scootz
|
| posted on 1/3/07 at 07:22 PM |
|
|
Unsprung Weight... Drilling Brake Disks
Is this a good idea, or am I heading for trouble?
If it's accceptable, then what diameter holes should I be aiming for?
Ta
|
|
|
|
|
zetec7
|
| posted on 1/3/07 at 07:32 PM |
|
|
I did some reading on that, and it's just not a good idea. It's done by manufacturers supposedly to aid rotor cooling, but at the same
time it reduces the swept area, thereby requiring greater pressure to achieve equal braking, therefore increasing heat... Manufacturers also cross
drill their rotors before they are heat treated so they won't crack between holes, the holes are champfered, and the rotors are high-speed
balanced after drilling. That would be hard to do on your own.
It won't decrease weight enough to make a difference. Eat a lighter lunch (or visit the loo before a drive) and you'll save more
weight
http://www.freewebs.com/zetec7/
|
|
|
nitram38
|
| posted on 1/3/07 at 07:33 PM |
|
|
Cross drilling has to be done accurately, otherwise you will get a weight imbalance.
It is mainly do to reduce brake fade, but as a consequence, you will go through brake pads quicker.
Better to buy them ready done.
|
|
|
MkIndy7
|
| posted on 1/3/07 at 07:38 PM |
|
|
I always thought Groves were to prevent Glazing of the pads and to remove dust..
And Drilling was to stop a build up of gasses between the pad and the disk.
Not sure where I read that from but I remember it being a reliable source.
|
|
|
snapper
|
| posted on 1/3/07 at 07:55 PM |
|
|
The Car Brake Bible, well worth a read.
Brake Bible
I personaly would not fiddle with something as vital as my brakes especially as if you got it wrong you could have exploding disc brakes.
Not a nice thought.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
snapper
|
| posted on 1/3/07 at 07:55 PM |
|
|
The Car Brake Bible, well worth a read.
Brake Bible
I personaly would not fiddle with something as vital as my brakes especially as if you got it wrong you could have exploding disc brakes.
Not a nice thought.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
scootz
|
| posted on 1/3/07 at 07:56 PM |
|
|
Cheers folks!
Trip to workshop aborted!
|
|
|
dern
|
| posted on 1/3/07 at 08:42 PM |
|
|
A mate did this on his westfield. His wife did a cad drawing on to paper which he then used as a guide using just a pillar drill. He had no problems
but short of the small weight saving I can't really see the point although they do look better I guess.
R1 (2003 FI) powered Locost in progress
Fireblade/Impreza
|
|
|
SeaBass
|
| posted on 1/3/07 at 09:04 PM |
|
|
Yikes... I wouldn't do this.
The mere thought of a disc cracking at high speeds would put me off, never mind losing the brakes.
Cheers
|
|
|
chriscook
|
| posted on 1/3/07 at 09:09 PM |
|
|
Neither Cross-drilling or grooves do anything useful - they are more of a styling feature. I can't see that the weight loss will be huge and
you'd be better off getting the discs thinned - but absolutely has to be done properly and on both sides to avoid Disc Thickness Variation
(DTV). You CANNOT do it on a normal lathe the tolerances are too critical.
|
|
|
snapper
|
| posted on 1/3/07 at 09:34 PM |
|
|
Chriscook
click on my link to the car brake bible, yes grooves and drilling do have advantages, possibly questionable on light sevens but you can't have
brakes that are too efficient, you can have them set up wrong.
Brakes work on the physics of turning kinetic energy into heat and then venting that heat off as quick as possible. Friction caused by the pads on the
discs converts that kinetic energy to heat.
The grooves help cut through any pad glazing from the heat and dispurse gasses
cross drilling does something with eddy currents between the two surfaces and the standard vented discs helps get rid of heat more quickly.
I need to lie down now.
Do read the car brake bible it will explain it better than me.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
C10CoryM
|
| posted on 2/3/07 at 03:41 AM |
|
|
As you have already decided drilling rotors is not worth while, and dangerous.
I had a chat with an engineer/racer who specialized in friction materials. He led me to believe that modern pads do not gas on the same level as
the older ones did, making slotted rotors obsolete (mostly). Ive also personally seen drilled rotors break causing a hard crash.
