This is an unusual Ask MO Anything, as this question was delivered not by a reader but by me. During the presentation for the T100 Bonneville I rode last week, I asked why Triumph chose a 270-degree crank for its new Bonneville parallel-Twins rather than the 360-degree orientation of Triumph’s originals. Miles Perkins, Triumph’s Head Of Brand, attempted to give me a satisfactory answer but admitted I’d be better served by a response from one of Triumph’s powertrain specialists.

2017 Triumph Bonneville T100 First Ride Review

A couple days later, my inbox was blessed with an email from Triumph Motorcycles America’s Public Relations Manager, Phil Read Jr. (Yes, the son of 7-time Grand Prix motorcycle champion!). Read had passed along my question to Triumph’s Chief Engineer, Stuart Wood, and here’s what he had to say.


There are two crankshaft configurations that we considered for the new Bonnevilles: 270-degree and 360-degree. We have produced both in the past and we have detailed, first-hand experience of their characteristics as perceived by a rider.

The 360-degree crank gives even firing intervals and the 270-degree crank a characterful, syncopated exhaust sound. Both have their merits from a sound-character perspective.

We chose the 270-degree configuration to improve the refinement of the new engines. At 1200cc, these are the largest capacity Bonnevilles that have been made. The 360-degree and 270-degree crank configurations produce reciprocating out of balance forces as the pistons travel up and down the bores. The motion of a piston up and down a bore can be described mathematically. The most significant parts of this motion can be described as primary and secondary that is once per revolution and twice per revolution.

103116-2017-triumph-bonneville-line

These forces can produce vibrations if they are not balanced. We incorporate a pair of primary balance shafts that balance the primary vertical forces and also the fore and aft primary forces and pitching couple that can be left if no balance shaft or only one balance shaft is used. The next stage is to balance the secondary reciprocating forces. With a 360-degree crank, the secondary forces produced by each piston add together to double their force. With a 270-degree crank they cancel one another out.

Firing pulses and exhaust sound are characterful. There is nothing characterful about secondary vibrations. They are high frequency and generally an irritation to a rider. With a large-capacity engine, these vibrations would tend to be greater than with a small-capacity engine. We believe that using a 270-degree crank configuration for the new Bonnevilles gives a characterful but refined engine that will be appreciated by riders.

  • Andrew Horton

    Mr Wood has supplied a truncated version of the 270deg vs 360deg story, one worth telling as the Bonnevilles’ are retro bikes after all. Back in the pre-Bloor days when the Japanese started producing their first inline four “super bikes” Triumph found themselves on the wrong end of a power/capacity war not only with Honda but with Moto Guzzi & Ducati as well. Triumphs problem was its narrow crankcase long stroke parallel twins precluded the normal “more cc’s or more revs” pathway to power with ever increasing vibration levels. Phil Irving, engine designer of the 1000cc v-twin Vincent Black Shadow & Repco – Brabham F1 title winning v-eight, designed & built the first 270deg crank parallel twins for Triumph as a way of eeking out more performance with extra refinement from the existing Triumph engines. The designs never saw production & a few years later Triumph folded.

    Years later Yamaha the most adventurous of the Japanese regarding engine configurations and the most historically studious, revived the design for the YZE750T & YZE850T 7 time winning Paris-Dakar race bikes. On the back of that success Yamaha sold world wide for many years the XTZ750 Tenere off road bike, the TRX850 sport bike & the TDM850 – the prototype for todays soft roader adventure bike craze. The XTZ1200 Tenere is still a 270deg crank parallel twin. John Bloors’ new Triumph came late to 270deg cranks, starting with the America cruiser & Scrambler, but now they are finally building a Bonneville performance bike with you could say the story has come full circle – or at least 270degrees.

  • Tom Dinchuk

    Edward Turner ( Meriden Triumph) even in 1966 felt the 500/650 twin was pushing it for a 360 parallel twin due to vibration and other issues. His ideas for a 350 double overhead cam twin or even a four cylinder model were more in line for where he thought Triumph should go. They never did ; It took Bloor’s reinvention of the marque to get there. I’m a big fan of Meriden bikes ( I’ve owned quite a few of them)…..I now ride a 2001 Bonnie and my brother rides a 2016 Street Twin (Bonnie) Both are light years ahead of the old models ( no regrets!).

    • Larry Kahn

      I have 2007 Bonny 360-degree engine and they did a great job with the balance weights. I’m one sensitive about vibration and am very pleased with how smooth the Bonneville is. My boxer BMW friends are annoyed it’s notably smoother than their machines. And it’s a bit smoother than my Ducati air-cooled. Looking forward to trying the new 1200. Triumph’s got an impressive line.

