SBGarage

These numbers all vary with tire compound, size, temp, and track. To yield any relevant numbers youve got to do back to back testing on the same track at least.

Rotor temp is a function of surface area, heat dissipation, and rotor mass. The solid rears have little, little, and littler. Moving air over the face of a solid rotor is a waste of a trip to Home Depot. You guys want to battle this so hard for some reason. I don't know why it took 16 years, but there are legitimate solutions. There's 16 years worth of threads showing the stock rears don't work in performance applications... I'm surprised that the response is: wait, is a vented curved vane rotor just snake oil? I don't know if it's just acceptance or complacence but we've had 20mm vented rears on the RX7 since 1984... And holy pickles batman, no threads about overheating rears . This isn't a mission to Mars, it's common sense, and it's astonishing the S2000 community is still splitting hairs over vented rotors vs solid rotors.

SakeBomb Garage

Well, the Lowes route is cheaper. Effectiveness of cooling a solid disc with an air duct?





Sorry I mis-read your comment. You can't determine Cf required based on temp of the rotor or pad. There are too many variables in trying to nail a particular bias based on temp. In fact fluctuating temps also change the Cf of the pad (changing your effective bias). The OEM brake bias is heavily front weighted... Honda was very conservative and left lots of braking on the table to cover their butts. Remember the width and compound of the tires change your effective bias, as you can brake harder with wide slicks in front vs skinny street tires. The more braking G's you can generate (wider sticker tires) the more weight transfer to the front axle you generate, and the less rear bias you want. Honda needs to cover all bases, and therefore are VERY conservative with their rear brake bias. Race cars have an in-cockpit brake bias adjuster to allow the driver to trim the rear brakes juuuust before the point where the rears are locking first, which will change based on tire temp, track condition, etc. Anyway, long story short rotor temp doesn't tell you what pads to run. We are recommending one step lower friction pad in the rear to remain conservative and close to the Honda prescribed bias (to cover our butts) but I will unofficially say the stock bias valve is heavily front biased and a square pad setup has worked well for us in testing. We have not tested with slicks, or on wet roads... hence our conservative recommendations.

Urge

No doubt this set up has more thermal capacity and cooling than ours. It also costs 50% more and weighs 50% more.
We can make an even larger rear rotor set up that cost more and weighs more, but is it effective for the S2000? Is it OVERKILL and simply adding weight or cost.
Also, we know most of our customers have spent years dialing in their brake bias so going larger and changing that will upset the balance of the car that most have tried so hard to set up.

Like our front set up, we took the weight of the S2000 and the typical HP range into consideration (250-500HP). HP is simply pushing the weight of the car to certain velocities on the straights so, the more power you have the more heat you have to take out.

The goal is to keep the brakes with in an operating temp range and not go over with as little weight as possible. Especially rotational, unsprung weight. Rotational weight can have a 2-3X effect vs static weight. So 4 lbs rotor difference can have a 8-12 lbs weight effect on the car PER corner and we know we all Fight to remove that kind of weight were we can. You may not feel that in the butt dyno, but it is measurable over a few laps.

Now how much rotor is really needed can be argued all day long so it all comes down to real experience. We have sold 38 pair of our Flow Rear Rotors not one person has needed more rear brake. Every one that has tracked has noted an noticeable improvement in braking through reduced temps, front or rear wear, improved braking performance or braking consistency.

Quantitatively our customers have validated the braking improvement. As noted, brakes cool fast and to have a 150 F temp difference after a cool down lap goes to show how much cooling we really happening on track. Potentially could be 300 F or more which is significant.

We support and sponsor about 10 competitive race teams with our brake kits. We can't afford to give them away as we are small shop so we discount them as much as we can. Our discount is typically only half of what they usually get and they still come to us based on our design as we provide a significant braking improvement AND REDUCE WEIGHT. Every race team has noted, they dont need more because I ask every time.

DavidNJ

Each pad is designed to operate in a specific temperature range. The temperature of the rotor directly effects which pads can be used. Hawk DTC-70 pads have a range of 800F-1200F, DTC-60 700F-1100F. The newer DTC-50 pads have a range of 500F-1100F which would seem to make them preferable, but they don't seem to be in Honda sizes.

Coefficient of friction affects front/rear balance. Aren't you recommending pads with a lower coefficient for the rear to compensate for the large OD of the RX-7 rotors?

Ideally, front/rear rotors would be sized and cooled so they ran similar temps and used the same pads. Swapping pads to achieve balance isn't a good policy, there just aren't enough similar pads with different coefficients but similar modulation characteristics. It is primarily done to compensate for sizing errors usually caused by the class rules or parts availability.

The RX-7 rear rotor/caliper is a very viable way to add a brake with more heat capacitance and cooling to the rear of the S2000. But it can't a priori be said to be better than another different rotor solution without actual track measurements. Even then, the result may vary track to track based on peak braking requirements, on the power and chassis setup of a specific car, and on the driver.


Whether one setup is overkill or not would depend on actual measurements. Given the number of people racing your rear rotor, have any bought $80 worth of temperature paint and taken any measurements?

The primary advantage of the Urge rotor over another solution would be maintaining OEM front/rear balance since stock OD and caliper piston size is retained.

A couple of pounds of weight or a fraction of an inch in diameter would never be noticed with respect to performance. The effect of the rotational inertia is fairly small because the radius is small and the differences are very small. If someone can feel or measure that difference on a race track they could also feel a pea under 20 mattresses. A bigger effect would be having less water before the event or eating a light breakfast.

It would appear that the Urge setup may be better if the stock front caliper or a setup equivalent to the stock front setup is retained. I think that would include the StopTech and the Spoon front brake setups. If a BBK with larger diameter rotors and/or pistons is used, then the RX-7 setup may compensate.

A note on coefficient of friction. A higher coefficient of friction means more braking can be achieved with for a given pedal effort. Often that is needed to take advantage of the increased traction of race tires. A lighter pedal is also easier to modulate. That only is relevant if the pad is operating within its temperature range; the coefficient of friction drops off quickly both above and below the intended temperature range.

Soviet

How did ya'll end up modifying the rear brackets? Or did you purchase the modified bracket ahead of time?

freq

I thought that was the beauty of the Urge 2 piece rear rotor? It was plug and play in place of an OEM rotor.

EDIT:

Rear Pad Management

• When installing 2 new pads, each pad needs 2mm shaved off
• OR 1 new pad can be installed with a partially used pad, continue swapping pads to maximize use across both sets of pads

Rear Bracket Modifications

• 5 mm needs to be removed from the long, inside of the bracket & 3 mm from the short, outside of the bracket
• We can do this for $100 + $100 refundable core swap (US only, International must modify locally)
• US customers can modify themselves to save time & money

Soviet

Im particularly interested in how folks have modified the rear brackets themselves. I just took my OEM brackets to a machine shop and they didn’t want to modify mine. I’m considering using a die grinder but wanted to see if anyone else had other ideas.

freq

I too was considering these. Have you reached out to URGE?

Soviet

Yes. No response yet (Friday night) but I’m looking for DIY experiences.

spaded.racer

When looking at these I was going to buy ones already cut by Urge. I ended up going a different direction.

You have a Dremel? Looks like some patience and a handful of metal cutting discs would make quick work of it.