The Roadster S - based on the BMW Z4 3.0 - was introduced at IAA 2003. It didn’t replace any existing Alpina models as no Alpina version of the BMW Z3-series was produced.

The Roadster S uses the same engine as the B3S. This engine is based on BMW´s 3,0 litre unit, found in the 330i and the Z4 3.0 for example. In standard version it produces 231 bhp, in Alpina´s version it delivers 300 bhp and 362 Nm. Please refer to the E46 B3S section for more information about this engine.

The Roadster S uses a 6-speed ZF gearbox, which is different than the B3S. Also, the final drive was changed from the regular Z4 3.0 - 3,23 instead of 3,07.

The suspension has been uprated with stiffer springs and modified dampers. Tires are changed from the Z4 3.0 standard runflat tires to Michelin Pilot Sport, 235/35 ZR19 at the front and 265/30 ZR19 at the rear, fitted on Alpina Dynamic wheels just like the Roadster V8. Alpina Classic wheels are available as an option. The Roadster S uses the same brake set-up as the Z4 3.0.

Inside the Roadster S is equipped with sport seats in Alpina design leather, new instruments with blue background and red needles, a hand-stitched leather steering-wheel, Alpina floor mats, Alpina door sills and a silver-plated production plaque. The exterior changes are very subtle, front and rear spoiler lips are fitted. These make the car more stable at speed while maintaining a very low CW-value. The Roadster S also has two large exhaust pipes.

For the Roadster S, Alpina claimed a 0-100 km/h time of 5,3 seconds. However Auto, Motor und Sport measured a time of 5,0 seconds. Topspeed is quoted at 265 km/h, or 270 km/h with the optional hardtop.