mark kibort

not true. all braking, as long as the system has the capability, will stop the car the same. grab that tesla and put on GTS brakes and it will stop the same, guaranteed. not repeatatly, but for one shot, it will. again, the new materials and larger sizes only help with heat management and control modulation. they are better sure, but not at a one time stop.

Yep, agreed!!!

you are dead wrong.
there were differences between the 04s and 08 GT3 braking systems. ABS included, plus, different tires.
F1 increase stopping performance was due to tires and greater downforce. the tire is what allows the rate of change of kinetic energy@!@!
sorry. tire and driver or ABS is the limiting factor, not the braking system. why do think the lap times dont improve with the GT3 cup with CF brakes vs non CF brakes. what that buys you is better feel, modulation and heat managment. my race car will not stop faster with CF brakes on the first lap. sorry,im at the limit of the tires and I know it , because its clear when i use or choose to not use the abs system. with CF brakes or larger rotors, you get better feel, easier to threashold brake, skill wise, and heat managmment.

I never boil fluid, havent in many years, but i can push the brakes so hard that there is greatly reduced stopping power, certainly track dependant. brakes fade not from fluid boiling, but from tempurature of the pads and rotor. CF, larger rotors help with this.

Ive seen lots of glowing rotors at the track, but as I said, its usually after all components are heat soaked. never on the first turn of the first lap, even if that is the highest speed, braking area of the track. thats just the way it is.
brakes have a certainly optimal temp range . outside of it, they dont work well.

your examples are a little crazy , as they are manufacture specs and tire compounds are critical, MOST important for those tests, as would be the ABS system if used.

tv

Must be gearing then,


No matter where it happens or how many times it happens stopping is turning kinetic energy into thermal, mechanical into heat. PERIOD. If you don't agree with that then you are not worth talking to.


With your thinking we are to believe that the tires are glowing orange on 1 stop. And that my 928 would perform no different if I put on huge ceramic discs with the same tires. And if we put circa 1935 drum brakes on all 4 corners on those 458's at Monza they will still stop the same on the first lap.

Pure Stupidity. You have F1 example ***-backwards also.

Randy V

Any suggestions on best price/source for front GTS rotors?

mark kibort

your not thinking. ( and i agree with your rate of stopping vs heat generation totally and entirely)

BUT, you are forgeting one thing! the first stop , takes all that energy and turns it into heating all the components. brakes, calipers, rotors, wheels , lug nuts, and even the air in the tires. the second stop, the brakes can be near 600 degrees to start, there is no place for the heat to go now, than convection and then you have fade. this is where the CF , brake cooling, larger rotors, etc comes in to play. you are totally ignoring this!!


Think about this. would there be a difference if i could magically replace my entire braking system with new cool parts after every turn??? you betcha!!!!
here is an analogy.

If you have 100000000hp, and you put it in a 928 on street tires, how much can be put down to the pavement. anyone that has a 928, knows that only a certain amount of power can be used during 1st gear acceleration. this is due to grip of the tires. (optimal slip angle and coefficient of adhesion determine this). in other words, probably in most cases , all 928s with 300 to 500+ will accelerate the same for the begining of 1st gear because of grip.

same thing with brakes. when im threashold braking from 130mph down to 40. i dont need better brakes, i need more grip!! the brakes have a BHP as well, and that is well in excess of that of what the tires can transfer.

I will easily race anyone in two versions of my car, one with carbon fiber vs my stock brakes for a lap. or during a lap where the straight isnt so long that fade becomes an issue. did you ever see me tailing 4x lemans winner derrek bell at laguna. going into a corner, me with stock S4 brakes and pagid orange pads, i was able to get close enough under braking where the anouncer commented on "look at the braking capacity of the 928!!" did you see the 14" rotors, 2 piece, best of the best of everything on the audy S4 turbo with 550hp??? why did i have no problem keeping up with braking?? we all had the same tires!!! think about it!! it makes PEFECT sense. if you dont have grip,and the brakes have the power capacity to slow the car, it doesnt matter what the braking system is, they all will be able to apply this power to slowing down.

