Brake Math/Torque Spreadsheet

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Legacy777
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Brake Math/Torque Spreadsheet

Post by Legacy777 »

I may have posted this before, but I've had some time to go through the spreadsheet and clean things up, and make quite a bit of improvements. The biggest being a 'Brake Torque Calculator'. Let's say you want to swap some WRX brakes onto your 90 Legacy. Choose your car from the drop down menu, and the WRX as what you want to go to, and the calculator will spit out the percent change in brake torque and whether the shift is frontward or rearward.

If you don't see your vehicle in there and have information on your car, please let me know and I will add it. Likewise, if you see anything that looks incorrect or suspect, please let me know.

http://www.main.experiencetherave.com/s ... kemath.xls
Last edited by Legacy777 on Tue May 06, 2008 8:28 pm, edited 1 time in total.
Josh

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Post by professor »

Pretty cool.

I put in what I did to the wagon (WRX in front plus performance pads all 'round) and it showed a 38% increase in front bias. I did not notice this so much because it seemed to me that the front was very weak in stock form, and with the warped rotors I had it was downright dangerous. It feels very well-balanced now.

The brake upgrade was definitely the best money I've spent. Calipers get old and getting essentially new ones plus rotors and pads for $150 is a steal.
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Post by Psychoreo »

im supprised there aren't more comments about this, so here's mine.

THANKS JOSH!!! this thing is amazing. I was all about adding WRX brake stuff up front and H6's in the rear, but after viewing this, i'm thinking 05 GT stuff. should be fun.
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Post by jamal »

Psychoreo wrote:im supprised there aren't more comments about this, so here's mine.

THANKS JOSH!!! this thing is amazing. I was all about adding WRX brake stuff up front and H6's in the rear, but after viewing this, i'm thinking 05 GT stuff. should be fun.
well, I already commented on it at USMB.

Why did it make you change your mind about the WRX/H6 stuff? It keeps the bias the same and is less expensive. I'm doing it, and with good pads I think the only time I'd have to worry about heat is on a track. Seems to me that LGT stuff would be overkill.

After playing around with that, if I had a turbo I'd keep the rears and get 4-pots. Better feel, better heat capacity, similar bias, and vented all around for the win.
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Post by Psychoreo »

Yea, but the LGT stuff i can get damn near for free because i know someone that totalled one. body is damn near completely scrapped, but the brakes are still good. that and with a "performance pad" it should send ~10% of the brake bias frontward.
stupid electrical work...
Legacy777
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Post by Legacy777 »

Big issue with the LGT brakes is the need for 17" wheels
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Post by Psychoreo »

awww.....really? damn. Meh, then it's back to the wrx/h6 stuff
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Post by Imprezive »

What program do I open thing thing with? I guess I'm not that computer savvy....
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Post by entirelyturbo »

Imprezive wrote:What program do I open thing thing with? I guess I'm not that computer savvy....
MS Excel.
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Post by AWD_addict »

Wow, this sheet is awesome. Thanks Josh!
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Post by Legacy777 »

Welcome
Josh

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Imprezive
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Post by Imprezive »

Wow, this is pretty damn sweet! I am impressed!
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Post by napphappy »

AWSOME resource! Thanks

only input.
Line 55 & 56 on the brake data page. Its kinda confusing. I know there are a total of 4 pistons and they are different sizes. Is there a way to to do it so its easier to understand?
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Post by BAC5.2 »

Josh,

Is there a way to input information? Like if I were to use an aftermarket caliper, how to determine biasing and percentages and such?

Also, you say the effective rotor diameter of STi 4-pots is 10.02" but the 02-05 WRX uses a 9.72" effective rotor. With a quarter inch + difference, how can people use OE WRX rotors with STi 4-pots? Mistake on your part or misguided people using STi 4-pots with USDM WRX rotors?
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Legacy777
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Post by Legacy777 »

napphappy wrote:AWSOME resource! Thanks

only input.
Line 55 & 56 on the brake data page. Its kinda confusing. I know there are a total of 4 pistons and they are different sizes. Is there a way to to do it so its easier to understand?
If you have any suggestions on how to change things I'm open for suggestions. I thought about it when I was putting this together, and really didn't come up with anything better.
Josh

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Legacy777
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Post by Legacy777 »

BAC5.2 wrote:Josh,

Is there a way to input information? Like if I were to use an aftermarket caliper, how to determine biasing and percentages and such?

Also, you say the effective rotor diameter of STi 4-pots is 10.02" but the 02-05 WRX uses a 9.72" effective rotor. With a quarter inch + difference, how can people use OE WRX rotors with STi 4-pots? Mistake on your part or misguided people using STi 4-pots with USDM WRX rotors?
There's not a user-defined input section. I suppose it's something I could look into adding at a later date. What kind of information were you looking for? Just brake torque percent change between stock and aftermarket?

You can play with this brake bias calculator as well...
http://www.tceperformanceproducts.com/b ... lator.html

As for the effective rotor diameter. That information is correct (per the fsm).

Effective rotor diameter is a calculated number, but the easiest way to think of it is the actual rotor diameter minus the pad height. Or for effectived disc radius, you subtract pad height divided by 2.

What that is giving you more or less is the point at where the centeroid of the pad is contacting the rotor. With the 4-pots, the pistons I believe are set further toward the perimeter of the rotor. Because of this pad shape will be different and the effective disc diameter will be different. If you look at the numbers, that works out to be that the 4-pot pistons are .16" further outward then the wrx 2-pots.

The caveat to this is that the method I mentioned above to find effective disc diameter is a reasonably good approximation, but not hands down accurate. Here's an excerpt from an email I got from one of the guys I had been chatting with at TCE. He emailed someone he knows at ford designing brakes.

"/Todd, mostly just giving you a hard time about the ER, technically you need to find the centroid of the area of the pad, and the distance from there to the center of the rotor is the ER, but, it's tons more work, and requires more info (like the the entire pad shape) and the answer will virtually always be within a couple of mm of your calculation"
Josh

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Legacy777
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Post by Legacy777 »

I got a pm regarding effective disc diameter/radius and what it is. I wanted to post it in this thread in case any one else is curious.

In terms of calculating torque, torque is nothing more then force (lbs) x distance (moment arm) (ft/in), which gives you units of ft-lbs or in-lbs of torque.

In terms of braking, your brakes apply a torque opposing forward motion. The effective radius is the moment arm/distance from the center of the applied force (ie centroid of the brake pad) to the center of the rotor.

If this still isn't clear let me know.
Josh

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Post by BAC5.2 »

Ahh, gotcha. I thought you were talking about overall brake rotor diameter.

My bad.
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Post by Imprezive »

Cleared things up just fine. I thought it was the radius of the circular area where the pad makes contact with the rotor....if that makes sense...
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