EBC Red front pads and rotor question

[SHOw-Me State]

Hello all,
Just wanted to ask feedback here before trying to reach EBC.  Looking at replacing the fronts on my 2011 SHO non-PP.  My research and understanding is that the only difference between the non-PP and PP package is the pads.

So, looking at the excellent post from Glock-coma in another thread (I inserted below), EBC actually has two different pads technically.  However, I would assume that the material is exactly the same--I mean I'm sure it is whatever the Red material is for both.

If that is true, then I have another question.  It appears that there is a fair amount of 'un-swept' area of the discs in the pictures I have seen posted.  I'm wondering why.  Additionally, hard to tell from the picture, but I wonder if the non-PP pad actually has more area??  I'm thinking if the pad material is the same for either Red pad, maybe EBC can elaborate on which on actually has more surface area, and theoretically more performance?

Just finished installing ebc usr7510 front rotors and dp31767c pads.
Here's a pic of the non PP dp31825c pads on top
And the PP dp31767c on the bottom.
I do not have PP but the pads went in just fine.

I'll have some installed pics tomorrow.

 

[glock-coma]

Yes that is true the bottom pads are the performance pads and it does seem that it has less swept area in the nonperformance pads.

After having the brakes for approximately 10 months you can definitely tell the contact area on the rotor is different.
If I had to do it again I would put nonperformance pads on.

These brakes do make a huge difference in stopping ability once they're broken in properly, the pedal feel only has a slight change.
I'll try to get some pics later today but it's been snowing pretty bad here in NE Ohio.

 

[ajpturbo]

I thought the pp rotors were bigger and the rear rotors are vented compared to solid.

Also a bigger swept area could mean less performance. Think of a pucked clutch disc compared to a full face ..less surface area = more psi if the pressure applied is the same

 

[SHOw-Me State]

I'd have to dig up the info, but I thought the '10-'12 models didn't have different rotors (at least on the front), but '13+ did between non-PP and PP??

From mounted pictures I've seen, it looks like the inner 1/8-1/4 of the rotors are not touched/swept by the pads.  Not sure why.

This is where I was curious, by looking at Glock-coma's picture, if the non-PP pad would actually cover more of the disc.

The pads themselves look very close in actual area, but hard to compare since shape is different.  Your point about PSI versus swept area is good.  I guess a compromise has to exist between higher PSI (smaller area) versus friction/drag (larger swept area).  If the area of the pad is close or very similar, I would think have more sweep would help.

To be honest, I will have to look at my stock setup.  I'm curious now if that inner portion of the disc is unswept even in a stock setup......

 

[ajpturbo]

I think you are grasping at straws....I have GT500 brakes on my mustang, rotors and calipers. They are 6 piston Brembos with 15" rotors and there is a good 1/2" gap of unswept area between the hat and pad.

Changing the pad compound is the best brake upgrade you can do for the dollar.

 

[IHeartGroceries]

I'm not sure it is something that ought to be dismissed so thoughtlessly. While I agree material has a large impact, contact area would certainly result in appreciable effects, for better or for worse.
I'm no expert, but if it is anything similar to the importance of tire contact patch, the effects certainly aren't negligible.

 

[ajpturbo]

It's not even clear that the non PP has a larger swept area anyway...When I look at the 2 pads the PP Doesn't touch the inner part of the rotor but does on the top because of the curvature.

The NON PP is flat on the bottom so doesn't follow the rotor curve and doesn't touch the top of the rotor fully, call EBC LOL

 

[glock-coma]

Bad pics due to weather

 

[ajpturbo]

That's how my 14' Gt500 Brake rotors look. I just called EBC and they said it's exactly like a clutch disc. Less surface area will create higher clamping force. They have to get back to me since they have to contact England LOL...But the guy said the swept area will be really close. A larger swept area will give longer pad life.

 

[SHOw-Me State]

All great input!  Thanks for the additional pics Glock-coma!

