I don't do physics

I don't do kinetic energy

I don't do piston diameters

I do drive my car (albeit a Mk2 Octavia, not a Fabia)

I do have 350mm discs with 6-pot Brembo calipers from a Porsche Cayenne

I do know that if I stamped on the stop pedal hard enough they would either launch me through the windscreen, or stand the car on its head

Surely the number of occasions when tyres lose traction in these days of ABS etc etc should be almost non-existent

I would change the tires anyway. Was simply keeping this about the brakes

Thanks for the info on the CSA Sy. I'm a bit of a layman. What is cross sectional area and how do you work it out?

Here's the info from their website

PB Brake kits take stopping power to the next level! Everything required for installation is included in the kit;

No modification is required as each of our kits has been specifically designed for your vehicle. Unlike other brands in the same price range, we offer 11 different sizes of caliper to perfectly match each rotor diameter, and we refuse to offer over-sized calipers on small rotors for looks.

PB kits are precision engineered, utilizing state of the art CNC technology and using only the finest materials. There truly is no better value for money brake kit on the market today.

I don't do physics

I don't do kinetic energy

I don't do piston diameters

I do drive my car (albeit a Mk2 Octavia, not a Fabia)

I do have 350mm discs with 6-pot Brembo calipers from a Porsche Cayenne

I do know that if I stamped on the stop pedal hard enough they would either launch me through the windscreen, or stand the car on its head

Surely the number of occasions when tyres lose traction in these days of ABS etc etc should be almost non-existent

Didn't realise your brakes were that big Bryan! They sound beasty

Can't wait to get my D2 kit fitted! Still not arrived yet though. :(

I remember a mate telling me not to upgrade from 288mm to 312's on my Mk1 vRS because the wheels were more likely to lock under braking. I thought that was rubbish so got them fitted anyway and didn't say a word. Painted green he was none the wiser. Going down a bypass with him to a roundabout and I wanted to go straight on. Left the braking late and didn't stamp on them until the last second. He screamed like a girl, the wheels didn't lock and we negotiated the roundabout with no problems.

I'm not sure if comparable, but I know my car stopped better (a LOT better ) when I had 323mm 4 pots up front, and was still on stock 232mm rears, with the cheapest stock discs and pads (as they didn't really do anything) - This probably explains why the fabia can be a little tailhappy under braking on track

I remember a mate telling me not to upgrade from 288mm to 312's on my Mk1 vRS because the wheels were more likely to lock under braking. I thought that was rubbish so got them fitted anyway and didn't say a word. Painted green he was none the wiser. Going down a bypass with him to a roundabout and I wanted to go straight on. Left the braking late and didn't stamp on them until the last second. He screamed like a girl, the wheels didn't lock and we negotiated the roundabout with no problems.

Im sorry but thats not possible

I'm not sure if comparable, but I know my car stopped better (a LOT better ) when I had 323mm 4 pots up front, and was still on stock 232mm rears, with the cheapest stock discs and pads (as they didn't really do anything) - This probably explains why the fabia can be a little tailhappy under braking on track

Its the best way to allow the car to trail brake as well. My rears dont get upto temp that much either, even on a hot day, so upgrading the pads wouldnt help much unless i was doing LOTS of laps(but thats no use for the street) and larger reardiscs would just reduce the temps even further. I was advised by VWRacing, KPMRacing and TAROX not to bother touching the rear brakes on mine.

Im sorry but thats not possible

I'm sure he said it because he wanted to put me off doing anything on my car that would make it "better" than his Golf. 312mm upgrade was the best thing I ever did to the Mk1 and I never had brake fade on the road.

What size is the d2 kit Jason?

Have you upgraded the rear brakes too Bryan?

Have you upgraded the rear brakes too Bryan?

Yes, it's got Audi S3 calipers with 310mm discs

What size is the d2 kit Jason?

330mm 6 pot.

Sweet

Really looking forward to seeing this at the mega meet

330mm 6 pot.

Cool don't think I'll have a problem with the 330mm 4pots up front and the 286mm rears

I would change the tires anyway. Was simply keeping this about the brakes

Thanks for the info on the CSA Sy. I'm a bit of a layman. What is cross sectional area and how do you work it out?

Most people who do the brakes I would imagine wouldnt be running the stock ditchfinders anyway.

Workingout the CSA is easy enough, provided yo ucan find the manufacturers literature on it. Most companies display it on their website though.

Take the Stock Fabia II vRS Caliper. Which has a single 54mm diameter piston. (Pi * Radius² = CSA) therefore 3.14 x 27² = 2289mm²

Now looking at aftermarket pistons sizes, Boxster 4 pots have a 40mm and 36mm piston each side: 40mm + 36mm = 1257mm²+1018mm²= 2275mm² So very close to the stock setup ~0.5% lower

So looking at comparable setups that will work with the master cylinder (Ive borrowed this from DaveB of VAGBREMTECHNIK from another forum, this guy is a brake SPECIALIST and is very very highly regarded) As said before by the Brake Guru, for some reason you only count the one side and you ideally want to be within a tolerance of Minus 0-1% and +8-9% max, so its better to use a larger CSA than it is a lower one, but only within reason:

These are good matches:

AP Racing 6-pot CP7068 (355x32 ) > 2350 mm² (small bore version of CP7040 caliper for Mk.V/VI)

AP Racing 6-pot CP5570: 27.0 + 31.8 + 38.1 > 573 mm² + 794 mm² + 1140 mm² = 2507 mm²

Boxster: 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²

Boxster S: 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²

993 Turbo: 36 + 44 mm > 1018 mm² + + 1520 mm² = 2538 mm² (on the edge)

Brembo GT 'A-caliper': 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²

But these are poor matches and wil not make good brakes despite being readily available as kits.

