Also, all the wheels that fit our competition kit will fit this.
See list on our site.

 

In the photos it shows the CP9440 caliper but on your site it says it's the CP9448 caliper? Why the change? Doesn't the CP9448 caliper bring the bias really far forward when combined with the larger rotor?

Also on AP racing's site, it says the CP9448 should be used with a 378mm rotor that's a minimum of 28mm thick. Your kit uses a 338 x 26mm which is smaller and thinner than recommended...

 

Great catch!! We actually use the CP9441 and not the 9448.
The 9441 has smaller pistons and paired well with our rotor thickness and diameter. We are updating the site quickly.

When we first started working with Essex on a 4 piston Radical kit for the S2000, the first caliper/rotor combo we tried was the 9448 and 340x28 with 60 vanes rotor.
We settled on the 9441 and 338x26mm rotor to get the right balance and air flow with 72 vanes.

We will offer a discount for the great catch.

 

It seems with the CP9441, the bias is shifted rearwards, is that a problem? Will it cause any rear lockups?

As for the rotor choice, what's the reasoning with the larger size and thinner rotor? It seems the recommended size is 330x28mm.

 

Love the great questions..

On the 9441 Radical pistons the effective piston surface area is smaller than OEM, but the centerline of the pistons are 17% further away from the hub than OEM with our brackets, bringing us with in a few % of OEM torque bias.
Our radical kit has the closest to OEM brake torque bias with an overall bias of 65/35 which is optimal for a 50/50 weight distribution car.

Most other BBK have 10-15% larger effective piston surface area than OEM AND a 5-10% larger effective radius providing 15-20%+ increase in front brake torque and significant increase in front brake bias.
This means a lot more front lock ups and a significant reduction in rear braking potential.
With a 50/50 weight car, even with brake dive, there is a lot of braking potential in the back and significantly shifting brake bias forward will reduce overall braking potential.

A good proof point is our rear rotor kit which doesn't change brake bias, but simply prevent the rears from overheating, has proven to lower front BBK temps by 40F after a cool down lap, which likely means over 100F on track.
Our rear BBK customers experience 30-50% reduction in front pad and rotor wear, meaning the front BBK is overheating less and performing better and more consistently.
This proves there is a lot of opportunity for improved overall braking with an optimized set up that includes rear improvement.
So a major shift forward in brake bias would would actually stress the fronts more than needed and reduce rear braking potential, reducing overall braking performance.

As far as the rotor choice, most BBK focus on larger thermal mass, and that is simply reducing the time to heat up.
The goal is to shed heat quickly, hence vented rotors, cooling ducts, curved vanes, etc.
For example a vented rotor would work much better than a non vented rotor with twice the mass.

So, we wanted to find a rotor that flowed even better than our base kit to go along with the Radical caliper stiffness upgrade, with out a giant jump in mass.
Our base kit actually is a lower weight rotor than OEM, but can support 2X OEM horsepower with track abuse because it has 60 Vanes or >2X OEM. It sheds heat really well.
For the Radical kit we found a rotor with 72 vanes or 20% more than our base kit or ~3X vs OEM with only a slight increase in weight, yet still 20-50% less weight than other BBK not the market.
Its a perfect compliment to maximize heat dissipation with out adding unnecessary unsprung and rotation weight to the car, reducing acceleration, grip, cornering and braking performance.

I hope this answers your questions.

 

Yah I think the CP9441 is a better choice than the CP9448. Glad you guys went with that change in the end. I guess the change in bias is small enough that you can tweak it with a different pad compound to adjust the coefficient of friction.

Interesting point about the rotors. I guess it's definitely good to have the extra surface area from the 72 vanes vs 48. Weird how I don't see that CP7472 part number on AP's site. Is there any risk that it'll be discontinued?

 

Rotor shouldn't be discontinued, Essex buys them by the Pallet.
We do have an alternative option to buy as well if needed.

As far as the bias, I went and did the calculation, we are the only kit with in a few % of OEM Bias and arguably more optimal.
All other BBKs are increase front torque 10-20% meaning way too much front bias for a 50/50 weight car.

 

Thanks for the info. Now I'm thinking wheels.

I see you guys have a list for your regular kit but not the radical kit. It seems the radical kit leaves more space so that should help. Any idea if CE28 in 17x9 +63 would fit?

 

Every wheel that fits on the Competition kit fits on the Radical kit.
Here is a template for the Radical kit, please print to scale in acrobat to test fit your wheels.

 

Brakes are goddamn amazing. Also clear my 17x9 +63 Advan RSII (with 3mm spacer to clear the control arm) with ease.