Would still like to see this as a direct comparison against - A. stock system - B. a stock system with Wilwood Calipers. I'm not convinced that larger rotors and better calipers WITH modern low profile rubber won't be an improvement (albeit less than one might hope)

 

Don't forget vehicle weight in that deceleration recipe.

 

Ordered my Wilwood D8-6, D8-4 combo from Todd at TCE recently. Great to deal with and a great product!

Bill

 

Yes the modern rubber will definitely be a huge improvement (thus making the stock proportioning valve even more useless, do to being a even less balanced system) but if you can lock up the brakes with two fingers or lock up the brakes with 1000 tons still locking up the brakes, does not change distance, bigger brakes equal more stops before overheat that's all.. that is your fronts only.. your backs will never ever hit there full stopping potential, and you will never lock them up or even close, especially with the stock proportioning valve.


O yes! Every pound counts.. 1lb =5hp~ and and moving weight like in the suspension or drive train is even worse...
I am at 3000 flat

 

Where in the hell do people get the idea bigger pads will make you stop faster???
The stock system can lock up the brakes.. so can a willwood.. so, if you have enough pad to lock em up, your best stopping power is just before lock up... so this is the same amount of rubber being pulled on, its the rubber on the road that counts and how close you can get all 4s to lock up but not quite. Stock proportioning valve is like 70/30.. yup.. 30% to the backs... got to change and dial in the new knee brake valve, the you will get way more stopping power from the rears.

 

Bigger brakes, better pads etc make it easier to modulate the brakes right at the threshold, hence they help the driver repeatably get the shortest possible stop.

If you want the shortest stop possible, then it doesn't only matter that the brakes can lock-up the wheels when you stomp the pedal as hard as possible. It also matters that the driver can module the brakes right at the lockup threshold throughout the WHOLE stop. You need to maintain the bolded parts of your argument throughout the whole stop, and that is certainly easier to do with a better braking system, even if both the better system and the one it replaced could lock-up the wheels.

Sorry, but the argument that the brakes can't be improved once the brakes can lockup the wheels is simply false.

 

To a point.. that is more the pads... take away the pad and what you have left is the caliper, and now the stopping distance between $3000 brakes or $300 brakes may be, what? 1-2%?? Not enough to justify the price, no that justification can only be made for lighter suspension and more stops on the track,

 

This is correct! The bigger rotors, better brake pads, and "better" calipers (which the Willwood D8-6 piston are, not the 4 pistons,and aluminum for weight savings) assuming the tires are the same will allow for MUCH better brake modulation throughout the whole braking period which will reduce the brake distance versus a system that does not allow the same modulation..it is not just stomp on the brakes until impending lockup....there is much more to the equation. A bigger brake pad increases brake swept area and will allow for shorter distances although this is not an option with the willwoods, same C3 brake pad. The reason the 6 piston caliper allows for greater brake modulation versus the 4 piston caliper (OEM or Willwood) is there is a more even distribution of the caliper clamping force over the entire brake pad against the rotor.

I do agree with Paul, though, if the rear brake proportion is only 30%, which is LESS than the brake proportion on a typical FWD car, then increasing that percentage to 40-45% on a 50:50 weight distribution C3 would decrease braking substantially.

On my 01 GP that I upgraded the front 11 inch rotors to 12 inch rotors, no other change, the car definitely exhibits a greater rate of deceleration BEFORE ABS activation, than with the 11 inch rotor. The time to ABS activation with the 11 inch rotor was longer, not much but on the street, 1-2 seconds can be the difference between hitting something and not.

Same phenomenon, with the HEMI total brake upgrade to my Chrysler 300. 14 inch front rotors (versus 12 inches), MUCH bigger brake pad, Dual piston floating caliper (versus single piston caliper) and 12 inch rear vented versus solid. In this case, there is a BIG difference in slowing the car down on the street and highway. The 2 systems are absolutely not the same. Why? 14 inch rotors allow for much greater clamping force, bigger brake pad increases friction area against the rotor and total brake swept area which allows for faster deceleration, Larger caliper on larger rotor allows for not only greater clamping force but that force is more evenly distributed on the brake pad. In addition, the rear 12 inch vented versus solid 12 inch rotor allows the pad/rotor combo to run MUCH cooler, even on the street. With the 12 solid rotor, the rear disc on a 90 degree day was SUPER hot and extreme heat with a street pad will fade AND was eating brake pads quickly.

Yes, if you smash your foot to the floor immediately, 2 similar brake systems will show similar brake distances. That is not how most people drive on the street. The difference is what is happening BEFORE the impending lockup.

 

i talked about "modulation" as you want to call it,, the point just before lockup, and keep it there,,, and yes, the closer and you can stay at that point and the longer you can keep it at that point will be the best stopping, and a larger area would help one do that... that being said, I could do that all day in my C3 with the stock calipers and upgrades race pads. but yes, for those that can not, a bigger rotor will help achieve this. BUT, better yet, if you truly want a better ability to "modulate" the brakes, put on a hydroboost... then you start to have true linear peddle feel..

