Brake Math/Torque Spreadsheet

Where the power meets the road.

Moderators: Helpinators, Moderators

Post Reply
Legacy777
Site Admin
Site Admin
Posts: 27552
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Brake Math/Torque Spreadsheet

Post by Legacy777 » Fri Jan 27, 2006 4:53 am

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

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

professor
Third Gear
Posts: 832
Joined: Tue Jul 27, 2004 6:12 pm
Location: Providence RI

Post by professor » Fri Jan 27, 2006 3:39 pm

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.
That beer you are drinking cost more than my car

Psychoreo
Second Gear
Posts: 360
Joined: Tue Jan 18, 2005 11:07 pm
Location: Enfield, CT
Contact:

Post by Psychoreo » Mon Jan 30, 2006 4:39 am

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.
stupid electrical work...

jamal
Vendor
Vendor
Posts: 2485
Joined: Thu Dec 11, 2003 11:34 am
Location: Missoula
Contact:

Post by jamal » Mon Jan 30, 2006 11:47 am

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.

Psychoreo
Second Gear
Posts: 360
Joined: Tue Jan 18, 2005 11:07 pm
Location: Enfield, CT
Contact:

Post by Psychoreo » Mon Jan 30, 2006 7:18 pm

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
Site Admin
Site Admin
Posts: 27552
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 » Tue Jan 31, 2006 4:46 am

Big issue with the LGT brakes is the need for 17" wheels
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

Psychoreo
Second Gear
Posts: 360
Joined: Tue Jan 18, 2005 11:07 pm
Location: Enfield, CT
Contact:

Post by Psychoreo » Tue Jan 31, 2006 8:15 pm

awww.....really? damn. Meh, then it's back to the wrx/h6 stuff
stupid electrical work...

Imprezive
Fourth Gear
Posts: 1428
Joined: Wed Jun 22, 2005 4:07 am
Location: Northern CA

Post by Imprezive » Sat Mar 18, 2006 8:24 pm

What program do I open thing thing with? I guess I'm not that computer savvy....
1992 T-Leg = 195whp 197wtq SOLD :(
1988 4Runner RIP
2006 Suzuki DRZ400sm
2007 Miata
1994 Miata
2003 WRX Wagon
2016 Mazda 3

DerFahrer
quasi-mod-o
quasi-mod-o
Posts: 5993
Joined: Thu Dec 05, 2002 7:06 pm
Location: Orlando, FL
Contact:

Post by DerFahrer » Sat Mar 18, 2006 8:59 pm

Imprezive wrote:What program do I open thing thing with? I guess I'm not that computer savvy....
MS Excel.
2000 Subaru Legacy B4 RSK

"Der Wahnsinn ist nur eine schmale Brücke/die Ufer sind Vernunft und Trieb"

*Formerly subyluvr2212*

Please email me at fahrer4184@gmail.com if you want to contact me.

AWD_addict
Fifth Gear
Posts: 2774
Joined: Sun Nov 23, 2003 12:22 am
Location: Western WA!

Post by AWD_addict » Sat Mar 18, 2006 10:36 pm

Wow, this sheet is awesome. Thanks Josh!
90 L+ wgn

Legacy777
Site Admin
Site Admin
Posts: 27552
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 » Sun Mar 19, 2006 6:07 am

Welcome
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

Imprezive
Fourth Gear
Posts: 1428
Joined: Wed Jun 22, 2005 4:07 am
Location: Northern CA

Post by Imprezive » Sun Mar 19, 2006 7:24 pm

Wow, this is pretty damn sweet! I am impressed!
1992 T-Leg = 195whp 197wtq SOLD :(
1988 4Runner RIP
2006 Suzuki DRZ400sm
2007 Miata
1994 Miata
2003 WRX Wagon
2016 Mazda 3

napphappy
Second Gear
Posts: 512
Joined: Fri Jun 03, 2005 12:57 am
Location: Gig Harbor, WA

Post by napphappy » Tue Mar 21, 2006 11:51 pm

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?
1997 White BG Ltd 5MT, EJ22T with Wiescos, EJ20R Heads, Two large dents R.I.P
1995 Impreza EJ22T DOHC Hydra EMS, 20g, EWG, 3in APS TBE, AWIC

BAC5.2
Moderator
Moderator
Posts: 9026
Joined: Thu Jan 29, 2004 8:47 pm
Location: Maryland www.andrewtechautomotive.com
Contact:

Post by BAC5.2 » Mon Mar 27, 2006 5:25 pm

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?
2009 Outback 2.5XT. 5MT. Satin White Pearl.
2009 Impreza 2.5i Premium. Blue.

[quote="scottzg"]...I'm not a fan of the vagina...[/quote][quote="evolutionmovement"]This will all go much easier if people stop doubting me.[/quote]

Legacy777
Site Admin
Site Admin
Posts: 27552
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 » Mon Mar 27, 2006 8:09 pm

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

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

Legacy777
Site Admin
Site Admin
Posts: 27552
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 » Mon Mar 27, 2006 8:23 pm

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

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

Legacy777
Site Admin
Site Admin
Posts: 27552
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Post by Legacy777 » Tue Mar 28, 2006 7:57 pm

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

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

BAC5.2
Moderator
Moderator
Posts: 9026
Joined: Thu Jan 29, 2004 8:47 pm
Location: Maryland www.andrewtechautomotive.com
Contact:

Post by BAC5.2 » Tue Mar 28, 2006 8:52 pm

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

My bad.
2009 Outback 2.5XT. 5MT. Satin White Pearl.
2009 Impreza 2.5i Premium. Blue.

[quote="scottzg"]...I'm not a fan of the vagina...[/quote][quote="evolutionmovement"]This will all go much easier if people stop doubting me.[/quote]

Imprezive
Fourth Gear
Posts: 1428
Joined: Wed Jun 22, 2005 4:07 am
Location: Northern CA

Post by Imprezive » Wed Mar 29, 2006 12:01 am

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...
1992 T-Leg = 195whp 197wtq SOLD :(
1988 4Runner RIP
2006 Suzuki DRZ400sm
2007 Miata
1994 Miata
2003 WRX Wagon
2016 Mazda 3

Post Reply