Brakes from other vehicles?

[BRAWL]

I have a set of Brembo calipers from a Nissain Skyline R33 GTR. Would these be able to be adapted to fit the 86 or is it more hassle than it is worth?

I would like have to get a custom rotor for it, but I assume it could be done?

Can I get opinions and thoughts?

[ft_sjo]

Yes it can be done with custom fabrication. You may need a change of wheels though to accommodate.

[JRitt]

The piston bore sizes are likely not optimized for the proper brake bias/balance on the FT86. The items that can alter the bias are disc diameter, piston bore size, and brake pad coefficient of friction (mu). All of the below items assume that you don't want to change your brake master cylinder (which 98% of the people reading this likely have no desire to do).

If you held everything else constant on the car and just increased the front disc diameter, you'd shift brake bias towards the front of the car.

I don't know the piston area on the GT-R off the top of my head, but it is likely far larger than the piston area on the OEM FT86 calipers. That would further amplify the brake bias towards the front.

Now if you add a larger rear disc and larger rear caliper piston area, you can shift some bias back to the rear. That said, to be optimized for the BRZ, the front increase in brake torque and rear increase in brake torque would have to be in the same proportion to keep the overall balance the same as the OEM setup. That is possible, but highly unlikely.

The results of improper bias: All four tires are likely not sharing the proper amount of work. In most of these cases, the car is front biased, which means the rear tires aren't being used to their full capacity to stop the car...resulting in longer stopping distances than stock. Also, you run the risk of having ABS problems, or premature intervention. Finally, if the overall piston bores in the calipers are substantially larger than stock, you will be displacing a lot more brake fluid into those calipers. That can mean that your brake pedal travel will be longer.

In summary...upgrading to Brembo's from another platform such as an GT-R, STI, Evo, or 350Z would primarily be a cosmetic upgrade only. The brakes would look better, but that's about it. Your actual performance would likely be worse...and possibly be much worse. Longer stopping distances, longer pedal travel, potential ABS issues, pad taper because of the 'upside down' calipers, etc. So if you want your car to look good parked, putting OEM calipers from another application is a good solution. If you want it to have the best braking performance possible...not so much.

All of these factors need to be considered when you design an aftermarket brake system upgrade to work with the OEM master cylinder on your car. The proper disc size, piston bores, and piston stagger all need to be calculated to achieve proper brake bias and performance.

Hopefully that helps.

[BRAWL]

Originally Posted by JRitt

The piston bore sizes are likely not optimized for the proper brake bias/balance on the FT86. The items that can alter the bias are disc diameter, piston bore size, and brake pad coefficient of friction (mu). All of the below items assume that you don't want to change your brake master cylinder (which 98% of the people reading this likely have no desire to do).

If you held everything else constant on the car and just increased the front disc diameter, you'd shift brake bias towards the front of the car.

I don't know the piston area on the GT-R off the top of my head, but it is likely far larger than the piston area on the OEM FT86 calipers. That would further amplify the brake bias towards the front.

Now if you add a larger rear disc and larger rear caliper piston area, you can shift some bias back to the rear. That said, to be optimized for the BRZ, the front increase in brake torque and rear increase in brake torque would have to be in the same proportion to keep the overall balance the same as the OEM setup. That is possible, but highly unlikely.

The results of improper bias: All four tires are likely not sharing the proper amount of work. In most of these cases, the car is front biased, which means the rear tires aren't being used to their full capacity to stop the car...resulting in longer stopping distances than stock. Also, you run the risk of having ABS problems, or premature intervention. Finally, if the overall piston bores in the calipers are substantially larger than stock, you will be displacing a lot more brake fluid into those calipers. That can mean that your brake pedal travel will be longer.

In summary...upgrading to Brembo's from another platform such as an GT-R, STI, Evo, or 350Z would primarily be a cosmetic upgrade only. The brakes would look better, but that's about it. Your actual performance would likely be worse...and possibly be much worse. Longer stopping distances, longer pedal travel, potential ABS issues, pad taper because of the 'upside down' calipers, etc. So if you want your car to look good parked, putting OEM calipers from another application is a good solution. If you want it to have the best braking performance possible...not so much.

All of these factors need to be considered when you design an aftermarket brake system upgrade to work with the OEM master cylinder on your car. The proper disc size, piston bores, and piston stagger all need to be calculated to achieve proper brake bias and performance.

Hopefully that helps.

Exactly the answer I was after! Thanks mate

I will just keep trying to sell them and not bother with Plan B

[troek]

man i saw this a day too late. my buddy just bought some r33 calipers for his r32. we could have done business.

