I have my '73 Coupe and I'm planning to upgrade to wilwood calipers all around. I'm running 15" X 8" with 4" backspacing wheels all around and plan to keep the 15's. I am looking at the four piston calipers for the rear and see that Wilwood offers a 6 piston caliper for 15" wheels for the front. Wilwood tech services says the 6 piston calipers will fit with my wheels but before I purchase them and do the fit check, I was wondering if anyone is running the Wilwood 6 piston calipers on 15" wheels and ran into any other clearance issues besides wheel clearance.

 

I've got them on my car and they fit fine.

You can do a search here and find some threads where I detailed the info gathered for a magazine article.

JIM

 

why D8-6 vs D8-4 calipers. ? I don't think they provide any extra clamping force with 6 piston vs 4 piston ? They use the same brake pad.

 

Fit just fine. Had them about 4 years. They've been fantastic. I did not encounter any fitment issues.

 

Piston area is near identical but the six will extend pad wear by balancing pressure points on the pad.

 

Thanks guys, It's nice to hear from the people have knowledge about the products they sell and from those who have installed them.

 

I am curious why you are changing calipers?

The big advantage of the wilwood calipers are that they are made of aluminum versus cast steel which are much lighter and great if you race since their heat rejection is superior to the OEM calipers. The brake performance between an OEM 4 piston caliper and the wilwood 4 or 6 piston caliper is negligible on the street and you will not realize shorter brake distances.

The only way to truly reduce brake distances on the street is to use the OEM 4 piston caliper with a bigger rotor (13/14 inch along with 17/18 inch rims) which not surprisingly NO ONE offers a bracket to use the OEM caliper with bigger rotors...(no money in that modification) OR

Wilwood's 4/6 piston aluminum caliper with 13/14 inch rotors....same size caliper with 4 pistons requires a bigger rotor for reduced brake distances...no way around the physics!

I actually have a real world example:

On my 01 Pontiac GP I was able to swap out the front 11 inch rotor for the 01 impala (same car) 12 inch rotor utilizing the impala caliper bracket and the same exact OEM caliper....No other change...Noticeable difference in braking with the 12 inch rotor versus the 11 inch rotor with the same caliper....very noticeable!

Want to dramatically increase the effectiveness of the C3 brakes which are outstanding BTW:

17/18 inch ultra high performance ZR rated tires
Stainless Steel flex lines to the caliper-no hose expansion with brake application, better brake feel, better brake modulation
High performance brake pads like Hawk or Performance Friction!

 

Bigger rotors won't stop you quicker. All a bigger rotor does is decrease the needed pedal pressure so the wife won't break a high heel during a quick stop. The two things that determine how quick you can actually stop a car is the vehicle weight (less is better) and the tire grip/traction coefficient (higher is better).

Bigger rotors will last longer, due to less caliper pressures on them during operation, but they're always heavier, adding mass and rotational inertia to the vehicle, and additional unsprung weight to the suspension. There's no free lunch. That's physics.

 

Unfortunately this is incorrect about larger rotors providing the same braking force as smaller rotors, everything in the brake system being the same^. Physics again and not the physics you referenced above! This point is really NOT debatable if have a solid understanding of physics.

Brake Disk Sizes
"The disk size has two items to address: diameter and thickness. The diameter is easier to understand and easier to see. As a simple rule, the larger diameter of the rotor, the more force that is available to stop a wheel, just like using a longer wrench makes it easier to break a frozen bolt loose. If you kept the same caliper and same pads, but installed a larger diameter rotor, you would get greater stopping power. This power can be referenced in Newton-meters of torque. Factory rotors are sized according to many factors: wheel sizes, calipers used, unsprung weight, tires, price, etc. Initially, it would seem that the largest diameter rotor that can be obtained should be used, but those other factors must be kept in mind. Even, a reasonably larger diameter rotor will provide increased stopping power.
"

You need to read this:

http://www.wcengineering.com/articles/brakes.html

Every major super sports car today has gigantic discs for this very reason....not for looks or unneeded unsprung weight!

 

You both are right, but arguing different points.

A larger diameter rotor will increase the moment arm of the braking force so that, for the same amount of pedal pressure the braking moment (stopping power) is increased. That is effectively the same as applying more pedal pressure with the same sized rotor.

