The science behind what makes Triumph’s Speed Twin so special,
How come a bike that produces less power per cc than a Honda Super Cub is the best machine for a B-road on a British summer’s day? It’s all about thrust…
‘Textbook torque curve, crisp response, short gearing and feelgood thump’
TRIUMPH’S SPEED TWIN doesn’t impress at spec level. Its twin-cylinder engine is 1200cc, but with a dyno-tested 95.4bhp at the wheel (matching its claimed 96bhp) it only has the same sort of power as Honda’s CB650R – a bike half its size. In fact, on horsepower-per-cc the chunky Triumph is less powerful than Honda’s Super Cub step-thru. Britain’s sporty retro isn’t about bragging rights, however. With a textbook torque curve, crisp response and road-biased gearing, the Speed Twin is the exemplar of accessible, feel-good thump. And on dappled summer roads it creates unrivalled sensations.
Tuned for grunt
Torque is the work done by an engine; think of it as the size of its punch (horsepower is essentially torque multiplied by revs, and so is how frequently this punch can be delivered). Ride a bike that builds grunt and delivers its biggest punch at high revs, such as a sporty inline-four, and there can be a rush in drive at the top of the range. Bikes with meaty low-rev torque give in-your-face smacks as soon as the clutch is out, but willingness fades as revs rise; the motor’s flailing its fists, but the punches get ever-smaller. Triumph’s 1200cc twin doesn’t make a traditional peak. The firm’s triples are famous for a luxurious glitch-free spread across the rev range, but the Speed is a step on again (see graph, right). In an ideal world the torque curve would be a horizontal line, and the 1200 is the nearest yet. There’s 80 lb.ft of stomp or more all the way from 3500 to 6250rpm (rev limit is 7200rpm but the tacho indicates almost 8000rpm, nearly 1000 into the red). Thick, even torque puts a Speed Triple to shame, and at real road revs you’re always at or near peak torque. The motor’s happy with any of three gears on a flicking B-road and you never wait for revs.
Geared for the road
It helps hugely that the Speed is geared to exploit punch. Its 1200cc HP version of the Bonneville motor is as used in the Thruxton, and as well as 17bhp more than the trad’ T120 version it has short gearing. Primary and gearbox ratios are the same, but
POWER AND TORQUE
Over-re ne an engine and you loose character – early Tiger 800s had super-smooth torque but felt a bit at and uninspiring. With two fat pistons, a 270-degree ring interval and serious punch, the Speed Twin provides easy-access drive across the revs and feels good too. the final drive has a five-tooth larger rear sprocket and a one-tooth smaller front. It’s a truly massive difference.
Using numbers from the torque curve, gearing data and tyre size, you can produce a thrust curve. This is force at the rear tyre; the quantity of thrust actually pushing you down the road. To illustrate how impressive the results are we’ve overlaid the curves with a Triumph Speed Triple RS – the supernaked that defines flexible road bikes (see over the page). With its spread of torque and short gearing, the Speed Twin is way more accessible – at realistic road speeds it pushes harder in every single gear.
‘Epic sensations from sitting Hailwood-style at lean and revelling in the roll-on wallop’
Usable performance
Punch and gearing make the Twin hilarious and fabulously usable at the same time. At 22mph in first – as soon as the clutch is out – it has 25% more thrust on tap than the more powerful Triple, so feels oh-so playful. At 62mph in third the twin’s 540 lbs of thrust gives snappier corner exits and easier off-the-crest wheelies than the triple’s 461 lbs; in fifth at the same road speed, the retro has almost a third more thrust than the RS for swifter overtakes. You might think snappy gears and a short rev range mean your left foot is a blur, but it makes the Triumph easier to ride. Stumble across a mini-roundabout on a cross-country blast, find that open sweep is actually a tight elbow, and it thuds out hard in a tall gear. 0-60mph is 3.44s; quick, but it needs two shifts as second doesn’t quite hit 60mph. Pulling away in second is easy, calmer, yet just as brisk – the best run is only two-tenths slower, and on average it’s actually 0.02s faster in second. There’s real flexibility for you. The Thruxton also has this engine and gearing, of course. But by housing this usable, stimulating, engaging motor in an easierturning upright chassis the Speed Twin does something else. The sense of control from the commanding stance gives even greater confidence to use the thrust exiting corners (and allows full use of top brakes, which stop the Twin in a shorter distance than the Triple’s swanky radials). Sensations from sitting Hailwood-style at big lean and revelling in the roll-on wallop on corner exit feel epic on glorious British roads. It’s calm but rapid, relaxed yet engaging. Summertime bend-swinging perfection.