I'll do a 60mph (got to stick to law abiding speeds - and emergency stopping on a dual carriageway is a little silly) to 0 stop with 288mm and then the same thing with 312mm at some point next week or the week after - and will try to make sure the conditions and location are the same

Will set up a video recording of the speedo so you can time it for yourself rather than relying on my figures.

Bigger brakes won't make you stop quicker if the existing brakes can already lock the wheels for you, I think was his point - because the tyres are the weak point, not the brakes' ability to transfer kinetic energy.

That's all very well if you can lock the wheels, but you can't. ABS makes sure that doesn't happen. The question is then which setup delivers the most deceleration during the pulse that the ABS allows the pads to be in contact with the disc and on that basis, I think the bigger brakes will stop you quicker.

That's all very well if you can lock the wheels, but you can't. ABS makes sure that doesn't happen. The question is then which setup delivers the most deceleration during the pulse that the ABS allows the pads to be in contact with the disc and on that basis, I think the bigger brakes will stop you quicker.

I agree, yegnold has forgotten that his VRS has Anti lock brakes which throw all his reasoning and maths out the window. of course 312's are quicker at decelerating a car. That being said 312's are a must when performance ugrades are carried out, especially the remaps etc.

Another important part of the braking performance is brake fluid, often overlooked, and recommended every 2 years with dot 5.1 reqd. on 312's when used on the track.

I also can see no problem with the OE brakes when maintained correctly as above on a bog standard VRS that is just used on public roads.

What difference does having anti lock brakes make to the amount of kinetic energy transferred when braking?

What difference does having anti lock brakes make to the amount of kinetic energy transferred when braking?

The question you're asking is not relevant to the amount of braking force applied. What does matter is that on 312's braking torque is increased due to the force is applied by the brake piston onto the brake disc but at point closer to the circumference of the wheel. In actual fact the brake pad surface and piston pressure is the same as in the 288 set up. Hope that makes sense.

lol, can of worms !

all i wanted to say was my brakes are good and cost me bugger all lol

The question you're asking is not relevant to the amount of braking force applied. What does matter is that on 312's braking torque is increased due to the force is applied by the brake piston onto the brake disc but at point closer to the circumference of the wheel. In actual fact the brake pad surface and piston pressure is the same as in the 288 set up. Hope that makes sense.

Never thought about that - very important though - thank you!

So are you still upgrading ?

Yep! Got nothing to lose apart from money

EDIT:

Regarding anti lock brakes 'not letting tyres skid'. Here is my point.

Imagine running cheap tyres that aren't very grippy. The ABS will work a lot more than when you run expensive, grippy tyres. ABS works as follows: It releases and rapidly reapplies the brakes. When a lock up is detected, it releases, then it applies again, etc. This is why on **** roads and on ice you can feel the ABS applying and releasing very quickly indeed.

Are you telling me that with ABS you can run really crap tyres and really good tyres and stop in the same distance?

My argument was:

- If your existing 288mm brake set up frequently has ABS working to maintain your braking/steering ability, the brakes are plenty powerful enough and your tyres/grip levels are the limiting factor.

- If your existing 288mm brake set up does not get the ABS working and you stop smoothly, the thing that is limiting how quickly you stop is the 'power' of the brakes - the rate at which they can transfer energy. Having more pad/disc contact (and consequently more friction, and torque as explained by sootie above) means that your braking power will be increased.

I might not have put it across quite as well as that but that was what I meant. I don't see the relevance of having ABS with regards to braking power

Edited 28 April, 200917 yr by yegnold

Still do your brake comparison test though.

You will find that the 312's will deccelarate the car much quicker, especially from higher speeds, like 80mph for instance, you won't notice much difference below 60mph. Lets us know what think of them when done and don't forget the brake fluid!

Thanks Sootie. I just updated my post above yours to explain my point about tyre grip levels.

I believe that VAG have updated their brake fluid to use 'Super Dot 4' instead of normal dot 4 fluid - I was considering replacing my fluid with that. Would it be a worthy investment to use dot 5 instead, then?

By the way I'm confused - I've never said that the bigger brakes wont stop you quicker? I'm lost!

I used a GTech Accelerometer to measure mine before the swap. Once mine are bedded in I'll repeat the runs. If you want to borrow it, I'll send it to you as long as you promise to send it back;)

I'm asking this for just for peoples opinions:

Why will it make a difference on the road if the car has been chipped or not?

If you are trying to stop a vRS weighing X at 70 mph, what difference does it make if I have 130 BHP or 170BHP??

If you are trying to stop a vRS weighing X at 70 mph, what difference does it make if I have 130 BHP or 170BHP??

It makes no difference at all, but it makes sense that a car that accelerates more quickly decelerates more quickly too.

It makes no difference at all, but it makes sense that a car that accelerates more quickly decelerates more quickly too.

Good point, if you arrive somewhere quicker you are going to need to slow quicker kinda logical reallly.

I do love these kinda threads, so does Ali, there was a storming one on the same subject over on the SXOC and it got really funny.

Are you laughing at how we're all catastrophically incorrect in our arguments, Ross?

Yengold- As you say crap tyres won't stop you quicker than than good tyres whichever brakes you have. With bigger brakes the ABS will just operate faster. ABS does not need re-calibrating everytime you make changes to the brakes, all it does is monitor the rotation of the hub by means of a transducer and will operate/reoperate the brakes when the hub is turning/static.

