Suzuki 370/400
After looking at the ubiquitous big singles from Honda and Yamaha, Steve Cooper turns his gaze towards Suzuki, and the singles that were marketed under the ‘SP’ prefix.
And now a resumé of a series of bikes that commenced with a machine designed to be both easier to use and more accessible, a considered upgrade that failed to fire people’s imaginations, and a last throw of the dice that became a wholly unexpected success.
The story begins circa
1976, when Suzuki realise that Yamaha have a runaway success on their hands with their ground-breaking XT500. Suzuki take note of the bike’s pros and cons then task their R&D teams to come up with a viable alternative. The various teams, with input from the marketing guys, conclude that the Yamaha’s greatest issue is its mass when ridden off road. All fuelled and oiled, the XT tips the scales at a fairly meaty 155 kilos, so Suzuki conclude that if they are able to offer a lighter bike with a similar power-to-weight ratio then they have to be on to something good. The resultant SP370 came within a hair’s breadth of meeting the design criteria yet, to all intents and purposes, the first Suzuki fourstroke single since the 1950s failed to measure up; in the real world the bike effectively fell between two stools. It wasn’t appreciably more powerful than the 250cc four-strokes it was supposed to surpass, nor did it have the measure of Yamaha’s still hugely popular XT500. The SOHC motor went well enough and even if it didn’t exactly offer anything new or radical it wasn’t a dog either – and yet it was almost as if Suzuki’s engineers really weren’t that bothered. With less ground clearance than many 175 strokers the SP could be a handful off road – the handling was cited as being a little woolly, on the dirt it had a tendency to try to high side when the power was applied out of bends, the build quality wasn’t the best and its pricing took it perilously close to numerous far more capable machines. The SP370 lasted just two model years, along with an enduro-type strippedback version sold as the DR370. Upping the capacity to a nominal 400cc to deliver the SP400 did little to bolster sales, even if the price was pitched a little more realistically for the ’80/’81 models. Although Suzuki would go on to make some significantly better fourstroke single engines, their first stab at a middleweight had effectively bombed.
Despite what many would take as a serious slap in the face, Suzuki reckoned that they still had some mileage to extract from the original designs, even if they weren’t going to be used as trail bikes. Rather than simply abandon the engine, which in all honesty wasn’t a bad piece of kit, Suzuki came up with a plan to produce a rider friendly, non-intimidating, factory custom cruiser otherwise known in the US as a ‘soft chop.’ With kicked-out front forks, a peanut-style fuel tank, King & Queen-look seat and high rise, pull-back handlebars, the bike was launched for the 1980 model year. Despite the reputation of the 370/400 trail bikes, the newly named GN400 sold in decent volumes to a demographic not obsessed with handling, performance, quarter-mile times and the like. Suzuki were very well aware that the 350-400 capacity band was a huge seller stateside. Honda’s CB350 K series had been America’s top-selling machine bar none when new, and Kawasaki’s Z400/440 twins were among the firm’s most successful machines in the pivotal US market. With sub 28bhp and torque figures around 22ft-lb, the GN400 was no hooligan tool yet its target market accepted it and loved it for what it was… a totally unpretentious, single cylinder, easily accessible machine that ran reliably and required little other than basic servicing. In a rather roundabout way, Suzuki had strangely succeeded in delivering a slightly gauche and camp AMC middleweight that immediately found a willing fan base.
The 400 sold in decent enough numbers from 1980-1983 to finally return some of the SP370’s development costs before being put out to pasture, but this removal from the stock lists didn’t spell the end of the GN by any means. Even before the last of the 400s was being sold, a 250cc version of the now surprisingly successful bike was rolled out, and at last Suzuki had hit the mother lode. The new quarter-litre version proved to be so successful that it found a ready market in every continent where its robust build, ease of use and simple servicing requirements saw it still being offered as late as 2006 in some countries. Despite being almost a fully paid-up lemon as a trail bike, the Suzuki four-stroke engine proved to be one of the company’s most long-lived power units.