Brake calipers for road race rotors

[ssanto]

I picked up a used road race car (roller) but it didn't come with brake calipers. The guy had some super expensive AP racing NASCAR brake calipers on there that were way out of my price range.

The front rotors are pretty massive, 13" diamater and 1 5/8 (42 mm) thick. I'm looking for entry level calipers that will fit this... haven't had much luck finding something yet. It seems that these are thicker than anything I can find available.

The rear rotors are a more reasonable 13" by 32 mm thick.


Any suggestions?

Thanks,
Sal

[Peter Mc Mahon]

Used nascar stuff?

[Chad-1stGen]

Those are crazy thick rotors for long races. Are you planning to do endurance style racing with it? If not, I'd ditch those thick rotors. Not only are you going to have to pony up for a severe duty race caliper but you are going to be carrying a lot of unnecessary weight in that rotor (and caliper).

Typical 20-30 minute track days or race sessions don't need anywhere near that level of mass.

[Sbeck09]

The argument towards these heavier duty components is longevity and heat management. At your level you could potentially run a full "season" on a single set of pads/rotors. So do that math before you focus too much on the up-front cost of even used parts since replacing these every other event can add up super fast.

Otherwise, the spindle will determine what other options you have. See what you can find out for cross compatibility and it will likely open you up to multiple other options. There is a guy on here that adapted a used AP brake set from a NASCAR to his No Limit IFS front spindles.

[ssanto]

I might split the difference and move the 32 mm rotors up to the front since those calipers are more readily available. And then get new (and smaller) ones for the back.

I'm thinking 4 pistons in the front and 2 pistons in the back. Or maybe 4 pistons all around.

It's got a dual master cylinder on the brake pedal. One says 22.2 mm (0.875") and the other says 20.62 mm (0.812"). I'm pretty sure I need to figure the sizes of the master cylinder pistons into the calculations of what brake calipers to get. The car also has a little wheel you can turn in the cockpit to adjust front/rear brakes (that's what I think it does anyway).

This is all new to me... any suggestions?

Oh BTW, the brakes are manual. No booster or anything like that.


Thanks,
Sal

[Sbeck09]

Correct on the non boosted brakes. Generally speaking, full race cars don't or can't use boosted brakes for a few reasons. The little knob is indeed your brake bias adjuster. It changes how much pressure is applied to each end of the car when you press the pedal typically via moving a balance bar (you can see it linking the two calipers at the pivots). You'll have to play with it a bit at first to get it right. Aftermarket street car setups are adjusted with what is essentially a valve restricting rear pressure with a similar knob.

Call the brake companies you are looking at buying from and they can help make recommendations on caliper size. It's not really about how many pistons, but more about piston size/surface area. You'd be surprised how often more pistons does NOT = more surface area. There is a specific calculation that any reputable company can use with those measurements to determine the best match.

[ssanto]

Can someone shed some light on what makes expensive brake calipers better than cheaper ones.

Take two brake calipers that have the same number and size of pistions... $150 bottom line Wilwood vs $1000 AP brakes. Same pistons and sizes in the caliper. Same brake pads. Same rotors.

Why is the setup with the AP brakes better? Is it a "brake fade" issue where both would perform equally on the first stop? What does the caliper have to do with brake fade?


Thanks,
Sal

[Sbeck09]

For starters, I think AP charges too much because they can. That said, their calipers are billet machined monoblock calipers where the wilwood is just a 2 piece casting. What that means is a massive difference in strength. You can tell this in brake feel and consistency because the AP caliper is so much more rigid. The AP will maintain more consistent pressures longer due to less heat expansion. You can tell a difference from the very first stop. But this all matters most under extreme conditions.

[ssanto]

Thanks. I think I'm going to get the second-cheapest set of Wilwood 4 piston calipers that I can get. Right now I've got 1.625 thick rotors in the front and 1.25 in the back. It'll be cheaper overall if I swap the front rotors for a set of 1.25's. Or move the back ones to the front and get a set of 1 inch rotors in the back.

The car was setup for a 700 HP motor and a professional driver. I'll probably have a 400 HP motor and I've never road raced before.

The cheaper I go, the quicker I can get to the track. I know that I'll be starting off slow and learning as I go. And then as I get to where I can push the limits of my equipment, I can upgrade the equipment. That'll help spread the cost out over time and I'll be able to tell the difference in better parts.

Does that make sense?

[Chad-1stGen]

For a track car you want to get a Superlite forged caliper at a minimum if going Wilwood. It's much stiffer and better suited than their Dynalite stuff. They make much bigger calipers. As mentioned above, you are gaining caliper rigidity and pad size (good for endurance) as you increase the caliper size.

