Brake Conversion Questions - Page 4

curly2k3 · #46 10-15-2006, 07:26 AM

i know my driving style on the course isnt the ideal one, however my friend that is leading points with his WRX agreed with me on all of my complaints about the brake system, so i dont think that a person thats been to 2 driving schools and leads points is wrong either. dont get me wrong, i think they are great for daily driving and street use, and on the track the only times i have any problems is in places where is on and off alot in a short period of time followed by a fast stop for the finish.

benebob · #47 10-15-2006, 09:59 AM

Quote:

Originally Posted by curly2k3

i know my driving style on the course isnt the ideal one, however my friend that is leading points with his WRX agreed with me on all of my complaints about the brake system, so i dont think that a person thats been to 2 driving schools and leads points is wrong either. dont get me wrong, i think they are great for daily driving and street use, and on the track the only times i have any problems is in places where is on and off alot in a short period of time followed by a fast stop for the finish.

Your freind drives a new car with new brakes, you don't. Go drive an 92 Subaru Loyale and you'll complain about the brakes impensly and that vehicle was made the same year as yours. Change your fluid and get quality pads. You won't have a problem provided you drive properly. There is no need for a fast stop at the finish. You've already passed the gate.

curly2k3 · #48 10-15-2006, 10:05 AM

i beg to differ, not about the car stuff but the course, you come through the cicane and have to come to damn near a dead stop before a 90* turn out of the course always, its basiacally a coned shoot that you have to come to almost a stop in before you turn out. but yeah, i think i will buy some wilwood fluid and some different pads then go from there

shotgunslade · #49 10-15-2006, 10:32 AM

I guess I don't understand. Do we have 2 alternate realities here. I've never experienced significant fade, except for some minor fluid fade. I would have to guess that my 20 to 30 minute sessions on a road course would be more stressful on the brakes than a 30 second autocross run. I know that one of the functions of slotting or even drilling the rotors is to relieve gas from the pads which might otherwise decrease pad rotor contact. I'm wondering if that is the cause of your fade.

benebob · #50 10-15-2006, 02:09 PM

Quote:

Originally Posted by shotgunslade

I guess I don't understand. Do we have 2 alternate realities here. I've never experienced significant fade, except for some minor fluid fade. I would have to guess that my 20 to 30 minute sessions on a road course would be more stressful on the brakes than a 30 second autocross run. I know that one of the functions of slotting or even drilling the rotors is to relieve gas from the pads which might otherwise decrease pad rotor contact. I'm wondering if that is the cause of your fade.

Yeah, me thinks there is something majorly wrong with his system. Dave and I can run in the same heat 5 minutes apart and do nothing to our braking ability.

UberRoo · #51 10-15-2006, 02:17 PM

Quote:

Originally Posted by benebob

... Or you could simply learn to drive right...

Professional drivers (i.e., competent drivers) suffer from inadequate brakes just the same as the rest of us. You know those air ducts around the disks on NASCAR and Formula-1 cars? They're not for cosmetic purposes. I'm fairly certain those guys know what they're doing.

"Driving right" uses a LOT of braking. The idea is to spend as little time braking as possible, but braking as hard as possible during those times. You spend more time traveling at a higher rate of speed. The whole concept of late-braking in a nutshell.

Some tracks have nothing but high-speed corners and require relatively little braking while the rest of the time is throttle-open driving with plenty of cooling time. Other tracks are little more than a series of straightaways and hard stops followed by an abrupt corner. The correct way to brake on a track like that will kill your brakes.

benebob · #52 10-15-2006, 05:28 PM

Quote:

Originally Posted by UberRoo

Professional drivers (i.e., competent drivers) suffer from inadequate brakes just the same as the rest of us. You know those air ducts around the disks on NASCAR and Formula-1 cars? They're not for cosmetic purposes. I'm fairly certain those guys know what they're doing.

"Driving right" uses a LOT of braking. The idea is to spend as little time braking as possible, but braking as hard as possible during those times. You spend more time traveling at a higher rate of speed. The whole concept of late-braking in a nutshell.

Some tracks have nothing but high-speed corners and require relatively little braking while the rest of the time is throttle-open driving with plenty of cooling time. Other tracks are little more than a series of straightaways and hard stops followed by an abrupt corner. The correct way to brake on a track like that will kill your brakes.

Obviously you're smarter than anybody else here that doesn't have the issues you complain of. Sorry to insult such an excellent drive. Just don't kill anybody with your excellence.

UberRoo · #53 10-15-2006, 09:23 PM

Quote:

Originally Posted by benebob

Obviously you're smarter than anybody else here that doesn't have the issues you complain of. Sorry to insult such an excellent drive. Just don't kill anybody with your excellence.

I haven't heard any brilliant solutions. What do you propose I do about brake fade? Not use the brakes?

NeedForSpeed · #54 10-16-2006, 02:07 AM

As often as you change brake fluid, you must have a favorite. What is your favorite fluid and who makes your favorite svx brake pads.