Eventually the limiting factor is when the car skids, so increasing the rotor diameter doesn't necessarily decrease your stopping distance.

Edit: I was assuming no fade during the braking. Larger diameter rotors will most likely have better fade resistance, so repeated high speed stopping would be better.

 

Actually..(and we've had this discussion before) he's absolutely correct.

That maximum stopping is tire adhesion as both of you define. You cannot change that value by changing the rotor or the caliper or anything else. A locked up tire is a locked up tire. How you ACHIEVE that is what's being altered.

Maximum tire torque is maximum tire torque....massive rotor with a bit of pedal effort or small rotor with a lot of pressure (and broken heal- I love that one!) the net result is the same: lock up.

Larger rotors ARE more efficient and durable. And have less fade etc etc. They are simply an alternative form of boosting final torque. And doing so in a better way than a high Cf pad or pushing with two feet on the pedal.

Some of you have snow on the way I assume. A 14" rotor won't stop shorter on snow than an 11" rotor yet it has far more "power" (a terrible and confusing term) than the 11" part.

 

[QUOTE=jb78L-82;1593590180]I am curious why you are changing calipers?

The big advantage of the wilwood calipers are that they are made of aluminum versus cast steel which are much lighter and great if you race since their heat rejection is superior to the OEM calipers. QUOTE]

And they don't leak like "current" new / rebuilt units.

Here is my pile of wasted money 1 set lip seal 1 set o-ring + 1 warranty o-ring replacement. I went with D8-4 units.

 

Friend, you seem to be immune to learning basic physics and engineering. I'll try to explain it in basic terms.

The car stops by a very simple principle: A retarding torque on the tire/wheel assembly. The retarding torque is supplied by the caliper supplying a clamping force applied at a distance (the rotor radius). This retarding torque then tries to slow the tire/wheel assembly. The tire/wheel assembly doesn't give a rat's behind how that torque is generated, whether by a modest size rotor and firm pedal/caliper pressure, or a larger rotor and high heel preserving lower pedal/caliper pressure.

Once the retarding torque reaches a value that overwhelms the tire/asphalt interface grip coefficient, the tire/wheel will lock up. No increase of rotor diameter or caliper pressure will stop the car any faster than the traction limit the tire/track grip allows.

Race cars use bigger and thicker rotors for two reasons: Most real race cars don't have power brakes, so the added diameter (actually, the radius) of the rotor reduces the required pedal pressure needed to slow the car down (the high heel preservation law). The second reason is when they are trying to get a rotor to last for a "long" time during endurance races. The larger radius allows a softer pad compound and lower caliper pressure to be used during the race. This extends rotor life. The greater mass of bigger rotors also distributes the braking heat energy over a larger surface, extending rotor and pad life.

Nobody runs a bigger rotor than they have to. Bigger rotors are heavier and generally more expensive.

As I said before, the only things that will stop a car quicker is lighter vehicle weight and higher grip tires. Rotor diameter isn't one of those two.

That's the physics. Where am I wrong?

 

Let's go a step farther.

What has changed over the past 50yrs? Tires mainly.

With increases in tire quality and stick it's entirely (did I say that?) possible that the overall stopping power (still hate it) or vehicle torque has not been able to keep up with the newer rubber being offered.

In this case a larger rotor can bring back some of what's been lost on trying more aggressive pads or pushing to hard with your leg. That new DOT legal slick may well push the demands of the stock brakes on a car from the 70 beyond their capabilities: line pressure is through the roof, pads are over heating and so on.

You can continue to band-aide it with off the shelf parts. OR you can move to a larger rotor. By going larger you get not only the thermal values but take easier advantage of the new rubber without taxing the system with as much abuse.

Will this stop the car sooner?? In this case possibly. It would depend on how abusive you were with the old and smaller parts. If it took you 2.5 seconds and all your effort to lock up the old stuff with new rubber and only 1.75 seconds with the larger parts that's a net loss of X feet (you do the math) in distance.