Q7/Touareg/Cayenne (three variants):

34/36/38 mm : 907.920 + 1017.876 + 1134.115 = ~ 3060 mm²

32/36/38 mm : 804.248 + 1017.876 + 1134.115 = ~ 2956 mm²

30/34/38 mm : 706.858 + 907.920 + 1134.115 = ~ 2749 mm²

Forge: 707 mm² + 1046 mm² + 1164 mm² = 2917 mm²

996 Turbo: 40 + 44 mm > 1257 mm² + 1520 mm² = 2777 mm²

From what i remember him saying, bigger CSA will equal more braking power provided its not to crazy in size that the master cylinder is overwhelmed, in addition the bigger CSA will lose braking "feel" and make them on/off in operation. Smaller CSA has less braking power, but more feel, hence the ideal tolerances stated above.

Bear in mind that i am comparing brake options for the Fabia II with a 54mm piston diameter. You need to find out what stock piston CSA the Mk1 fabia I vRS caliper runs.

These website quotes of "these are designed for your car" I dont believe personally. All they will do is look at their pre designed off the shelf caliper options, and hopefully select the one that is closest to the stock setup. Id wager the only custom work will be the caliper carriers.

Cool don't think I'll have a problem with the 330mm 4pots up front and the 286mm rears

I run 323mm 6 pots with 256 rears and I have no issues at all. I even had a Le Mans racing driver (Jonny Cocker) and a rally driver (I forget his name though) really work my car hard then comment on how good my brakes were at Silverstone. Hence why Im happy to ignore other "brake experts" as their opinion matched exactly what i felt myself.

Question for you though

• Seat Leon Fr/Seat Leon Cupra: Both have identical weight, identical tyres, identical wheels, identical rear brakes, identical master cylinders, identical everything that is except front brakes: Fr has 312mm brakes, the Cupra has 345mm brakes.
  
• Seat Ibiza Fr/Seat Ibiza Cupra (Racing brake upgrade): Both have identical weight, identical tyres, identical wheels, identical rear brakes, identical master cylinders, identical everything that is except front brakes: Fr has 288mm brakes, the Cupra has 312mm brakes (with 3 extra pistons)
  
• VW Scirrocco 2.0TSI/VW Scirrocco R: Both have identical weight, identical tyres, identical wheels, identical rear brakes, identical master cylinders, identical everything that is except front brakes: TSI has 312mm brakes, the R has 345mm brakes.
  
• BMW have similar examples, as do Renault and Ford etc, but i cant be arsed looking at them just to prove a silly point.
  

The question though is, of the above, when running the same tyres, rear brakes, master cylinder etc, all exactly OEM with no unsanctioned modifications, which cars have the best stopping power?

Answer

post#7

Braking torque of a brake assembly should be matched to tyres grip based on speed, weight (including dynamic weight transfer) and speed

From 60mph-0mph they will have the same stoppig distances if weight is the same, if lighter (like Scirocco R compared to TSi) stopping distance will be shorter, but NOT becasue brakes are bigger lol.

WIth above example "R" has higher top speed and is lighter so will need more braking torque. Rather obvious, no?

I am all for upgrading brakes etc but doing it with a thinking cap screwed on and not just becasue BIGGER is better . Sometimes it is sometimes it is not... - depending what is being upgraded. Also worth remebering that brakes in road going cars are have brakes sized for full load of pasangers and luggage. Have one person driving it and brakes are "overspecified" - this is pretty intuitive I hope.

One more thing to think about - why do you think racing braking technique is to stomp on the anchors as hard as you can (but without breaking traction) and as the car slows down you're supposed release the pressure on the brake pedal? What is the thinking behind ? Why do they teach to do it that way?

Why your brakes were deemed to be so good by pro drivers?

You had car lowered so less dynamic weight transfer - brake bias goes backwards

Your wheels are lighter, brakes are lighter - less unsprung weight

You had hgh performance tyres - a key ingredient

All of the above transferred to your bigger brakes being able to use uprated braking torque translating into better "feel" and better (have you measured braking distnaces before upgrades and after?) braking performance. With all your upgrades brakes upgrades only made sense.

If I was to put your kit on m otherwise stock car (provided braking torque remained the same) all I could gain would be cooler running brakes but no better performance. If braking torque was to be increased (on purpose or not) my stpping distance would increase.

Don't be so defensive, I am not after you mate, relax

You havent answered the question. Which of each pair of cars wil stop in the shortest distance. The one with the larger brakes, or the one with smaller brakes?

I did, read again

In the real world, tyres / grip are always never pushed by the stock braking systems. Therefore I say like for like, bigger brakes = better stopping performance, until you reach the limit of the tyres, so then you get better tyres to improve further

OK, im thick, please right down the car that you think will stop the quickest of each pair. Assuming they are going say 100mph.

Leon Fr/Leon Cupra

Ibiza Fr/Ibiza Cupra (with Racing brake)

Scirocoo 2.0TSI/Scirocco R

You had car lowered so less dynamic weight transfer - brake bias goes backwards

But grippier pads and larger discs = greater braking torque therefore moving that bias back forwards.

It's all torque

Give up Sy, it's not worth it.

Give up Sy, it's not worth it.

I know, but my wife is away visiting family, so im home on my own bored and this amuses me no end