TZR250

Brilliant biking inventions…The Aluminium Beam Frame

The old adage states that racing improves the breed – and so it has always been proved thus!

All the electronic gizmos you have on your latest road bike? Yup, come from racing, four-stroke racing from when GPs went that way in 2002… Radial tyres? Same, but this time in the 1980s courtesy of Michelin and Freddie Spencer, etc. etc. etc…

And, in the late 1970s in 500cc Grand Prix racing, things were changing big time. Bikes were becoming more powerful, tyres were handling that power better and the chassis of the racing bikes themselves were ‘stiffening up’ as a result. They had to! In the 1970s the frame of a racing motorcycle was pretty much a conventional steel tube frame, or spine frame and this was starting to show its age.

Yamaha were the first to move to the idea of using an aluminium frame for their GP racers back in 1980 when the OW-48 was introduced with square-section construction clutching the parallel-four, two-stroke motor.

Kenny Roberts swopped between the ally and steel framed OW during the 1980 season to hold onto his 500cc World title. 1982’s OW61 saw the first frame design which could really resemble what we would call a ‘beam’ frame and this model also saw the first of Yamaha’s V4 two-stroke 500cc motors make an appearance. Kenny Roberts’ final year of racing in 1983 saw the first ‘Deltabox’ frame appear on the OW-70 that he rode to second in that year’s 500cc championship, behind Freddie Spencer.

Yes, the beam frame seems to have been a Yamaha invention. But, while the Deltabox may have been a Yamaha-patented design, there often isn’t a copyright on a good idea and many feel that the genius of Spanish engineer Antonio Cobas is the man we all have to thank for the frame on our modern-ish machine.

If we go back to 1980, Cobas was at home in Barcelona designing frames for race machines and it was while doing so that he decided to look at different ways to harness the power produced by race bikes in different ways: including the use of a ‘beam frame’ like the beams he had to use to prop up his house, which had a number of structural defects. After all, if a beam could keep a house in one piece, why not a bike?

Cobas became a legend in the smaller classes, engineering bikes for the likes of Sito Pons, Alex Criville and Alberto Puig. Around this time Cobas began to develop stronger, lighter twin-beam frames, fabricated from aluminium. The precise details are lost in history, but it’s thought that his designs for the 125/250cc machines were soon being emulated by the factories and 1983’s OW-70 was the first 500cc machine to copy his ideas.

So, for Yamaha this became the ‘Deltabox’ and its general design was that from the steering head to the swingarm pivot, the frame is made of a triangular box, rather than a rectangular one, which means it’s therefore stronger. To fabricate the frames, alloy is introduced under high pressure into a vacuum held die, which limits air-bubbles which would otherwise reduce strength and integrity of the frame itself.

This means the rails can be thin where needed and thicker where you want more strength. The result is a frame around four-times more rigid than previous designs – just what you want for a race bike…

It took some time before the ‘Deltabox’ appeared on a road machine, but when it came – it was amazing. The 1986 TZR250 2MA had the word DELTABOX writ proud on the frame itself. Here’s where we excuse ourselves: we’ve seen DELTABOX, Delta-Box and Delta Box on Yamaha frames… whatever, it’s their name eh?

From this moment on, biking changed. Yamahas seemed to have the edge. In 500 and 250cc GPs the YZRs handled, while road machines like the Genesis, EXUP and FZR were often the best in their class… Most of the road bikes had alloy frames (save for the FZR600 which used steel) but soon others would copy – as Yamaha had done themselves…

As is often the case, new ‘names’ for these frames would be contrived. Kawasaki had their E-Box frame, seen on ZX-10s and KR-1s, some called it a ‘diamond alloy frame’ while others didn’t call their frames anything. If there’s a nod to how well it worked, well, even Suzuki ditched the double-cradle frame in 1996 with their GSX-R750 WT SRAD… what more do you need to know?

But – when it comes to names – only Yamaha were bold enough to keep their ‘Deltabox’ going – at least on road bikes: Yamaha’s YZF-R1 and R6 family used later versions called Deltabox II (on first-gen R1 and R6s of 1998/1999) and Deltabox III on second-gen R1s and R6s. Suddenly the YZFs seemed to drop the Roman numerals, they’re just ‘Deltabox’ frames now.

Either way, the ‘beam frame’, ‘alloy beam’, DELTABOX, Delta-Box or Delta Box had been with us for more than 35 years now and despite the sprinkling of trellis frames and monocoques, it’s still the best way to grasp a motorcycle engine…