IT was always inevitable that, having released the K1600GT and GTL, rumours would begin suggesting that BMW is planning more machines based on the new six-cylinder engine. And now those rumours are up and running at full speed on various web forums.

The six cylinder motor was first shown in the naked Concept 6, so it's no surprise that the most heavily suggested follow-up to the K1600GT is an unfaired “R” version, effectively replacing the K1300R. When the Concept 6 was originally shown two years ago, its designer David Robb admitted he'd like to see something similar in production but that there were no plans to build it at that time.

However, since concept bikes are made specifically to provoke a reaction from potential customers, giving their makers a steer about future model direction, it makes sense that such a machine should be in the firm's thoughts.

Certainly the straight-six engine would appear to suit a naked bike that could flaunt its cylinders more openly than the demure K1600GT and GTL, and the motor's torque-heavy state of tune would also work well in a naked machine. However, since the new six is actually less powerful than the older four-cylinder “K” engine (160bhp in the K1600GT vs 173bhp for the K1300R), it might need re-tuning to beat its predecessor should a six-cylinder naked machine become avalilable.

Of course, if there was to be a K1600R, then it would make sense to create a K1600S as well, leaving no room at the inn for the old 1300cc four-cylinder motor.

But... The K1600GT starts at £15,300, a full £1800 more than the old K1300GT (which it effectively replaces, as well as superseding the mammoth K1200LT). Would it be possible to make a six-cylinder machine that could match, or even come close to, the K1300R's £10,450 price? And would the bigger engine offer a significant advantage over the existing four? Finally, could a six-cylinder BMW out-pose and out-muscle the Ducati Diavel that's scrambled the “big naked” market this year?

Rumours or not, the chances are that should a naked six cylinder appear it won't be until 2013 at the earliest. BMW already has a full plate when it comes to new projects, with a 700cc scooter and a new R1200GS in the works for 2012, plus plans to re-enter the cruiser market that it deserted seven years ago when the R1200C was discontinued.