[c4racer2]

I would change out the front to 1.25” thick as that will fit a broader range of calipers.

What does the car weigh ?

[ssanto]

What does the car weigh ?

About 3200 with lead. I can probably remove the lead for autoX and some time trials events.

[ssanto]

I called Wilwood and they suggested the following...

My car already as:
- 3200 lbs
- 0.812 (13/16) front master cylinder
- 0.875 (7/8) rear master cylinder

They recommended:
- 4.8 to 5.18 front piston area
- 3 to 3.4 rear piston area

Sound about right?

[vette427-sbc]

Whats the pedal ratio? I would spend a little extra $$ if you can on a stiffer caliper.

32mm = 1.25"

[ssanto]

Whats the pedal ratio? I would spend a little extra $$ if you can on a stiffer caliper.

32mm = 1.25"

pedal is a 6:1 as far as I can tell (hand measured)

[ssanto]

Hmmmm... the AP calipers the car was running before I bought it was a 6 piston with 9.34 sq inch piston area. Interesting that wilwood suggested a caliper size of about half that.

I guess he had much more HP and more speed so he needed much greater clamping force. But with the extra piston size in the caliper there also came double the pedal travel. I’d also suppose that those high dollar calipers could handle those forces where the wilwood superlites wouldn’t.

[c4racer2]

You sure about that ?

That’s massive.

I have the biggest stoptech calipers ST60 and they are just under 6

It actually doesn’t matter all that much you just need to get the right front to rear ratio to get you close to your desired braking mix - normally in the 70/30 range for a pro touring car maybe 65/35 for a nascar type chassis.
Anyway then masters need to be sized appropriately. All has to work as a system.

[ssanto]

You sure about that ?

That’s massive.

I have the biggest stoptech calipers ST60 and they are just under 6

It actually doesn’t matter all that much you just need to get the right front to rear ratio to get you close to your desired braking mix - normally in the 70/30 range for a pro touring car maybe 65/35 for a nascar type chassis.
Anyway then masters need to be sized appropriately. All has to work as a system.

Yep. That's what the AP racing website says. Although he drove the car professionally on some K&N West Series road race circuit... so I suppose it was kind of a different beast.

[c4racer2]

Biggest AP calipers I am finding is 50sq-cm which is 7.75 sq-in.

Anyway really doesn’t matter. It’s a ratio of piston area to master bore area and pedal ratio to get clamping force. And then it’s sizing the rears correctly to get the right front rear brake ratio.

In the wildwood line I would go with the aero6 stuff and the larger piston size which I think is 5.4

What masters does the car have?
With a PA of 8 or so it’s probably 1 1/8” maybe even 1.25”

The wildwood probably needs more like a 7/8”

My ST60s with a 5.9PA use a 15/16”

That’s assuming a manual brake system.

Some rough numbers to give you a starting point. Really need to do all the math to size it correctly.

[Shawn0331]

I also recommend not running the Dyna's up front. they're known to flex quite a bit. Like C4 had mentioned i would go with the big piston Aero 6 calipers up front.

[Sbeck09]

I have aero 6 calipers for my setup currently. I would say that Baer calipers are the better option when you think of good value vs good, solid performance(not that wilwood is bad). I just didn't think it through before I bought. They are less money than AP, but known to be stronger than wilwood.

Food for thought.

[c4racer2]

StopTech ST60 are very good. Extremely rigid. But not exactly a budget choice.

[ssanto]

Crap... the Wilwoods Aero6 won't work with my rotor and wheel combo.

My rotors are 12.88 inches. The wheels are 15" racing rims with 14.5" inner diameter (7.25 radius). The AP calipers that were on the car before barely fit with 7.24 inch radius to the outside of the caliper. The Aero6 are bulkier at 7.6 inch radius which won't fit inside the wheels.

I'm not changing wheels. So either I need to find different calipers that fit like the AP's did or get smaller rotors.

Luckily, Wilwood has "Narrow Superlite" calipers that are 7.23 which will fit my rotors and wheels. So it looks like I'm boxed into those.

[ssanto]

Anybody have input on the benefits between these two calipers:



Wilwood Billet Narrow Superlite 4R Radial - $404
Wilwood Forged Superlite 4 Internal - $185


The biggest PA I can get on the Billet ones is 4.8. And I can get 5.18 on the Forged ones.

The math says I'd be better off with the forged calipers because they would have more brake torque. I'm assuming the billet would be stiffer which would be better.

Any suggestions? These are the only calipers that fit my wheels. The Aero ones are too big.


Thanks,
Sal