 

All these opinions about brake lockup and shortening the stopping distance is nice for the sake of documenting how fast you can stop your Vette, but here is the simple reason I am improving my brake system on my 73. I live at an elevation of 62 feet. If I take a drive up to Lake Tahoe, I travel up to over 8,000 feet in elevation. The back roads are tricky and they are filled with 15 mph corners and very steep inclines. I rarely need the brakes on my way up the hill. What goes up must come down, right? On my trip back down the mountain I hit 15-20 mph curves on 8-10% declines. I have spent hours upon hours behind the wheel in training and tactical driving, so I do know what I'm doing, however no doubt I'm on the brakes and I want a reliable system that is going to slow or stop me quick without the worry of fade when I'm accelerating through a 20 mph blind curve and I spot some obstruction or another vehicle in the lane directly in front of me. Yes the stock brakes and suspensions on our Corvettes are great, but I truly enjoy the drive, so brakes, suspension, steering, frame and all drive train components on my Corvette and getting upgraded. That my friends equals .04 cents of my opinion.

 

Paul you screwed your self on 14 inches front and rear you need big up front and smaller piston Sq inches and rotors rear

Stock brakes even with the best pads do not have the Sq inches of pistons to take advantage of modern ultra high performance tires. They don't have the clamping force. Hydroboost bridges the gap before after market r&c

 

yea, wildwood wanted me to go smaller in the rear also.. I just wanted the area for better heat distribution. and with the adjustable valve, i work my back tires more than most all here.

And the stock brakes can lock up or "modulate" new tires, just for not as long before overheat:-)

 

I disagree with your assessment. What Paul is saying is in principle correct. The vette's brakes are sized such that in a panic stop the ***-end won't lock up and come around making a bad situation uncontrollable. However in a controlled stop where the driver hasn't completely jammed on the brakes, the car is then not at the point where maximum weight transfer has unloaded the rear wheels to the point they lockup. Under that condition the rear brakes could, if oversized, contribute more to braking. The proportioning valve, with its so called knee in the pressure curve protects against the rear brake locking up first, by reducing rear pressure only when the driver jumps on the pedal. The integrated (i.e. overall) contribution from the rears in a modulated stop is higher and the stopping distance should decrease compared to a system without the valve. There are a number of web sites that describe this fully.

That said I would like to see a post from Paul that describes more exactly what he's done. The proportioning valve can only reduce pressure so it can't add to the rear's effectiveness..

 

I described the workings of this on another thread, but will explain it again here...

the stock proportioning valve has about a 70/30 split, that is to say, if you are running 100psi. there will be 70psi up front and 30 psi in the rear.. great for GM to not get sued and for jo-blow to stay safe.
the stock unit was designed for stock tires and suspension at the time of manufacture.
But we have come a long way since then in tire design. And todays tires are a lot more sticky, and on top of that, we are changing the sizes, especially in the back with much much wider tires. All of this combined makes the stock valve worthless to any racer or want to be (like me:-)) racer.

Now how the new knee brake proportioning valve works is totally different. KBPV

The KBPV will have a 50/50 balance in the rear and front, not a 70/30... BUT this is only up to a level that you adjust.. how you do this? Go 40mph, slam on the brakes and if all 4 lock up, turn back the **** a bit,, keep doing this until the backs just do not lock.
Now you have it set, that there will be a 50/50 pressure in the system until you are on edge of rear lockup, then the knee breaks happens, from that level forward the fronts keep at a linear upward pressure, but the backs got to a 50% pressure..
i.e. lets say you set the lock up at 200 psi.. so all the way to 200, the back and fronts get the same pressure, but after 200 is changes... at 220 the backs would be 210... at 300 the backs would be at 250.. see the pattern here?
and it works amazing... and i am not talking about stopping the car on it nose, I'm talking about putting you through the front window stopping.. and the stopping is also more controllable with the feel of less weight being transferred up front.

 

I have 13.25 GT1 GNX thermotec titanium fronts. 12 inch rear with about 1/2 the piston area and it's well balanced with 335 rear tires

 

Mines a '68 - 255/45/18 on front - 285/45/18 on rear. Stock brakes with HP plus pads. No power assistance. I prefer it with no power brakes. I know that in an emergency situation if I hit the brakes hard it won't lock-up and will slow in a controlled manner. However - with close to 600 engine HP it feels at time that a ships anchor might have more effect such is the pressure needed to stop the car. Yeah, Hydroboost or vacumn booster could be fitted to reduce braking effort - but - they won't actually improve the breaking efficiency will they?
I have a car that will out perform most modern performance cars in terms of acceleration - I also want a car that will decelerate like a modern car.
Yes the larger swept area of larger discs, the bigger frictional area of larger pads that feature multiple pistons for a linear pressure over the contact area must at the very least reduce the effort extended by all operating components within the braking system - thereby allowing more linear braking control - but............ I need to see the proof that the 'big' brakes give the improvement one might reasonably expect after shelling out thousands of $$$$$$$'s (in my case even more ££££££££££'s)
Maybe I'll simply need to go and do my own thing - like an earlier Rolls Royce with twin front calipers ~

 

Years ago I saw a road racing c4 with twin aluminum c4 calipers the rotors were covered with fine heat cracling. No air ductwork and 16 inch wheels

 

Paul, I'm still a bit unclear on your rotor/caliper sizings. Are they the same sizes front and rear?

 

Yes, same size front and rear, 14" I believe.. not 100% on that, but they are the biggest willwood makes that will fit in an 18" wheel