My $600 Big Brake Kit

[Racecomp Engineering]

Originally Posted by Ryephile

Great find @eikond!

I have some questions though, since my Google-fu is terrible right now:
*Aren't the stock front calipers 2-piston sliders with 42.8mm pistons?
*Your Z32 TT's are fixed calipers with 4x 40.4mm pistons?

If that's all true, then the piston areas are 2,877mm^2 and 5,128mm^2 respectively. That would be a massive front-bias movement. Sorry @Dave-ROR, your equal and opposite reaction idea isn't a perpetual machine that creates magi-double piston area in the formula. There's a fixed amount of piston area, and thus force, for any particular caliper, regardless of it's piston amount and orientation.

Now, what's happened here is since there's so much more front piston area, the master cylinder requires much more pedal travel to get the same line pressure. Chances are the car now has a longer and softer pedal. The pad mu is totally unknown and of course impacts brake torque significantly.

Using Legacy777's spreadsheet, the rotor diameter change is resulting in about a 5% front bias change.

You only use one side of the caliper for piston area.

The spreadsheet you linked to notes the following:

"The caliper piston area calculation for fixed calipers only utilizes the pistons from one side of the caliper."

Also on the TCE brake bias calculator site:

"Note: multi piston calipers express their values using one HALF of the caliper body. This accounts for the floating aspect of the single piston caliper. A six pot caliper would be 1.625/1.125/1.125" for example. True clamping force would be double that but also double the single piston of a floating caliper taking into account the 'pull' of the outer pad to the rotor surface. Using total area (all six for example) would require you double that of the floating caliper also- thus the net result is the same whichever way you do it."

http://www.tceperformanceproducts.com/bias-calculator/

EDIT: The piston sizes everyone uses for BRZ are wrong. They're ~40.4 mm front and rear.

- Andy

[Dave-ROR]

Originally Posted by Ryephile

Great find @eikond!

I have some questions though, since my Google-fu is terrible right now:
*Aren't the stock front calipers 2-piston sliders with 42.8mm pistons?
*Your Z32 TT's are fixed calipers with 4x 40.4mm pistons?

If that's all true, then the piston areas are 2,877mm^2 and 5,128mm^2 respectively. That would be a massive front-bias movement. Sorry @Dave-ROR, your equal and opposite reaction idea isn't a perpetual machine that creates magi-double piston area in the formula. There's a fixed amount of piston area, and thus force, for any particular caliper, regardless of it's piston amount and orientation.

Now, what's happened here is since there's so much more front piston area, the master cylinder requires much more pedal travel to get the same line pressure. Chances are the car now has a longer and softer pedal. The pad mu is totally unknown and of course impacts brake torque significantly.

Using Legacy777's spreadsheet, the rotor diameter change is resulting in about a 5% front bias change.

That would all add up to a huge front bias increase. I don't feel like calculating it right now, plus without knowing the pad mu's it's fruitless.

If I were tackling this from scratch I'd want to find a front caliper with smaller pistons, but for $600, an inch more rotor diameter and 6mm more thickness, on top of EBD that everyone has seemed to forget about, this is probably a decent DIY solution even for light track use.

Bravo!

I agree it's not exact, but you are still wrong because it's a lot closer to double than it is to zero. Ask any brake system engineer in the world about this, I know some that have worked at Brembo, designed calipers for NASCAR and other pro series. They will tell you the same, use one side of the fixed or double the sliding. @JRitt will tell you the same thing also.

All brake force calcs use one side, fixed or not, evidenced by your own link.

BTW, I did reference EBD indirectly to that point (referring to it as a modern ABS system since it's all the same system for this discussion), however a faster lockup STILL causes ABS to work more which reduces effectiveness (which is why threshold braking is still the best, you never lock/release/lock/release/repeat).

edit: I should have read Andy's post first

Edit 2: Rye, I'm flying to DTW tomorrow to head to Gingerman, might be back in the area sunday night, then heading to Toledo for a few days to visit family. Adhoc FT86club bar meet? We can all discuss Z32 calipers lol

[mike the snake]

The plot thickens.

