The R171 features a number of revisions compared to its predecessor, the R170: a 30mm longer wheelbase, increased length (72mm) and width (65mm), 40% increased use of high strength steel, seven-speed automatic transmission, adaptive two-stage airbags, head/thorax sidebags and a revised roof mechanism (marketed as the Vario roof) deployable in 22 seconds (previously 25 seconds) with a rotary-pivoting rear window enabling a more compact folded roof stack and trunk storage increased by 63 litres with the roof retracted. Optional features include remote operation of the retractable hardtop as well as an innovative forced air, neck-level heating system integral to the headrests, marketed as "Airscarf".