Bigger brakes?

Yep that's how I understand it .... that's why I haven't upgraded my brakes on my 308 YET ... I'm running full race Porterfield pads and had no problem (read past tense) locking the fronts until I changed spring rates and shocks and lowered the car. It completely changed the way the car brakes.

Stock it would nose dive and stand up on the front wheels .... seems like this would put more downforce on the tires and make them grip more but based on what I described above the weight transfer pushing the car forward must of been greater than the increased grip created by the weight transfer? ... I'm still trying to visualize what's going on there completely.

Now with stiffer springs, etc. I mash the brakes and you just better hold on and keep her pointed correctly ... I think the fronts will just barely break loose but there's a lot going on when she's decelerating that hard ... almost feels like the rears are starting to break loose first 'cause she feels a bit squirly right at the limit.

I was wondering the same thing 'cause I also wasn't getting any brake over heating until I did my suspension upgrade. This apparently is allowing me to put more heat into the brakes 'cause tires aren't just breaking loose now, hence at some point I'll be getting bigger brakes.

Does what I expereienced make sense? I couldn't figure why all you guys would go to bigger brakes until I did my suspension upgrade .

cheers

 

In a nutshell, bigger brakes = better stopping power and better heat dissipation. But there’s a lot more to it that just bigger rotors – think total system including brake bios and overall car suspension, including bigger wheels to fit the bigger calipers into. And with bigger wheels you can have bigger/ wider tire – of course, you will need to modify the fenders to get those bigger tires tucked under….. I’m sure you get the picture by now.

BTW, locking up the brakes does not mean you are stopping better / shorter. It means you can not stop the car with the tires /brakes that you have.

 

Yes, the ultimate deciding factor in your braking performance is your tires. You tires stop your car, your brakes only convert friction into heat.

In various performance tests that I have seen, bigger brakes perform better on track settings where a higher, more constant need to dissipate heat is required. More surface area means more area to dissipate heat.

On the road, most drivers will never encounter these levels of heat, rendering bigger brake kits slightly useless.

Most normal cars have a safe amount of rear brake bias to ensure that the front locks up before the rear. Playing with this bias by running slightly different pad materials between the front and rear brakes can have an excellent effect on how a road car brakes, because it utilizes the extra braking force available from the rear tires (just don't allow for too much rear bias...if you know what I mean).

Tire pressure, size, stickiness and variability of pad material and brake bias will serve you better on the road than a big brake kit will.

Just my .02.

 

But I think the question is - If I can lock up the wheel with the current brakes, am I going to get more stopping ability with bigger brakes?
It seems like the answer would be no. If you can lock up the wheel in any circumstance that seems like just a tad more power than you'll ever want. Seems like tires would be the next logical performance upgrade, but Luckydynes makes an argument for starting with suspension.

Smaller brakes (should) mean(s) less unsprung mass, so you (should) get a performance advantage there. Also this means that you can run smaller wheels and tires which (should) weigh less, but also (should) have less rotational mass for improved turning, stopping and accelerating. Yeah, that's why the 430 is such a dog compared to my GT4.

(I would use the same argument I make with my skinny-tired motorcycles to the guys who think that wider tires mean better handling. "What handles better, a light wheel or a heavy wheel?" A light wheel, they respond. I point to my little narrow rims and narrow tires. Now what's your question again? I try to leave before they realize that Moto Guzzi must have used a lead alloy when casting wheels. It's good for,....ummm... stability! yeah, that's it.)

 

One big thing people are missing, which is why some brake companies are better than others, is how good the system components really are.
Just because you can lock up the brakes and skid doesn't mean you have enough braking power. Think of stopping a bike by putting a broomstick through the wheel spokes. It will definitely lock up, but hardly makes for an efficient stop.
Good brakes will allow one to modulate the braking to the very edge. If you can use 99% of the braking force available, the car will stop as quickly as it can. Bad brakes, usually the stock ones on most "normal" cars, might go from 80% braking power straight to 100% lockup with no modulation in between. If the calipers, pads, lines, etc, are flexing and absorbing pedal energy, then it will require more input to stop the car.
A good example would be breaking loose a stubborn bolt with a small crappy brand ratchet and a larger Snap-On one. With the small one it takes a lot of effort to break loose the bolt. Since it's a small handle, one must push really hard and we know that it's difficult to modulate when doing so. The bolt will go from not budging at all to all of a sudden breaking loose. That would be ones tires barely slowing down the car to all of a sudden just skidding. Now throw in the fact that the little ratchet was flexing and the socket was twisting, and one can hardly control at what point the bolt goes from stuck to totally breaking loose.
Then grab the larger high quality Snap-On ratchet. It won't flex (noticeably) and the socket fits perfect and doesn't twist. When one goes to loosen the stubborn bolt, it's easy to apply gradual effort without Herculean strength and slowly break loose the bolt and get it turning. It's easy to modulate how fast the bolt turns.
So many people overlook this stuff when dealing with brake systems. Many brake systems will begin to stick at high braking power and then go straight to locking up with nothing in between. This is the big difference between companies making garbage brake systems just because they can CNC some metal, and the leaders whose products are seen on race vehicles that teams are willing to pay a premium for.