Thanks again, great thread.

Quote:

Originally Posted by benebob

Your freind drives a new car with new brakes, you don't. Go drive an 92 Subaru Loyale and you'll complain about the brakes impensly and that vehicle was made the same year as yours. Change your fluid and get quality pads. You won't have a problem provided you drive properly. There is no need for a fast stop at the finish. You've already passed the gate.

ItsPeteReally · #55 10-16-2006, 06:46 AM

It might be interesting to see what braking performance is actually required required to stop a standard SVX from various speeds.

These are only ‘rough and ready’ calculations, someone else can refine them further, if they feel the need, but I feel that they are fairly representative.

Lets assume that the standard car weighs around 1590 kilograms and that the total weight of all four brake disks is 20 kilograms, and that the specific heat of iron is 449 Joules per kilogram per degree centigrade.

We will brake the car from 3 different speeds at 0.8g deceleration.

Firstly a 60 mph stop. (26.6 m/s).

Code:

Kinetic energy dissipated (½mv²) = 565333 joules
Time to stop = (37.5/9.8)/0.8= 4.78 seconds
Average brake power dissipation = 166  kW.
Average brake disc temperature rise  = 63° C.

This is a little over simplified; in real life the front brakes would do more of the work, the rears less.

Code:

Assuming a 70:30 braking bias.
Front brake temperature rise = 88 ° C
Rear brake temperature rise = 38° C

Now a 100 mph stop. (44.4 m/s).

Code:

Kinetic energy dissipated (½mv²) = 1570370 joules
Time to stop = (44.4/9.8)/0.8= 5.66 seconds
Average brake power dissipation = 277 kW.
Average brake disc temperature rise  = 175° C.

Assuming a 70:30 braking bias.
Front brake temperature rise = 245 ° C
Rear brake temperature rise = 105° C

Now a 150 mph stop. (66.7 m/s).

Code:

Kinetic energy dissipated (½mv²) = 3533333.333 joules
Time to stop = (66.7/9.8)/0.8= 8.5 seconds
Average brake power dissipation = 415.5 kW.
Average brake disc temperature rise  = 393° C.

Assuming a 70:30 braking bias.
Front brake temperature rise = 551 ° C  
Rear brake temperature rise = 236° C

It is interesting to note that, in the last case, the front discs will be visibly glowing red!

So what does this tell us?

We can be reasonably confident that Subaru designed the standard braking system to cope with at least one 150 mph stop. Stops from more reasonable speeds put considerably less energy into the braking system.

Repeated stops and the capacity of the braking system to recover from them is perhaps a more worrying feature. I can envisage no disc venting system being able to dissipate meaningful quantities of heat in short time periods. I suspect that many brake upgrades are more for show than for go (or should that be stop?).

So what upgrade would work? Well there really is only one that can make a significant difference, and that is to fit a larger and heavier disc. Its additional mass will mean less temperature rise, and its larger surface area will provide greater heat dissipation. There are downsides to this approach too, more unsprung weight and more expense being the most important ones.

If you think you have braking problems then it is probably due to a defect in the standard setup.

Finally, boiling brake fluid is not brake fade, it is catastrophic brake system failure.

benebob · #56 10-16-2006, 07:22 AM

Quote:

Originally Posted by NeedForSpeed

As often as you change brake fluid, you must have a favorite. What is your favorite fluid and who makes your favorite svx brake pads.

Thanks again, great thread.

Valvoline sythetic. Cheap and 7/8ths as good as race fluid for 1/4 the cost. Rear pads, anything you want as it really doesn't matter, fronts we have axis front pads on our racer but they're very messy. I don't drive my street SVX much anymore so usually just put on a decent set of ceramics.

benebob · #57 10-16-2006, 07:23 AM

Quote:

Originally Posted by UberRoo

I haven't heard any brilliant solutions. What do you propose I do about brake fade? Not use the brakes?

Then you obviously can't read. You're a waste of my time so enjoy being an idiot.

UberRoo · #58 10-16-2006, 05:08 PM

The feeling is mutual.

benebob · #59 10-16-2006, 05:51 PM

Quote:

Originally Posted by ItsPeteReally

Finally, boiling brake fluid is not brake fade, it is catastrophic brake system failure.

Techinically your right but keep in mind that most people tend to assume that they are experiencing fade when the fluid/water reaches that point and probably 99% of on road brake loss is boiling fluid/water. Since very few people actually change their fluid over the life of a vehicle its easier to lump it in there then explain it otherwise.

TomsSVX · #60 10-16-2006, 05:55 PM

to sum it up with personal feelings aside, the brakes on the SVX are adequate enough even for racing. Just set the system up best that works for you... If you still warp brakes or experience brake fade(not a tired leg) then go ahead and upgrade to something else. I have a feeling you will not find the thousands of dollars invested in bigger brakes worth it

A good piece of advice from a very knowledgable racer, quiet and smooth is almost always faster than loud and rough

Tom