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
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
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
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.
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.
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.
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.
Cheers folks!
Trip to workshop aborted!
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.
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
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.
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.
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.
quote:
Originally posted by snapper
The Car Brake Bible, well worth a read.
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.
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.
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...
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.
quote:
Originally posted by chriscook
You CANNOT do it on a normal lathe the tolerances are too critical.
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
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?
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
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
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]
quote:
Originally posted by gazza285
JoelP, hows that prop? Still saving it for me?
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]
quote:
Originally posted by nitram38
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.
[Edited on 4/3/2007 by nitram38]
. It only adds the weight of the push rod to the unsprung weight.
The cam and shock are supported by the chassis and are added to the sprung weight.
The push rod weighs a lot less than a shock and spring.
Read Page 25 of "Chassis engineering" by Herb Adams.
I think you are confusing the two terms.
As I said, how does it reduce the unsprung weight? The cam is not part of the unsprung weight as it is supported by the chassis? Well so are the
wishbones! If the component moves with the wheel then it is unsprung and adds to the inertia of the suspension travel, hence the moving part of the
shock is added to the unsprung weight as it is unsprung, Half the spring weight is added too as are all links, pushrods and cranks/cams as these are
unsprung. Ask yourself, which side of the spring is it? If its on the chassis side then it is sprung, if not it is unsprung.
Should really be talking about mass not weight as well.
Your original post asked how it reduced unsprung weight, suggesting that there was none to be gained.
Now you are saying that it is half of the springs etc, which is it?
None or some?
I never said that the amount of weight would be huge, only that it would be better than bothering to drill the brake discs.
The very original post was about reducing unsprung weight by drilling discs.
More weight would be saved on the unsprung weight by moving the shocks/springs inboard.
If there were no benefits to inboard suspension, why do most formula cars now do this? It can't be just aerodynamic gain, because this could be
overcome with aero profiles over the shock/spring.
[Edited on 4/3/2007 by nitram38]
I'd go for ally versions of the hubs you are going to use and also ally versions of the brake calipers, you'll save way more that way than
any drilling of disks 
Jason
quote:
Originally posted by nitram38
If there were no benefits to inboard suspension, why do most formula cars now do this? [Edited on 4/3/2007 by nitram38]
quote:
Originally posted by nitram38
More weight would be saved on the unsprung weight by moving the shocks/springs inboard.
You are still confusing sprung and unsprung.
Words like "reduce" and "unsprung" were used in my original post.
My quote that you just used about weight, you should reread.
It said the weight on the unsprung would be reduced. I never said it would reduce sprung weight.
At least you have admitted that there are more gains to be had by moving them!
Tell me, have you built a car with inboard suspension or are you working from theory?
[Edited on 4/3/2007 by nitram38]
Nitram, gazza is correct. It increases unsprung mass. Its been hammered to death many times in the past.
Unspring mass is NOT how much weight your contact patch applies to a pair of bathroom scales. Imagine a hot air balloon - it would at times weight
nothing, but it still has a lot of mass (ie you push and it doesnt move fast).
Unsprung mass is also not the total weight of all moving components. It is about half the wishbones (as only one end moves), exactly half the spring,
the part of the shocker that moves etc.
To accurately represent and compare unsprung mass, you would need to apply a force vertically to the wheel and measure how fast it accelerates upwads,
then work backwards to find a mass. The mass you caluculate would not be the same as the sum of the parts, nor is it the pivot factor.
Imagine a see-saw. If this was actually a heavy top wishbone, and your wheel/tyre/hub had no mass, then you could conclude you have NO unsprung mass
at all, as no weight is being pressed onto your contact patch. However, try moving the rocker and you realise that it would not react at all fast to
bumps.
And if all that doesnt convince you, im not sure what more i can add.
quote:
Originally posted by nitram38
You are still confusing sprung and unsprung.
[Edited on 4/3/2007 by nitram38]
. Where did the word "mass" suddenly enter the discussion.
I think there is a difference between weight and mass.
At least there was when I went to school!
You are now saying something completely different.
[Edited on 4/3/2007 by nitram38]
quote:
Originally posted by scootz
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
About five posts ago. You do not reduce unsprung weight or unsprung mass, you are adding to both weight and mass, you are still increasing inertia. Thick of it as a pendulum somebody once told me. The more weight and/or mass you have to move the worse it is, you've got to move the wheel and stub axle, the wishbones, the pushrods, the crank/cams, the moving portion of the shock and effectively half the spring. Not all count 100% but all are counted as they all sit on the unsprung end of the suspension.
quote:
Originally posted by gazza285
About five posts ago.
nitram, you're wiggling! Weight is irrelevant. The original poster is simply mistaken by using the term 'unsprung weight', its
totally irrelevant. Mass is all that counts.
quote:
Originally posted by JoelP
nitram, you're wiggling!
quote:
Originally posted by nitram38
quote:
Originally posted by gazza285
About five posts ago.
