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andicati · 03-07-2005, 03:07 PM

Our learned friend JFP is mostly correct. Comparing the various brake systems we see the following:
Boxster Front 298 x 24mm
Rear 292 x 20mm
Boxster S Front 318 x 28mm
Rear 299 x 24mm
996 Twin Turbo Front 330 x 34mm
Rear 330 x 28mm

The increase in brake area shows:
Boxster => Boxster S: Front +20%; Rear +7%
Boxster => Twin Turbo: Front +33%; Rear +41%
Boxster S => Twin Turbo: Front +11%; Rear +30%

These calculations are based on rotor machined area, not the actual swept area which will vary slightly, but it gives you an idea of why the Boxster can massively benefit from an upgrade to S brakes as most of the braking bias is towards the front. The Twin Turbo brakes are only +10% larger than the S at the front which will most likely be hard to notice under normal driving conditions.

BUT! I don't have an S, just the standard Boxster. I do however, have Twin Turbo brakes. The marriage of the two seems be a good thing for slowing me down, especially after I have fitted a supercharger. As JFP suggests, larger rubber should follow the larger brakes. Luckily, I have the larger rubber already, wearing 225/45 and 265/40 17" Potenzas.

After spending a couple of hours on the car with a micrometer today, I have learnt that the rear calipers and rotors will be a simple bolt on with an 8mm spacer installed between the rotor and the wheel hub (as opposed to wheel spacers that are between the rotor and the wheel). I will see if I can utilize either the H&R or Eibach spacers, but they are both 7mm and will likely require the OD to be shaved a bit. Otherwise I will make my own.

The front system is going to be a bit more tricky. The caliper mounting bolts are 130.6mm apart on the Boxster compared to 142.3mm on the Twin Turbo. Also, the calipers will need to be raised 19mm above the wheel carrier to accomodate the large diameter rotor. This will then likely necessitate a 5mm wheel spacer to make sure my 3 piece speedlines clear the calipers fully, although I am praying that they will clear as is. I have a bracket design in mind, and will get this worked out on CAD to see if it will fit - anything to avoid $1400 + $1000 labor to install new wheel carriers!

I have been taking pics as I go along, so I will post these sometime soon so that other fools who follow won't be quite so foolish as me.

03-07-2005, 03:07 PM	#12
andicati Registered User Join Date: Feb 2005 Location: Atlanta, US Posts: 18	Our learned friend JFP is mostly correct. Comparing the various brake systems we see the following: Boxster Front 298 x 24mm Rear 292 x 20mm Boxster S Front 318 x 28mm Rear 299 x 24mm 996 Twin Turbo Front 330 x 34mm Rear 330 x 28mm The increase in brake area shows: Boxster => Boxster S: Front +20%; Rear +7% Boxster => Twin Turbo: Front +33%; Rear +41% Boxster S => Twin Turbo: Front +11%; Rear +30% These calculations are based on rotor machined area, not the actual swept area which will vary slightly, but it gives you an idea of why the Boxster can massively benefit from an upgrade to S brakes as most of the braking bias is towards the front. The Twin Turbo brakes are only +10% larger than the S at the front which will most likely be hard to notice under normal driving conditions. BUT! I don't have an S, just the standard Boxster. I do however, have Twin Turbo brakes. The marriage of the two seems be a good thing for slowing me down, especially after I have fitted a supercharger. As JFP suggests, larger rubber should follow the larger brakes. Luckily, I have the larger rubber already, wearing 225/45 and 265/40 17" Potenzas. After spending a couple of hours on the car with a micrometer today, I have learnt that the rear calipers and rotors will be a simple bolt on with an 8mm spacer installed between the rotor and the wheel hub (as opposed to wheel spacers that are between the rotor and the wheel). I will see if I can utilize either the H&R or Eibach spacers, but they are both 7mm and will likely require the OD to be shaved a bit. Otherwise I will make my own. The front system is going to be a bit more tricky. The caliper mounting bolts are 130.6mm apart on the Boxster compared to 142.3mm on the Twin Turbo. Also, the calipers will need to be raised 19mm above the wheel carrier to accomodate the large diameter rotor. This will then likely necessitate a 5mm wheel spacer to make sure my 3 piece speedlines clear the calipers fully, although I am praying that they will clear as is. I have a bracket design in mind, and will get this worked out on CAD to see if it will fit - anything to avoid $1400 + $1000 labor to install new wheel carriers! I have been taking pics as I go along, so I will post these sometime soon so that other fools who follow won't be quite so foolish as me. __________________ http://home.comcast.net/~andicati/images/allmytoys.jpg It's all about the corners.....