F1, is a different animal as well. that is where grip is greater than capacity of the prior brakes. downforce was part of that equation as well. even indy cars have much more downforce now than before, and stop quicker because of that.

dont go extreme on me. we are not talking drum brakes or too small of brakes, although there are some old systemt that can do the job for a lap or two before they overheat and are done.

The S4 brakes with 13 or 14 " rotors can do the job of most any brake set up. like i said, ive competed against porsches, and other exotics with CF brakes and it didnt seem to be an advantage at all.

your published stats are skewed by tire and driver as well as conditions. certainly tires

get your facts of kinetic energy being turned into heat energy straight. all systems only have to have the ability to deal with the heat based on the rate of change of kinetic energy (power). if they cant , then they wont. its as simple as that. if they can, and one deals with it better (pad coefficient of friction at temps, vs pad pressure), then both can do the same job, but one might not be able to do it repeatably.

WallyP

F1 braking has no relationship with the "real world" in several aspects...
- F1 rules require 15" wheels. This is purely to limit brake size, which leads to really, really exotic carbon/carbon brake systems that are changed really, really often.
- F1 tires are pretty exotic, with very short life traded for max grip.
- F1 cars have huge downforce and very low inertia. Lifting off the throttle at speed in an F1 car results in over 1G slow-down without touching the brakes, just from aero and engine drag.

No point in bringing F1 into any brake discussion...

Jon B.

Randy, I would think that Roger would probably be one of the best to contact. Pretty sure he offers the cross drilled TT versions, and the solids .

ROG100

Stock GTS front rotors are $270 each
Cast hole GTS front rotors are $175 each

mark kibort

As a data point on brakes not being as critical as one might think for overall stopping distance. If your car can engage ABS fully, it means that you are at the limit of the tire, not the braking system. (there are some sutblties that can effect this , but true for this discussion). This is because ABS engages when the brakes try and stop the car faster than the tires allow, and the system releases brake caliper pressure. racing brakes do this very fast, street cars do it slower and you will be worse off in stopping distance if you rely totally on ABS to stop. (to me, it feels like im on ice if i fulley engage ABS, and stopping distance proves this.)

so if you want to stop faster, you better get a tire or a suspension system that allows you do do this again, the fancy brake systems are really about pedal feel, moduulation control (i.e. less pedal pressure for a given braking force), and heat management

when i went for a 25% bigger rotor, more mass, etc, there were no differences on stopping power , only fade resistance. remember, i ran the S brakes in World Challenge with 11" rotors and race pads. i had to be so careful when intraffic to not cook the brakes. they worked, but faded after a lap or so. There are plenty of WC guys, when going from the single piston calipers and then going to the big ST40 stoptechs that saw no improvement in lap time, but a much greater feel and ability to modulate after the upgrade.

mark kibort

I think you can still get zimmerman GTS rotors for under $200 each. I forgot where though.

However, the main point i can see here is that O-behave has a way to get an adapter to use Cayenne rotors. if so, thats a Zimmerman 100 dollar rotor that is 330mm (13")

Lets see the adapter a lttle closer!!!!!

Mark

mark kibort

yep!

ALSO, dont compare a 997 GT3 (2007) as you did "TV", with a (2004) 996 GT3. you saw the braking distances , from road and track, differ by about 15ft (ii think it was 97 feet vs 113ft). Hmmmmm....... really, not only were the tires different, the tire sizes were different as well as the driver, conditions, etc But the main fact, the cars are not allike. their balance is different, and so are their suspension systems. the 997 has a computerize suspension control , as well as the dimensions of the car being different too! comparing a full generation change of the highest level of technology with porsche is like talking to yourself. If you think that is worth bringing up to validate your point , which it seems like it was, in your words, "the discssion ends there".


the picture below was at the time attack off the main front straight. notice the flame off throttle and the gowing rotors up front. this happens after a couple of laps , not in the initial lap.

tv

Some very interesting stuff, science fact, about what is happening;



The amount of traction which can be obtained for an auto tire is determined by the coefficient of static friction between the tire and the road. Static friction is the amount of friction between two surfaces when they are not slipping, like a tire and the road under normal circumstances. If the wheel is locked and sliding, the force of friction is determined by the coefficient of kinetic friction and is usually significantly less. Anytime you lock brakes it takes longer to stop. Assuming that a wheel is rolling without slipping, the surface friction does no work against the motion of the wheel and no energy is lost at that point.


