The Weight Barrier of Motorcycles

I've always tried to make my motorcycles as light as possible, but I went a bit over the top with my first original chassis design back in 1972. It was a little Hodaka-engined roadracer for which I built a sheet-aluminum monocoque box frame, which also contained the fuel. All-up weight was just 120 pounds. It worked, but it was, shall we say, not robust. I learned that light weight has its limits, but I never forgot that less weight can improve every aspect of performance, from acceleration, to braking, to handling, to fuel economy, and rider confidence.

It was the late 1980s, when aluminum frames began to be regularly seen on high-performance production motorcycles, that awareness of lighter weight was perhaps at its peak. The new frames were not radically lighter than the steel frames they replaced, but they were very visibly a new development that attracted more attention than the relatively invisible reductions in engine weight that were going on at the same time.

Weight reductions were never spectacular, but over the years many parts were converted from steel to aluminum while also being miniaturized. We began to see details such as hollow axles, bolts with dished heads, aluminum nuts, and case screws with 8mm instead of 10mm heads. Then, about 10 years ago, the trend of ever-lighter high-performance motorcycles seemed to end. Suzuki's GSX-R1000, for example, was made lighter until 2007, at which point it became heavier. It's the same story for Yamaha's R1 (though the 2015 redesign did shed significant weight). What happened? Several coincidental developments.

Suzuki, for one, began to see durability problems, experiencing frame cracking on the 2005–2006 bikes. And then there was the imposition of minimum weight rules for World Superbike and other production-based racing. If, say, the minimum weight for 1,000cc fours is 162 kg, it makes little sense to some manufacturers to produce a bike that would be less than that weight when stripped and prepped for racing. Ironically, racing rules essentially became a major disincentive for further weight reduction. Lastly, of course, there was the economic downturn that began in 2008. Development budgets were cut, making it harder to justify the extra engineering of weight reduction, and sales were down, so any increase in sales prices resulting from decreased weight would have had little support.

Is weight reduction, then, a thing of the past? Thankfully there is another example, another way to reduce weight that most manufacturers haven't followed. It consists of finding ways to eliminate whole structural elements of the motorcycle. The Ducati "frameless" concept seen on the Panigale range is a case in point. Its rear suspension pivots the swingarm on the engine cases, attaches the shock to the cases with a small bracket, and pivots the suspension rocker arm on another plate attached to the swingarm pivot shaft and to the engine. No frame holds these parts. What's eliminated here is the whole rear section of most frames, with their two crossmembers, and the weight saving is drastic—between 20 and 30 pounds, depending on which bike we're comparing.

Is the frameless concept, in turn, the end of the road for weight reduction? That's where things get more futuristic. Taking the Panigale rear suspension, which mounts directly to the engine, as a model, would it be possible to mount the front suspension to the engine just as directly? The Panigale mounts the fork to a large aluminum box that in turn mounts to the engine. Would it be possible to eliminate that box structure as well? The answer is yes, but that's the subject of a future column.