Big Brake Kits - Real Numbers

[jagman]

I was not intending to belittle your post , but sometimes we get caught up in a world of Data and forget the bleeding obvious ,aided by the tuning world

probably the biggest improvement to the braking system would be a small electric fan and some flexible conduit plumbed into the disc dust shield to provide forced cooling

why don't race cars do this ? I don't think they are allowed , we however don't have rules:eyebrows:

[JamieP]

I have some new front and rear pads for my brembos i can measure (tape measure) if you want.

[Wez]

probably the biggest improvement to the braking system would be a small electric fan and some flexible conduit plumbed into the disc dust shield to provide forced cooling

why don't race cars do this ? I don't think they are allowed , we however don't have rules:eyebrows:

 

Why would you use an electric fan when you can channel the air that you are driving through?

[Terminator]

I thought ducted cooling of brakes was very difficult, very easy to make matters worse. I have certainly found recently that the UK brakes do not like repeated high speed scrubbing. They just fade. Stamping harder just makes matters worse. I think the UK's need top operate at a lower temperature, than some of the bigger brake kits.

Edited August 7, 2010 by Terminator (see edit history)

[Tricky-Ricky]

I like your thinking - stamp harder, save the cash!

 

I'd like to make it clear that I am not a "big brake kit seller" or anything like that - I only posted the numbers up as people have been talking about comparing calipers and kits and how good the UK parts are so I thought I'd share the numbers.

 

 

 

Good point.... The pad thickness doesn't play any role at all, it is the depth as shown by the blue arrow here. I should have posted that earlier to make it clear.

 

http://i828.photobucket.com/albums/zz202/danc8000/0c5d71c9.jpg

 

Hydraulic pressure is directly linked to the braking torque and is completely linear..... double the pressure = double the torque. However it is almost impossible to throw that into the mix to show up anything useful. This comparison was only to compare one brake setup to another for a given set of inputs (same pad compound, same pedal effort, same master cylinder etc).

 

As Jagman said - stamping on the pedal will increase the hydraulic pressure and increase the braking torque, that is a fact. However, it has to be kept constant in order to make any meaningful comparison between setups or else you could quite rightly say that the brake system off a Fiesta is as good as that on a Supra as long as it's balanced, you can stamp hard enough on the pedal, the seals can handle the pressure and the whole lot can cope with the heat.

 

Just to add, i wasn't knocking your very informative write up either, just wanted to get certain points clarified for the people who wont necessarily grasp the finer points straight off, and there are those who will pick, so better to have it all covered;)

 

I agree it should be made a sticky as there is about as much info as anyone contemplating a different/bigger brake set up is ever likely to need, thanks for going to the trouble and all the calc:salute:

[Wez]

I thought ducted cooling of brakes was very difficult, very easy to make matters worse. I have certainly found recently that the UK brakes do not like repeated high speed scrubbing. They just fade. Stamping harder just makes matters worse. I think the UK's need top operate at a lower temperature, than some of the bigger brake kits.

 

This is where the difference between road or race compound is highlighted, a race pad can function at much higher temps. On my track car with UK setup, race pads and decent rotors I melted the dust caps and decals on the calipers without experiencing fade

[jagman]

Why would you use an electric fan when you can channel the air that you are driving through?

 

Great if you are moving , the heat energy is exactly the same whichever brakes you have ,just spread over slightly different surface areas - all the discs centrifuge the heat out and the ducts move heat away from the area while moving along with the wheels .

once stopped in pits or traffic lights there aint a lot of heat being moved , so fans would help ..

"I thought ducted cooling of brakes was very difficult, very easy to make matters worse"

how and why ?

[dandan]

No sweat chaps - don't worry about the questions or "picking" - doesn't bother me Like I said, I put this little lot together a while back for myself when trying to make some decisions about a kit.

 

There's a few bits of info I need to complete what I have so far (Brembo, K-SPort and AP rear piston sizes and confirmation of KAD rear caliper pad depth) and then it'll be reasonably complete and useful.

 

I have nothing useful on the Stoptech and Rotora so the people running those kits need to come forward

 

Jagman's question about ducting....a lot of people duct to the outer face(s) of the discs rather than feeding the "eye" on the back to pump out through the vanes. This doesn't give ideal temp variations in the discs and can (apparently) lead to problems. Not something I've looked into first hand though.

 

Jamie - the pad sizes would be useful to check which one of the two in Brembo's catalogue is correct. The length of the blue arrow on the pad picture on the previous page is the key one (the depth or height of the friction material - not the backing plate).

Edited August 7, 2010 by dandan (see edit history)

[Kirk]

On my track car with UK setup, race pads and decent rotors I melted the dust caps and decals on the calipers without experiencing fade

 

To be fair though wez your UK setup isnt quite like everyone elses

 

Realy interesting thread this one, shame i dont understand everything although its probly quite simple

[jagman]

Realy interesting thread this one, shame i dont understand everything although its probly quite simple

 

It is very simple....