Now, how does it apply to ABS and car tires? Keep in mind that as a car tire rolls, there is a patch of rubber that is actually stationary and static friction is in effect. We want to maintain this static friction for as long as possible (for grip, traction, and control). If the rubber starts to slide across the asphalt (when the wheel locks up), we lose the benefit of the static friction force and the stopping force exerted by the tires on the car. ABS reduces the brake pressure allowing the wheel to turn thereby continuing to slow it at the maximum possible rate

Factors Affecting The Coefficient of Friction;
The main factors affecting the friction coefficient are road surface texture and condition and tire composition.Condition of the roadway refers to the presence of snow, ice, sand and other lubricants. The presence of any of these will make the surface more slippery, which reduces the coefficient of friction.

Texture of the road surface refers to the natural roughness of the asphalt. A relatively new asphalt roadway has a "sharper" surface with a high coefficient of friction. An older well-travelled asphalt roadway has a smoother, slicker surface with a lower coefficient of friction.

Tire composition and wear surprisingly plays a lesser role in determining the coefficient. It appears as though road surface texture and condition are the more important factors.
Jones and Childers report coefficients of friction of about 0.7 for dry roads and 0.4 for wet roads. The tread design represents an "all weather" compromise. If you were an Indianapolis race driver, you would use "slick" racing tires with no tread. On dry surfaces you might get as high as 0.9 as a coefficient of friction, but driving them on wet roads would be dangerous since the wet road coefficient might be as low as 0.1 .
Rubber Dry Asphalt 0.9 (0.5 - 0.8)1)
Rubber Wet Asphalt 0.25 - 0.751)
Rubber Dry Concrete 0.6 - 0.851)
Rubber Wet Concrete 0.45 - 0.751)



Tire shape;

People who say wider tires make more grip because ;''there is more rubber on the road' are wrong. They are both wrong that it makes mroe grip and that there is more rubber on the road.

When you make a tire wider, you alter the contact patch to be wider , but it reduces in length. So depending on sidewall stiffness, a wider tire can actually give less rubber on the road.

Wider, low sidewall tires will cool better than narrow tall tires.Back to contact patch, you can safely assume that contact patch stays roughly the same area with wide or narrow tires (as long as the load stsys the same).A wide tire will generate more lateral force per slip angle making cornering better. F1 cars DO NOT have wide tires for linear acceleration.As we know a wider contact patch gives better cornering performance, a narrow but long contact patch is what you want for linear acceleration. The F1 patch will be wider and shorter for good cornering, the drag patch will be longer and narrower (relatively) for good linear acceleration.Wider contact patch sacrifices linear traction for lateral, narrow tyres sacrifices lateral for longditudinal traction. And the most important thing about tyres is not contact patch area but that they are correct working temperature.

A wider tyre does not give more grip, but it allows you to use softer rubber without reducing the lifespan of the tyre. It's the softer rubber that gives you more grip.
the amount of frictional force is proportional to the surface area of contact, but it is also proportional to the pressure with which the two surfaces are "pressed" together.

If you increase the surface area however, you will by definition decrease the pressure since pressure is "weight divided by surface area." So a change in surface area will cause two counterbalancing effects that leave, as you said, only the weight of the object to be considered.

Back to the real world: as you said, larger tires are used in order that softer material can be utilized. The greatest force required from the tires occurs during cornering. If a certain force were required to make a turn at high speeds with thin tires, the material itself could fail (similar to the fact that a rubber band will snap). You can see that this happens in racing when you get a close look at the old tires at they are replaced: small chunks are often ripped out.

This failure is not a failure of the frictional force; rather, it is a "stress" related failure of the material. Wider tires will reduce the stress per unit area of each tire.






The bottom line is this-- BRAKES STOP CARS, not tires. Some tires are better than others and allow the brakes to do a better job. Getting tires too hot will reduce static friction, leading to slip. More efficient brakes, ones that dissipate heat faster, will stop any car better than less efficient brakes. Wider tires are better for cornering, less efficient for stopping and going.







