/info.asp?section=Disc...

I believe them!

Steve

Believe what??? All you have produced is a link to a website showing different disc patterns INCLUDING drilled discs made by AP Racing. Any unsprung mass reduction reduces the load on the suspension.

From DBA's website AND relevant.

http://www.dba.com.au/2006/consdocs/C006.asp

I rest my case your honour!!

[stevesingo]

I suggest you read the small print.


I reference to the face types...

D = Cross drilled,
drilled holes chamfered).
Still preferred with some pad materials but can compromise disc life.

RD = Radiused drilled,
(cross drilled but with a radiused run out to reduce noise and improve life compared with standard drilling patterns).
Mainly used for aesthetic reasons on road applications.

Relevance restored

I haven't had time to read your link yet.

Steve

[stevesingo]

8Tech said:

Any unsprung mass reduction reduces the load on the suspension.

True, but to state that you have a 1470g reduction in unsprung mass is not in true context. You have in face have 475g reduction of unsprung mass on the front per side and 250G reduction of unsprung mass on the rear per side.

A difference which could easily be seen in two same size tires of different makes.

Steve

[GreenV8S]

8Tech said:

I rest my case your honour!!

I wish you would!

Even on that site you reference, where they are clearly saying their drilled brakes are not suitable for hard use, they admit that the drilled discs are not as durable as grooved or plain if they are getting hot. And of course the claimed reasons for using drilled rotors in the first place goes out the window unless you *are* getting them hot. Their suggestion that they are still good enough is the pragmatic answer given that they are in the business of selling uprated brakes that the vast majority of their customers will never actually use in anger, because for most road cars these uprated drilled discs are fitted as a fashion accessory and not because the brakes need the extra ventilation.

Judging by the weight saving you're claiming you must be removing an awful lot of material. Just how many holes are you drilling in these discs? The weight saving is utterly irrelevant, but the more holes you have the more significant the disadvantages will become.

[bennno]

8Tech said:

As a firm believer in drilled discs for both weight reduction and heat dissipation (amongst other things), I recently decided to do a factual analysis of some one-off discs I have just done to justify my claims/opinions.

Discs are large at 332mm vented fronts and 324mm solid rears, so results would be %wise better on smaller discs and MUCH better on discs with alloy bells.

Taking into account all of the following

* Loss of surface area because you now have a hole
* The area of the chamfer of the holes drilled
* The minimum mass of cast iron at 7850Kg/m3
* The surface area of the drilled holes
* The number and diameter of the holes (obviously)

and ignoring

* Temperature differential across the disc
* Surface area of internal vanes
* material could be HEAVIER than stated
* % weight saving because it depends on "bell" material and thickness.

I can state that the discs I just did have a surface area increase, available to further dissipate heat of 40,000 mm2 or 17% on the front discs and 19,300 mm2 or 20.2% on the rears.

Each front disc is 485g lighter and each rear disc is 250g lighter, giving a total unsprung weight loss of 1470g or 3 1/4 Lbs. Not to be sniffed at!

I just gotta getta life!

8Tech.

thats dangerous, are you really saying you have drilled a load of holes in some new disk rotors to save a paltry 3/14lbs?

stress fractures spring to mind, would love to see what the insurance company would decide in that scenario

also the best braking performance is with a solid disk due to maximum surface area

Bennno

[8Tech]

stevesingo said:

8Tech said:

Any unsprung mass reduction reduces the load on the suspension.

True, but to state that you have a 1470g reduction in unsprung mass is not in true context. You have in face have 475g reduction of unsprung mass on the front per side and 250G reduction of unsprung mass on the rear per side.

A difference which could easily be seen in two same size tires of different makes.

Steve

I absolutely agree, but then it is STILL a weight saving and enthusiasts will pay more for a genuine BBS lightweight wheel than a heavy oriental copy. So the fact that a worn tyre, different brand tyre, lighter wheel etc can also save weight, it still does not detract from the fact you are saving weight, mass that also in fact has a centripital force when spinning to change steering direction, and also affects overall wheel assy mass and therefore energy required to accelerate these wheels centrifugally.

[Batfink]

I dont see any use of drilled disks with modern pad materials. I know for a fact Carbone Lorraine actively tell customers not to use them with their pads.

[Roger645]

8Tech said:

stevesingo said:

8Tech said:

Any unsprung mass reduction reduces the load on the suspension.

True, but to state that you have a 1470g reduction in unsprung mass is not in true context. You have in face have 475g reduction of unsprung mass on the front per side and 250G reduction of unsprung mass on the rear per side.

A difference which could easily be seen in two same size tires of different makes.

Steve

I absolutely agree, but then it is STILL a weight saving and enthusiasts will pay more for a genuine BBS lightweight wheel than a heavy oriental copy. So the fact that a worn tyre, different brand tyre, lighter wheel etc can also save weight, it still does not detract from the fact you are saving weight, mass that also in fact has a centripital force when spinning to change steering direction, and also affects overall wheel assy mass and therefore energy required to accelerate these wheels centrifugally.

From your own link;

HOW MUCH METAL IS TAKEN AWAY WITH CROSS-DRILLING
AND SLOTTING?
On a typical large sedan/wagon street vehicle we take away 180 grams from each cross-drilled and slotted disc, or less than 2 per cent of its total weight. Multiply this by four and you have your total vehicle weight saving 720 grams.

Although this is the sort of gain that a Formula 1 team would spend thousands of dollars attempting to achieve, it is not enormously relevant with a conventional car in normal road conditions.

[8Tech]

Gosh, Can't believe I got it so wrong! Can someone please urgently call BMW Motorsport and tell them they and I have got it all wrong and our brake discs are all going to fall apart? Thanks.

[GreenV8S]

8Tech said:

Gosh, Can't believe I got it so wrong!

Yeah, it's depressingly common to see drilled discs on road cars, they look all motorsporty and a great fashion statement.

[stevesingo]

8Tech said:

Gosh, Can't believe I got it so wrong! Can someone please urgently call BMW Motorsport and tell them they and I have got it all wrong and our brake discs are all going to fall apart? Thanks.

stevesingo said:

RD = Radiused drilled,
(cross drilled but with a radiused run out to reduce noise and improve life compared with standard drilling patterns).
Mainly used for aesthetic reasons on road applications.

Steve

And of course the latest crop of M cars have peerless brakes, not.

Steve

[bennno]

following this thread through, removing the brakes completely or fitting much smaller ones would also make a massive difference in terms of reducing unsprung weight?

bennno

[Roger645]

8Tech said:

Gosh, Can't believe I got it so wrong! Can someone please urgently call BMW Motorsport and tell them they and I have got it all wrong and our brake discs are all going to fall apart? Thanks.

ISTR you being less than complimentary about the Motorsport divisions V10 engine, so are they good at this engineering stuff or not