Cobas’ influence

The extent of Cobas' work on the NSR250’S chassis development was implicitly recognised by HRC in October 1988, when they went testing at Jerez with their 1989 prototype and enlisted him as a consultant to advise on the new bike’s chassis design. That early test ensured that the 1989 Honda looked much more like Sito’s Cobas-modified 1988 machine than before, even if HRC failed to incorporate all Antonio's modifications in the revised 1989 model. Thus while they altered the riding position from 1988, so that as on the Cobas-modded version the fuel tank was shorter and fatter, and also increased rear suspension travel by 2mm to 118mm on the Showa shock, there was still plenty for Cobas to do when he got the bikes back to Europe after the first three overseas races. His modifications, originally unique to Sito’s bike but then largely emulated by HRC on Shimizu’s machine included: • raising the rear ride height to effectively steepen the head angle and increase front end bias further • making up a range of eccentric cups to permit further variation in the head angle – average setting was an ultra-steep 22 degrees • covering in the bottom of the seat to close off the slipstream and reduce the possibility of being drafted by a slower bike (i.e. Yamahas!) • making a completely new rising rate link for the Showa shock to offer a different curve • designing the pro-squat rear brake linkage, though for internal reasons this was made by Honda to Antonio's specification and was not available until almost mid-season. But while it was the Cobas modifications to the chassis which made the Campsa NSR250 stand out from the clutch of other Hondas that season, it was the performance of the 90º V-twin single-crank crankcase reed-valve engine that was responsible for Hondas’ supremacy over their Yamaha and Aprilia rivals. After their subtle redesign for the 1988 season, HRC initially made few changes to the engine for 1989. But once the extent of Yamaha’s threat became apparent in the first few races, Honda stepped up development dramatically, using Shimizu’s bike as a rolling testbed for the work that would eventually earn them their third 250cc world title in a row. The electronic ignition had a range of five different chips offering an altered curve, though unlike on the Aprilia/rotax system you had to actually swap the chip over rather than flick a switch to change them. Surprisingly, though, Santi Mulero said they used the same design of cylinders and pipes for all types of circuits, and though two types of Keihin carburettors were available, Sito only raced at Laguna Seca with the newer kind. With such a wide spread of power it did allow you to hold a gear between corners if you wished, like the last two right-handers before the pits at Calafat, thus saving two time-wasting gearshifts up and down again. The Honda engine’s great advantage was not so much in terms of outright power, though, but in torque. You could short-shift at 11,000rpm where necessary or convenient – like on the last left sweeper before the line at Calafat, where Sito’s favoured one-down/five-up left-foot gearshift made it hard to shift up from third to fourth while cranked hard over. Solution: short-shift at eleven grand, crack the throttle wide open, and let the Honda’s ultra-flat torque curve pull you through. Doing this in preference to buzzing the engine in third enabled me to get peak revs of 13,000 in fourth 80-100 metres earlier down the straight, and provided a lesson in how to ride this bike to best advantage. You must consciously use one gear higher than you might with a rotary-valve Rotax or Aprilia, taking corners in second rather than bottom gear, third gear rather than second, using the finely-honed suspension to keep up momentum, and trust the strong midrange torque to pull you out of the turn. This flexibility makes the choice of gear ratios perhaps less critical than would otherwise be the case, but in any event the side-loading cassette-type cluster had a wide choice of options, ranging from five each for the bottom four gears, to seven each for the top two. Antonio Cobas’ talents come into play again here, thanks to the computer programme he’d developed to enable his riders to select the optimum gearbox for each circuit and each set of conditions. The Sito Pons 1989 world champion Honda NSR250 was that rare thing – a racebike that was above reproach for its era. After five years of development, it had become one of the all-time greats in racebike design, with four world titles to its credit out of five attempted. Just as well Yamaha didn’t stop trying to turn the tables, which they did in 1990 courtesy of John Kocinski!