 

Smaller brakes require more pressure to the piston caliper to squeeze the disc rotor to stop specially at high speed,
therefor it produce more heat. Bigger brakes usually have more pistons working together so they don't need the extra help/pressure to stop. Bigger disc/rotors have more materials that can absorb the heat and have more cooling fins or vents to help dissapates the heat.

 

Technically true, but I don't think it is very important. The heat in compressing the fluid should be very very minor compared to the conversion of forward motion to heat (that's what brakes do). This amount of heat/energy does not change. If you are slowing a car from 60 to zero in five seconds you generate X amount of heat/energy no matter how you get there. Where that heat/energy goes, how it is generated etc., can vary, but conservation of energy says that it will be the same if you use six piston Brembos or a parachute.

 

Not true. The amount of heat is a function of the work done not the pressure. The work is a function of the mass of the car, rate of deceleration, duration of deceleration (speed). As TopElement notes, more pistons gives you the ability to precisely modulate the braking force so you can easily edge up to the limits of traction (stopping power).

This is true. Bigger brakes distribute the total heat load and give a larger area to dissipate the heat. That gives them superior performance on repetitive stops.



Locking up the brakes will reduce your stopping power. The coefficient of sliding friction is almost always lower than the coefficient of static friction. This basically means that you want the tires still turning. They can be very close to sliding (limit of traction) but you don't want to cross that line. That is why a very skilled driver can out stop anti lock brakes.

So theoretically, if you can lock the brakes you could bring them to the edge without locking. This would maximize the stopping power so you get equal stopping power from the current brakes as big brakes. The real issue is that smaller brakes don't have fine control as you approach the limits of traction so you tend to cross over the line and slide the tires, this gives you worse braking even if you modulate so you stop sliding.

Plus the heat loading issues already mentioned come into play with repetitive stops. If the brakes get hot enough you won't be able to apply enough pressure with a single piston to approach the traction limit, maximum braking. Think about when you drove the family car down a long downhill and there was significant brake fade from over heating. Multiple pistons allow you to apply more pressure to you don't feel as much fade. The big brakes dissipate heat better too.

 

Tyres tyres tyres!!!

 

The EVO stops like it hit a brick wall, but it has huge Brembos, and 235 width tires on all four corners.
(Compared to 205/225s on the 328. Due to a lot of Aluminum and CF, the EVO weighs about the same as the 328.)

But one thing I've found with the EVO is that it's difficult to keep those huge brakes warm in urban traffic. And they don't modulate all that well when cold.

The 328 doesn't stop as short, but it has much better brake "feel".

 

You basically have it right. I left out 2nd and 3rd order effects. For example I assumed that the suspension was rigid, not true, so the loading and effective friction on each tire didn't change. Theoretically compressing fluid causes it to heat and expanding causes cooling. BUT if you absorb heat when expanded the higher pressures of stopping with smaller pistons could result in a higher fluid temp. OK, enough esoteric speculation that is probably WAY beyond what is detectable.


Remember force = mass * velocity^2 so lighter cars have an advantage. It also explains why stopping distances go up in a non-linear fashion.
Friction is µ = f / N, where µ is the coefficient of friction, f is the amount of force that resists motion, and N is the normal force. Normal force is the force at which one surface is being pushed into another.

Combine everything and you get this --

Braking distance can be calculated using the equation d = V^2 / 2gµ

Where:
d = Braking Distance
g = Acceleration due to gravity (9.80 m/sec^2)
V = Initial vehicle speed (m/sec)
µ = Coefficient of friction between the tires and the roadway



Surfaces µ (static) µ (kinetic)
Steel on steel 0.74 0.57
Glass on glass 0.94 0.40
Ice on ice 0.10 0.03
Teflon on Teflon 0.04 0.04
Tire on concrete 1.00 0.80
Tire on wet road 0.60 0.40
Tire on snow 0.30 0.20


Hope this all helps

 

I think you meant force = mass * acc

or energy is proportional to mass * velocity^2

or energy = 1/2 * mass * velocity^2

but yes your point is still correct... mass of course matters!

Brakes slow the car by converting kinetic energy to heat energy. Since kinetic energy is proportional to velocity^2, that is why stopping distance is not linear.

 

I am not sure about the math behind it, someone else here can explain that part. But from personal experience on my race car (non Ferrari) I was locking up my brakes on a regular basis, put in larger rotors and went from 2 pot calipers to 4 pot calipers, larger to match the new disc, stopped locking brakes and improved the braking power/performance massively. Everything else remained at a constant, suspension, brake bias, track, tyres, tyre pressure. only change was disc's, pads and calipers. Definitely gains to be had with bigger brake rotors.

Now, the real question, do you *need* to improve your brake's performance?

 

What brand of rotors are you using?...and, what Porterfield pad part numbers?

 

Makes a lot of sense. Getting past having an initial massive poorly damped forward weight transfer will make a huge difference.

It used to transfer 80% of it's weight forward, winding the springs up. Then the springs rebounded and you locked the fronts as the weight came off. Getting that under control was a smart first step to better braking.