      • Kenneth

        I usually think of my 360-degree ’11 Bonnie as “smooth,” as well, but believe it’s just the character of the vibrations that is unobtrusive, avoiding the high-frequency vibrations that numb hands and/or feet.

  • Born to Ride

    I assume that by “pitching” they mean angular oscillation about the longitudinal axis of the engine(the one that is lined up with the wheels), induced by the force couple exerted when one piston rises and the other falls. So my question is, if the fore and aft forces are balanced, and the vertical forces are balanced, where does the pitching couple come from? Or am I looking at this dynamic from the wrong frame of reference?

    • Andrew Horton

      Unlike a 90 deg v-twin that a 270deg parallel twin shares a 270deg then 360deg firing order with the parallel twin has its bores offset requiring two crankpins & thus a rocking couple that requires a balance shaft (or two)

      • Born to Ride

        The way I had understood the article, the bore offset produces the transverse couple that rocks the motor fore and aft, and that it is balanced by the “first” balance shaft. Perhaps I am mistaken and that is in fact the pitching they were referring to.

    • DickRuble

      Maybe by pitching they mean the tendency of the engine to rotate around the crankshaft, in the direction of rotation of the engine. Not as much an oscillation (which implies periodicity) as a pulsing correlated with the angular acceleration/deceleration of the crankshaft.

      • Born to Ride

        Yeah I considered that too, but they specifically said a balancer was dedicated to canceling fore and aft movement which I would think included the tangential force, in the longitudinal plane, applied to the cases by the acceleration and deceleration of the crank. The couple induced by the acceleration of the pistons would be ocillatory because the moment applied to the body(through the crank bearings) changes direction at some cyclic rate. But Yes, the constantly changing angular acceleration of the crank ensures that this cycle isn’t exactly periodic. This article brings forth more questions than answers. Haha

  • JMDonald

    All engines have advantages and disadvantages in their inherent design. This begs the question, what is the best engine configuration? I have owned everything from a single to an inline four including two boxers and a V4. The only configuration I haven’t owned is a six of any kind. Smooth is in the eye of the beholder.

    • DickRuble

      I’ve read that the inline 6 is inherently self balanced, hence its use in BMW automobiles and more recently motorcycles.

      • JMDonald

        I’ve read that also. I rode a friends K1600 but only for a half hour or so. The power was so astonishing that I didn’t notice if it was smooth or not. If it wasn’t I’m sure I would have noticed. It’s a big bike. Nicely done but too big for my sensibilities.

      • Max Wellian

        I believe that like Ducs L twins, that applies to primary vibrations. They still likely have secondary vibrations they contend with via a balancer of some sort.
        The inline 6 also sounds like a chainsaw without a good muffler. Triumphs 1200 sounds a lot like a Duc sans the rattling clutch.

        • Kevin Duke

          Nope, inline-6s have perfect primary AND secondary balance. Also, I beg to differ about your perception of the way they sound. Check out this link and then watch the video at the halfway point to hear what I think is a wonderful engine note: http://www.motorcycle.com/manufacturer/bmw/2012-bmw-k1600gtl-review-90469.html

          • Max Wellian

            Thanks for the balance info.
            As to the sound, it sounds fine with stock cans. I heard one leaving a gas station once that was without the stock baffling. The rider was getting on it heading out into the mountains. It sounded atrocious.

      • Kevin Duke

        Yep, inline-6s make wonderful powerplants! Try to blag a ride on a K1600.

  • Ingolf Stern

    “characterful”?!?! FFS. harley uses the same maneuver to get bikes sold. if it weren’t for that and black tee-shirts, the MoCo would be dead.

    • Kenneth

      Yes, that “maneuver” provides exactly what so many riders want (just not the ones who drool over spec charts and change bikes frequently, never quite satisfied). Promoting and selling what lots of people want is what a successful company does. Not understanding such simple logic, however, is baffling.

  • DickRuble

    The real question is: what is the crank configuration that delivers the smoothest functioning for a parallel twin? You have to add TWO balance shafts just to compensate for the vibrations induced by the 270-degree crank. All just for “characterful” sound.. Talk about stupid.

    • Dale

      What is the answer to your question about which crank configuration delivers the smoothest functioning of a parallel Twin ?