[finch1750]

Originally Posted by Dave-ROR

Are they the same piston sizes? If so, why are adapters made for them to fit a WRX (honest question, doesn't make much sense if they are the same as the WRX ones)? The WRX four pots have less piston area than our OEM calipers, so given the same rear setup (we have LGT rears stock which are bigger than the WRX rears), brake bias will move further back.


If these are the same as WRX, then why run them at all? I'd rather run LGT sliders up front with the LGT rotors instead. The only benefit you'd get is brake feel out of fixed calipers.


I went from curious to maybe against this setup if the piston sizes really are WRX 4 pot sized.

The adapters were made because of the price. The mount is the only difference and z32 brakes are much cheaper than the 4/2 pot set-up. Production volume was higher plus they are a lot older so more used ones around for cheap.

And I'm confused, are you talking about installing only the front brakes with the stock rears? If the 2 pots are small diameter how could it shift bias rear? I was under the impression swapping to WRX 4/2 pot set-up was very similar in function to stock, just gain a bit of feel but mostly the looks.

Originally Posted by Racecomp Engineering

If the piston area is smaller like it is with suby 4 pots, you are still adding a larger diameter rotor with the LGT rotor. So the brake bias point may be moot. Maybe.

I dunno what the piston sizes are on the Z32 calipers so whatever.

- Andy

I have been researching the exact set-up and the piston size is the same for the z32 calipers as the WRX4/2 pot set-up. This goes for the front and rear from what I recall. I'll try to find my notes to confirm.

[eikond]

Originally Posted by Dave-ROR

Edit 2: Rye, I'm flying to DTW tomorrow to head to Gingerman, might be back in the area sunday night, then heading to Toledo for a few days to visit family. Adhoc FT86club bar meet? We can all discuss Z32 calipers lol

I want in on that.. though I'm not much of a bar fly.


I still don't get how the sliders can double braking force. I get the equal and opposite force theory.. but it seems like that would be pad against rotor and vice versa.

let's throw out a random example.. say you have a styrofoam ball. Let's say you have two arms (most of us do) and they have equal muscle strength and maybe you can exert 100lbs of force. If you put the styrofoam ball against the wall and pushed with one arm you be exerting 100 lbs of force and could compress the ball a certain amount. But if you put the ball between your two arms and pushed on each side you would have 200 lbs of force you would certainly be able to compress the ball more right?

Just seems like common sense that more total piston area would be able to push with more force.

[Dave-ROR]

Originally Posted by eikond

I want in on that.. though I'm not much of a bar fly.


I still don't get how the sliders can double braking force. I get the equal and opposite force theory.. but it seems like that would be pad against rotor and vice versa.

let's throw out a random example.. say you have a styrofoam ball. Let's say you have two arms (most of us do) and they have equal muscle strength and maybe you can exert 100lbs of force. If you put the styrofoam ball against the wall and pushed with one arm you be exerting 100 lbs of force and could compress the ball a certain amount. But if you put the ball between your two arms and pushed on each side you would have 200 lbs of force you would certainly be able to compress the ball more right?

Just seems like common sense that more total piston area would be able to push with more force.

In your example the wall doesn't move. In a sliding caliper, the force of the piston pulls the other side of the caliper, and thus it's pad, against the rotor.

[Ryephile]

Originally Posted by eikond

Just seems like common sense that more total piston area would be able to push with more force.

I agree, but it looks like logic isn't right in this case.

The pressure from the two slider pistons are acting on the caliper to both push the pad and pull the slider. There's no pulley system to create (let alone double) torque. In a fixed caliper, all pistons are pushing against the rotor, not half of them. So far I haven't read an explanation that clearly explains this alleged "doubling" of force a slider caliper has.

If I'm wrong, assuming the pads are the same mu as stock, the total rear bias increases by 6.6%. Put a slightly more aggressive front pad and the bias will shoot forward.

[eikond]

Originally Posted by Dave-ROR

In your example the wall doesn't move. In a sliding caliper, the force of the piston pulls the other side of the caliper, and thus it's pad, against the rotor.

But the act of pulling the other side towards it should take half of the force away?

I give up. Lol. Too late. Need sleep.

