427Hotrod

I'm about to install a complete Wilwood D8-6 and D8-4 aluminum brake caliper system and their rotors on my car. Decided I needed to do some baseline 60-0 testing to see how my old stock stuff is actually doing.

My car has pure stock manual brakes on it that have actually served well over the years. They've always had a great pedal and have hauled this 3750lb (race weight) hulk down from 140+mph on many a drag strip. Some quite short!

I made quite a few back to back stops and didn't have any fade issues. The biggest variances were with how hard I actually worked it to make it stop.

1- 151 ft- nice quick stop but not anywhere near full brake application to get an idea of how hard I could push it on that surface.
2- 123 ft- Worked it much harder-no brake lockup or drama.
3- 118 ft- back to back-but now I knew I could work it harder.
4- 109 ft- hit it hard and kept it right on the edge of lockup.
5- 135 ft- real hard and locked up front wheels early and rears near the end.
6- 111 ft- very similar to test 4.
7- 113 ft- another good one!

I am planning some major HP and speed increases in the future and want to make sure the brakes are up to snuff to handle it, hence the new system. I'm sticking with stock sized pieces so I can continue to use my 15" wheels and tires.

Though I always felt it stopped well, I was pretty impressed with how it did considering the tires are nothing sticky at all...just stock street rubber. The fronts are skinny, drag suspension, heavy weight etc. etc.

The bad boy Z06 Corvette's of a couple of years ago do 60-0 in the 105-110 ft range and the newest baddest of the bad ZR-1 Vette's with 15.5" carbon rotors and huge tires can get down in the sub 100 foot range. But of course they are a few hundred lbs lighter too!

More to come!

JIM

vetsvette2002

If your braking performance is what you state, why do you need to "upgrade"?

427Hotrod

Hoping to shed a little weight and maybe stop even cleaner. I looked at lighter race type brakes, but considering the weight of this car and that it truly is a street car...I'm staying with stock type one piece vented rotors.

I've always thought it stopped pretty good and today proved that. Looking back through old road tests show big block C-2's doing it in the 135 ft range usually with the skinny little bias ply tires of the day. They really were a good system that still works well today.

My brakes were a nice little $300 sleeved setup from the late 90's. Today there are some pretty neat options out there that weren't available back then.

JIM

MiguelsC2

Probably the 800+hp BB under his hood.

Best braking car I ever had was my 930 Porsche. In the day. They were the same brakes as the 917 racers. I think the 60-0 was under 120. That car could bruise your eyeballs in a panic stop.

With my current tires,(stock 4 wheel discs) my C2 is close.

The numbers nowadays are amazing.

c66vet

Depending on what 15" wheels you are using the Wilwood calipers may not clear the wheels. I tried to use Wilwoods with my reproduction knock offs and the calipers were too big. Check it out to be on the safe side.

427Hotrod

I'll be trying them with multiple wheels including factory 8" Rally's, Cragar's. Bogarts and M/T's. Thanks for the heads-up.

As mentioned, I'll be adding some more power soon....on out to the 4 digit area and I need to make sure it can get stopped. What works at 60mph might not last long at big speeds when called on. But 60mph is a good baseline and about all I could readily test before I tear it all down. I know how it stops today at 150+...so I'll be able to compare that too...though subjectively.

JIM

JohnZ

The key variable here is "huge tires"; C5/C6's have over twice the contact patch surface applied to the pavement (and ABS, so lockup isn't an issue). Brakes stop the wheels, but tires stop the car.

Unless you're concerned about repetitive max braking (like in road-racing), I don't think you'll notice any difference after changing the calipers (unless you go to "huge tires").

427Hotrod

I agree....the big tires make things a LOT more predictable and allow you to really use the brakes available. I was able to get some pretty repeatable results but it was taking a lot of concentration and *feel* on my part to do it.

I'm going to like the lighter weight this combo will give. I looked at real race type stuff but just wasn't comfortable for real street use with a car this heavy and there is just so much you're going to do with 15" wheels that aren't mega wide. If someone is contemplating changing leaking calipers to some *lifetime warranty* parts store ones that often take a few tries to get a set that doesn't leak, or installing properly sleeved calipers from a vendor who know's what they are doing, but then paying to ship the cores back..these can make for a good option, or at least I think so at this point.

I expect the better pads will allow less fade when I'm at the track and have to make back to back runs with little to no cool-down time. Of course I could have installed the pads with what I have now, but then I don't save weight or get the new improved caliper designs. I started with this testing so I definitely will know how they perform before I lay into them at the track the first time. Not the same as 140+ stopping, but at least a start.