      • DickRuble

        Don’t really know.. I am guessing 180 in terms of vibrations. The firing is uneven but that should only affect the sound and add some extra complexity to the intake. The 360 has even firing but acts like a big single and, reportedly, is easier to build. The 270 seems to me to have all the negatives; uneven firing and inherent vibrations.

        • Andrew Horton

          I have to disagree. 270 deg engines are the smoothest parallel twin configurations I’ve experienced. I’ve ridden or owned all of the available parallel twin configurations except for the Husqvarna Nuda 900, which has a uniquely phased version of the BMW F800 engine.

          Currently I own only one Parallel twin, a Yamaha TRX850 – highlighted in your wikipedia link- that has a 270deg crank & balance shafts. Ive put over 180,000km on this bike & would describe its vibration as “chunky” – like my old Guzzi – at low revs. As revs rise to its 9000 rpm cutout it smooths out considerably. Never in its rev range is it harsh, buzzy or brittle in its feel. At cruise it has a nice, comfortable throb. At WOT you are never in doubt there are some big bits of metal whirling around down there!

          Ive also ridden a TRX850 race-bike with the balance shafts removed & boy did that vibrate! Having ridden a Yamaha TDM900 – based on the TRX motor- I can say that Yamaha balanced that to be totally smooth (boringly so actually) so the refinement can be dialled in or out by the manufacturer by balance shaft design.

          The total opposite is my friends F800 – 180deg parallel twin with third dead conrod balance weight. At low revs it is smooth but as revs rise it develops a harsh, brittle buzz like an old school inline four. Its frankly joyless to ride, encouraging short shifting to keep away from the vibes.

          I have had a couple of GS 500 Suzuki’s and ridden GPz500 plus a GPz250 Kawasaki. These bikes are short stroke 180 deg engines that are acceptably smooth at cruise and mildly buzzy at their quite high redlines. Having grown up with British 360deg twins I can say they really ride like a siamesed bore single, with both pistons moving in unison… again ok at low revs but filling rattlers up the range.

          • DickRuble

            In terms of primary balance, the 180 is balanced. You can’t feel the vibrations of the 270 because it has two counterbalancing shafts. Without any counterbalancing, the 180 is the smoother engine.. The F800 is a 360 with an extra conrod (not 180).

          • Andrew Horton

            My bad with the F800 typo. The description of the engine in use is accurate though. A 180 may have good primary balance but is poor in secondary, hence the buzz. Off the top of my head I cannot think of a 180 engine without a balance shaft, making it no different in practice than a 270. Both need balance shafts to be acceptable in street bikes. To ward off any misconceptions a 270deg engine does not need two balance shafts, the TRX850 engine has two because of its origins in the Mk1 TDM850, a 360deg engine that certainly needed two balance shafts.

            Its interesting that you referenced the CB500 family of twins as Honda fitted a 270deg crank to their NC700/750 bikes. Having ridden examples of both lines I can assure you they are equally smooth slow & dull. The 270 crank in the 700/750 offers the smallest whiff of character, but no more than that.

    • Max Wellian

      I own a Thruxton 1200. It makes very good power throughout its 7k rpm range and gets better than 50 mpg even spanked hard. I’d say it’s pretty efficient.
      It’s also very smooth except at the top of its rev range and sounds great 😉

  • Robby McHenry

    I’ve been riding Bonnevilles since 1969, my first bike being a 1966 Bonneville. I currently own 6 Triumphs, the oldest being a 1966 Bonneville and the newest, a 2005 Thruxton. What I have always loved about the engine is the sound and feel of the even firing order produced by the 360 degree crank. The 270 degree crank produces the firing order, sound, and feel of a 90 degree V twin. If I had wanted an engine like that, I would have been riding a Ducati or a Guzzi all these years. It makes me sad that Triumph chose the 270 degree crank for all of the new 2016 Bonneville models, for two reasons. One is that from this point on, new Bonneville riders will not know what a real Bonneville is, and the other reason is because I will never again want to buy a new Bonneville.

    • Old MOron

      I’m kind of new to Triumph appreciation, so I don’t have a strong preference. But I’m glad to know there are MOrons who keep the faith.

      • Robby McHenry

        I’m not opposed to progress. I love my ’05 Thruxton with the 865cc engine. It is a vast improvement over the Meriden engines, but retains the spirit, feel, and personality of the originals. I just feel that when bringing out a new version of an iconic motorcycle, it is sacrilege to change the basic architecture of the engine.