 

that's weird.

 

You think? Seemed to make sense to me. Tell the truth never really put much thought into it, had the brake set up gifted to me (part of another deal), fitted it and my lap times came down due to less lock up and being able to brake later.

 

I'm sure it has much more to with modulation ability and "feel" rather than actual "power." Clearly if you can lock up a wheel you have enough clamping force, you don't need more, you actually need less. There's a brake pedal and not a brake switch, and there's a reason for that.

As I mentioned before larger rotors and wheels should be heavier and have more rotational inertia and thus be harder to slow down. I wonder if this is actually an advantage. Over a slight bump when the wheel is slightly unloaded a lighter or smaller diameter wheel might have a chance to lock where a heavier or larger diameter wheel will not. And once that wheel locks and starts to skid it will likely stay that way when it is reloaded. Hmmm. Just a guess.

 

I would say you are bang on with that Brian, it definitely added more "feel" to the pedal.

 

Almost every stock car, as delivered from the manufacturer, can lock the brakes - and at any speed that the car can attain - at least once.

The main problem most of us experience is with Repeated quick stops. What happens is that the discs and pads become very hot with the first high speed stop. If you speed up the car quickly, before the discs have a chance to disipate the built up heat, they start at a higher temp as the next high speed stop is initiated. If this sequence is repeated a few more times, ALMOST EVERY PRODUCTION FERRARI will overheat the brakes. That is boil the brake fluid and get a very soft pedal with poor stopping ability or a very hard pedal, with overheated pads and the car just doesn't want to stop, no matter how hard you press on the pedal.

This is a frequent Tracking complaint with stock brakes, I have seen it repeatedly in each of the following forums: 308, 328,348, 355, and even the 360. If you look at the posts, the primary problem is that the discs are too small for the heat to be disipated under continuous very hard driving.

More heat resistant pads are a help. To better withstand the higher temperatures, fresh, high boiling temp fluid is also another often needed. Ducthing more air to the disc is a help as well.

Often a combination of all of these measures will give satisfactory results, untill you can go faster.

Bigger Stickier tires are always a help in slowing down and as you do so, you will try to dissipate more heat in a shorter amount of time.

Two less obvious points:
1) Brake performance is not linear with temperature. When you change from stock pads, particularly if you use different pads front and rear, you can have significantly different braking results with different temperatures - try to use the same front and rear pads.
2) At elevated temperatures and pressures, calipers flex, hoses swell and if you are enjoying differential heating/cooling front to rear, brake feel and controll are likely to be less than linear or predictable.
3) The best balance and human controllability is not likely to be found at the last gasp maximum effort pedal push, so:
It is to our advantage to reduce the effort to a mid range effort for better controllability. We can do this three ways, either through:

a) hydraulic advantage, bigger caliper pistons, or more of them, or a smaller master cylinder
b) or with a longer lever arm, bigger discs, (this disregards the liklihood of smaller od tires).
c) or lastly with higher coefficient pads, (a flat coefficient of friction/temp curve would be very nice too).

I have no data to support this, but my intuition tells me that a large diameter disc, (not necessarily massivly heavy) will provide less effort and more controllability.

More later, (before my browser times me out and i loose this),
hth,
chris

 

Non ABS cars need to rely on properly engineered F/R brake torque. They do not have the luxury of Electronic Brake Distribution ABS, which allows the driver to mash the brake pedal and the modern marvel of electronics distributes the braking effort to just keep the tires rolling and directional controll is maintained.

If i am understanding things correctly, the 355 uses the same size pistons front and rear and so does the 360, (although a bit larger). This near equality of front to rear torque would result in the rears locking very, very early if it were not for ABS and electronics.

We lesser mortals, (non abs), must rely on developing braking skill to hold just shy of locking, or more realistically, sneaking up on lock, quickly, feeling incipient lock and easing up a bit....

So, Feel becomes very important.
So, lower profile, stickier tires, stiffer suspension, stainless lines, better fluid, higher coefficient, more heat resistant pads,smooth roads and practice all help.

Specifically,

Girodiscs 308 brake kit is better balanced than the Brembo Big Brake kit. I have no experience with the european big brake kits.

I relied heavily on Martin at Girodisc to try to build a very high capacity brake set up, using brembo or Girodisc parts. I found a F-50 set of calipers and 14 inch discs on ebay and with a lot of help from Martin fitted them to the front. With a bit more effort, i adapted the 360 challenge rear brakes, including the parking brake to the rear of the 308. Even with carefull balance of the hydraulics, we still had to use an adjustable proportioning valve in place of the stock unit. The master cylinder provided a significant challenge, (read $$$ machining) but it all worked out awsomely - super linearity of braking, (controllability) with Zero fade on the track.

For sure, these discs are a bit heavy and performance would be improved across the board with lighter discs- but these were ferrari bits and readily available.

6 used calipers, 2 used, (but refurbished discs) all new adaptors, hats, pads, mc and used prop valve, with a bit of cnc machining ran about $7k

Hope this is some help,
chris
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Great analysis and comments. Very educational for me. Thanks.