Its about energy , the car is moving and has energy built up this energy is transfered during braking

1/2 MVsq = the calculation of energy

1/2 times the mass times the velocity (speed)

the car weighs say 1500 kilo multiplied by its speed (squared)

so a supra going 10 miles an hour and one at 20 miles an hour does not take twice the energy to stop but

1500 x 10x10 = 150000/2

1500 x 20 x20 = 600000 /2

4 times the energy !!!!

so a supra going 170 miles an hour = a shit load of energy:D

 

All this energy is converted to heat via friction , between the pads and discs , thats a shit load of heat , can you see that no matter how big the discs and pads are its still huge amounts of heat , even with discs twice the size of stock its enough energy to get them glowing hot with a couple of high speed stops

The pads at the front have a sharp edge , this gets hotter and wears more quickly ,so the multi piston calipers can have smaller pistons here to compensate a bit for that .

All this heat has to go somewhere , it goes into the fluid,lines,caliper,pads ,discs,tyres and surrounding air

As the various parts get hot they in turn pass their heat on , a bigger area /size dissipates heat better - but is an extra 1 inch diameter disc going to dissipate that much more heat ?

to aid heat transfer the wheels can direct cooler air over the brakes/hubs/etc , so can cooling ducts in the plastic wheel arch, so can the discs themselves by the small channels between the discs that "throw" out air centrifugally between the discs.

once the car stops so does the cooling !!!! But the metal parts can retain loads of heat for a long time - thats why I suggest cooling fans

Its also why you take your foot off the brake after a big stop , as the pads contact only a small area of the disc and this can exchange heat to them with contact and so warp the discs with different temps across the disc

Edited August 8, 2010 by jagman
sp (see edit history)

[jagman]

http://home.wanadoo.nl/this-is-me-at/brembo/brembo.html

 

Here is a good read , especially the bit about floating discs and the advantages over solids also gives data on energy per cm so rough estimates could be made, given disc sizes larger than stock

[jagman]

From the link above I think it is clear that heat is the main concern, controlling the heat and keeping within limits is the single most improvement in braking

80% of the heat is in the discs themselves.

Most heat is generated at high speed

brake pad pressure not as important as you would think

enclosed wheels don't help

floating discs more heat tolerant

pad compounds dictate heat range

etc etc..

 

 

I maintain that electric fan cooling can only help when high speeds are used in braking .

 

If you never go over 70 you have no worries

[TLicense]

We tinkered a bit with fan cooling of brake discs on the Williams back in 2003 I think it was.

The problem was getting the fan to not hinder the normal mass flow at high speeds.

We ended up with a fan being geared off of the wheel axle so it span at incredibly high speed.

Eventually we developed a brake duct that could cool the disc more efficiently anyway.

 

But yes I totally agree that heat management is probably as big a factor as the mechanical braking torque, which should be born in mind when selecting an upgrade.

[jagman]

In a way the Supra has a bigger challenge than F1 , twice the weight + ,and similar top braking speeds , without the budget or ceramics.

Some recent electric motors , now run astonishing Rpms compared with 2003 .

Small and cheap efficient, fans for low speed and stationary cars would work I feel ,easy to do as well .

I will try it , nothing ventured nothing gained !

[paul mac]

Interesting post Dan, i have a few points though, I presume the figures you are quoting is brake torque. From my hazy recollections of HNC physics i can just about remember that the pad area is in the equation somewhere. You obviously have the pad height but are you presuming the pads are all the same length, what is the formula you are using to calculate your figures, are you using a standard coefficient of friction as this will increase (or decrease) dependent on the area of the friction material.

 

 

 

ps my rear pad height is 45mm

[dandan]

Pad size is 100% not in there Paul. It plays no part although a lot of people think it does. The area cannot affect the coeff of friction, the coefficient of friction is a physical property of materials in contact and is not related to size.

 

This comparison is done with an arbitrary pressure applied to the piston areas to generate the clamping force. This clamping force is applied at the effective radius and the coefficient of friction is used to give the retarding force (acting at the effective radius) which is obviously 90degrees to the clamping direction.

 

There is a calculator here that looks like it follows the same approach...I'd need to run some comparison numbers at work to see if they tie exactly.

 

http://www.tceperformanceproducts.com/brake_bias_calculator.html

 

And a couple of halfway interesting links where they mention pad area...

 

http://www.automotivearticles.com/Braking_Basics_and_Break_in_Practice.shtml

http://www.driverstechnology.co.uk/brake-pad-area.htm

[paul mac]

yes i think your right now you explain it (damm that red wine) i may be confusing friction force here, as i said its all a bit hazy , i am sure i remember contact area coming into the equation though i'll have to get out the old books, so the percentage figure you quote is clamping force generated by the hydraulics and not brake torque

[dandan]

It is brake torque but that is only related to clamping force by the coefficient of friction. For comparison's sake it can be thought of as the same thing if the coefficient of friction is constant. For my numbers I was using a shade under 0.4 but it doesn't really matter as I am not looking for absolute values - only relative values between different setups.

 

What I was really doing was investigating brake bias on big brake kits to see how far they deviate from OEM and comparing that to my options for my own custom made kit. To get the brake bias you need the front and rear braking torque but once again - only in relative terms.

