SDLS1Rider

Do you require a larger rotor to make a significant improvement in braking?

I have a C5 coupe. I would like to install a 6 piston brake caliper, like a C6 Z06 caliper upgrade. But these calipers and most brake kits won't fit within the stock 17 in. rims.

There are certain brake kits for 17 in rims. However, I had someone point out that without the larger diameter rotor, the bigger calipers will be useless. A larger rotor will provide brake pad contact farther away from the wheel centerline. This will produce more stopping torque. It makes sense on a chalk board. But does that mean upgrading to a 6 caliper/4 caliper set up will not provide a significant braking improvement?

Everett Ogilvie

It's a good question, and a larger diameter rotor can provide greater brake torque (simply because the position vector in RXF is longer - the torque/moment calculation). Many folks feel that additional available brake torque beyond what is required to lock up the wheels is meaningless, and there are some folks who say you don't necessarily need the largest diameter rotor that will fit inside your wheels, and simply go with the largest diameter rotor that provides "enough" brake torque.

I guess I am one of these guys because I recently REDUCED the size of all 4 rotors on my car (14" ---> 12.8") when I installed Gary's T1 AP Racing brake kit front and rear. I reduced available brake torque, but I also significantly reduced rotational/inertial effects. I think the rotors in the kit are used in one of the NASCAR series so they are proven race parts, and the fact that NASCAR Cup cars are limited to smaller diameter rotors than some series because of their rules/wheels, but their brakes are SO powerful and proven, says a lot about race parts vs. high performance "street" technology.

I say go with "enough" rotor diameter, but definitely go with the most heavy duty caliper and rotor that you can find in the right sizes. Things to optimize are clamping force, caliper rigidity, heat capactiy (in the rotor and caliper), ease of maintenance etc. I chose smaller rotors, but more heavy duty proven race parts and so far so good and the brakes were very impressive at their first outing at Road America recently.

damenh85

I agree with Everett's statements. I would also add that to "add a significant improvement in braking", it is necessary to identify what current limiting factor is. For example, if you can lock up the brakes (or activate ABS) throughout an entire session/race, it means you are most likely grip limited. Therefore to add improvement, you might adjust brake bias, move to a stickier tire, add aero, etc. Increasing rotor diameter probably wouldn't help in this case.

However, if you find that you can't lock up the tires (whether it's due to insufficient brake torque, system overheating...), a larger rotor (among other things) may be quite helpful. So I guess the oft-quoted engineering answer applies yet again- "It depends..."

AU N EGL

With STOCK C5 now C6 Calipers and STOCK / NAPA Rotors.

Castrol SFR brake fluid

and WILWOOD H or PFC02 brake pads, I can lock up my front tires. Car stops so hard if feels like it is doing a motorcycle stoppie ( rear wheels dance ) Hawk DTC-70s are even more aggressive

I also use 305 FRONTS tires

The more meat you have upfront and the more aggressive brake pad the better the stopping power.

Bigger Calipers are not always for harder breaking. Long term use less wear and tear on parts YES.

Going to a StopTech ST60 or ST40 front will work just fine.

I think most ppl dont feel their brakes work too well is for these few reasons;

1. The brake pads they use are too soft or warn out. Stock pads or ever HPS or HP+ and forget ceramics brake pads.

2. their front tires are too narrow

3. Old brake fluid

4. they are afraid to use the ABS

I toss my calipers each winter do to caliper spread

Ideally HardBars new AP racing T1 system, StopTech or wilwood would be very good choices.

Bill Dearborn

I used the LG G Stop kit on my 03Z for 4 years. It worked great and made up for some of the deficiencies in the stock calipers such as allowing too much pad taper along the length of the pad thus causing long pedal situations as the pads wear. The kit permitted use of the C5 stock rotor and would fit under OEM C5Z06 front wheels.

The new Hardbar kit looks very good and is getting great reviews on this forum so it is definitely something you should look into. I think the chief advantage of bigger rotors is their ability to handle more heat so the brakes don't get overheated. Usually more brake cooling is the lowest cost and a lot of times the most beneficial mod you can make so it should be one of the first things to do.