Yes, crossdrilled/slotted rotor can save weight when you are not using brakes a lot. For example, here is a sprint car front rotor
http://www.speedwaymotors.com/pl/900-949+3RD,940-2705_L.jpg,848,6711_Steel-Front-Rotor.html
They only use the brakes in traffic (rarely) and in case of a wreck so less weight/ weak brakes are acceptable. Most only run 3 brakes as well. Try
that on a circuit racer and you would be upset .
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
|
|
|
MikeRJ
|
| posted on 2/3/07 at 08:30 AM |
|
|
quote:
Originally posted by snapper
The Car Brake Bible, well worth a read.
Not convinced about using at as an authoritative reference on brakes. In respect to drilling, it mentions eddy currents passing through the disk; an
eddy current is a rotating current induced into a solid conductor by a magnetic field. How this applies to disk brakes I don't know.
It also mentions the vanes in vented disks creating a "vortex", which just seems like the author felt the need to use some impressive
words. A vented disk is simply a centrifugal fan, air enters from the hub end of the vanes and is emitted at the circumference of the disk.
|
|
|
02GF74
|
| posted on 2/3/07 at 10:56 AM |
|
|
quote:
Originally posted by MikeRJ
quote:
Originally posted by snapper
The Car Brake Bible, well worth a read.
Not convinced about using at as an authoritative reference on brakes. In respect to drilling, it mentions eddy currents passing through the disk; an
eddy current is a rotating current induced into a solid conductor by a magnetic field. How this applies to disk brakes I don't know.
as you say, you need a magnet, therefore it is bo77ocks.
in my MGB days, there was mucho talk about drilling - reasons for it was it increases surface area, a fair bit if you do the sums, also allows water
to be pushed off the surface into the holes - usefulf for off-readed to push mud out of the way.
weight wise it isn't going to make too difference that you would noticve. safer to put on smaller dismeter alloys.
|
|
|
chriscook
|
| posted on 2/3/07 at 04:42 PM |
|
|
I've not read the 'car brake bible' because I've had conversations with the braking consultants at work who specify, design
and develop braking systems for vehicle manufacturers... I'm trusting what they say.
|
|
|
martyn_16v
|
| posted on 2/3/07 at 06:59 PM |
|
|
if you are serious about saving weight then you'll have solid discs, in which case drilling is even more pointless as the holes don't lead
anywhere...
|
|
|
nitram38
|
| posted on 2/3/07 at 07:06 PM |
|
|
A better mod would be to change your brake calipers to lighter ones and move your shocks inboard.
Changing your cycle wings to carbon fibre and your hubs to aluminium will help aswell.
|
|
|
JoelP
|
| posted on 2/3/07 at 11:23 PM |
|
|
quote:
Originally posted by chriscook
You CANNOT do it on a normal lathe the tolerances are too critical.
I dont like to argue with people who probably know more than me, but how accurate exactly does a disc need to be? A lathe in good order can be right
to thousandths, this must be good enough surely?
|
|
|
Blakey_boy
|
| posted on 2/3/07 at 11:33 PM |
|
|
The accuracy in disc's set up with grooves and holes is down to microns (Thousandths of a millimetre)
And weight balance is down to as much .0001 grams.
Thats how accurate it has to be for brake discs
|
|
|
gazza285
|
| posted on 3/3/07 at 01:18 AM |
|
|
Can't see it myself, recommended runout figures are much larger than microns, and why would they need to be balanced to .0001 grams when they
are so close to the centre of rotation? Why .0001 grams when there is a bloody great rubber and brass valve sitting much further out from the centre
swinging around?
And I'd better tell me father to stop skimming discs for all the local garages (and flywheels, which are much more critical) on his lathe after
40 years (without complaint) because its not accurate enough! Why is it not accurate enough, he makes bloody piston rings on it FFS.
Think about it, you are placing a highly machined part onto a (usually) used hub, which may or may not be rusty, or had its bearings replaced, or have
been in a knock. How many garages do you know that check the mounting faces for runout before putting new discs on?
Waste of time drilling them yourself though.
Nitram, why would moving the shocks inboard reduce unsprung weight? All it does is move the unsprung weight nearer the centre of the car and add the
pushrods and bellcranks, or the top rocker to the unsprung weight.
