I've read several threads both here on NAM and at Motoringfile.com about the JCW Brake Kit......some posts in favor and some opposed.

The plus factors include "improved braking, " warrranty (and maintenance?) coverage; OEM quality and testing, etc. The negative appear to be cost, minimal improved braking, lack of flexibility in pad choice. Some say just change the stock pads, rotors, and use a higher quality brake fluid. Others say that for the money you should consider other BBK's like Brembo, StopTech, B3, Wildwood...etc.

JCW says this about their Kits:
Two internally ventilated brake rotors 294mm x 22 mm for the front axle
Two coated red floating brake calipers with the John Cooper Works logo for the front axle (improved caliper construction in comparison to standard brake)
Brake pads integrated in the front calipers with enlarged brake pad surface area and enhanced performance

But I haven't seen any size comparison between the stock rotor and brake pads versus the JCW.

Does anyone know the diameter and thickness of the stock front MINI Cooper S rotor?

How about the diffference in size between the stock vs JCW front pads? Any side by side photos?

We're talking about an investment of $ 1,358 installed at a MINI dealer, so I'm trying to decide before the car I've ordered arrives in a few weeks.

Dimension information and photos would be appreciated.

Charlie

 

The stock front rotors are 10.9 inches. The JCW rotors are close to 11.6 inches, so they're roughly 3/4 of an inch bigger in diameter.

 

Regarding increased braking surface, just try good ol' PI x R^2.

I'd use millimeters for my base units, vice inches, as some variations in conversion will occur.

Gimme a moment or three, and I'll see what I come up with..

Cheers,
Matthew Z.

 

Actually Matt, that's not correct.

The rotor is only 3/8" bigger in radius. So this won't be a huge change to the torque value.

However....

What you may want to calculate is the swept area of both packages. That's what you were driving at but didn't put into proper perspective. SA is NOT the only driving force to determining a good brake package but it can be a guide to things.

Swept area is that rotor surfaced covered by the pad for one rotation of the rotor. To calculate this you'll need the width and height (really the other way but we view it as this) of the pad. Call it 2x3. Then get the numbers on the other pad, call it 2x3 also. Now using this info take the OD of the rotor and subtract the area produced by the smaller circle by way of pad width. (10.9 Area - 8.9 area <10.9-2>) and you'll have the circles.

(10.9/2=5.45x5.45x3.14159=93.315)-(8.9/2=4.45x4.45x3.14159=62.211)=31.104Sq"

(11.6/2=5.8x5.8x3.14159=105.683)-(9.6/2=4.8x4.8x3.14159=72.382)=33.301sq"

Someone check my math but I see this as about a 7% increase.Not bad, but not huge.

For giggles and grins here's a 13" kit to compare things with.
(13/2=6.5x6.5x3.14159=132.732)-(11.25/2=5.625x5.625x3.14159=31.604)=101.128 Or about a 31% increase in swept area.


And of course this does NOT take into account ER as stated in the other thread below. The effective radius has huge impact on things. You can have a loss of swept area but more torque with a larger ER. That's why most racing pads are tall and skinny rather than short and fat. A short fat pad has less effect on torque. Although it CAN cover a lot of area in one rotation it's just not too effective at the slow speed and radius of the pad nose.

What's it all mean? Well anytime you can add swept area (and ER) you have a more stable and efficient brake system. More mass per rev means less strain on the part. Greater ER means less pressure requirements as well.

I'm beat, need a beer.

 

Todd, your math would give a good example, if the pads were the same area, the pad is actually almost .4 inches taller. this gives some good increases in SA
using your math below, I get
9.2/2=4.6*4.6*3.14159=66.476
105.683-66.476=39.207
31.104/39.207=0.79 ~ approx 31% increased SA (unless my logic is wrong here)
roughly the same increase as the 13" kit.....pretty impressive in my book. This kit also adds a good amount of thermal mass to the rotor, reducing the fade effects induced by overheated rotors.
this is a tall, fat pad. it also has an increased ER, so this kit adds BOTH; SA and ER.

 

Something is amiss with your calculations. 31% and the same as a 13" kit? Simply thinking of the differences in rotors you can see this doesn't add up.