My reasoning for bigger brakes with more engine power is that you are more likely to drive faster therefore the need to stop quicker becomes a factor.

Did you dream off brakes last night?

Edited 29 April, 200917 yr by Soot1e

Of course bigger brakes stop you quicker. The fastest way to stop? Lock all 4 wheels. The only advantage to not locking the wheels is you lose steering. Bigger brakes and ABS is a good thing. You get maximum braking for the available grip.

Locking the wheels will almost double your stopping distance compared to a car correctly braked. If you don't believe me try it out on a deserted road. Apply the brakes properly and see where you stop from a fixed braking point. Go back and do it again with your wheels locked (you may not be bale to do this with ABS). You will be amased at how much further it takes to stop.

I was allowed to do this on a brake test track when working for a brake manufacturer by one of the test drivers.

No, I did not dream about brakes last night.

I've just had another read through all the new posts and there seems to be a lot of commonly held mistakes about brake performance.

Here's a quick outline of brake performance :-

• Bigger brakes will not stop stop a car quicker. They will allow the car to do more repeated stops without overheating the brakes. They will give a more responsive brake (better feel) due to the braking surface being centred further out.

• The tyres are the limiting factor on braking performance on road cars. Without ABS you can lock the wheels at any speed. Tyres that have more grip will allow you to stop quicker. An easy way to think of this is when it is wet you can't stop as quick as there is less grip. Racing cars can stop really quickly in the dry because they have grippy slick tyres but they can't stop at all using slick tyres in the wet but they are using the same brakes!

• ABS brakes do NOT shorten your stopping distance. All they do is allow you to steer the car with the brakes fully on as the wheels will not be locked. A really good driver can often out-perform an ABS system and reduce the stopping distance through skillful application of the brakes. But I do mean a really good drivers (test drivers and racing drivers). I have seen test drivers in action and believe me that they are the top 0.000001% of skill level. Often they are better than racing drivers at brake testing because they do it all the time and often under all sorts of controlled conditions.

• Bigger brakes allow more energy to be absorbed and converted to heat. Bigger cars have bigger brakes because they weigh more and can usually go faster. Automatic cars often have bigger brakes than an identical manual car as they have greattly reduced engine braking and the brakes are worked harder and more often.

• My wife drives an Octavia VRS diesel and I have a Fabia VRS. The Octavia has the bigger brakes and feels like it will stop quicker. However, this is an illusion as the Octy has really grabby brakes due to either having a higher friction brake material or a larger servo so it needs less brake pedal pressure. It is very easy on the Octy to get the ABS working compared to the Fabia. The Octy feels a bit like the old Citroens with the brakes working from the high pressure suspension pump and the brakes being really on or off.

I have seen a formula one car up close on a few occasions and the amazing thing about them is not how quick they are but how quick they stop. They literally seem to beat the laws of physics and stop like they have hit a brick wall. This is becasue they have incredibly grippy tyes and huge ammounts of downforce to allow the tyres to grip and put the lareg braking forces down onto the road.

I've driven 45,000 miles on standard Fabia vRS brakes and never had any problems with them. If you find them so bad then either you're driving like an total idiot on public roads, your brakes are defective, you can't drive properly, or you should have bought a racing car instead if a small hatchback.

To clarify - I don't find them bad, I just fancy something to do and want to use the car on track more frequently.

If you search through all of my posts on this forum relating to the 312mm brake upgrade, including comments in other threads, you will see that I've always said that the standard 288mm items are more than sufficient

Here:

http://briskoda.net/fabia-i/front-pads/141531/#post1652678

Here:

http://briskoda.net/fabia-i/front-pads/141531/#post1652576

and here:

http://briskoda.net/fabia-i/312mm-brake-upgrade/26421/#post1384664

Since I posted those threads I have developed my taste for doing more track days - hence why I AM upgrading.

Edited 29 April, 200917 yr by yegnold
Added in links to posts in past about 312mm upgrade.

I saw a good quote on one forum. "Speed is desirable, stopping is essential"

I was going to argue with you, Shadowphax, about the size of brakes because a large diameter disc has less breaking torque than a smaller one i.e. its easier to stop. But the brakes don't stop the vehicle, those bits of rubber around the outside of the wheel do, and they are the only bits in contact with the road.

I've found this an interesting read: StopTech - Balanced Brake Upgrades

Edited 29 April, 200917 yr by Jim H
Speling

I've found this an interesting read: StopTech - Balanced Brake Upgrades

3) Repeated hard stops require both effective heat transfer and adequate thermal storage capacity within the disc. The more disc surface area per unit mass and the greater and more efficient the mass flow of air over and through the disc, the faster the heat will be dissipated and the more efficient the entire system will be. At the same time, the brake discs must have enough thermal storage capacity to prevent distortion and/or cracking from thermal stress until the heat can be dissipated. This is not particularly important in a single stop but it is crucial in the case of repeated stops from high speed - whether racing, touring or towing.

Is essentially a much more informed and better explained version of the 'physics lesson' I was giving earlier in this thread

Also, later in the page

5) Front to rear brake torque bias should be consistent with the dynamics of the specific vehicle.

looks to suggest that if we are upgrading the fronts by a particular percentage, then the braking torque of the rears should be increased by the same percentage too, to maintain the braking balance of the vehicle.