calculating brake force???

[ks71z28]

I have experamented with several systems on 2nd gen Camaros

1- 12" rotor and 2.75 single piston Wilwood caliper, 1" master

2- 12.8" rotor. 1.69, 1.69" 2 piston PBR caliper. .87" Master

3- 12.9" rotor. 1.62, 1.12, 1.12" 6 piston Wilwood. .87" master

4- 12.9" rotor. 1.75, 1.75" wilwood 4 piston, .87 master

By my calculations, system 4 is the strongest brake torque, 2 is second, 1 is third, and 3 is the worst.

#3 is Wilwoods 6 piston kit for the second gen, 1st gen, and corvette. So why would it be an "upgrade" I am trying to work out some details in theory before bitting the bullet.

My concerns

4 piston with 2.75 bore, has more clamping force than a 6 piston with 1.62, 1.12, 1.12 bores- why 6 pistons???

2 piston floating caliper has same clamping force as 4 piston, and more than 6 piston fixed caliper. Is a fixed caliper going to somehow create more clamping force in its design??

Sorry if this seems like babble, but I am not buying into some of these kits out there that are "Bike Brake" set ups that mathmatically any better than a stock set up. the calculators I used measure caliper force and torque at the wheel.

I would appreciate some input. I went from set up #1 with power brakes, to set up #2 with manual brakes, and now couldn't lock the brakes with both legs, and now considering set ups #3 and #4.

thanks

[chicane67]

My concerns

4 piston with 2.75 bore, has more clamping force than a 6 piston with 1.62, 1.12, 1.12 bores- why 6 pistons???

2 piston floating caliper has same clamping force as 4 piston, and more than 6 piston fixed caliper. Is a fixed caliper going to somehow create more clamping force in its design??

Sorry if this seems like babble, but I am not buying into some of these kits out there that are "Bike Brake" set ups that mathmatically any better than a stock set up. the calculators I used measure caliper force and torque at the wheel.

I would appreciate some input. I went from set up #1 with power brakes, to set up #2 with manual brakes, and now couldn't lock the brakes with both legs, and now considering set ups #3 and #4.

thanks

1. 4 Pistons... but less pad surface area. Pad surface area has a lot more to do with available brake torque at the rotor. It will require less pressure to produce the same friction ratio.

2. The 2 piston unit probably has much less caliper distortion and flex... so its roughly the same as the 4 and more than the 6. Between fixed, floating and radial fixed... there is very little difference mechanically.

3. You are too hung up on caliper force and are splitting hairs. That... and your talking about Wilwood... don't expect miracles.

4. You couldn't lock up the wheels on that specific configuration because the master was too larger for the application. Try a 15/16 or more like 7/8 for a manual application.

[ks71z28]

When I talk to someone at Wilwood, and ask why someone would replace the calipers with their 6 piston calipers, whcih have the same piston area, and slightly less pad area, they reply, "well alot of guys are using them, and like them better" I really would like some hard facts before I spend the money.

[RSX302]

Here's something a little fun to play with...

http://www.jakelatham.com/radical/info/brake_calculators.shtml

[RSX302]

My concerns

4 piston with 2.75 bore, has more clamping force than a 6 piston with 1.62, 1.12, 1.12 bores- why 6 pistons???


thanks

Per Willwood Pad taper

I was looking at going to the 4 piston 2.75" because I was so upset with the SL6's not stopping with the 1", 15/16" MC. I got the 7/8 MC as Willwood suggested but decided to go with a 5/8"mc after doing some calculations. This with the BP10's work perfect on the street. Just what I was looking for!

[ks71z28]

Per Willwood Pad taper

I was looking at going to the 4 piston 2.75" because I was so upset with the SL6's not stopping with the 1", 15/16" MC. I got the 7/8 MC as Willwood suggested but decided to go with a 5/8"mc after doing some calculations. This with the BP10's work perfect on the street. Just what I was looking for!
with a 5/8" master, isn't the pedal travel excessive???

[ks71z28]

Ron that is nearly the same calculator I used. The small bore of the SL6 drops the wheel torque by 20% over the stock rotor and caliper! I am amazed at some of these systems. My GT-2 race car uses 4 piston 1.75 bore calipers and 12" rotors, and it weights 2000 lbs! I can't imagine using smaller calipers on a car that is 3400 lbs.

[RSX302]

with a 5/8" master, isn't the pedal travel excessive???

With the SL6's not at all. If it were more piston area, yes...but then I wouldn't have needed the 5/8mc. And of course, make sure you use the smaller 3/16" tubing for disc brakes.

I think I have about 1/2" of pedal travel. Nothing I feel would be concidered excessive. This is with a 6:1 pedal ratio.

[SHANE 73Z]

Hey Ron,

I had a couple questions for you but you beat me to some of the answers already. I was curious about your pedal ratio.

