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If already posted, couldn't find easily so I'm posting info now - don't have account for pics but I can supply for a reply with pics...
288mm vs 308mm - 2 sizes on the 9-5, both using the same pad size - how? The pad area is the same yet the discs are 2 different total diameters? Once both are side by side it's now obvious - the pad area is set to the edge on both, the inside area on the larger disc is used to vent to the outside of the rotor and out the wheels, the smaller goes to the hub, the vents are on the back side and vent to the hub instead. So while the pad area is the same, the swept area is larger, and the heat dissipation capability is greater. Using the same caliper and pad only requires a different mounting bracket to the hub - which being a simple piece of metal is cheap to make in 2 different configurations, thus saving on only 1 caliper and pad.
I'm sure most of the mechanics on here know already but this eluded many posters on here at first who have asked about discs -
SO if you have the base model (or possibly arc?) then the 288 is likely installed - if you have the Aero (or the sport package on the 06+ with suspension and seat upgrade) then you have the 308.
The simple guarantee is to look inside the wheel, and if there's a gap between the hub and the pad then it's outward vented and 308mm. If it's straight from pad area to hub and no gap then 288.
BTW don't get caught out by the rears on the 04-05 ARC model - all of the cars usually use the same solid rear discs, but just like their experiment with softer subframe bushings, they decide to install larger vented rear rotors - so best to remove the rear wheel to check for vents or not...
posted by 99.106.3...
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