    • TheMarvelous1310

      Oh, shut it with the dogcrap traditionalism. If you knew enough of Triumph’s history, you’d know they were working on an engine with that exact firing order before they folded the first time! Which is also to mention that this is, what, the THIRD Triumph company?

      • Robby McHenry

        I don’t care if Triumph builds some twin models with 270 degree cranks. After all, the 865 America, Speedmaster, and Scrambler models all had the 270 degree crank. But, Triumph should have respected the tradition of the Thruxton and the T120 Bonneville models and retained their 360 degree crank. Triumph made the decision to buiId retro models in order to trade on the traditions established by the Meriden version of the company. However, to bring out a new version of an iconic motorcycle, go to all kinds of effort with styling of engine covers to identify the engine with the famous sixties version, and then change the basic architecture, feel, and sound of the engine is just not right.

  • Max Wellian

    Great question!

  • Craig Hoffman

    Have spent some time riding a friend’s new Thuxton R, it sounds great with a pair of V&H megaphones on it, and it is very smooth vibration wise. My only complaint is it only revs to 7K. Another 1,500 RPM and another 10 hp on top would make it the perfect retro sport. Beautiful bike though. I think Triumph made the right choice with the crank layout.

    • Kim Durkee

      There are plenty of good aftermarket solutions which will give you what you want. 10 HP is easy and pumping out 100 HP is very doable while still retaining reliability. Just changing your silencers probably added 3 HP.

      • Craig Hoffman

        True. The easiest mod would be for us to not live in Colorado, as the elevation takes a toll on power. I tend to forget that. The Thrux squirts out of corners really nice, even here in thin air land, and probably yanks really well at sea level.

        My bike is a modded ’06 FZ1 that made 131 hp at the wheel here in Denver at over 5,000 feet, which translates to over 150 at sea level. It is very fast, even here in Colorado 😉

  • kenneth_moore

    “Characterful.” Really? I suppose the bike is “heritageful” as well.

  • methamphetasaur

    Quick answer- so it will potato potato like the Harleys.

    • Kevin Duke

      The Triumphs don’t actually do the potato thang. That idle cadence requires a single-crankpin V-Twin.

  • Bare1

    I had an ’06 Scramber with the 270 crank. My whole impression of the Triumph was that I found it neither Characterful or Heritageful. It’s a modern bike with a resemblance to the older Triumphs, but it like any other bike has evolved way past its antecedents. It’s much bigger then the 50-70s bikes. It doesn’t sound the same, in fact, they’ve been trying to make it sound like a Harley, which is another reason they picked the 270 crank. Actually that crank makes it sound like a thumper to me. And it has no Character or Soul. It was one od the most hated bikes I ever owned.

    • Tom Dinchuk

      Actually it sounds more like a Ducati with it 90 degree layout. Harleys with their
      single crankpin 45 degree configuration fire at around 315 and 405 ; giving that uneven loping sound ( a little like a heart beat). I have both a Harley and a 2001 Bonnie ( both their exhausts sound great to me). Also remember, some triumphs racers ( Meriden in the 60’s) ran 270 cranks in their dirt trackers because of their torque characteristics made them hook up so well on the track.
      If you ever heard them (back in the day) you’d probably love their sound.
      Cheers, Tom

      • Bare1

        I raced them back in the day with 180 cranks. That’s why I know these modern Triumphs sound nothing like the the old ones, and living in SOCal I hear plenty of the old Brit bikes constantly. I belong to the BSA and Norton Owner’s Clubs, along with the 59 Club. Hanson Dam ride tomorrow, Pretty much the biggest Brit bike get together by a dam site.

  • TheMarvelous1310

    I’ll just leave this here, for those who have trouble visualizing the firing orders. https://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Straight-twin_engine_with_different_crank_shaft_angles.gif/220px-Straight-twin_engine_with_different_crank_shaft_angles.gif Funny enough, I thought Triumphs ran the 360deg cycle! Shows what I know, huh?

  • disqus_9GQw44dyM0

    I don’t mean to totally derail this conversation, but you guys know a lot more than I do about this stuff and I’d like to learn. So…I ride a Honda Hawk-GT 650, V-Twin. Why does my bike have much more engine braking than the various types of Triumph parallels you are speaking of? Frankly, on the curvy mountain roads I ride on, I prefer it. Thanks!

    • Kevin Duke

      Engine braking has little to do with engine configurations. Carburetion/EFI tuning is more likely to blame. Cylinder displacements, too.

      • disqus_9GQw44dyM0

        Wow. I was under the assumption that all V-twins had more engine braking than any other motor configuration. Thanks for the input.