I think they were lost in a server crash before I joined this site. The older posts often have images missing. PM FBB to get the pics. He may still have them to send you. BT
Goyal, Stoptech has some great looking brake stuff: http://stoptech.com/user/SearchResults.asp Try a search for Movit Brakes. They have some serious brake upgrades for the 355 & maybe the 348. Slight hijack here, I'm working on a 355? Brembo cliper upgrade for the 308. I believe the fronts are the ubiquitus Ferrari 355 front calipers with 40-36mm calipers and lug mount. Is this correct?? What size are the rear pistons?? When did Ferrari go to the Radial mount? The 360?? or were there some 355s with radial mont Brembos?? See the 308 M/C size thread for info on the parking brake issue. Does anyone know what size the 348, 355, 360 master cylinder bores are?? I don't know for sure but i suspect that the 308 is running an ATE 19mm, (3/4 inch) bore and a few guys are working on bigger caliper upgrades for the old slow 308s, me included. hth, MII, (mired in ignorance) ;-) chris
Personally, I dislike everything about StopTech and would never consider using their parts. IMO, it's best sticking to Brembo or AP Racing products when upgrading the brake system. fatbillybob: Would you happen to still have the pics that were posted? Really interested in seeing these custom parts.
nope sorry... Nobody has been able to answer my question. If braking a car is all about tire adhesion then the limit of your braking is always about 1 g on a streetcar without aero. Therefore, if you can threshold brake you small brakes and the ABS trigger that means the ABS is sencing tire slip vs velocity. If the small brakes work the ABS, please tell me what a big brake does besides add unsprung weight and adding maintenance costs in parts?
Better heat transfer so that brakes fade less over the course of a race, I'd wager. Bigger brake rotors have a larger surface area...greater surface area dissipates heat better. Cooling your brakes with air ducts or CO2 should duplicate most of what larger brakes give you, I'd think. You want brake rotors just large enough to be technically **able** to lock your brakes at any given speed (though obviously you don't want to actually lock them). Then you just want to keep them cool enough so that their stopping power doesn't fade. You can do that by increasing brake rotor surface area or by increasing the flow of heat away from the rotors (e.g. brake cooling). You could use a fan, air ducts, CO2, alloys that dissipate heat better, etc. And then at the current limit of our braking technology there is active braking. Army battle tanks are capable of spinning treads in reverse (e.g. on loose desert sand at high speed) to stop faster than mere passive braking, for instance. One day treads will make it onto dragsters (greater traction).
Even though small rotors may activate the ABS, it doesn't mean they will stop just as well. Larger rotors provide much better modulation, and will stop better even if ABS kicks in. It's like trying to loosen a bolt with small and large ratchets. The small one may break it loose, but it will take a lot of force, and it will suddenly jerk when the bolt comes loose. A large ratchet requires less force to turn the bolt, and it will be gradual and easy to modulate as it breaks free.
There's no law that says the coefficient of friction is limited to 1, eg - glue or sticky rubber. So presumably you can get more than 1 g if you can supply the braking power. I was also looking forward to seeing your pictures.
A rock climber who stops his own vertical fall has displayed 1G of braking power...a rock climber who stops his own and his helpless twin brother's vertical fall has displayed 2G's of braking power.
FBB, Some of us do not have abs, in fact some of us have a swept area/ton comperable with the good old camaro/firebird. The above "wrench" alanogy applies. in the two cases where i have stepped up the size of the brakes, i have noticed that it was easier to get right to the edge in threshold braking, To be able to just ease off a bit and unlock that flaming tire. When Eric, of Girodisc fame, mentiones that the 355 had less than adequate rotors for track use, i was wondering where that left us old 308 guys. With the better leverage of a bigger disc and more piston area, i can use less pedal pressure, maybe a bit less compliance in all of the pieces. for sure lower temperatures - easier on all of the pads, seals and discs. my .01 cent, chris
IMO "No Doubt" has the best explaination of what I believe but have no technical expertise to accept as true. Basically, braking is all about heat transfer/conversion and how you do it is up to you, i.e. cooling and or bigger brakes with a higher heat capacity. I am not sure I buy the "modulation" issue. To me big brakes are like big horsepower. If you have a 700hp 348 racecar with slicks you get an undriveable car. All you do is spin tires. If you have infinately giant brakes you touch them and you get lock-up. So where exactly is the "modulation" unless the "modulation" is specific to the average human range of foot pressure. Here is my real world experience with a 348 racecar. Maybe I'm just too slow a driver but I still run stock pads stock rotors full cage slicks and giant 3" brake ducts through foglight ducts. I never boil fluid and my pads and rotors last a long time. My slicks last about 3 weekends which about right for the average budget racer. I threshold brake with ABS going 90% of the time. I wonder if big brakes will do me any good. Yet I repeatedly hear how the 348 brakes suck even more than the 355 and the 355 giant brembos are the only way to go. Well I have never been with another 348 or 355 in a wheel to wheel race so my datapoint is the only one I have. So guys there is my experiance your mileage may vary. I am still very interested in big brakes just a bit skeptical.
