Front sport brakes on the rear?
 

(Moving the stock front sport calipers and rotors to the rear)
I looked for this in the search section and did not find it... so here goes:

I have the AP racing 6 piston BBK on my Nismo 370, but elected to do the fronts only (after-all the front does 70% of the braking work). I've got SS brake lines and race fluid all the way around plus better pads and drilled/slotted rotors on the back, but I kept the stock Nissan rear calipers and rotor size. The AP racing kit for the rear is nearly as expensive as the front.

My thought was this... why not do the BBK on the front, then move the 4 piston sport calipers and 14" rotor size to the rear? Has anyone done this? I assume all we would need is a bracket solution to hang the larger calipers. Can this be done?

It would create huge problems with brake balance that would probably be difficult to resolve. The piston area on the 4 piston Nissan caliper would be WAY too large to match the upgraded front system. BBK's often alter the piston size it the caliper to maintain proper brake balance for the entire system that's why your 6 piston front BBK still works well with your 2 piston Nissan rear system.

So, to clarify... You are saying that the four-piston rear kit that AP sells has different piston bore sizes that are engineered to balance with the 6 piston fronts? The actual pistons themselves (on the 4-piston AP rear calipers) are smaller internally than the 4-piston stock fronts?

If this is the case, does it mean that the rear wheels would lock up sooner or harder than they should under braking because the calipers would clamp too hard or too quickly?

also your parking brake wont work with the front rotors mounted on the back.

As Gaurddad mentioned, it would screw with the brake balance. The only way you could fix that w/o playing with different piston sizes would be to play with brake bias which with the stock system isn't possible. Also as Fuct said, you would no longer have a parking brake.

yea you are better off to just keep your stock rear brakes and upgrade to better pads and rotors if anything. maybe saving pennies to do the BBK upgrade that matches your front eventually. you can also sell your front set of calipers and other hardware left over for a pretty good chunk of change too

well, a few things come to mind.

A. you are assuming that the distance from the hub to the mounting holes and the distance from the mounting holes to the outer edge of the brake pads is the same front and rear. May or may not be the case.

B. that the spacing between mounting bolts is the same and you could just bolt the fronts on the rears in the existing holes.

C. Once you do figure out how to mount the fronts on the rears, it may not be 14" rotor, because of points above, and no matter what the size is, you need to find a rotor that has a parking brake drum incorporated into it.

You should just save up for the AP rears, especially if you track. I had a 6 piston front only Brembo upgrade and the rears were just overworked on the track. I went through rear pads like I go through beer, very quickly.

Question 1: Yea, that's the usual way they balance the system.

Question 2: Yea, rear lock up would be a huge problem.

A drum parking brake is built in to the rear rotors not the rear calipers, so the rear rotors would need to be retained. Unfortunately, the rear rotors are substantially thinner than the front rotors so pad and piston retention could be a serious problem.

Sell your OEM brakes and save your money for a BBK for the rear. You'll get a a matched system not a huge headache from a home made system. I had front and rear BBK's on my 04 GTO, well worth it on looks alone.

Thanks... All good points.

Better to invest in the rear set-up and drink the beer too!

If everything bolted up and fit right, you could get a remote brake bias controller for pretty cheap. I think like $80 bucks. I know Tilton makes them.. I had one on my corvette. I am not sure if you have to buy their pedal system but I dont think so. A custom e-brake solution shouldnt be THAT difficult.

Here is a thread I started on G35Driver trying to defend my Wilwood’s on my old G. I think it can be of some use in understanding how brake bias works.

Stop-Tech’s front BBK reduces stopping distance by utilizing a smaller piston area than stock. Yes, the Stop-Tech front caliper has less stopping torque than the stock caliper.

The proper question to ask is the size of the pistons and the rotor. I’ll explain.

First, all brake kits operate on the same principals. Hydraulic fluid is pushed through a line that compresses a piston which pushes the pads on the rotor.

Second, total piston area determines the torque of any given caliper. For example, the stock caliper on a 2005 6MT has two 1.75 inch pistons. Do some math and the total area is 4.8 inches. This calculation uses the pistons on only one side of the caliper. So, a six piston caliper’s piston area would be based on 3 pistons. Strangely, the stock sliding calipers brake as if they had identical opposed pistons (why? Ask a physicist).

Third, the number of pistons does not affect torque. I doesn’t matter if you get 4 inches of piston area with one big piston or 9 tiny pistons.

Fourth, rotor diameter effects brake torque. For example, if the only modification you did to your stock brakes was increase the front rotors to 14 inches then front brake bias would increase 2%. A 13 inch rear rotor would reduce front bias 2%. That rear rotor upgrade is starting to look pretty good now...

Fifth, our cars come from the factory overly front brake biased (74% front/26% rear). Although this increases stopping distance, a front biased vehicle is easier to control.

Therefore, reducing front brake bias will balance the car and decrease stopping times. However, shift the bias too far and the rears may lock up before the front. VERY DANGEROUS!

Stop-Tech has determined that magic amount of brake bias to magically balance a 350z/G35. I would love to know the piston area of the Stop-Tech front BBK.

So you want to know the effectiveness of your specific BBK. Get a ruler and measure the piston areas and rotor diameter.

Then use a brake bias calculator like the one at Tech; Brake Bias. If the ratio is the same as stock, then your brake distance will be unchanged. If the ratio is more front biased you will take longer to stop and unnecessarily burden your front brakes.

If you are going front only, make sure the total piston area (and front brake bias) is slightly less than stock. A general rule of thumb is no more than 5%. Also, search the forums and call the distributor to determine if there are any problems with that specific BBK locking the rears.

For example, I have Wilwood 6 piston calipers on 13 inch rotors. The total piston area is 4.06 or .74 inches less than stock resulting in 72%/28% bias or 2% more rear bias.

A Wilwood 6 piston superlight BBK with a 13 inch rotor will stop in a shorter distance than stock.

Of course different BBK's will have better heat dissipating characteristics, pedal modulation, etc... but that is for another post.

You also need good tires to stop the car, else you will just ABS it

ResIpsa... Awesome explanation, I will check the math on my set-up, good to have this explanation!

I used the calculator and got 66.4% bias for the stock sports brake, so are you saying I can go down to around 62% front bias safely without locking the rear wheels on track? I used 1.732 and 1.614 front piston size, 1.614 rear piston size, 0.4 front and back Cf, 14 front rotor and 13.8 rear rotor, and 3.543 front pad height and 2.882 rear pad height. Thanks.

Anyone knows? :tiphat: