Contour Enthusiasts Group Archives Forums Modifications Brakes Rear disc conversion ?

I haven't noticed any ill effects, but I'll keep a watchful eye out when I do my spring service.

Yeah, well, that too, because nothing looks gayer than drums behind nice open wheels.

well hold on just a second there MFE, now when using sport suspension (stiff koni's + eibachs) the car barely sways much at all (front to back) the rear take on a whole lot more ability to slow you down (however still under weighted) and yea i am gonna toss in proportioning valve in in mine, i want them locking at the same time Ill take my car out and let people know whats the deal.

Physics is physics. Body lean/roll/squat/dive is not what I'm talking about. I'm talking about the fact that when you hit the brakes the front tires get loaded a lot more and the back tires get unloaded a corresponding amount. Wouldn't matter if the suspension was locked in place, the effect is still there. And my main point was this notion that they're "taking alot of the braking stress off the front brakes. cuz they are clamping down more.". The fact that they're "clamping down more" doesn't change the fact that the forward weight shift is what it is and the rear brakes don't change that. They might be taking braking effort off the front under partial braking but if they are, you're going to be in a world of hurt when you really need them in a panic.

well i dont know what physics classes you took but as you said physics is physics... think of it logicially. car tilts forward during braking (we agree on this) with stiffer suspension it doesn't lean as much thus less weight is shifted onto it(cuz the weight doesn't change in the car)... DUH, cuz the springs/struts keep the body flatter (if thats a word). Lets take this model for example.

0 = standard
+ = X amount more
- = X amount less
*note: not an exact science im drawing

if (0)-(0) is the car's weight distribution at standing
(++)-(-) during standard braking

if (0)-(0) is the car's weight distrubution at standing
(+)-(0) would be the new balance of the brakes given a more even distribution of weight.

Just like 4wd cars they can get more grip to the ground than a 2wd car. Now thats a rather wild example but true to form.

Now having less weight on a given grip point (tire to ground) will evenly distribute it (during braking). MORE weight on rear LESS on front... rear brakes will be more effective with an increased fricton. the springs keep the weight from flying forward. Balancing out the brakes better. Now whether these brakes are actually balanced is a question none of us can answer as of yet. But Suspension does assist in launches and braking, that i can ASSURE you of.

Whatever you say, chief. Enjoy your brakes. Darwin smiles on and P.T. Barnum is laughing in his grave.

hehe, dont fret dog, i just wanted to make sure everyone else knows what is true in the world, not just speculation. Indeed, enjoy them! ill try to post w/ some words about them if/when it rains over here!

Been following this for some time, and I'm confused by some of the comments made that just done jive.

First I'll tell you that a change in suspension and or a change in weight distibution WILL have a significant effect on how a car brakes. Most FWD cars see extensive front braking simply due to their balance. Add some larger rear brakes and as it was pointed out; you may be seeing your own tail lights.

The term "appplying the same clamp forces" or whatever it was has no real impact on what is happening here. Clamp loads are not what this debate is about. BIAS is what is changing. Meaining if you car is at its limit at 80/20 bias at the point of rear lock up and we throw 300lbs of sand in the trunk, then the numbers will likely change to 70/30. At this point the same amount of line pressure will be working the rear brakes harder, so we can then add more line pressure to get all of them to work harder without the potential for lock up. Intesting test; brake testing with and without weight in the trunk.

Now if we road race the car and gut it out pretty heavily, this does not really aid us as hoped as most of the weight removed is in the area we need it. But that's a trade off for overall reductions. So we put some Konis on the back and valve them stiff to help control body roll or pitch into a corner. This keeps the tire patch and weight in contact with the road longer thus allowing the rear brakes to contribute to the working being requested.

I've got some really neat formulas that can show what changes are netted to the brake torque when we upsize either end of the car, not a true change to the overall package as real world braking also has to take into account this weight issue and its biasing of the brakes.

Having been a SHO dude for years we often spoke of the 'prop valve' in the rear of the SHO, bunk. It's not a proportioning valve at all, it's a simple height sensor. When the rear of the car goes UP the valve shuts OFF the rear line pressure. This means nearly zero line pressure to the rear under extreme condtions. But if we bypass it, the car slows much better under moderate conditions, then ABS takes over under extreme loads. This shows us that the weight transfer to the front is so extreme that we cannot use what's back there. Unless we find a way to control that shift of weight under braking- stiff struts out back, heavy springs up front, reverse rake, whatever it takes. But each of these may have its own drawbacks elsewhere.

Lastly, larger brakes in the rear won't make your car a racer no matter how hard you try, they will 'enhance' the ability of YOUR car (depending upon other mods) to take advantage of what you may be able to achieve. I doubt a simple disc to drum of stock parts will have a significant effect one way or the other. However I'd run the same MC and any proportioning valve set up off the disc car when doing the change.