Actual rocket science: The geometry magic that helps Triumph's Rocket 3 handle so well
One look at Triumph’s Rocket 3 R and you’d imagine it handles with all the deft agility of a Mississippi paddlesteamer. But ride the 2458cc beast and you’ll be amazed at how easily it turns, given its mammoth mass and stretched-out stance.
In part that’s thanks to a couple of clever steering geometry tricks employed by Triumph’s chassis engineers. But to fully understand what they’ve done, we need to remind ourselves what rake and trail are.
Rake is the angle the bike’s steering stem sits from vertical. It’s not, as pub experts may tell you, the angle of the forks. Most bikes’ rake sits between 23° and 30°, while Buell’s Firebolt had a steep 21° rake, while Harley’s FXDR enjoys a lazy 34°.
Trail is trickier to get your head round. Imagine shining a laser pen down the steering stem – a fancy laser that can pass through wheels and mudguards. Trail is the straight-line distance from where that red dot hits the road back to the centre of the front tyre’s contact patch.
Typically trail is around 100mm. Triumph’s 2004 Daytona 955i had a super-short 78.7mm, while Harley tourers use 170mm.
Trail generates self-centring forces in a wheel, creating stability. If your front wheel kicks to one side, trail helps bring it straight again. However, for a fixed amount of trail, the strength of this self-centring force is weakened as rake angle increases.
Higher rake and trail values also require more steering effort to turn in, hold a line and pick a bike up straight again. In short, it’s a trade-off between stability and agility.
Quickly we can see the challenge of trying to build a whopping 2.5-litre power cruiser that demands a low, long musclebike image, mustn’t handle like a greased hippo, and still needs to be stable at 138mph. This is where Triumph get clever.
On most bikes forks and headstock run parallel, but on the Rocket they’re angled differently. While the forks jut out at the same relaxed 32° as the old 2.3-litre Rocket III, behind them the headstock sits at a much steeper 27.9°. It’s a neat bit of visual misdirection – the rake is less than it looks.
However, kicking the front wheel far off into the distance while pointing the headstock straight down at the floor leaves insufficient (or even negative) trail, causing stability problems. So down at the bottom of the forks Triumph use a second trick: front wheel spindle offset.
The wheel isn’t mounted inline with the centreline of the forks, but slightly behind it. Moving the front wheel back this way builds in more trail, improving stability. And all without sacrificing the long, low, lazy look that the Rocket is famous for.