What is the point on bigger disc setups?

[Swompy 0]

IF you banging on about the tyre grip what about the engine braking effect when you change down a gear or two whilst braking?

[Macdaddy 10]

The brakes on my RS4 are way bigger yet the corrado brakes stop exactly the same......... Errr not!

 

 

Seriously tho if it helps.... Bigger discs don't stop you quicker, you'll also need larger pads to increase the surface area.

 

More friction generated = better stopping power...... Why the hell have I just wasted 2min typing this more to the point!

[Nick 17 10]

Timmah you have shown me the way of light thank you :) I am now going to go outside remove 288mm conversion and replace it with my nans saxo brakes. Then use my grandfathers welder, weld 3 steel wheels together per corner and have 18J wheels for more mechanical stopping power. If all fails with mounting the saxo brakes i have some wonderful V Brakes on my mountain bike :)

 

Once again i am amazed at the profound knowledge we have collectively as a forum :) What a guru

[jaded2882 0]

Bigger brakes equals more surface area to cook bacon on when they're hot.

[guildmage 11]

Tried to read the whole thing... still couldn't get my head round what you are saying... googled it and found this: http://www.fastfordmag.co.uk/files/2009/10/FAF273.brakes.pdf

 

It maybe is non scientific, maybe bit too childish and maybe too-much-Ford-not-so-much-VW, but I read it and know a bit more about brakes. Don't flame me if it's off-topic and not related to you conversation, someone else may find it useful, I did ... well I know now what a brake torque is :)

[KipVR 1]

Jesus, just read this post.

 

Your mother must be proud.

[VR6Joni 0]

My 2p.

Bigger, fatter disks wear less and stay cooler as has been explained multiple times earlier.

Because of this large disks are less stressed, therefore the braking surface stay's smoother and disk warping is minimised. Therefore the brake pad can apply a more constant braking force throughout a whole revolution of the wheel, thus preventing skidding and the ABS kicking in. Add to this 4 pot callipers which allow the pad to follow the face of the disk even better and you have a significant improvement in braking.

 

I have tried 280mm performance disks and pads, they still gave poor brake progression and faded after a few roundabouts on some local bypass's.

I then upgraded to 312mm disks and pads (mediocre spec), pedal feel improved slightly and fade was quite difficult to induce.

Then onwards to 4 pots with 312mm performance disks and mediocre pads, pedal feel and brake progression was vastly improved over the 280mm setup and once again fade was very difficult to induce.

 

So to sum it up brand new 280mm V's 312mm will probably not see a reduction in braking distance, but pedal feel is better so with some driver skill an improvement is possible.

But with used real world disks, 312mm will have a small reduction in braking distance due to disk face remaining more true (flat) there giving more uniform braking effort through out the disk revolution. Add 4 pots and the improvement will be even greater.

And if you want to spend even more, add floating rotors for another improvement in performance.

 

Therefore in the real world which we live in, bigger brakes are better! fact!

Edited August 30, 2012 by VR6Joni

[KIPVW 0]

Here's one for you. take a dual carriageway at a quiet time in the evening, 2 Corrado VR6's one with standard 280mm brakes the other with 288's fitted drive said cars at 60 mph and then both agree before hand which sign or lamp post you are both going to start braking at, and do a complete emergency stop ( nothing behind you of course ) then watch the driver of the Corrado with 288's smile at you in your rear view mirror as you continue moving forward quite some distance further.

 

Repeat several times and even swap drivers too and get the same results.

 

Bigger brakes stop quicker FACT! now stop bloody winding people up :)

[Kevin Bacon 5]

My assumption is that bigger brakes are better because KevHaywire said so. That's what most of the 'fact' round here is based on ;)

 

Well of course. Everything I say is gospel and disagreeing with me is a bannable offense ;)

 

Seriously though, many good examples given and points raised.

 

Timaaah, does have a points: If the ABS has engaged, the tyre can offer no more grip at that moment in time. But his argument is sadly one dimensional and I'm surprised people were being so patient with him, constantly repeating himself.

 

Tyre grip is constantly variable. Road camber changes, diesel spillages, winter vs summer, inflation pressure etc, far too many variables. And that's just the tyre. We haven't mentioned damper oil viscosity, damper leaks, bush condition and shure (varies with temp), etc etc.

 

It's also an impossible test to prove because to fit big brakes that will make the 'vs' argument hold some weight would require bigger wheels and therefore bigger tyres, different compound of rubber etc, which totally changes the dynamics.

 

Plus no one has mentioned repeatability. So the standard brakes can make the ABS lock. Wow, big deal. So can a Daewoo Matiz with it's saucer sized discs. But how long can they survive that before overheating and warping? Not long.

 

And No account is being made for braking effectiveness *BEFORE* the point of locking up either, or the fact the Corrado has a very old ON/OFF style ABS system compared to modern brake distribution technology.

