Be aware that "RX-8 space saver wheels" often appear on ebay, but aren't the right ones and don't work.
Mazda did list an option for a space saver wheel for the RX-8 (PK01-89-4700), which came with a mounting frame (FE01-V8-360) to fit it inside the boot under the parcel shelf.
There are other space saver wheels, even many Mazda ones, that have the right PCD (Pitch Circle Diameter aka stud hole layout) to fit the hub but they don't have the same rolling diameter as the RX-8 OEM 18" wheels fitted with 225/45R18 tyres. The space saver must be fitted with a Bridgestone T125/70MR-17 98 tyre.
Fitting a tyre with a rolling diameter even 3% different to the other wheels causes the RX-8's sophisticated DSC/ABS/TCS systems to trigger, as that wheel is rolling too fast or too slow compared to the others.
The systems will assume that the odd wheel is either spinning, locking or sliding, and attempt to compensate, by reducing engine power, braking other individual wheels, or reducing brake line pressure. None of these are good idea, hence my use of the term "don't work" rather than "don't fit".
Space saver wheels have even been bought and sold on this forum, in good faith, as the seller was unaware of the history of the spare they've been carrying in the boot.
At least one owner had a space saver supplied by their Mazda dealer when they bought the car new. It wasn't used for many years, until it was leant to another member who found they had a flat tyre as they went to leave a club social event. On the drive home "the dash lit up like a Christmas tree" and "the engine went into limp mode". Eventually we determined that the space saver was actually one for a Mazda 6.
Even with the correct space saver fitted, the DSC/ABS/TCS systems can still be triggered prematurely, as the rolling diameter isn't a perfect match and the grip/traction is also much reduced. Some will argue that the space saver should be fitted to the front axle, an a RWD car, in order to prevent wheel spin.
I suggest that it should be fitted to the rear offside, not for any vehicle dynamics reasons but so it is clearly visible to vehicles approaching from behind, such that they can see why you're keeping your speed under 50mph.
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- Spin Doctor
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