I think this is a fun test folks ought to try on their own and see how well their's actually perform. I see lots of folks have trouble with air in the system etc and many seem to still be driving them with poor operating brakes. This is a way to compare against one that is working very well dead stock.

JIM

toddalin

This is a falicy. The total size of the contact patch is not governed by the size of the tire. It is determined by the tire pressure and weight of the vehicle. The shape of the patch and therefore heating of the tire is based on the tires.

MiguelsC2

So by your reasoning. A 10 inch wide tread has no more contact area than a 6 inch tread width? So my C2 hooks up much better. Not because of the larger treads I have. It's the air pressure and wieght that made it hook up better. Funny, those variables didn't change when I swapped tires. But for some reason my C2 has MUCH better traction.

With all due respect!

toddalin

Exactly.

Assume the contact patch to represent a rectangle. Also assume you put 30# of pressure in your tires and you car weighs 3,000#.

At 30# of pressure you need 100 square inches of contact to support the weight of the car.

100 sq in x 30 lb/sq in = 3,000# of support

So, if the weight is balanced to the four corners, each tire uses 25 sq in to support 750#.

So if the tire is 10 in wide, the contact patch is 2.5 in long.
10 in x 2.5 in = 25 sq in

If the tire is 6 in wide, the contact patch is 4.17 in long.
6 in x 4.17 in = 25 sq in

So why do wide tires handle better?

When the tire rolls onto the sidewall and the tread looses contact with the road it is happening along a 2.5 in length with the wide tire, but with a 4.17 in length with the narrow tire, so the narrow tire looses more tread on the road for the same amount of shoulder roll.

On the other hand, a drag tire may work better if it is thinner as the surface area has a longer continual contact with the road (i.e., 4.17 in as opposed to 2.5 in) thereby generating more heat into the rubber making it softer.

I may be crazy, but that's how it works.

silvercamaro

Toddalin,
Your statements above are true, however, your comment:
"The total size of the contact patch is not governed by the size of the tire. It is determined by the tire pressure and weight of the vehicle. The shape of the patch and therefore heating of the tire is based on the tires."

- is misleading. The total footprint is governed by both the tread width and and tire pressure. The footprint does not change proportionally to the inflation pressure, and I'm thinking you already knew that.

toddalin

Yes it does once you get past the initial deformation of the surface rubber associated with the tread. Half the air, twice the footprint. It's as simple as PV=NRT.

silvercamaro

Using the ideal gas law is greatly oversimplifying tire modeling. It is that simple if the footprint is a perfect rectangle that varies by pressure, but it's actually known as a "1.6 ellipse" shape (where the major axis is 1.6 times the minor). Also, the tread void ratio will heavily influence the area on the trailing and leading edges.

To quote John Dixon:
"Tire vertical stiffness generally increases with load capacity, rim width, and decreasing cord crown angle. There is a variation of typically 10% for a given size and pressure, from various manufacturers."

Tire vertical stiffness has a direct relation on the minor axis' footprint, and changes between tire models and rim widths. Performance oriented tires have stiffer carcasses for reduced lateral deflection, and this stiffness can further be enhanced by a wider rim width.

Not trying to start a pissing match or anything, but tire sizes and other factors have real-world effects and actually do make a difference in vehicle behavior.

toddalin

All things being equal (which they never are), the formula holds and if you mount the identical tire with no tread, pattern, etc. to distort things (basically an inner tube), the footprint size of contact patch is related to the air pressure and weight applied to it, regardless of how wide it is.

We are talking about the air pressure holding the car up and its relation to the contact patch, not the cords, sidewalls, and treads. Let enough air out and you can sit on the rim and the car won't go down any further regardless of pressure below that point.

silvercamaro

But those are the items that hold the car up along with the air pressure. How can they be dismissed?

Agree to disagree I guess.

toddalin

Yes, but consider the case where someone simply lets a bit of air out of their tires to increase adhesion at the drags.

Say they normally run 36# and they reduce it to 30#.

The deformation of the rubber, the sidewalls, the crown shape, etc. would hardly change. But on a 3,000# car with 10" wide tires, the contact patch grows from 20.8 sq in (or 10" x 2.08") to 25 sq in (or 10" x 2.5"). So the size of the contact patch grows by 20%.

Avispa

Heck with all this tire math....Hotrod lives right down the road from me and wants to put 4-digit HP in a midyear. I GOTTA see this car!


I'd be a little skeert of he stock brakes at that kinda HP, too.

92GTA

Holy ****, I actually learned something reading this thread

turbocat

I'm still confused. My tires on 17" rims have tread that is 50% wider than stock. Would bigger rotors and calipers help me stop my 66 convertible faster or not?