If the pads arre out further from center line then the ER is greater. But ONLY if the pad itself is taller and skinnier, not shorter and fatter. This will of course be the case but for those following the numbers it needs to be said.

PAD HEIGHT IS REALLY NOSE TO HEEL, NOT TOP TO BOTTOM. In the case of the FSL that would be 1.75 x 4.75 and obviously they are viewed the other way in the caliper thus I call it 'nose to heel'.

The pads are .4" taller. If by taller in the true meaning you mean that they are out .375" further on the rotor then this has moved the ER out as we stated. And conversely the nose of the pad is further out as well. The ER for simple terms is the radius of the average of the pad. i.e. if the pad is 1.75" wide as on a FSL caliper the ER is (Rotor dia/2)-(1.75/2) or on a 13" rotor: (6.5/2)-(1/.75/2)= 5.635".

On the 11.6 rotor the ER is PERHAPS <guessing at pad size to be maybe 2.25" x something>; (11.6/2)-(2.25/2) or 4.675"

But we are a bit off track. The swept area is the outer DIA less the inner DIA. In the case of the 13 that's 13 circle area less 9.5 area circle.

The 11.6 nets only 11.6 circle area less 7.1 circle area.

Pads are taller in the case of a 2.25 part than that of the 1.75. And total area of the pads stock can be more in some applicatoins. In fact the pads for the DP calipers are smaller in area I bet than the stock MINI pad. Is that bad? No, not really. Pad size has nothing to do with brake torque- aside from determining ER. A big pad last longer. It does not stop better. Most 'better' pads for alternate calipers- Wilwood, AP, ST, Brembo etc. etc. are all long and skinny. This creates the ER that is needed. And as the rotors are larger the SA is greater as well.

*Note this is only for informational use. I have no beef what so ever with the product that started this topic. The questions arose simply took us down this path! AND yes I agree that any increase in rotor mass in this case is very helpful.

 

Fellas........................

I just asked a simple question (or 2).

Can someone tell me the difference in size between the JCW Kit rotors and the stock MINI front rotors; and if anyone has a photos (or dimensions) of the difference between the JCW front pads and the stock MINI pads, I'd appreciate that.

Thank you minicoopermike for the diameter difference. Anyone know the difference in thickness?

Todd, thank you, but I'm lost with your discussion between matt and polmear.

Please, just some dimension is all I need. Thanks

Charlie

 

Todd,
I'm stating pad height (my definition of tall before) as the outer rad - the inner rad , in the case of JCW pads, this is ~60mm ( I assume thickness of pad, and width of pad to remain close enough to stock to be inconsequential in the calc)
so you are subtracting a much smaller circ area (~174-5 dia) from a much larger circ area (~294 dia)
maybe I'm wrong about adding ER with this kit, but I believe that it is larger in this set-up.

Chief, I would assume that the most that the thickness increases is 4mm, but that is a guesstimate at best. I also assume that the rotor offset increases, because a new 'backplate' is included with the kit.

some pics are here:
http://www.mini2.com/forum/showthread.php?t=85247

I know there are others, I remember seeing some pics comparing JCW to stock rotor...just can't find them....durn!

 

Cool. More info is good.
So doing some quick math I come up with the following:

Stock rotors 48sq"
11.6 rotors 68sq"
13 rotors 62sq"


On the other hand the ER:

Stock rotor 4.45"
11.6 rotor 4.8"
13 rotor 5.5"

So, what's the difference? Honestly, the ER will return better results. For three reasons; 1. Total rotor mass is still greater for thermal cap, 2. The torque value is greater with the 5.5 set up, 3. With the larger ER you can use less piston area for the caliper. Why? For better feel and response.

Plugging it into the spreadsheet if the pistons of a 11.6 kit are about 2 x 1.375 then that's about the same as the stock bias. Because the ER is not much greater there is not much change in total rotor torque. A larger rotor kit will use less piston area. Can't speak for all caliper set ups. On the other hand, if the pistons are 1.75 there will be a shift in bias to the front. About 10% actually.

** Sorry this thead took a turn from asking for some basic info, but it's been an enjoyable conversation too. And understand that the data here is for infomative reasons only. This is not pointed at any one kit, rotor, caliper, manufacture etc. The data simply is what it is.