Brake rotors; weight vs size for track use

[rascal]

I am modifying my NB8A to suit track work.

As such will be getting new slotted discs and new pads.
I got to thinking that since I am buying news ones anyway is it worth it getting the larger NB8B rotors and making adaptors to mount the orig caliper further out to match the new rotor size.
(ie similar idea to 949racing.. http://www.949racing.com/index.asp?Page ... ProdID=207 )

Would the extra diameter be of enough benefit to outweigh the extra weight of the bigger rotor? My car is and will remain naturally aspirated.

I am running 15x7 Buddy Clubs so cant go any bigger than NB8B (and dont want to spend zillions) so thought this might be a simple almost free upgrade.

Also what pads are good value to use as track pads? (ie not mega expensive but not cheap nasty ones either)

Or am I best to stick with standard size rotors to as not to upset front to rear balance and just run good pads..

Rus

[Fatty]

nb8a rotors (slotted dba) with good pads (hawk hp+ front and rear) perform very well on my turbo na6 (120rwkw) so i doubt you'll need to upgrade....

just get good pads and rotors.

[rascal]

Hi Fatty,

Cool. Thanks for the info..

Rus

[wun911]

To me a larger rotor would be a "bigger heat sink".

Have you ever experienced fade or boiled the fluid on the track or on daily driving?

If not maybe its just added weight slowing you down.

[rascal]

Yes, bigger rotor would help to dissipate heat better, though it was more a question whether the bigger rotors were necessary, and just extra weight for minimal benefit. The car will only have double digit kw atw so every bit helps...

I am yet to do a track day in this car (only owned it three weeks) and after having re-done things two and three times over with the previous track car, am keen to avoid heading down the same money pit path again, and want to do it correct the first time.

Sounds like std size slotted rotors and HP+ pads all round will be plenty.
I'll run with that..

[orx626]

Hi Rascal, the best thing you can do for heat dissipation is to improve cooling airflow to the brake rotor/caliper assembly. See if you can add some ducting. Having a big heat sink is not the solution because once the heat sink is hot where does the heat go?! All you are doing is slowing the time it takes for the rotor (heat sink) to get hot. For sprints this may be suffice, but on a track car you've got to get the heat out of the heat sink and into the ambient air for the brake operating temperature to be controlled.

Cheers,
Danny

[Hellmun]

If your not running forced induction you should be fine on the standard brakes unless there's something faulty with them. They really are excellent for the weight of the Mx5. Just make sure your slider pins are greased properly, with good fluid and good pads. I'm currently running DBA4000 front rotors, RDA slotted rear rotors, RBF600, stainless lines and the carbotech X12's all around. Havn't had brake fade yet since the pads wore in.

[rascal]

Hellmun,

Where did you get the pads and rotors from, and how much did they set you back?

[Hellmun]

I got them before the dollar went downhill from 949racing. http://www.949racing.com/

[16bit]

be aware though - xp12's are a TRACK ONLY pad. very high friction co and start working at 250 degrees f. they are not recomended for amature drivers.

[rascal]

16bit,
my car will be a track only car so no probs there, and I've been racing for over 10 years so like to think I'm not an amateur driver..

Hellmun,
How did you decide on the xp12s? I notice on 949racing site they mention the Spec miata's are running xp10 front and xp8 rear.
(also how much did they charge for shipping from the US)
Sorry for all the questions
Tks
Rus

[Hellmun]

Actually I got XP10's instead of XP12's now that I look at my order form...I think when I ordered them there weren't XP12's available for the sport brakes on the NB8B+ or the XP16's. I've just remembered them because those were what I wanted .

I didn't want to pay the huge price for Ferodo's, the HP+ I melted easily and the hawk blues sounded far too destructive to rotors for getting to and from the track on. Carbotech's seemed a better compromise for a high-temp pad with good bite but still livable to and from the track. They squeal at low speeds but otherwise...they've had over 10 trackdays on them already and they have over half-meat left. They faded my first 3-4 trackdays even after break in on the last laps...but the 6 days since I've had no problem at all.

I paid $44 USD for postage but I got front/rear pads, plus stainless lines and 16 lug nuts. So it should be less for just the pads but not sure how much. Emilio at 949 is pretty quick at email replies so you could get an up to date quote pretty easy. I think the Hawk Blues are probaly cheaper if your trailoring the car for a similar if not better level of bite and heat resistance.