Also, what kind of MCs are you running? I am running .70" right now and just dont think they will generate the feel I want. I am sure I am running a little more caliper piston area than you are, but that is in conjunction with a 5.3:1 pedal ratio.

It sure sounds like you hit the pedal feel Im looking for.

Thanks,
Shane

[RSX302]

Ron that is nearly the same calculator I used. The small bore of the SL6 drops the wheel torque by 20% over the stock rotor and caliper! I am amazed at some of these systems. My GT-2 race car uses 4 piston 1.75 bore calipers and 12" rotors, and it weights 2000 lbs! I can't imagine using smaller calipers on a car that is 3400 lbs.

The SL4 was the one I was looking at which I think would have been fine with the 7/8 tandem mc because of having more piston area. (maybe 3/4"mc max) It's the same caliper as the SL6. I guess they couldn't get the piston area in the caliper when they went to 6 pistons due to space limitations. The SL6's in my opinion works better in a power assisted set-up then manual because of the reduced piston area. (Or go to a smaller master like I did) Going to a smaller size caliper doesn't necessarilly mean you will get better or wrose stopping power or less reliability. Piston area, mc size and pad cf will determine stopping power. A bigger caliper usually means - bigger pad = longer lasting = reduced heat build-up etc. (ie: weight of car or racing demands)

[SHANE 73Z]

Sorry for the thread jack Kieth,

Just a couple thoughts. As long as you get the hydraulics & pedal ratio correct, there isnt a problem with the small bores. I am guessing you are trying to stick with a tandem MC and that limits options for that item, when dealing with the SL6.

I hate to say it, but we live in a first-gen world. That said, I would venture to guess that Wilwood did not take into consideration the light (5.3:1) pedal ratio of the second gens (but the first gen has the near universal 6:1 from the factory). I have yet to see many 2Gs with the SL6 calipers and guess that Wilwood is listening to the 1G customers & ignoring/missing the pedal ratio disparity.

Shane

[RSX302]

Hey Ron,

I had a couple questions for you but you beat me to some of the answers already. I was curious about your pedal ratio.

Also, what kind of MCs are you running? I am running .70" right now and just dont think they will generate the feel I want. I am sure I am running a little more caliper piston area than you are, but that is in conjunction with a 5.3:1 pedal ratio.

It sure sounds like you hit the pedal feel Im looking for.

Thanks,
Shane

Wilwood Pt# 230-3370 remote mount master. .625 x 1.3 stroke

[SHANE 73Z]

Thanks Ron,

Looks like I have an arithmetic assignment for tomorrow.

Shane

[RSX302]

Sorry for the thread jack Kieth,

Just a couple thoughts. As long as you get the hydraulics & pedal ratio correct, there isnt a problem with the small bores. I am guessing you are trying to stick with a tandem MC and that limits options for that item, when dealing with the SL6.

I hate to say it, but we live in a first-gen world. That said, I would venture to guess that Wilwood did not take into consideration the light (5.3:1) pedal ratio of the second gens (but the first gen has the near universal 6:1 from the factory). I have yet to see many 2Gs with the SL6 calipers and guess that Wilwood is listening to the 1G customers & ignoring/missing the pedal ratio disparity.

Shane

Unfortunately the tandems currently limit you to 7/8. It was either buying new bigger piston calipers or buying and fab'ing a dual MC set-up. I choose the duals. Going with the duals will give you more flexibility and the MC's are cheaper. Would work with the 5:1 pedal ratio

[gsxrken]

I
I would appreciate some input. I went from set up #1 with power brakes, to set up #2 with manual brakes, and now couldn't lock the brakes with both legs, and now considering set ups #3 and #4.
thanks

Ron said it earlier, but pad choice could clear up all of your complaints. Pad friction improvements of 25% will transform the stopping ability much more than a few more PSI at the pistons.

I was mortified with my 6/4 Wilwoods performance. Wouldn't lock them up until about the 3rd hard stop. I tried 3 MCs smaller and smaller and still hated it. I bought a manual pedal and side-by side MCs (3/4" & 1") but never got around to installing them b/c of a back injury. Then I swapped the pads to their BP20 and was instantly happy with them. I actually have to watch how hard I use the brakes now, especially noticeable at the end of the dragstrip when braking for the first turn off. I still intend to go manual with the dual MCs, but that is now just for feel and control, not an attempt to get better braking.

[Payton King]

Having the same problems. Have the 6 piston wilwoods on front with the 13 inch 2 piece rotor, 13 inch rear with the 4.

Pedal ratio is 5.3 or so with a custom twin master set-up and balance bar. Running a 5/8 on front and 3/4 in the rear. Generating 1000 psi on front and 800 psi rear.