This is an abstract sort of way of looking at things. Reality is that for same-same conditions the larger rotor won't produce shorter distances. But I would agree that moving to larger parts will allow a driver to take full (and sooner) advantages of a boost in tire adhesion. (this is no different than changing pad compounds on the track to boost bite)

For the daily driver, enthusiast most of that is about pointless. You can achieve the same given mathematical increase in "power" with a simple pad change. Get a set of the most abusive race pads and try them out-go to 60mph and lock up the tires. You'll stop on a dime. Take them out and put in a normal pads. You'll still stop on that same dime if you push hard and fast enough- if the tire is the same old bias ply rubber from 40yrs ago! lol

There's nothing wrong with larger parts. And keeping up with tire tech today it's part of what makes the business hum.

 

One final thought for those who may be reading and not fully grasping the discussion from all sides.

I have a number of interactive calculators to help see cause and effect of such things you can see pressure changes, torque values...change piston size or qty, rotor size and pad coefficient of friction values.

BIAS CALCULATOR

Forget about the whole "bias" thing here.

Look at the line: Front Rotor Torque In.lbs.: 6125.625

Think of this as your tire in a skid. Maximum adhesion. Tire wall approaching..!

Now with that value in mind plug and play alternatives to the value above. No matter what you choose to alter this 6125 is the end, the impact, the 'oh sheet' moment.

If you use a larger disc as discussed you'll see that you'll exceed the 6125. To get back to 6125 you'll find you need less 'leg' to induce this same skid. (no broke heel..!)

ANY what you alter the above values this is the target number- you're done for! lo

 

You're certainly familiar with the technical details of what I'm talking about below, but FWIW, here's my brake story and reasoning.

I've gotten a bit more practice on figuring out braking issues than I would like, but they've been mostly because of my own restrictions regarding my car's modifications. I like doing a lot of track days (strictly low key amateur stuff I admit), and I have two items that are constantly in conflict. I'm running a big block, so my speeds are reasonably high coming into the braking zones. But I like the stock look (meaning 15" wheels) for my car when driving it on the streets. I run 17"/18" wheels on the track, but I'm still restricted to 11.75" rotors on the car as they're the only thing that fits under the stock 15" wheels. To get decent stopping abilities I'm forced to run an aggressive pad on those 11.75" rotors. I get great stopping performance (both distance and pedal effort) with that combo, but rotor life obviously suffers (even with additional air ducted to the rotors). To reduce the requirements on the stock rotor size and prevent having to keep going to a more aggressive pad when I run stickier tires, I've also spent a ton of time and effort getting weight out of the car. My '69 (with full factory interior, no gutting) is now at 2780#. My brake setup doesn't have the bling of some other vehicles, but the lower vehicle weight and aggressive pads allow me to brake with most any other car on the track.

 

Heat is what kills braking effectiveness i.e. brake fade. So to reduce brake fade, use bigger rotors that can absorb more heat. I had a rear rotor over heating on my truck caused by a partially seized parking brake. Fixed it. So, I went for a spin with the parking brake fully released. Took my ir temperature tool and looked at the temperature of the f/r rotors. The larger front rotor that works harder than the rear was cooler than the smaller rear rotors. Heat is the enemy of the braking system.

 

Change that to dissipate, and you might have a point.

 

1. There was an issue with the installation instructions (and illustration) and whether the C-3 corvette was front-steer or rear-steer. Anyway, I apparently installed my front calipers in the improper orientation... I haven't switched them since they work fine and I haven't had a reason to mess with the brakes....but I probably should. (I searched for the post concerning this but could not find it??).
{NOTE: I found the thread discussing this issue -- here is the link:

https://www.corvetteforum.com/forums...upgrade-2.html

It has been over 2 years since that discussion so you will want to check your installation illustrations .... you'd hope they were correct by now}






2. Also, the rear calipers were really supposed to be bled before installation so the bleed port was at the highest point. I should do this also, but as mentioned above they work just fine and I haven't had a reason to go do this. Next time I have to go under there I'll do this.

3. I recommend using a pressure bleeder. Mine have worked great from day 1.

Just some things to keep in mind.

 

Pretty sure you both have a point. In the case of ongoing friction, like the sticking e-brake, dissipation would be the greater benefit of a larger rotor. In the case of panic stops, the larger heat capacity due to the larger mass would be the benefit. Under "normal", high stress conditions like in an autocross, you'd probably see some benefit of both attributes. To the earlier point though, you'd see the benefit at the cost of dollars and unsprung weight.