You started pulling my answer apart long before then. When the question was about unsprung weight.
.
unsprung weight is an oddity. When people refer to unsprung mass or weight, they are on about how well a wheel will react to a bump. To go over a
bump, the wheel needs to be free to move quickly up and down.
There are many ways you could measure unsprung weight, and a low figure would not consistantly get you over a bump well. Equally, a high figure isnt
always bad. Imagine if you attached a lead weight to your wishbone at the outer end, and then slid it in to the inner end. Clearly you would be better
having it at the inner end, where the wheel would have more leverage over it. In this case, unsprung weight (measured as the sum of total moving
parts), would not change, whereas UW measured as the literal weight on the contact patch WOULD change. (im beginning to feel like calvinx with all
these capital letters! )
Also, top rocker suspensions would have an unfair advantage on the contact patch method as the rocker is balanced, but it does still have to move.
Using unsprung mass, measured as i described above, removes all the variations. And though it may sound like a technicality, its an important
difference.
Inboard suspension with pull/push rods does have a significant advantage in F1, as drag at 200mph is crucial. Also, using carbon parts, the weight
isnt much affected. And total weight is irrelevant, since they all have to carry lead ballast to reach minimum weights (iirc, ferrari had 100kgs of
ballast one year).
Sorry if you have taken this as a personal attack, its not, i just feel the need to get involved in good discussions 
Nothing taken personally, through discussion, we might all learn something. But it would appear we are talking about two different things. Mass and weight.
Hmmm.
I have been fiddling with racing motorcycles for years and years so think I can cut through some of the bulls*^$" on the subject of brakes and
unsprung weight:
Unsprung weight should be seen as a percentage of unsprung to sprung weight. On a car drilling the discs will make no noticeable difference, on a
lightweight racing motorcycle the better ratio can make the difference between winning and losing.
Now to the reasons for drilling discs:
I have never noticed any increase or decrease in braking performance in the dry between drilled or solid discs, the reasons are simple:
If the clamping force is the same in both instances and the system uses the same pads etc the pads will be clamped at a lower force per square cm with
undrilled discs but the surface area is larger, again this ratio is constant. Take away surface area and keep the clamping force the same you get an
increase in pressure per square cm. This means you have a constant ratio so all things being equal and as long as you don't take this to
it's logical conclusion (be sensible) it should make no difference.
Cooling:
Yes you do increase total surface area by drilling the discs but the increase is in an area with lower useful surface because it's out of the
direct airflow so drilling the discs should make little difference. lowering the volume of the disc will also remove some of it's ability to act
as a heat sink so during braking it could overheat on the surface and between corners it could actually cool down to below its ideal temperature to
bite reliably on initial application.
The only time disc drilling seems to be worthwhile is on a motorcycle in wet weather, car discs are fairly well protected in comparison and generally
made from micro porus cast iron which is too heavy (and rusty) for motorcycles which usually have thinner stainless steel rotors on display. The move
from cast iron to stainless steel on motorcycles in the 70's is when disc drilling started and it was due to the lack of wet weather performance
with the stainless steel discs not cooling or weight. Please read any motorcycle magazine with road tests in the early 70's.
On a motorcycle with stainless discs the pads can literally aquaplane over the surface of the disc, drilling is like having treaded as opposed to
slick tyres. The water needs somewhere to go!!
I have two Kawasaki H2 750 motorcycles from the early 70's, one with drilled discs which gets used if the weather looks dodgey and a nearly
concours version which has solid original SS discs and never sees rain. The rain bike was lethal in the wet until I got the discs drilled Quod Erat
Demonstrandum.
The above is what is true in my little quantum universe. Please feel free to ignore the truth and continue arguing.
quote:
Originally posted by Tripnut
Please feel free to ignore the truth and continue arguing.
hahahahahahahahah
FWIW, I cross drilled all the discs on my single seater racing which is only now used for hill climbs and sprints and the brakes are now far better than when undrilled. I marked the discs with a template that I had made and drilled the 1/4" holes using a pillar drill. The car weighs 520Kgs with me on board. They have not been balance but I dont have a inbalance problem. The pads were removed at the end of the season and yes, they were worn more than usuall, but given that I was more than happy with the improved braking I was more than happy to put a new set of pads in.....