Bill

redtopz

These fit under stock 17" rims:
http://forums.corvetteforum.com/nort...brakes-fs.html

0Todd TCE

Most factor "improved braking" to mean a shorter stopping distance. No quite so easy to put you finger on that as some may think.

Shorter distance means a few things: either an increase in tire adhesion, a reduction in time or less fade. Or a combo of any of them. (all I can think of right now...!)

To increase brake torque however you can: increase piston area, increase rotor diameter, or increase the pad coefficient of friction. In order of effectiveness I believe you'll find it is Piston Area, Pad Cf, then Rotor Diameter. (assuming a reasonable change)

Piston area is clamping, going up 20% for example nets a significant change in clamp load. Pad Cf is a huge factor too. Rotor size...not so much. A one inch change is only .500 radius so that's not really so much.

So we must need more piston area! Uhhhh, maybe not. Piston area with the same master cylinder in use makes more torque. But at the expense of a longer pedal. Longer pedal makes for more time.

So we need more pad! Maybe....as long as it's up to the temp demands and is not over braking or under braking for the need.

Ok, we need bigger rotors then! Probably....but not because they make more torque; they just do it more efficiently. The caliper and pad don't work so hard, the pad runs cooler. Other than weight not a lot of negatives.

Why do all the BBK out there use bigger rotors then rather than more piston area or pad? Because first they look good....that out of the way, because they allow you to retain lower piston area and less demanding pad.

The basics of a good brake system (quote me if you must from over five years ago):
1. Increase rotor diameter.
2. Decrease piston area.
3. Tune with pad.

Stick with that rule and you'll seldom go wrong. More efficient rotor, quicker reaction time and improved modulation, pads to match the demand of both tire and surface.

davidfarmer

I think a rotor with more mass can absorb and dissipate more heat than a smaller rotor. A 12" rotor will work fine, but a 14" rotor will hold up longer before suffering heat related issues (all things being equal). Anything larger than 14" is too much mass.

If you run a larger piston area in a caliper you screw up the pedal travel and bias. A larger, (or more importantly) stiffer Caliper will ideally have the SAME total piston area as OEM. Even stock brakes with stock pads can lock up the tires......it's coming up with a package that can do so for 20, 40, 60minutes etc.

For a Vette, I think a 14" front rotor, 13" rear rotor, with a solid monoblock style caliper (Stoptech, etc) with proper piston sizing is the way to go.

Everett Ogilvie

You are correct only if the larger diameter rotor is indeed of greater mass than the smaller diameter rotor. Case in point; the 12.8" diameter rotors I put on my car when I took off the 14" rotors. The 12.8" rotor weighs 2 oz. more than the 14" rotor (thicker walls). So - a greater thermal mass capacity in the smaller diamter rotor, which is the only reason I made the decision to go with it - had it been of less thermal mass capacity I would not have gone to it. So, I had 2 wins - a slight increase of thermal mass in the rotor, but WHERE the weight is carried (further inward) is highly significant! Overall I now have equal or greater thermal mass capacity, slightly reduced brake torque (for the rotor diameter contribution only, more than made up for with a superior caliper and a race pad with very high friction coefficient) and greatly reduced rotational/inertial effects (30% reduced).

The takeaway, at least for me (and I would suggest for guys looking for rotors) is if you can find a super HD rotor (a real race part such as the NASCAR rotors from Gary and Jeff) that is smaller diameter but heavier than what you are using, it may be worthwhile to give it a try.

John Shiels

You can run real fast with the 13" hardbar set up or Wilwood kit from LGM. Stoptech two piece OEM replacement is about 1 pound heavier than stock OEM one piece. So if you don't want to buy a bunch of rims they both work great.

Z06trackman

In a word, No.

For roadracing the improvement you are looking for is heat tolerance and perhaps modulation. You can improve modulation with a stiffer caliper, stiffer lines, stiffer caliper mounting components, and pads that modulate better. You can improve heat tolerance through more effective cooling, more heat capacity of the rotor and caliper, higher temp capability pads, and more insulation for the fluid. So, even if the rotor stays the same, there is much improvement to be gained, and as someone else posted, there are downsides to a bigger rotor.

