Measured changes for improved performance.
December 2010
Suzuki’s 2011 update of the GSX-R600 and 750 is very much like a MotoGP team’s midseason adjustment: minor in that it’s not a total redesign but moves steadily in a desirable direction. In the case of the 600, the 67.0 x 42.5mm inline-Four is rotated backward slightly, enough to allow it and the swingarm pivot to be moved forward. This shortens the wheelbase from its former 55.1 inches to 54.5. Shorter is better for quick handling, because when you turn the front, the wheelbase is the “lever” by which the steered motion of the front end steers the rear wheel.
In the outdated language of 40 years ago, the heavy-steering bikes admired back then “cornered as if on rails.” Locomotives actually are on rails; just try steering one. Today’s quick-responding bikes allow us to make midcourse corrections and quickly evade road hazards.
A similar set of changes to the GSX-R750 takes its wheelbase from 55.3 inches down to 54.7. Claimed curb weight of the 600 decreases by 20 pounds—from 432 to 412. The 750’s 2011 diet trims it from 437 lb. to 419.
Resculpted 2011 GSX-R600/750 bodywork is said to be more aerodynamic and, like many other parts on the motorcycle, lighter than before. According to Suzuki, the new vertically stacked headlight alone shaved more than a pound. Tailsection mimics the current GSX-R1000’s.
Both the 600 and 750 receive the Showa Big Piston Fork (BPF) that was so much discussed during the final racing season of Suzuki’s many-time AMA Superbike Champion, Mat Mladin. As tire grip and speed of maneuver increase, chassis and component stiffness must do so as well. On this fork’s radial mounts are new Brembo calipers. As racing-minded readers know, Brembo has come to dominate Superbike and MotoGP starting grids with calipers designed for smooth, reliable operation and structural stiffness that translates to a firm lever. Brake discs are 310mm diameter.
Small details in the specification indicate the importance of racing to sportbike sales. Compression ratio for the 600 is up a tenth of a point, from 12.8:1 to 12.9:1. Compression ratio is fundamental to engine torque because peak combustion pressure is roughly 100 times the compression ratio. The greater the pressure acting on the pistons, the greater the torque at the crankshaft. But push the compression too high and you get destructive combustion knock. Engineers play a sophisticated game, subtly changing combustion chamber shape to give combustion the speed to “outrun” the chemical changes that lead to knock, even at higher compression ratios.
The ’11 600 spec also tells us this model’s forged pistons have been designed with the aid of FEI and fatigue analysis. FEI is Finite Element Analysis, a computer technique that can predict the stresses in parts. The aim here is to make pistons light enough to reach very high rpm but without creating within them any stress they can’t survive. This is why today’s very low “ashtray” pistons have such gracefully shaped undersides. That grace is the shape of design for low stress.
Pistons operated at state-of-the-art racing speed gradually accumulate internal damage—metal fatigue—that eventually produces cracks. The hotter the metal, the faster this occurs. The need to make MotoGP pistons last through three races has required manufacturers to combine stress and temperature studies into a computational tool that can predict cracking. Suzuki is naturally applying this valuable tool to production piston design.
Con-rods of sportbike engines have during the past several years been shot-peened to increase their fatigue resistance. Also aimed at durability under heavy load is the chromium nitride coating of the piston rings of these GSX-Rs, replacing the chromium used previously. Around Top Dead Center at the beginning of the power stroke, the piston rings must seal combustion pressure while the piston is barely moving. This is hard on rings because they need sliding speed to lift them off the cylinder wall on a wear-stopping film of oil. The cylinder wall near TDC is also very hot—another problem. An old-tech cast-iron piston ring would form micro-welds to the cylinder wall under these conditions, which would break as the piston started its down stroke, forming wear particles. This is prevented by coating the rings with very hard material of a melting point so high that it cannot alloy itself to the cylinder wall. This is not new for 2011, but it is interesting.
Count a fully adjustable 41mm Showa Big Piston Fork and Brembo Monobloc front brake calipers among the front-end changes made to the middleweight GSX-Rs. The rear suspension is similar in design to that of past models but weighs slightly less.
In the same category is the Suzuki Exhaust Tuning system, which is the familiar valve between the header pipes and collector. Under ECU control, it closes down partly at rpm or other conditions in which exhaust pipe waves returning to the cylinder are positive and would interfere with cylinder filling by back-pumping exhaust gas. But Suzuki’s 2011 brochure also relates SET action to throttle response. Throttle response and idle stability depend to a large extent on the exhaust fraction remaining in the cylinders. Exhaust dilution is what gives pure racing engines their irregular high idle and “sore throat” throttle response off the bottom. By reducing exhaust dilution, SET allows street use of tuning levels that would otherwise lead to such unacceptable throttle response.
A new item in the spec is the statement that cams in these GSX-Rs are the first production application of a technology developed in Suzuki’s racing activity. While the brochure doesn’t tell us what this is, a guess would be that conventional cam design assumes that all parts—cam, valve and tappet—are rigid. But at racing rpm and stress, nothing is rigid; all parts “ring” with vibration like bells. Valve heads vibrate like trampolines and camshafts bend and rebound. This vibration can interfere with controlled valve motion, causing valve float or bounce after closing. For valve-train stability at the highest revs, cam design cannot afford to ignore such vibrations.
As in the previous model, the engine is made shorter by vertically stacking its gearbox shafts, and engine braking’s negative influence on corner-entry rear-tire grip is reduced by a ramp-type slipper clutch. Inside the engine crankcase, pentagonal holes in the number 2, 3 and 4 main-bearing webs cut power loss from the back-and-forth pumping of crankcase air from cylinder to cylinder.
Do all these details make you tired? Relax and let the engineers make it happen. Controlling the details is how bikes have become as good as they are. And there’s more. Everything the engineers learn also reveals new questions. Answering them is the future.
