The difference between the new Triumph Bonneville Street Twin and the previous Bonneville is only one thing: everything. It has a new engine, new chassis, new instruments, new fly-by-wire throttle, new traction control, new yadda, new razzmatazz, and new glafuncles. But sure, it’s hard to see changes on a bike that is an updated retro design that’s equally as retro as the previous retro version. So, the Street Twin’s new is a new that’s supposed to be felt, not seen. You will be able to feel it.
The Street Twin engine is a liquid-cooled, eight-valve, single overhead cam, parallel twin with sleeveless Nikasil-coated cylinders and a 270° crank angle. Plus, it’s now actually 900cc, not 865cc. This new powerplant has redefined performance parameters, with a claimed 55 rather than 67 horsepower, and 59 versus 50 pound-feet of torque. At a glance that might seem odd to give up so much horsepower. But it’s not odd. It may be initially disappointing considering the significant update to the platform, but if it’s higher performance you are after, Triumph will refer you to the new bigger Bonnevilles.
The engine has two counterbalancer shafts, one front and one rear, and each, of course, spins in the opposite direction of the crankshaft. Peak horsepower is at 5,900 rpm, and redline is somewhere just beyond that. For a liquid-cooled motorcycle, the Street Twin has efficient air-cooling fins on its head and cylinders. In other words, these fins don’t fib: they actually do assist in cooling the engine. The transmission has five speeds.
The EFI feeds through a single 39mm throttle body. By comparison, the Indian Scout 60, at 1000cc, has a 60mm throttle body. Considering that twice a diameter is four times the volume, these numbers are quite far from each other. Also, considering the Venturi effect, which defines how a constricted path results in a lower pressure yet higher velocity of flow, there’s a significant engineering disagreement here between these brands.
The Street Twin’s fuel management design results in increased fuel efficiency for a claimed 72.8 mpg at a steady rate of 56 mph, and 52 mpg at 75 mph. What we did verify so far is that when the bike is ridden hard for extended mountain miles in second gear, dragging toes through the turns and railing up to redline in the short straights between each of them, our mileage was 47.3 mpg, which is very impressive. Very. This shows that the Street Twin achieves a totally plausible range with its small, 3.2 US gallon, tank, that under normal use should exceed 200 miles per tank.
The Bonneville Street Twin’s chassis is steel tubes welded to a cast-iron steering head, bolted to an engine cradle. Rake is 25.1 degrees and trail is at 4.0 in (102.4 mm), which are common numbers. The suspension in front and rear is by Kayaba, with a 41mm conventional fork up front, and preload-adjustable twin shocks in the rear. Both ends have 4.73-inches of travel and the shocks are set up with ample sag and have progressive springs, for a soft initial travel.
The wheels are cast aluminum: 18 x 2.75-inch front, 17 x 4.25-inch rear, with classic-looking Pirelli Phantom tires made to Triumph’s specs. The tires are 100/90-18 front; 150/70 R17 rear. Braking at each end is by single Nissin 2-piston floating calipers, mated to a 310mm disc up front and a 255 mm one out back. ABS is standard. Seat Height is 29.5 in., and the claimed dry weight is 437 lbs.
Other features include Traction Control that can be turned off, ride-by-wire throttle, security immobilizer, and a USB socket under the seat. The hand levers are adjustable.
A single round gauge contains an analogue speedometer and a multi-functional LCD display shows gear position, fuel level, range-to-empty, fuel consumption rate, traction control status, service indicator, clock, and odometers. The gauge choices are scrolled with an “i” button on left handlebar. On the right handlebar is a nifty, combined start/kill switch, plus a four-way flasher button. Already Triumph offers over 150 accessories for the Street Twin, including bags, billet parts, exhaust, and gear.
Source: cycleworld.com
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