subaru 4 pot calipers and pads bias confusion

[br0wny 27]

All,

I'm going to be changing to the subaru 4 pot calipers off the wrx (not sti)(my mate gave me his free )) and am aware they may actually provide slightly less overall braking performance vs the stock gt86 calipers shifting the brake bias from what I have read about 4% rearward 

However, if I was to add a decent pad up front e.g ds2500/CLrc5+ etc and just run oem rear pads surely under hard (and possibly normal) use that would neutralize the difference in brake bias presuming that the 4% would even be noticeable with stock pads all around?

I may have got my head all confused about this but I know theres some very clued up folks here! 

Any help greatly appreciated

Dan 

[DanJ 374]

Are you just changing the fronts?

If you can measure the diameters of the pistons and the diameter of the discs then its a quick spreadsheet calc to work out the brake bias difference. IIRC its been done already somewhere on the FT86 forum.

Some people will be able to tell the difference, others won't notice 4%.

One word of caution with mixing pad compounds is that their coefficient of friction vs temperature will be different so you'll get different bias as they warm up, and how much braking the front and rear axles are doing directly affects how much more heat energy goes in to the front or rear brakes. That said the same is true with the same pads front and rear to a lesser degree.

[DanJ 374]

It was NASIOC not FT86....

https://forums.nasioc.com/forums/showthread.php?t=928642&highlight=brake+calculator

Not all the info you need, but a good start.

[br0wny 27]

12 minutes ago, DanJ said:

Are you just changing the fronts?

If you can measure the diameters of the pistons and the diameter of the discs then its a quick spreadsheet calc to work out the brake bias difference. IIRC its been done already somewhere on the FT86 forum.

Some people will be able to tell the difference, others won't notice 4%.

One word of caution with mixing pad compounds is that their coefficient of friction vs temperature will be different so you'll get different bias as they warm up, and how much braking the front and rear axles are doing directly affects how much more heat energy goes in to the front or rear brakes. That said the same is true with the same pads front and rear to a lesser degree.

Thanks for the reply Dan

Yeh just doing the fronts as they're direct fit unlike the rears hah

I think it was ft86 that i got the 4% difference from due to smaller overall piston diameter

I havent read of any having any major issues myself from people using the calipers and have read plenty positives but I dont want the car to become unsafe or unstable

I know i could just upgrade pads lines and fluid on the stock setup etc but thought I could gain some more blingy looking calipers here  

[DanJ 374]

No worries, the change in brake disc size also has an influence. I don't know if the 4% calc included that as well.

If it genuinely is only 4% I wouldn't worry about that, but I'd confirm its 4% first, I don't normally trust numbers off the internet unless I can see they've been calculated properly.

I've not checked the maths in that NASIOC spreadsheet, but it looks like its been done by someone who knows what they're doing.

[Kodename47 446]

3 minutes ago, DanJ said:

No worries, the change in brake disc size also has an influence. I don't know if the 4% calc included that as well.

There is no change in disc size. The WRX uses the same size discs.

[br0wny 27]

3 minutes ago, DanJ said:

No worries, the change in brake disc size also has an influence. I don't know if the 4% calc included that as well.

If it genuinely is only 4% I wouldn't worry about that, but I'd confirm its 4% first, I don't normally trust numbers off the internet unless I can see they've been calculated properly.

I've not checked the maths in that NASIOC spreadsheet, but it looks like its been done by someone who knows what they're doing.

I had a look on the spreadsheet but there is no brz  would i be right in thinking maybe the legacy GT uses the same brakes? If so it was 5.4% rearward on stock pads but 15% forward on performance pads...

[will300 812]

@br0wny Here are the stats for the WRX calipers, based on those figures its a 5.2% 2.4% increase in rear bias.

99-07 WRX:
Front:
-4-pot fixed caliper.
-(Tech: 4-pistons, each of diameter 40.4mm)
-294x24mm vented discs. (295x25mm, or any combination of is also frequently seen, and compatable)
-(Tech: A=294mm; B=57mm or 57.5mm; C=24mm; D=22mm; E=58mm; F=5 (5X100))

Rear:
-2-pot fixed caliper.
-(Tech: 2-pistons, each of diameter 38.1mm)
-290x18mm vented discs.
-(Tech: A=266mm; B=67.5mm; C=18mm; D=16mm; E=58mm; F=5 (5x100))

And make sure you refurb them, so they look like this 

 

[br0wny 27]

26 minutes ago, will300 said:

@br0wny Here are the stats for the WRX calipers, based on those figures its a 5.2% increase in rear bias.

99-07 WRX:
Front:
-4-pot fixed caliper.
-(Tech: 4-pistons, each of diameter 40.4mm)
-294x24mm vented discs. (295x25mm, or any combination of is also frequently seen, and compatable)
-(Tech: A=294mm; B=57mm or 57.5mm; C=24mm; D=22mm; E=58mm; F=5 (5X100))

Rear:
-2-pot fixed caliper.
-(Tech: 2-pistons, each of diameter 38.1mm)
-290x18mm vented discs.
-(Tech: A=266mm; B=67.5mm; C=18mm; D=16mm; E=58mm; F=5 (5x100))

And make sure you refurb them, so they look like this 

 

Aye they will be something liked that.

 

 

So 5% more rear bias still leaves me confused regarding brake pad choice. Do I match them all round or get new oem rears and decent fronts or decent rears and even better fronts hahaha. 

[will300 812]

Ignore me, it's 2.4% bias rear (I was comparing the stock with my own setup). Just run the same pad type all round. 

[br0wny 27]

47 minutes ago, will300 said:

Ignore me, it's 2.4% bias rear (I was comparing the stock with my own setup). Just run the same pad type all round. 

Not changing the rears to the wrx 2 pots so probs nearer the 5% 

[Ade 517]

On 5/16/2018 at 10:40 PM, br0wny said:

Not changing the rears to the wrx 2 pots so probs nearer the 5% 

The WRX 2 pots are exactly the same size pistons as our stock floating caliper, so wont change bias.