[OrbitalEllipses]

Originally Posted by JRitt

The piston bore sizes are likely not optimized for the proper brake bias/balance on the FT86. The items that can alter the bias are disc diameter, piston bore size, and brake pad coefficient of friction (mu). All of the below items assume that you don't want to change your brake master cylinder (which 98% of the people reading this likely have no desire to do).

What about swept area, Jeff? Does that alter bias or torque any?

[JRitt]

Originally Posted by OrbitalEllipses

What about swept area, Jeff? Does that alter bias or torque any?

No it does not. The distance from the center of the hub to where the center of the pistons squeeze the discs gives you your effective radius. If you hold piston size constant, the further from the hub center, the longer the lever arm = more brake torque. Swept area really only has to do with heat management. A larger swept area spreads the heat out more, but is just one factor in doing so. Other design features such as disc wall thickness, vane design, number of vanes, slot shape, pad volume, pad radial depth, piston material, airflow around caliper, etc. all impact how a system handles heat. In other words you can't just look at a setup and say, "that one is better because it has a greater swept area." That's just one small piece of the complete picture.

[BRAWL]

Originally Posted by troek

man i saw this a day too late. my buddy just bought some r33 calipers for his r32. we could have done business.

Story of my life I have them on ebay and have had them on SAU/aus300zx forums with only nibbles, partial interest and low ball offers. At this point, I am selling them for less than I paid

[ft_sjo]

So we shouldn't put any bbk on the front at all jritt? Even your AP based kits? Not without changing the rear brakes too?

[wparsons]

Originally Posted by ft_sjo

So we shouldn't put any bbk on the front at all jritt? Even your AP based kits? Not without changing the rear brakes too?

It depends on if the kit was designed to maintain the stock bias or not. Most BBK's will explicitly state if they work with stock rears or not.

[ft_sjo]

Well the Brembo's i'm fitting to my car (which are very common on various vehicles) have the same piston sizes are typical AP calipers designed for a 50-51mm pad height.

[JRitt]

Originally Posted by ft_sjo

So we shouldn't put any bbk on the front at all jritt? Even your AP based kits? Not without changing the rear brakes too?

That is incorrect. If a front big brake kit is designed properly to work with the OEM rears (which all of the kits we sell are), then it integrates seamlessly without issue. You just have to make sure whoever designed the BBK did their homework and selected the proper disc diameter and caliper piston combination. That's the key. Those two variables will determine how much torque output is on the front, which needs to match the OEM torque output.

For a simplified example: holding the rear brake setup constant and the brake pad coefficient of friction on the front constant... If you increase the front disc diameter, you decrease the overall front caliper piston area...the combination of those two needs to match the OEM brake torque output on the front of the car, which maintains proper front to rear brake bias. If you went with a larger dimeter disc vs. stock and kept piston area the same as OEM, you'd end up with more front torque/bias. If you kept the disc diameter the same as stock but went with larger piston area, you'd again have more front bias. Typically you would go with a larger diameter disc to increase system heat capacity, and then counteract the torque increase of doing so by reducing the piston area on the calipers being run on those discs.

If you added a larger diameter disc AND a caliper with larger piston area (which is the common scenario when adding OEM brakes from a different car...a GT-R in this case)...then you're getting a double whammy: more front brake torque because of the larger disc, and more brake torque because of the larger piston area. That shifts bias forward, your rears do less work, using less of your rear tires to stop the car, potentially increasing stopping distances, and/or problems with your ABS, a longer pedal because more fluid is displaced into the larger pistons, etc.

[Admiral Ballsy]

Originally Posted by JRitt

For a simplified example: holding the rear brake setup constant and the brake pad coefficient of friction on the front constant... If you increase the front disc diameter, you decrease the overall front caliper piston area...the combination of those two needs to match the OEM brake torque output on the front of the car, which maintains proper front to rear brake bias. If you went with a larger dimeter disc vs. stock and kept piston area the same as OEM, you'd end up with more front torque/bias. If you kept the disc diameter the same as stock but went with larger piston area, you'd again have more front bias. Typically you would go with a larger diameter disc to increase system heat capacity, and then counteract the torque increase of doing so by reducing the piston area on the calipers being run on those discs.

You would think. However, Subaru at least apparently doesn't feel that it's quite as big a deal. For example, the Legacy comes with two different sizes of front brakes (rotors are larger, caliper pistons are same size), depending upon engine/trim. However, the rear brakes are identical. And the master cylinder and booster part numbers are identical between the two setups as well.

[ft_sjo]

Originally Posted by JRitt

If you increase the front disc diameter, you decrease the overall front caliper piston area...

This statement has puzzled me a bit. Are you talking about area, or a ratio? If the only thing you've changed is the disc, then surely the caliper piston area is the same.