It takes lots of effort to stop. After 4 or 5 hard stops to get heat in the pads it does much better. I am going to pull a pad this weekend to see what compound I am running, but from what I read above the bp20 is the ticket?

[David Pozzi]

We put the Baer/pbr type brakes on Mary's second gen. I tried to go manual with it and tried master cyls down to 13/16" bore, I used early 70's Ford master cyls. With the 13/16" I could barely lock the front wheels if I really stood on the pedal, mary could not press that hard. There was no way we would want to open track the car and have to work the brake pedal that hard over 1/2 hour at a time.

I went to the stock type booster and a 15/16" master cyl and it was about perfect except the Baer provided pads would lock the rears up on the first hard application when cold. Once slightly warm, they worked fine but wore out the first track day. Anyway, a manual 3/4" bore might be about right or a 5/8". I just ran out of time to experiment further and went back to power boosted.

I believe any advantage of a 6 piston is in a slightly stiffer caliper due to the smaller bores leaving more "meat".

On pad size, formulas I've seen say to not consider pad surface area when calculating brake torque. It's piston load in pounds, X pad coefficient, X rotor radius, ÷ by tire radius.

This assumes the pads are correct for the application.
A larger pad will have a softer compound because the unit pressures are lower.

Older large piston caliper designs use much lower line pressures and probably have less flex of brake hoses (hysteresis).

[RSX302]

Ron said it earlier, but pad choice could clear up all of your complaints. Pad friction improvements of 25% will transform the stopping ability much more than a few more PSI at the pistons.

I was mortified with my 6/4 Wilwoods performance. Wouldn't lock them up until about the 3rd hard stop. I tried 3 MCs smaller and smaller and still hated it. I bought a manual pedal and side-by side MCs (3/4" & 1") but never got around to installing them b/c of a back injury. Then I swapped the pads to their BP20 and was instantly happy with them. I actually have to watch how hard I use the brakes now, especially noticeable at the end of the dragstrip when braking for the first turn off. I still intend to go manual with the dual MCs, but that is now just for feel and control, not an attempt to get better braking.

Intresting...are your brakes dragging or did you already have heat into them at the drags? I can't get my BP-20's to do that until I get some good heat into them. I was scared to death on the street during the first 5 or so stops. The low cf of the BP-20's don't get to the BP-10's until about 350-400 degrees. Amazing how the bite with only .4-.5cf makes a big difference in cold stopping power.

[ks71z28]

I appreciate all the input. Mary Pozzi's car and mine are very similar. I will likely stay with the C5 style brakes with a manual set up and 7/8" master. The car stops well at speed, but at low speed it doesn't stop well, a lot of effort, which may be due to the EBC "yellow stuff" pads. I have a lot of flex at the firewall, so I am going to try and remedy that with a brace. Trying to get good brake feel had been a difficult task. I just think that Wilwood needs to be careful in their marketing of "Big" brake kits. $3500-4000 is a lot of money for a brake system that may not be any better than a stock brake system with good rotors and pads. My C5 system is n't any better than the previous system, with 12" rotors and big single piston calipers. Again thanks for the input

[RSX302]

I appreciate all the input. Mary Pozzi's car and mine are very similar. I will likely stay with the C5 style brakes with a manual set up and 7/8" master. The car stops well at speed, but at low speed it doesn't stop well, a lot of effort, which may be due to the EBC "yellow stuff" pads. I have a lot of flex at the firewall, so I am going to try and remedy that with a brace. Trying to get good brake feel had been a difficult task. I just think that Wilwood needs to be careful in their marketing of "Big" brake kits. $3500-4000 is a lot of money for a brake system that may not be any better than a stock brake system with good rotors and pads. My C5 system is n't any better than the previous system, with 12" rotors and big single piston calipers. Again thanks for the input

I appologize for getting off track...
I looked up the yellow stuff pads and found that they are .5cf. If thats correct, then that pad will bite pretty good. I think if you go more then that you will get into the racing pads that are noisy and dusty. I think .4's are standard for the street and .5's are getting into an entry race pad.

I had the same issue with pushing too hard on the brakes and the only way I found to fix was doing one of the following: Smaller master, Bigger piston calipers or add power assist. The most inexpensive fix for me was the master.

I have no complaints with Wilwoods products, just was lacking the correct set-up information. But that makes them more money now doesn't it.
I hate the phase: "WE DO IT NICE CUZ WE DO IT TWICE"

Good Luck!

Ron

[ks71z28]

Ron you are way cool! We will see maybe next year, I will begin to mock up a set up with 1.88/1.75 " 4 pots or something. thanks for the info on the pads.

[SDMAN]

Here's something a little fun to play with...

http://www.jakelatham.com/radical/info/brake_calculators.shtml
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Havent seen that one. Spent some time modelling my new (as yet un-installed) brake system with it.

It was fun to play with. Thanks!