Another proof why BIGGER brakes are NOT always best!

[BXVW]

cat back exhaust doesnt do anything on n/a cars? why do they sell so many of them like that? what should be done to get power from a vr6 exhaust

[phatvw]

Quote, originally posted by BXVW »

cat back exhaust doesnt do anything on n/a cars? why do they sell so many of them like that? what should be done to get power from a vr6 exhaust

Wrong forum. This is about brakes.

[Kit_L]

This thread has some of the worst information i've ever had the misfortune to read through, i'm no guru but there are some utterly false statements in this thread.

There are entire books published on the subject, so i'm not even going to try explain concepts here.

Really rough overview:

Basically, braking has be set up to be proportional to the car/bike/truck..etc intended purpose, one of the most important parts of the design process is the expected average operational temperature. Fundamentally, different brake pad compounds provide different amounts of friction, at different temperatures, much like tyres for instance.

It is right to say the most important part of a brake set up is the pad choice, then brake fluid/hoses on a fast road set up.

On a race car heat dissipation to prevent fade, premature wear/warping the discs is of huge importance also the clamping pressure of the callipers has to be progressive, predictable for pedal feel to set up the pedal box hydraulics, also it needs to be greater to make use of racing compound tyres.

This is achieved by having bigger discs and larger callipers with a greater pad surface area.

To the point of the thread, bigger brakes are not necesserily better, it just depends on their application.

On the street... imho it is most dependant on actual weight of the car and the style of driving



Modified by Kit_L at 11:57 AM 10-3-2009

[Hedgehodge]

I'm glad I found this thread before I bought a BBK I wont lie though, they do look very nice but then again so would any rotor thats not rusty and shiny painted calipers.

Annoying though that I have a set of 15 winter tires and 17 summer. And wtf does less tire cost more different compounds my ass, still the same rating.

Seeing as how I have different sizes I probably want to stay with something that fits in 15's anyways; would it just be a good ideas to buy new:

• New Stock size fronts (drilled or sloted also don't matter right?) or should I just get the 337 stock ones
• New pads for front and rear (give me an awesome brand that doesnt sound like ****/dirty/nice stopping power) If I have to pick one I rather just have dirty brakes if they stop and dont scream.
• Upgrade rear rotors to 10.1 (will this still fit 15) http://www.germanautoparts.com/Volks...lf/Brake/74/16 ate rotors, I like anti corrosion
• Should I get better brake fluid than the OEM can from VW?

[VW-Pssst]

I'm glad I found this thread before I bought a BBK I wont lie though, they do look very nice but then again so would any rotor thats not rusty and shiny painted calipers.

Annoying though that I have a set of 15 winter tires and 17 summer. And wtf does less tire cost more different compounds my ass, still the same rating.

Seeing as how I have different sizes I probably want to stay with something that fits in 15's anyways; would it just be a good ideas to buy new:

• New Stock size fronts (drilled or sloted also don't matter right?) or should I just get the 337 stock ones
• New pads for front and rear (give me an awesome brand that doesnt sound like ****/dirty/nice stopping power) If I have to pick one I rather just have dirty brakes if they stop and dont scream.
• Upgrade rear rotors to 10.1 (will this still fit 15) http://www.germanautoparts.com/Volks...lf/Brake/74/16 ate rotors, I like anti corrosion
• Should I get better brake fluid than the OEM can from VW?

as stated multiple times this thread has many misleading statements...

My biggest observation with my BBK is at higher speeds. When going 70+ mph and slamming the brakes, the car freaking stops, Even 100+ and slamming the brakes your cars gonna stop. and fast! bigger rotation of the rotor and bigger pads and 4 pistons to stop is a huge increase of clamping power over your stock brakes. Its common sense on why it stops faster...

The brake fluid differences is temperature, so yes you can change it if you'd like but the DOT ratings are how much heat they can handle...

But yes I dont get how the less tire is more expensive >_< And having to change wheel sizes for winter does suck. But I do love my porsche 4piston brakes and 12.3" rotors. Much more of an improvement over stock. And gotta love the big Red calipers that read porsche nice and pretty

[GTijoejoe]

as stated multiple times this thread has many misleading statements...

My biggest observation with my BBK is at higher speeds. When going 70+ mph and slamming the brakes, the car freaking stops, Even 100+ and slamming the brakes your cars gonna stop. and fast! bigger rotation of the rotor and bigger pads and 4 pistons to stop is a huge increase of clamping power over your stock brakes. Its common sense on why it stops faster...

The brake fluid differences is temperature, so yes you can change it if you'd like but the DOT ratings are how much heat they can handle...