Thanks for the conversation today.. good stuff!

[Dave-ROR]

Originally Posted by finch1750

The adapters were made because of the price. The mount is the only difference and z32 brakes are much cheaper than the 4/2 pot set-up. Production volume was higher plus they are a lot older so more used ones around for cheap.

And I'm confused, are you talking about installing only the front brakes with the stock rears? If the 2 pots are small diameter how could it shift bias rear? I was under the impression swapping to WRX 4/2 pot set-up was very similar in function to stock, just gain a bit of feel but mostly the looks.

If using the same rears, and the same front leverage (this setup is not doing that though), the lower brake force WRX 4 pots (compared to our OEM calipers) would shift bias. Due to fancy ABS related tech (EBD specifically) that matter less than it use to, but can still engage ABS too frequently resulting is a loss of efficiency. Noticeable? Probably not without measuring equipment. The variable here is the bigger lever due to the mounting location being farther from the hub. It could offset that perfectly (or not) making this a perfectly stock bias larger heatsink upgrade. Or it could shift bias. I don't know the piston sizes on the rear of the car (OEM or 300ZX) so I'm not sure what the difference will be there.

Your (not you specifically, the end user in general) goal of a brake upgrade is key to component selection. All of these kits/setups serve a purpose, I wouldn't have done this setup simply because over time it would cost more than what I do run (I've bought pads for my caliper and the Z32 at the same time and the Z32 pads were clearly more expensive.. not a little.. but a fair margin more based on my pricing which isn't always retail). My setup also has a larger weight savings. It's also more track focused and not as street friendly (noisier, etc).

I have nothing against this setup to be honest, I just like these discussions and like to see actual data, costs, etc and don't want people to rush out and do it just because it seems like a good price. And no, I'm not saying it's not, I'm saying we don't really have that data right now.

[Dave-ROR]

Originally Posted by eikond

But the act of pulling the other side towards it should take half of the force away?

I give up. Lol. Too late. Need sleep.

Thanks for the conversation today.. good stuff!

I'll let some brake engineers explain it, JRitt has someone on staff I'm sure. They can do a better job then I can.

Force via caliper *BODY* movement vs caliper *PISTON* movement is the difference. Given the same exact piston area, brake force is the exact same (everything else being equal).

The key benefits of fixed calipers are feel, modulation, and pad wear (less tapering as force is applied more evenly across the backing plates).

This is from my race car. Sliding calipers can exert PLENTY of force on the pad:



And so can the piston

[Ryephile]

Originally Posted by Dave-ROR

...
Force via caliper *BODY* movement vs caliper *PISTON* movement is the difference. Given the same exact piston area, brake force is the exact same (everything else being equal).


And so can the piston

That's my point, ignoring frictional losses of the slider mechanism. I obviously get the whole Newton's 2nd law thing, fixed calipers are doing that with line pressure instead of sliders, otherwise rotors would be pushed off the hubs.

Nice picture. It looks like a fairly classic case of not enough mu. Did your bleeders [hell, anything] survive that much line pressure to bend the backing plates?

[mav1178]

Z32 calipers:

1990 NA = 26mm aluminum
1990-92.5 TT = 30mm aluminum
1991-92.5 NA = 30mm aluminum
92.5+ = 30mm iron

I've had all the versions. The switch to aluminum was a heat/warranty issue, not flex. Not an issue with lower weight cars.

-alex

[mav1178]

Originally Posted by SomeoneWhoIsntMe

z32tt's had the 30mm wide calipers, they're actually the same as the n/a calipers except they have a spacer in the middle to make them wider.

There's no spacer.

A comparison of all the Z32 calipers:

http://importnut.net/300zxbrakeswap.htm

-alex

[Dave-ROR]

Originally Posted by Ryephile

Nice picture. It looks like a fairly classic case of not enough mu. Did your bleeders [hell, anything] survive that much line pressure to bend the backing plates?

Piston didn't. Didn't check anything else. That pad was a $20 advanced auto set when we ran out of real pads and wanted to finish the race.

The other pad pictured was a real race pad backing plate wasn't nearly as crappy lol