Edited August 11, 2010 by dandan (see edit history)

[garethr]

IIRC the variables in the calculation are:

hydraulic pressure

coefficient of friction

effective radius (disc diameter - actually slightly outboard of the pad centre)

caliper piston area (of one side of the caliper).

 

For the same driver, the same master cylinder, the same pad compound, and the same disc material, you can ignore the first two, so for comparison purposes you need the total piston area for one side of the caliper and the effective radius.

[jagman]

Perhaps a little more perspective is needed ;

Even the crappiest pads/discs have the ability to lock up the wheels / reach abs limits (we are not talking about for how long or many times)

The Ratio for brake pressures is fixed -ie the master cylinder

The maximum retardation is locked wheel and abs , but the rate of retardation is controlled and going to be mostly due tyre selection ,compounds etc

If say larger front discs/pads were fitted the maximum retardation remains the same , however the rate that this happens may be faster , this faster rate of application would move weight faster to the front of the car (and more of it)

This would increase the loading /heat to the front brakes , and reduce the rear loading ( possibly lock up the rears too early?)

My initial feelings are tyres are the major factor in braking ability,more than the discs /calipers/pads

Discs/caliper/pads will determine "feel" ie reaction times and pedal feel , and how much load you move forewards onto them ie the point at which the rear locks up - and to work this out will give you the problem that it is tyre dependent and road surface dependent

My 2 pence worth

[dandan]

Jagman - I think it's fair to say that your "perspective" is something that has already been talked about a lot here on the board and nobody disagrees with it or is trying to say anything to the contrary. This is about direct comparisons between different setups....

 

Ultimately tyres, weight transfer heat etc are key limitations - nobody is disputing that and I'm not trying to show anything different by looking at the numbers. I'm not sure if you're getting the wrong end of the stick and trying to put forward an argument of some sort but nobody is actually arguing

[Wez]

Agreed, the numbers are just to show direct comparisons between different setups with most variables at a constant between setups, we all know there are lots of other factors involved but this is a like for like comparison.

 

Thanks again Dan

[jagman]

So what is the comparrisson? simply some mathmatical size difference that becomes meaning less , some "force" difference that also becomes meaningless

Toyota would have done all the calcs and based on their tyres ,caliper ,pads ,abs , wheels sizes, road surfaces etc

So any changes to improve , by going bigger can only be assessed by feel , weight saved , durability,heat recovery,pad wear ,dust and even then given perfect tyre tread and pressures and compounds and becomes anecdotal rather than calculated

[dandan]

So what is the comparrisson? simply some mathmatical size difference that becomes meaning less , some "force" difference that also becomes meaningless

Toyota would have done all the calcs and based on their tyres ,caliper ,pads ,abs , wheels sizes, road surfaces etc

So any changes to improve , by going bigger can only be assessed by feel , weight saved , durability,heat recovery,pad wear ,dust and even then given perfect tyre tread and pressures and compounds and becomes anecdotal rather than calculated

 

To be honest I'm not exactly sure what your answer to your own questions is trying to say or whether you are actually asking something you want an answer to. Anyway, I'll try to answer your question as best I can.

 

The comparison is a mathematical one...yes 100%.

 

For a given coefficient of friction, pedal force, pedal ratio, and boost ratio it tells you how the braking torque and more importantly the braking bias changes for various aftermarket options available. That's it.

 

If for example you decided to upgrade to KAD's six pot front caliper on your OEM 323mm disc then it's not obvious or published anywhere that the available braking torque on your front axle drops by almost 8%. That drop also ties in with a shift in the brake bias of almost 3% to the rear. A lot of people have absolutely no comprehension or appreciation of this and believe whatever they read thinking that they have "upgraded" their brakes. This is not necessarily the case and this is what I was looking into when I did the comparison. There is no error in the maths and the comparison is valid as long as you know what the assumptons and limitations are.

 

On a slightly different track, Paul Mac adapted an AMG kit to fit.....excellent, made a smashing job of it. However, if someone for example adapted the 997 turbo kit to fit they would be throwing the brake bias to the rear by almost 10% without means to address this. This is exactly the sort of thing I wanted to find out for my own benefit...and I did.

 

I'm not arguing against anything Toyota have done, quite the contrary. I am looking to see how the big brake kits we could lay our hands on have actually deviated from the original bias.

 

Does that answer your question?

[jagman]

The braking torque is the twisting action caused by the drum or disc on the shoes or caliper anchors during the application of brakes. The amount of torque is determined by the effective axle height and stopping force between the tyre and road surface.

Brake torque on the front wheels is absorbed by the knuckle and suspension control arm. In rear, it is absorbed by the axle housing and the leaf spring or control arm. Braking torque during an emergency stop is much higher than accelerating torque at full throttle. Brake supporting and anchoring members must, therefore, have sufficient strength to withstand these high braking loads.

 

http://www.the-crankshaft.info/2009/09/braking-system.html

 

If you have a read and see what you are trying to establish is possible given the variables and fixed data -and the only data you have ie the size of the discs and area of pads to use for comparrisons

Look at the brake bias bit in particular