Okay, I totally agree that less surface area would equal higher clamp.  So, for highest clamp, pad should be exactly the same size/shape as the pistons.  Not sure I would want that though.  I am not an engineer, but friction obviously has a part too.

So, looking at Glock-coma's recent pics and the original.  Wouldn't the two outer 1/4 portions of the non-PP pad still contact the outer portion of the disc, just like the outer curved portion of the PP pad?  In addition, comparing the non-PP pad to the PP pad in Glock's picture of pad in place on the rotor, wouldn't the 'extra' squared off portion on the inboard side of the non-PP pad also contact more of the inner portion of the disc?

I'm not sure the clamping force between the two pads would be that much different, as not sure the actual surface area of the two pads is that different.  But, just wondering if there could be slightly more contact/sweep with the non-PP pad.  Whatever it is, it is probably marginal (or straws) I agree, but seems if any small increase in performance there, guess it couldn't hurt.

Sorry been bouncing on/off between here and work--thus haven't even tried talking with EBC so far!

 

[ajpturbo]

Dude u are over thinking it...if less surface area equals higher clamp load then that alone would equal more friction also...I think u are backward in thinking that more area is more friction...I could see why u think that...splitting hairs here really...but if u want more bite or friction u need a pad compound that has a higher coefficient of friction....some brake companies display this some don't....but that usually comes at the expense of the rotor life .

 

[IHeartGroceries]

How is there more clamping force exerted due to a smaller contact area of the brake lining? If you were to increase the size of the contact area without increasing size of the piston, there'd just be a larger area of contact with less force applied around the outer edges. To increase clamping force, you'd increase piston area, or you'd increase the force the hydraulics can exert.

But, how is friction relative to clamping force? Friction is what is slowing a car, not clamping force. That's why brake fade is a problem. When components overheat, clamping force isn't lessened. Friction is. And that's what results in reduced stopping power.

 

[ajpturbo]

There is obviously more to it but less surface area equals a more concentrated pressure point creating more friction...argue with ebc lol..I'm just saying what the guy told me

 

[ajpturbo]

I did some homework for you's folks.

DP31767C PP = 52.6 mm^2 swept area

DP31825C Non PP= 45.7 mm^2 swept area

This from EBC

 

[Josephm]

Here is what he saying. P=F/A ...MEANING if the Presure stays constant, and the area decreases, the FORCE will increase.

Yes on a smaller AREA but with more FORCE on that smaller area.

 

[SHOdded]

You want more swept area when possible, so more friction action is available between pad & rotor.  You gain more braking effectiveness.  NOW the catch is to keep the braking action proportioned to OEM specs.  So if the distribution was 60/40, you don't want to significantly upset that ratio, especially with all-wheel-drive in play.  Upgrade the front brakes, you should upgrade the rear brakes also.  Either via a higher CoF brake pad for the rear, or increased swept area if the rotor has the potential for it.  All within the limits of tire grip.

 

[SHOw-Me State]

Thanks AJP for the numbers!  Work and my 20 month old have keep me tied up and not focused on my toys.  So, visual queues aside, the PP pad has more swept area.

Josephm--I agree with what you and AJP are saying, however I think you have your variables wrong in your statement.  P=F/A, so solving for Force, then F=(P)(A).  Force is the variable that is constant and is what is being supplied by the hydraulics on the pad (Area).  So, if Force is contant, Pressure changes invariably with Area.

Now as mentioned by SHOdded, we could have loads and loads of Pressure (or even Force if we actually increase that in the system) but it would be useless without available friction.  Since both pads are assumed to have the same CoF, higher swept area is better.  Is there a point where the higher Pressure would trump higher Area, for a given CoF?  Probably so, but I don't think our given system would supply.  Ford designed PP pad has more area and was copied by EBC.

 

[SHOdded]

Much easier to change CoF and swept area than pressure, can be independent of OEM brake system design.  Plus higher pressure would also be hard on the braking system/brake lines/caliper/pad/rotor, decreasing useful life.