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  • Lightweight Front Brakes

    I'm partially along on making lightweight front dis brakes on RED, my soon to be BP powered drag racer. You can gain quite a bit of horsepower by lightening the reciprocating mass of the front drive train, so I am going with lightweight rotors.

    I'm using Aspire knuckles for the bigger bearings and stronger bearing support so I had to source a solid rotor that I could have machined to be lighten. Looking at E-Bay I found Miata rear rotors that were solid and smaller and cheap and looked like they would bolt on to the Aspire hub. So I bought a pair and yes they did fit right on - so time for measurement to see what could be machined off.

    The rotor was 9-3/32" in diameter and .385" (3/8") thick. The new Wilwood snow mobile calipers I bought could use a rotor from 6 to 9 inches in diameter and from .160 to .190" thick (up to 3/16" thick - half the original thickness of the Miata disc). I wanted to keep a larger diameter so the brake pads would have something to grab onto and wanted to keep the rotor fairly thick to handle the heat. Remember, it is a non-streetable drag racer so the car only has to stop from speed once every 30 to 60 minutes - plenty of time for the rotors to cool off. Also remember this car has NO rear brakes, so the fronts will get hot.

    To lighten the rotors I had them machined down to 8-3/4" od by .188" thick. Compared to the Aspire manual trans vented disc it was a huge weigh savings - 4.6 pounds per rotor! So for the Aspire front brake set up, it was a total weight savings of 9.2 pounds of reciprocating mass for both brake rotors.

    To keep with the reduced reciprocating weight up front, I plan on using golf cart aluminum rims in either 6 x 12 or 7" x 12" size with 205/30 x 12" or 215/40 x 12" DOT rated tires. The much smaller tire OD will numerically increase my final drive ratio, meaning I don't have to put in a new ring and pinion gear. The small tires should get me in the 4.90 - 5.0 final drive ratio (still have to do the math) which will be good for both 1/8 and 1/4-mile drag racing.

    I still have to make the adapter plates for the new calipers, which will fit in between the existing mounting holes of the big Aspire calipers. Pretty straight forward.

    So far, so good. Still having problems putting up pictures, but I've written the webmaster. If you want to see how it all looks at the moment, send me your e-mail and I'll send them off to you.

  • #2
    Great Job Doug!

    You are making great progress and 9.2 pounds of rotating mass should make a huge difference. Can't wait to see this thing make a few runs!
    "The White Turd" 1993 Festiva 144k miles. (Winner of FOTM November 2016)
    sigpic
    "The Rusty Banana" 1990 Yellow 5 Speed Mud Festiva (Lifted with 27" BKT Tractor Tires)(Winner of "Best Beater Award" - Madness 12 - 201

    "Papa Smurf" 1992 Blue 5 Speed Shell
    "Cracker?" (name pending) 1992 White Auto Shell (Future BP Swap)
    "Green Car..." Scrap Car that Runs?!?
    "Red Car..." Complete Scrap Car

    "El Flama Blanca" 1993 Festiva 104k miles. (Lil Brothers Car)
    https://drive.google.com/file/d/0BzM...ew?usp=sharing

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    • #3
      That is a big difference compared the the aspire rotor! I'm sure the caliper is quite a bit lighter too.

      However, both festiva and aspire use Set11 bearings on the front inner and outer... and the festiva knuckle is quite a bit lighter than aspire. You could probably use the aspire hub in a festiva knuckle to retain 4x100 if you need that, unless there is another reason to use the aspire knuckles.
      ~Nate

      the keeper of a wonderful lil car, Skeeter.

      Current cars:
      91L "Skeeter" 170k, Aspire brakes, G15, BP, Advancedynamics coil overs, etc. My first love.
      1990 Kawasaki Ninja 250 - my gas saver, 60+mpg - 40k
      2004 MotoGuzzi Breva - my "longer range" bike - 17k

      FOTY 2008 winner!

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      • #4
        The Wilwood caliper that I am going to use weighs 1.2 lbs - they are pretty small and light!!!! I used the Aspire knuckle mainly because the forging is thicker around the bearing area (more support) and the distance between the caliper mounting holes is big enough that the Wilwood calipers can easily be mounted to them with a simple adapter.

        I don't know how much of a difference it makes but I'm using a G transmission with the intermediate drive axle. It's what was on the BP car that I had and I'm just transferring all the parts from one cat to the other. And at this point in time I'm just trying to get it assembled and running as $$$ are getting less and less for any more major projects....

        If you send me your e-mail (not sure I have it...) I can send you a couple of pictures of how it is shaping up.

        I'll look at everything again with your notes in mind and see if the Festiva knuckle would work better. I might have to use it for the very small rims I'm thinking of using -- to be determined.

        Thanks for the info and for following the project along!

        Doug Brown dk9betts@gmail.com

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