Right. The disc brake is a lot like the brakes on a bicycle. Bicycle brakes have a caliper, which squeezes the brake pads against the wheel. In a disc brake, the brake pads squeeze the rotor instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down. Check out the picture below. Keep in mind that your foot on the brake pedal is what presses the piston to create the squeeze that applies friction... ...for better brake modulation, you want that piston to return fast (faster is better), as that will release the squeeze. Improve that piston's return speed and you will improve your brake modulation. Improve heat dissipation and you will reduce brake fade. Bigger brakes that have a slow piston return speed aren't going to help anyone (especially racers), ditto for brakes that don't dissipate heat. Image Unavailable, Please Login
The brakes must dissipate the kinetic energy of the car, given by KE=(1/2 m v^2). FBB, From reading your posts I would guess the 'm' of your car is quite a bit lower than our street 348's, so less energy to absorb. That contributes to the good performance of your brakes. The expression above doesn't account for all the kinetic energy. There's also the kinetic energy due to the angular velocity of the wheels, tires and brake rotors themselves. This is given by 1/2 I w^2, where I is the moment of inertia of the rolling mass, and w is the angular velocity. Since you are running lighter wheels and much lighter tires the 'I' will be smaller, again helping your braking performance. Note that the velocity terms are squared in the kinetic energy expressions. So doubling the speed quadruples the energy the brakes must dissipate. Really fast cars have a lot more demands on the brakes, (no implication to your track speeds here FBB ;-)
Harmony, I like your explaination in terms I understand. You guys are right. I am much lighter on all counts. In fact lighter than "challenge" legal. So perhaps there in lie the difference. I'll have to get faster and perhaps the stock brake will need improvement. What do you say about weight transfer in heavy braking. I also do not have stock springs and very little nose dive on threshold braking. I'll have even less when my really heavy springs go in. While the ultimate weight of the car is the same the differences in weight transfer due to springs make a felt difference in handling under braking. What happens to heat generation in the four brakes? Does the lack of nose dive put more braking pressure to the rear and thus more heat? Is there a calculatable optimium amount of dive required for minimum stoping distance?
FBB, Ill take a stab at your question, with one big caveat. I have an admittedly fragile understanding of this stuff. Dissent and counter arguments are welcomed! Its counterintuitive but weight transfer isnt significantly affected by dive under braking since the cars angle is changing by just a few degrees, at least with our cars. If we were discussing an SUV with a roof rack itd be another story. What will determine weight transfer is the height of the cars center of gravity (CG). A high center will cause more weight transfer to the front wheels. Interestingly if the CG was at ground level there would be no weight transfer. So a car with a given CG height will have virtually the same weight transfer under braking whether it has soft or firm springs .once the car is settled. The softer springs take a little time to compress, and its not until the compression is finished that the weight transfer is complete. With a stiffly sprung car the weight transfer happens quickly. The advantage of the stiffer springs is that the car doesnt become as unsettled. When a car pitches under braking the camber and toe may be affected, changing (usually for the worse) the turn in behavior. With regard to your question, the optimum braking is achieved with roughly equal weight distribution on all four wheels. This is because the coefficient of friction goes down with increased tire load. This statement may not be helpful but it essentially means that the gain in front braking potential after weight transfer is smaller than the loss in rear braking potential. Having equal wheel loadings gives the maximum net stopping power. Unfortunately the only way you can control how much weight transfer you get is by moving the CG, and this is pretty well fixed with the design of the car. You could lower your car or relocate the battery but I suspect youve already played that card. Fortunately mid and rear engine cars are at an advantage here because they are starting out with more weight on the rear wheels. After weight transfer they are closer to an equal weight distribution than a front drive car. If you cant change the weight transfer about the best you can do is to make sure both ends of the car are operating at threshold braking by adjusting the brake bias. With our cars the ABS is presumably doing this for us.
