Mixing 996 and Boxster brakes

[steve_wilwerding]

Since getting 996 brakes on the rear of a 98 Boxster is a pain, I was thinking about just replacing the front calipers and rotors on my Boxster with 996 parts. Is this advisable? Will it cause problems with the rear brakes?

[Highlander]

"Is this advisable". Depends.

Do you have 16" wheels? If so, budget a new set of 17" or larger as the Boxster S/996 brakes do not fit under 16" wheels.

Why do you want the bigger brakes? They are heavier and so add rotating mass and unsprung weight.

If you are looking for better braking performance, they will definitely help.

If you want to "look cooler" they most certainly will fit the bill here :)

They will work with no problems other than the fitment and weight issues I mention above.

I say "go for it" :thumbup:,

Graeme

[steve_wilwerding]

First of all, I have decided against this.

Second, if someone else decides to do this, I was advised by TRE Motorsports to put 996 calipers/rotors on the front and move the front Boxster calipers to the rear (they will bolt right up to the stock rear rotors). Front Boxster brakes are roughly equivalent to rear 996 brakes, so doing this won't upset the brake balance as much as keeping the rear Boxster calipers in place.

[KevinC]

Hi Steve. I believe that adding the 996 brakes in front, while leaving the standard brakes in the rear, will *not* disturb the brake balance, whereas moving the front brakes to the rear probably will change the biasing significantly.

I know for a fact that the sizes of the caliper pistons in the standard Boxster brakes are the same as those in the 996/S brakes. It is the size of the pistons which determines how much braking force is applied. (The amount of clamping force on the pads is equal to the pressure of the brake fluid times the area of the pistons.)

The 996 brakes have larger rotors and larger pads. However, the same amount of clamping force is applied - it is just spread over a larger pad area. The larger pads, and (especially) the larger rotors keep the temperatures lower, but since the pistons are the same size, the total amount of braking force is approximately equal.

The pistons in the rear calipers are considerably smaller than those in the front calipers. (About half the area!) Therefore, when you move the front brakes to the rear, you will be providing more clamping force on the rear brakes than you had before, shifting the brake bias to the rear.

One can argue about just how bad this is. While you wouldn't want the rear brakes to lock up before the fronts, some additional rear bias will take some load off the front brakes and keep them a bit cooler. It is *possible* that the factory was overly conservative in setting the brake bias in the first place. Also, keep in mind that ABS should keep things from getting too far out of hand by stopping any wheel from fully locking up.

Bottom line - there is no *need* to mess with the rear brakes when upgrading the front ones to the 996/S setup. The rear brakes are still going to be much cooler than the fronts and the bias won't be affected.

Oh, and one more thing, while I am rambling - the rear rotors are 4mm thinner than the front rotors, so moving the front brakes to the rear will cause the pistons to extend further. This is probably OK, since I found that even when I accidentally extended the front pistons all the way to the rotors (no pads in place!) they still didn't go past the seals. However, I would be especially careful not to repeat this bonehead maneuver with the front calipers mounted on the rear rotors.