But yes I dont get how the less tire is more expensive >_< And having to change wheel sizes for winter does suck. But I do love my porsche 4piston brakes and 12.3" rotors. Much more of an improvement over stock. And gotta love the big Red calipers that read porsche nice and pretty

Keep in mind, only because you have more pistons or larger pads doesn't mean you have more clamping power. You need to compare the overall area of the pistons and pad height. BBK's normally reduce the piston area because of the increase in effectiveness from the larger brake disk (effective radius dimension). BBK's are trying to balance brake gain by giving you a larger disk and stiffer sometimes lighter caliper in return.
This of course will not always balance out because of the increased rotational inertia, so you need to understand the physics of what you’re doing before you weigh the advantages etc.

If you want it in a nut shell with 100% factual information here it is:
In any brake setup you are always limited between the frictional forces between the ground and tire interface. Every single OEM brake setup will be able to lock your tires ~1g stop, putting a different brake setup on your vehicle will not do anything other than provide more brake torque. That increased brake torque will do nothing if your tires are already locked, its useless.

So by upgrading your tires you can increase the available friction (given by the constant weight of your vehicle, we are neglecting down force etc. to keep concepts simple) and the increased brake torque from your brake system will allow for an increased decel 1.0+g. Now this is the general concept to understand brake torque and the threshold of locking tires. (now for some of you racers that already know that some % slip is actually good for the best frictional mu... we are going to ignore all that for now )

On to increasing your brake torque:
There are a various of ways to do this as many of you know, we are only going to entertain the corner brake system, no pedal/booster/master cylinder speak here, these generally only change effort by the driver.
To increase brake gain (torque) increasing your piston area will give higher clamp loads, increasing your effective radius (disk diameter) will give you higher moment arm for torque calculation Friction Force X moment arm = Torque.
... and by increasing your pad's frictional mu characteristics will give you higher friction forces. Friction force = Clamp force x mu

Now to put things into perspective:
In general, the only reason to increase your disk size is to compensate for heat energy. The increased energy comes from weight and speed, kinetic energy = 1/2*mass*velocity^2
Larger disks have increased rotational inertia, so limiting how large of a disk or mass you need is best by design. If you aren’t increasing your Vmax or doing multiple high g stops consecutively than most likely you don’t need larger disks.

What does heat do to your friction?
Friction characteristics changes with temperature, there is no such thing as single mu value for a pad. For street pads they are stable at low temperatures, giving good friction characteristics which often will dwindle off and decrease as temp increases. Race pads have high friction values but also need ample temperature to achieve those ranges, meaning, low temp conditions, race pads may have much lower mu values than street pads, which is exactly why race pads are not recommended for street applications…. You may go through that first stop sign or if on the free way that sudden stop may not be so sudden as the mu value is very low.

These temperatures for street vs race pads are in certain ranges, so depending on your application you want to stay within the temp range, this even changes from track to track etc… or auto-x. Many times people feel they need race pads for auto-x, but truth is, you still are not in the temperature range to justify race pads, your Vmax decels are very low compared to 150mph track speeds, and at the beginning of an Auto-x there is no warm up period (generally)

So IMO, if you want to start brake modifications.
1st: change your tires
2nd : change your pads, if you are dealing with fad and glazing, try yet another pad
Many OEM pads are NAO (non-asbestos organic), going up the chain…than low metallic, semi-metallic, than ceramics to deal with heat are the logical steps. Keep in mind metallics tend to dust, anything that has a high mu will eat your disk, this will also cause rusting and deposits on wheels.
3rd: Need increase brake torque, change your caliper’s piston area
4th: You need heat management, look in to brake ducting or increase your disk size, thickness vs diameter

This is a basic understanding, should help you understand why it is possible to increase stopping distance and decrease HP from the OP’s findings. Brake system’s are all about optimization, there are always trade offs, no perfect system exists. If you have other questions about things not discussed, just ask

Remember, brake performance and feeling are to different things which commonly get mixed up. Some is objective the other subjective, you can measure both, only one will prove which is better.

[evol_mk3]

Couldn't some bigger brakes just be crap?

Why would companies like Audi, Porsche, Lambo, etc., put big brakes on their cars... Or why do race cars put bigger brakes on? To go slower, really?

So, if I took my stock VR and did a brake test against a new Porsche, my VW should win? Or if I put smaller brakes on the Porsche it will brake faster????

[GTijoejoe]

Couldn't some bigger brakes just be crap?

Why would companies like Audi, Porsche, Lambo, etc., put big brakes on their cars... Or why do race cars put bigger brakes on? To go slower, really?