 

In general, a car's ability to stop in a shorter distance is a lot more involved than just the brakes and tyres. Think super cars. Their entire front end chassis setup is dedicated to stopping and changing direction as quickly as possible. They are able to deploy all of their massive braking power where a lot of other cars aren't. And do we find tiny little OE spec brakes on these cars? No we don't. Not even ones that weigh a little over a tonned. We find huge 6 pot calipers and 380+mm discs. Why? Because it's all about braking torque.

 

I've fitted a few bigger brake setups to my Corrado and for the same pedal force at the same speed, bigger brakes will stop the car in a shorter distance, no question.

 

If the OP would like to pay for a scientific test to be done at the Bedford Autodrome, I'm sure a few of us will come along :D

[Swompy 0]

You forgot engine braking Kev as per my post above the engine and lower gear will help slow the car too ;)

[Kevin Bacon 5]

/\ Yeah that as well :D

 

I also forgot to say that more powerful brakes on the same car may lock the ABS sooner, but will have done so in a shorter distance than the standard brakes.

 

"Better brakes" to me = shorter stopping distances, which is definitely measurable. Pedal feel is subjective but OEs have rightly moved away from the OP's 'simply push the pedal harder' attitude toward brake improvement.

[jaded2882 0]

To be fair to the OP, I have thought the same thing myself about the point the wheels lock up being the max amount of braking possible etc. etc. but there have been some very good explanations of the physics and benefits of bigger kit. Not sure where he's gone now, but at least I've learned something!

[Kevin Bacon 5]

It was clear he just had a bee in his bonnet about people stating "bigger brakes are better" without explaining why. I knew when I saw a 6 page thread about brakes it was going to a spicy one :D

 

But as we've demonstrated in our ramblings, it's not a B&W answer and no account was being made for shorter stopping distances or how good the brakes are before the point of lock up. You can lock the wheels on a BMX just as easily as you can a racer, but the Racer will stop in a shorter distance from the same speed due to the massive mechanical advantage of it's bigger wheels, even though it has much skinnier tyres. It really is simple physics at the end of the day.

[kdub 10]

Quick basic demonstration as why bigger brakes stop your car quicker in certain conditions.

 

60mph. Say you need 150nm of clamping force to lock up the wheels.

 

Small brakes = 50% pedal travel due to difference in clamping force/torque of smaller diameter discs

Big brakes = 40% pedal travel

 

That alone = faster braking time due to less pedal movement although we are taking 1/10ths of a second here it still equates to a distance of a body in motion.

 

 

Better example through torque/clamp force

 

Now continue with the same theory of clamping force/torque. Say the maximum force is 200nm for the little brakes and 250nm for the bigger due to the additional torque that can be applied due to the larger diameter of the rotor. Now at 100mph it will take more clamping force to lock those brakes up due to additional dive in the suspension and aerodynamics. So hypothetically if your doing 100mph and you require 225nm of clamping force the smaller brakes CANNOT take advantage of all the available mechanical traction for given suspension/tyre combination. That brief period where the smaller brakes can not apply the maximum amount of torque to use all the available mechanical grip is where the car with the bigger brakes wins.

 

On a back to back test with the same car etc it is the initial bite higher torque and the speed that it bites (less pedal travel required)where the braking distance shootout would be won or lost. Again we are talking fractions of a second but in a braking test from 60-0 it could be as much as say 5 metres. But on a 100-0 it could be say 3 times that which in a race situation is a lot.

 

Take that onto a track and for any given corner speed I will be able to brake later than you with the little brakes hence making up time.

 

 

Now bigger brakes have there disadvantages as well. With the additional torque it can be harder to modulate your brakes at slower speeds. But in motorsport applications that is why you change the master cylinder piston diameters to change the feel and modulation whilst still having the required amount of maximum torque vs mechanical grip available.

[Kevin Bacon 5]

/\ Good post. I was going to get into MC and caliper piston sizing, but thought it a bit too techy!

[Toad 0]

And we're forgetting to mention that larger brakes allow a bit more modulation of braking effort, thereby helping to prevent the wheels from locking up.

 

And how easy is it to lock the wheels up when travelling at 100mph?

 

I couldn't be bothered to read the long posts.

[Corradoholic 10]

all i know is that mr kipling vans have exceedingly good brakes........

[RedTyphoon 0]

From Brembo website

Where can I find test data on stopping distances?

At the speeds that stopping distance is generally measured from (60 to 70mph), the test is primarily testing the tire's grip on the pavement. As delivered from the manufacturer, nearly all vehicles are able to engage the ABS or lock the wheels at these speeds. Therefore, an increase in braking power will do nothing to stop the vehicle in a shorter distance. For this reason, we do not record stopping distances at this time. The Brembo systems will show their greatest advantages when braking from higher speeds, or when tasked with repeated heavy braking. The increased braking torque provides for maximum deceleration at speed, and the ability to absorb and quickly dissipate the intense heat generated during repeated braking insures that the braking system will perform at the same high level each time.

Edited September 1, 2012 by RedTyphoon

[G-Lad 0]

...and this thread just goes to show why we need to stop giving out such high grades for GCSEs!