Garden Grove, California - American tuner Vorsteiner has created this very special wide-body conversion for the BMW M4 to headline its display at the 2014 SEMA show.
The design brief was for a lightweight, all-carbon fibre body kit that had to blend so smoothly into the bodyshell that it didn't look like a kit.
It also had to make space for the widest possible rims and offset track, while allowing for a modicum of suspension movement and enough steering lock that the car would be driveable in traffic. And that's a big ask
The GTRS4 was first conceived the old-fashioned way, with pencil and paper, and once the designers were satisfied with the profile, the entire body of the donor car was scanned in three dimensions using blue-light lasers.
The new panels were then digitally mastered onto those scans and the first full-size templates were CNC machined to fit on to the basic body shell.
Any car stylist will tell you the most difficult part of a car to get right is the rear quarter panels; there Vorsteiner's creatives went back to basics, using traditional clay modelling and that most sensitive contour gauge of all: the Ball, Eye, Mark 1.
BOOTY-LICIOUS
The new front wings are 100mm wider than standard across the wheel-arches (and remember that an M4 is wider than a vanilla flavour 4 Series to start with) while the car's rear three-quarter panels are a dramatic 180mm wider across than the original M4 sheetware.
And all the while the stylists were being elbowed aside by the technicians, who wanted to cut in ducting to get cool air on to the brakes and hot air away from them.
The stylists struck back with specially designed three-piece 20" forge-alloy rims shod with 275mm front and 345mm rear Pirelli P Zero gumballs, whereupon the techies came up with a KW Suspension sleeve kit that allows for ride height adjustment while retaining the original BMW Dynamic Drive features.
Finally, ESS Tuning's ECU geek plugged in his E-Tronic laptop and tweaked the M4's three-litre biturbo straight six from the standard 317kW up to a knockout 405kW at the crankshaft.
Vorsteiner isn't quoting performance figures - nobody is going to take the slightest chance of getting a scratch on the show car until after the SEMA show closes! - but all the kit components are now available to bolt straight on to your M4, including the special rims, monogrammed floor and boot-mats, and the distinctive chromed badging you can see in the pics.