So, if I took my stock VR and did a brake test against a new Porsche, my VW should win? Or if I put smaller brakes on the Porsche it will brake faster????

The top speed and/or the weight of those vehicles is the factor... when you are taking in kinetic energy and squaring the velocity, it has a extreme impact from say a 115mph to 150+mph.
Lambo's for example are not very light, as well have top speeds 180+mph... why do you think motorcycles can have such drastic brake zones? Do they have huge brakes comparable to your car? of course not, its because they weight less than 500lbs.

Also I should add, the duty of the intended vehicle... a porsche/lambo/supercar category is intended for track duty, so instead of one high G stop, it is designed to take several back to back, significantly increasing the energy loading on the brake system.
Braking peformance has everything to do with energy transfer

In the category of race, many race car depending on class actually have very small brakes. Its in the benefit of pure race to become the lightest, smallest, highest cooling effectiveness as possible... big brakes are heavy. Every see the size of the wheel on alot of cars? There is only so big of a disk you can fit into a 15" wheel. Classes which state no use of carbon, than you have no choice but to use a huge mega 14-16" rotor for heat capacity....

Hope that helps your understanding

[frskniam]

Couldn't some bigger brakes just be crap?

Why would companies like Audi, Porsche, Lambo, etc., put big brakes on their cars... Or why do race cars put bigger brakes on? To go slower, really?

So, if I took my stock VR and did a brake test against a new Porsche, my VW should win? Or if I put smaller brakes on the Porsche it will brake faster????

I would also like to add that they do it because big brakes look pretty. Just like if you are after performance, you get as light of wheels as possible, so too with brakes... And in the end you have to make compromises somewhere.

[Hedgehodge]

I was just curious if my car should go from what its at to the bigger rear rotors since I'm going to change them anyways. The aniv. edition ones. I just had the rear calipers replaced and rather not replace them just yet.

Maybe upgrade my rears to 10" and leave the front ones the same size and then upgrade the rear calipers with that tyrol kit and I should be gtg with better pads and bleeding of the brakes? At the moment I only have aprchip/exhaust/TIP/17"summer/15"winter and a few other things but still stock turbo. Even if I went stage 3 turbo it would be a good idea for me to stick with this too?

Thanks for the response, learned a lot just it all still confuses me

v/r
Semi Sober Hedgehodge

[GTijoejoe]

that should probably be discussed in another thread, most likely for your driving stock disk size and bushing kit should suit what you need for the time being

Generally, you understand the specs of what you have compared to what you want to change too, disk size, caliper size etc... than you can understand if you're changing the brake gain effecting the bias.

[caraddict1]

I am new to this forum with a B6 Passat VR6 4MO. My last car was an B7 Audi S4 Avant which destroyed by a tree falling on it. It was equipped with the ECS Tuning BB kit from the Porsche Cayenne, cross-drilled and slotted, with 6 piston calipers. Since its just a migration from 1 car to the other, cost will be minimal. I need info on:

1. Will these brakes fit on the Passat? Are there any reasons I SHOULDN'T transfer the brakes from one car to the other?

2. If it is feasible, can someone suggest a source for an adapter bracket and whatever else I would need to make the Porsche brake setup work on the Passat?

Thanks for your input!

[night_OWL]

^ Similar situation, looking at replacing stock 12.3" rotors and single piston calipers on TT with 11" rotors and 4 piston calipers (either Brembo or Wilwood) from a VR6... Any installation issues I could come across? Are there any benefits to having the 4 pistions instead of the single?

[GTijoejoe]

I am new to this forum with a B6 Passat VR6 4MO. My last car was an B7 Audi S4 Avant which destroyed by a tree falling on it. It was equipped with the ECS Tuning BB kit from the Porsche Cayenne, cross-drilled and slotted, with 6 piston calipers. Since its just a migration from 1 car to the other, cost will be minimal. I need info on:

1. Will these brakes fit on the Passat? Are there any reasons I SHOULDN'T transfer the brakes from one car to the other?

2. If it is feasible, can someone suggest a source for an adapter bracket and whatever else I would need to make the Porsche brake setup work on the Passat?

Thanks for your input!

Please make a specific thread for your question, has nothing to do with this specific thread.
Just to give you something, yes you can transfer the brake kit from your Audi, the passat and Audi will be very similar.

[HYDE16]

Even after I upgraded the pads and brake fluid they stock brakes still sucked, ended up going with the Forge Motorsport Front Brake Kit and SS lines on my 2011 GTI. Looking forward to getting out for the next HPDE event to test this kit out.

-HYDE16 Reviews Forge Motorsport Front Brake Kit (MK5 & MK6 330mm Kit)-