From F1;

In physical terms we can state that energy is the capacity of a physical system to do work. When a car comes down a straight line at 300 km/h or more, it possesses lots of kinetic (movement) energy. Due to the fact that energy does not get lost, but can instead only be converted one form into another, the only way to slow down the car is to convert the kinetic energy into another form. Brakes as we know them both in race cars and road cars convert this movement energy to heat.

Formula One cars must sometimes decelerate in a matter of seconds from 350 km/h to about 70 km/h. During such heavy braking, the temperature of the brake rotor and pads can warm up from 400°C to more than 1000°C.

At 100 km/h, these values are just as mind-blowing 1.4 seconds and 17 meters! Under these heavy braking periods, a driver is subjected to a horizontal deceleration of close to 5.4G.

the disk/caliper tandem operating temperature increases by 100°C per tenth of a second for the first half-second of braking

17prospective buyer

Wow... sometimes i feel way too dumb to be a part of this forum.

SubieSeven

Click on over to Ed's 'Product' page for a few pictures of the adapter kit.

Jon B.

Woo! Ordering those here shortly!

mark kibort

so wrong on so many fronts, i dont know where to start.

first of all, start doing some research on stopping and cornering and the racing tire. slip angle, and percentage are both distance cousins and talk about optimal rubber distortion to maximize cornering and acceleration or deceleration. absolutely , wider tires can stop faster, just as they can accelerate faster . (ask any drag racer this) the occilating slip% of a dragster is just like ABS on decel.

again, brake size and cooling capacity have only to do with making brakes work at tempurature. intil they are heat soaked and beyond their limit, they all pretty much work the same (all racing brakes of certain size range, not old drum, or RX7 hockey puck brake pads. (or OB 928s )

ABS works by keeping the tires just at the limit of slip % to optimize stoping power of the brake system. without the tires, you have no braking. again, think racing slicks in the rain. you dont need a lot of force to equal the capability of the TIRE to slow the car down. the tire determins the stopping , no the braking system, though very important. (just as an engine is important to acceleration, but limited by the tires as well. you get wheel spin,you lose acceleration. just the right amount of slip, and you maximize the hp applied the road. this is limited and progressive up until you hit power and it doesnt exceed the grip or slip %.

again, big brakes, and then bigger brakes ONLY effect how the car will stop after a few laps, not one lap.

again, your comparison of the porsches with different brakes from 2004 to 2007 is a good one!! this proves you are NOT lookinig at the real factors of why the cars stop at differnet distances from 60mph. again, it has to do with setup, weight distribution, suspension, track width, roll centers and height, which determine the weight transfer which is result of those factors. if they change in the cars dimensions, the braking effectiveness changes. i.e. 997 vs 996 GT3s are different in areas of this. tire size, quality, drive, conditions, weight distribution, ride heigh and roll centers, as welll as several other factors that will change stopping distance having nothing to do with rotor size or pad quality. (assuming both are racing pads) 60 to 0mph is a mild test of braking. well within the max capability of any modern braking system, after a few turns at laguna, the differences will be seen , and thats the point of this.

street cars dont push brakes , racing does! (and if your street set up is not up to your task, put on some racing brake pads and that should solve the issue)

remember that race i reported back from?? one of the evo lancers was cooking and boiling fluid??? he had brembo big reds, 13 " rotors. basically more than i had ....... his lap times were 4 seconds slower......... i had no issues....... same tires., same pagid orange race pads....same weight of car, same hp...... same day..... same track.......... hmmmmmmmm

I dont know where you got the brake information, but it sounds very overly simplified.


BTW, there again, is no argument that the brakes job is to turn kinetic energy into heat. thats a given. BUT, its based on the cars ability to be connected to the road. the first article glazed over that. (the tires make the brakes more efficient ) its ALL tires, and the more sticky the tires ,the greater the deceleration rate. (based on the TIRE) not the braking system in most cases. again, on a single stop, you can keep the temps of the pads in the effective range and use pedal pressure to equal any stopping distance of better , bigger brakes . stop more often, longer , from a faster speed, and or start from a heat soaked system and all bets are off for the smaller , less powerful system to do the job. the pads get too hot, they cant develop the coefficient of friction and they subsequentialy cant slower the car at the rate they could on LAP one! this is why you get bigger brakes, not for 60-0 mph performance.

Mk