I wouldn't worry at all about rotor diameter as it relates to brake torque. Modern race pads make more torque than you need even with stock diameter rotors; nobody has trouble locking even a full slick if the brakes aren't overheated. If you want to use a stock rotor and 17" wheel, go for a high quality 4 or 6 piston fixed caliper, a race pad designed for the rotors temps you end up with (use temp paint) and the best cooling available. Wilwood for calipers and DRM / Quantum for cooling come to mind. (the kit Bill mentioned uses Wilwood calipers)

An additional benefit to this approach is that rotors are cheap!

For autocross, all you need is higher coefficient pads. I prefer to not use full race pads so that I am certain I have friction in cold weather. I use Carbotech AX-6.

SDLS1Rider

I want to thank everyone for the excellent feedback. I never thought about increased caliper pistons would result in a long pedal (but makes perfect sense).

In my application (canyon carving) I have not noticed any brake fad. But it appears that the idea that an upgrade is useless without larger rotors has been debunked. Also, I can't see that I really need a brake upgrade. It seems my C5 brakes are sufficient, and that a 6 piston caliper may be just a visual upgrade? While I'm sure I'll see an improvement, I don't see how the change would justify the expense.

Again thanks for the information. Posting this in here was a good idea.

0Todd TCE

To clarify a bit; an increase in pistons does not necessarily make for a longer pedal. An increase in piston AREA does.

While it may appear splitting hairs there's a huge difference here. Replacing a four piston caliper with a six piston unit is quantity and that alone means squat.

SDLS1Rider

But wouldn't an increase in the number of pistons mean an increase in area? Speaking in real world equipment of course. For instance the stock calipers have 2 pistons (fronts). Replacing them with a 6 piston caliper would almost certainly increase the area. Are we talking on the same page here?

If all of the pistons have the same diameter then I would be right. But if the diameter of the pistons in the 6 piston caliper are smaller, then you would be right. Is this what we are talking about?

longdaddy

these 2 posts pretty much capture all there is to it and are 100% in line with what my experience has been.

i agree that it would be better to have smaller rotor with higher density/mass and good geometry to dissipate heat. but it is still far better to have larger rotor than a smaller one that does not have enough mass to "store" the heat until it can be dissipated. that causes the energy to go into compromising the material of rotors, pads, calipers, etc.

at some point replacement cost/availability also comes into play.

davidfarmer:

Everett Ogilvie

0Todd TCE

I think you've petty much answered your own question haven't you?

Lasco001

Currently I have the Alcon in the C5.
Race for the use of good but not perfect.

I'm now an experiment.
I ordered the saddles of the ZR1, brake discs and pads I have in the ZR1 at Monza and Imola already tested several times. Braking is more fun than Speed​​!

Cölestin

SDLS1Rider

Pardon my ignorance but are the alcon the stock rotors?

I see you are from Switzerland and your conducting an experiment with the calipers (hydraulic piston casings) of your ZR1. Sounds like it's working out.

Thanks for contributing Cölestin.

Looks like the best brake mod for my purposes would be high performance rotors?

Lasco001

Hi SDLS1Rider

This pliers I have installed front and rear.
Of course, I have ven discs from Alcon.
Please do not misunderstand provided, the system also works really well.
But in a race, these brakes also come after 30 minutes to the limit.
The brake pedal is permanently on the ground, so pumping is announced.

http://www.hrpworld.com/index.cfm?tp...roduct_picture

Yes, I'm from Switzerland
best regards Cölestin

NB: Unfortunately I can not set pictures.
If you give me your email, then I send you pictures of my brake

hemipanter

We can look at two sides of the problem, the maximum braking force and how much braking we can use for a certain period of time. In the case of maximum braking power, the diameter of the disc and also the pad size will be of minor importance.
What determines the braking force is the friction of the tires, which in turn is using the weight distribution between all four wheels during the braking situation. Then, the braking force of the braking system must be evenly distributed in the same proportions between the four wheels.
The final line, it's about a balanced system and the physical weight distribution of the car and the tires.