BMW's four-cylinder K-bikes all receive a new larger 1293cc engine (from the previous 1157cc), with the 136cc displacement boost achieved via a 1mm bore increase and additional 5.3mm stroke. Connecting rods that are nine grams lighter work with 12-gram-lighter pistons and revised cam timing to give an extra 8.0 horsepower (for a claimed total of 175 at the crank) at 9250 rpm-1000 rpm lower than the 1200-and 7.4 ft-lb more torque (now 103 ft-lb) over the old engine. Also assisting in this area is a redesigned exhaust system utilizing a significantly shorter muffler and an exhaust valve in the collector; weight for the stainless steel unit has dropped from 22.9 pounds to 20.7 pounds, complete with catalytic converter.
Interesting options include the same power-shifter and 2D instrument cluster setup found on the HP2 boxer twin, and an "anti-spin control" system integrated into the standard ABS setup.
The K-bikes' Duolever front suspension gets a new lower longitudinal arm made from forged aluminum alloy that replaces the previous steel unit (reducing unsprung weight by 2.2 pounds), while the upper fork bridge also saves weight with a new hollowed-out design. A slightly redesigned wheel carrier and pivot point sharpens handling while incrementally increasing wheelbase. Spring and damping rates both front and rear have been firmed up, and the optional new electronically adjustable ESA II suspension system now not only can adjust damping and spring preload, but spring rate as well. By progressively pushing an Elastogran plastic sleeve (that assists the spring during compression) inside the metal spring via a stepper motor, the spring's rate can actually be altered.
The K1300R gains the same engine and suspension upgrades as the S model, with peak power incrementally down at 173 horsepower but identical torque figures. A shorter final drive ratio (2.91 versus 2.82) should result in quicker acceleration, however. While the K1200R had slightly steeper (more agile) steering geometry than its K1200S cousin, the K1300R has identical steering numbers to the K1300S. Most of the same performance options such as the power-shifter, ESA II electronic suspension system, 2D instrument cluster and anti-spin traction control are available for the K1300R as well.
The K1300GT's powerplant is basically the same as the R and S models with engine tuning biased more toward low-end torque. Horsepower is rated at 160 at the crank, with torque measuring 99 ft-lb at 8000 rpm; there is said to be significantly more torque at lower rpm levels, with 80 percent of the engine's maximum torque available from 3500 rpm. The shift lever now runs in special anti-friction bearings for faster and more precise gearchanges, and the fairing has undergone some subtle modifications, including new integrated tipover protectors. Steering geometry numbers remain the same more-relaxed setup from the previous K1200GT, but the new Duolever aluminum control arm gets fitted to the GT as well. The latest ESA II electronic suspension adjustment is likewise available on the GT as an option.
But one of the most important improvements to the K series BMWs (in our opinion) is the surprising move to conventional turn signal switchgear, with a single conventional push-to-cancel switch on the left handlebar finally replacing the tedious and idiosyncratic multiple-button turn signal switchgear of previous BMWs. Retail prices were unavailable at press time. -KK