If you want to reduce unsprung weight then as said use lighter calipers, alloy hubs and uprights, and if you want to spend some money on lighter discs
then get alloy bells and proper brake rotors. All cost money though.
JoelP, hows that prop? Still saving it for me?
DO NOT PUT ON KNOB OR BOLLOCKS!
|
|
|
C10CoryM
|
| posted on 3/3/07 at 03:17 AM |
|
|
Surface finish is important for optimal performance, but on street cars its not too important other than it can cause squealing. If rotor finish was
down to the microns the whole friction idea wouldn't work as well. Also, If you have 0.050" run out in a rotor you will not feel it
while driving. What you feel is lack of parallelism (one face is out of parrallel with the other).
All sorts of options to save unsprung weight. Drilling rotors on a street/circuit car is one of the last ones.
One thing I really dont like about what I read in the brake bible is that the larger rotors work better because more surface area. Its to do with
leverage rather than surface area. Maybe it clarified this elsewhere, I only scanned it.
Cheers
"Our watchword evermore shall be: The Maple Leaf Forever!"
|
|
|
gazza285
|
| posted on 3/3/07 at 03:43 AM |
|
|
quote:
Originally posted by C10CoryM
Surface finish is important for optimal performance, but on street cars its not too important other than it can cause squealing. If rotor finish was
down to the microns the whole friction idea wouldn't work as well. Also, If you have 0.050" run out in a rotor you will not feel it
while driving. What you feel is lack of parallelism (one face is out of parrallel with the other).
All sorts of options to save unsprung weight. Drilling rotors on a street/circuit car is one of the last ones.
One thing I really dont like about what I read in the brake bible is that the larger rotors work better because more surface area. Its to do with
leverage rather than surface area. Maybe it clarified this elsewhere, I only scanned it.
Cheers
Who's brake bible is this? C10CoryM talk sense. I like you knocking the big disc brigade over surface area Vs leverage. Push bikes have the
answer, and some motorcycles have rim mounted discs. Much more disc clamped by much smaller pads, result being pads get hotter and the dics stays
cooler + more efficiency.
DO NOT PUT ON KNOB OR BOLLOCKS!
|
|
|
chriscook
|
| posted on 3/3/07 at 08:21 AM |
|
|
I was probably over stressing the point on accuracy but you cannot just bung a disc on a lathe and skim it off without really knowing what you are
doing. Both sides must be machined with dismounting the disc as the thickness must be kept within tight tolerances.
Imagine what the brake pads/pistons are doing if a disc is going thick/thin/thick/thin as it rotates. They are being pushed apart and the pushing
closer together rapidly which can lead to judder and a pulsing pedal. How much you feel/hear for a particular amount of DTV will be dependent on how
sensitive the vehicle is to it.
If it is just runout (i.e. the disc is the same thickness) then the pads/pistons just move sideways together but do not move fluid between the master
cylinder ad calipers.
With regards to weight saving then as other have said use light calipers, solid discs and small wheels.
[Edited on 3/3/07 by chriscook]
|
|
|
JoelP
|
| posted on 4/3/07 at 07:41 AM |
|
|
quote:
Originally posted by gazza285
JoelP, hows that prop? Still saving it for me?
lol, its still there! Ive tried selling it since then anyway, with no joy. Just cant shift it!
|
|
|
nitram38
|
| posted on 4/3/07 at 07:58 AM |
|
|
gazza285, in answer to your question about unsprung weight, it has nothing to do with how much the car weighs or pressure exerted by a shock, but
everything to do with how much the wheel, hub, brakes and wishbones weigh.
Unsprung weight is the weight of your suspension and sprung weight is the weight of the rest of the car, chassis etc.
It is much better to have lighter unsprung suspension and slightly heavier sprung weight on the car.
The lighter your suspension, the better it will react to road changes.
Just think of your wheel as a pendulum.
The lighter the mass, the easier it is to move and quicker. If it is heavier, then it is slower.
There also aerodynamic benefits by getting the shocks out of the airsteam. The pushrods also give you another way of adjusting ride height if you use
LH/RH thread rod ends. This is much better than just adjusting the spring seats on your shocks.
I have seen cars that don't sit right because they have had to wind the spring seats up too much to stop the car hitting the floor.
[Edited on 4/3/2007 by nitram38]
|
|
|
