In this week's episode, Mark and Kevin talk about the origins of the parallel twin motor. What makes this motor so popular? And are they actually taking over the world? We answer all of these questions in this episode.
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00:00 Welcome to the Cycleworld podcast.
00:03 I'm Mark Hoyer, Editor-in-Chief, and I'm here with Kevin Cameron, our Technical Editor.
00:10 Today we are going to talk about how parallel twins are taking over the world.
00:15 The parallel twin has been around forever.
00:18 It had a heyday.
00:19 It faded away, and now it's back with a vengeance.
00:23 What do you think, Kevin?
00:26 Where do we start?
00:28 In 1937, Triumph brought out Edward Turner's Speed Twin Triumph, and at that time, they
00:39 were moving up from one cylinder.
00:42 The entire pass of the motorcycle, with the exception of a few V-twins, had been singles.
00:50 They were moving up.
00:51 Right now, we're, at least in terms of cylinder count, are moving down.
00:57 The sport bike era, four cylinders was the norm.
01:01 There are a lot of people now who are saying, "I kind of like those four-cylinder jobs."
01:06 However, people vote with their checkbooks.
01:13 The parallel twins today are vastly superior to what was on offer in 1937, or even in 1957,
01:23 because the early engines were only crudely balanced.
01:29 The present-day engines are so much smoother, because they have balance shafts.
01:38 They are, in terms of displacement, I guess you'd call them mid-displacement engines.
01:47 They often have 270-degree crank pin spacing, which gives them that, dare we say it, Ducati
01:55 sound.
01:56 Yeah, V-twin.
01:57 Yeah, whereas the classic Triumph BSA Norton sound is a flat drone.
02:06 Yeah, well, I went to the press launch in the 2001 Triumph Bonneville, when they came
02:12 out with the new Bonneville, and they stuck with the 360-degree crank.
02:19 I like vintage bikes, and I was riding Triumphs, and I've had a Norton, and all that.
02:23 I enjoy that sound.
02:24 Even BMWs have a pretty similar sound, because of the way that they're tried.
02:30 It is a little bit refrigerator compressor, but also evocative for people of a certain
02:37 age, but nobody cared.
02:39 They did the 360, and they made 18 old dudes happy, but once they introduced the 270, it
02:47 was vastly more popular, and everybody else, pretty much since, has been doing that.
02:54 We get rid of the 360.
02:55 A lot of the Japanese ones in the early days were 180, and that had its own kind of vibration,
03:01 because they weren't balanced either.
03:03 We had 180s in-
03:04 Rocking from side to side.
03:07 Yep, making its own kind of tangle.
03:11 Yeah.
03:13 Well, the vibration of the classic parallel twin is such that when a modern rider is lent
03:22 one from a friend, by a friend, comes back rather stupefied looking at, "Are they all
03:30 like that?"
03:31 Yes, I'm sorry to say that they are.
03:34 In order to move that up and down shaking to a much less perceptible forwards and back,
03:42 they were balanced at percentages up to 85%.
03:49 They knew they had a problem.
03:50 Yeah.
03:51 At idle, like your Norton Commando, the wheel shake-
03:55 Oh, that classic front wheel wobble, where the front wheel is shaking forward and back.
03:58 I'm riding something that's alive, right?
04:03 You say lending your bike to a friend.
04:05 I traded bikes with a friend.
04:07 I traded my Norton Commando for his RZ350, which was also at that time even a relatively
04:13 vintage bike, but much smoother, lighter pistons than I believe a 180.
04:18 Much different, and I let them go.
04:22 It also had the classic, I think, Grand Touring grip, so they're shaped like a tennis ball
04:28 already.
04:29 Yes.
04:30 They're bubbled in the middle, but a Commando has isoelastic mounts, so there's that tuned
04:38 area where the engine can do its-
04:40 The whole engine, yes.
04:42 The engine and the swing arm can swing around.
04:44 These great big rubber mounts, isoelastic mounts, and so they mounted the engine and
04:48 swing arm in the frame, and it moves around like this.
04:53 With isoelastics, they're tuned.
04:55 It's 2800 RPM to maybe 4000.
04:58 It's quite smooth, relatively speaking, but we rode three miles, and he pulled over, and
05:06 he's like, "How do you ride this?"
05:12 I really enjoyed my Norton Commando.
05:14 I almost wore my shirt with the Norton Commando on it today, but now they're spectacular.
05:23 We get the 270 crank mostly for the sound, right?
05:26 There's no other reason to do it.
05:29 We have mostly for the sound, but now we're throwing the balance shafts at it, and we
05:33 get as much vibration as we want, and we can tune to the vibration that people enjoy because
05:38 you do want something back from your bike, usually.
05:42 Well, this is a problem that the electric motorcycle industry will have to address.
05:48 No, it's no doubt.
05:51 You've got to imagine the engineers at Harley-Davidson scratching their head like the Harley-Davidson
05:56 motor company, and we have this sound that we've patented, and now we're doing electrics.
06:03 Even if they are split off as live wire, what do you do?
06:06 They put the heartbeat into theirs.
06:08 It's important.
06:09 They put the idle heartbeat.
06:10 You turn the thing on, and the idle, it would go da-da.
06:14 The motor oscillates, yes.
06:15 Yep, and it gives you a little shake to know I'm alive.
06:19 I'm really actually here.
06:21 And I'm mechanical.
06:23 Yeah, but underway, they're just perfectly smooth.
06:26 It's got a little gear winding that they engineered in to give you maybe the Jetson sound.
06:30 But back to parallel twins, so we can tune any vibration we want, but why are parallel
06:37 twins taking over the world again?
06:40 Well, my take on that is that when 2008 hit and the motorcycle industry or the motorcycle
06:49 sales in the US took a dive, the industry responded with what I think of as novelties,
06:58 lockable storage and urban transport module and all these modern sounding sort of almost
07:06 politically correct descriptors.
07:12 But what people, they didn't sell particularly well.
07:16 Some of the stuff sold, NC700X, but where are they today?
07:24 What happened was it looked like people wanted regular motorcycle qualities at a lower price.
07:32 And one way to get a lower price is a lower parts count, fewer pistons, fewer valves,
07:41 fewer tappets, and possibly less metal overall.
07:47 And the second way in which parallel twins help to keep price down is that these engines
07:54 are versatile.
07:57 The same engine can power a sporty street ride and an adventure style bike, and maybe
08:04 a general purpose bike without requiring a lot of add-ons.
08:09 Well, let's talk about that because a high performance inline four, they're moving the
08:17 power up, right?
08:20 We're typically concentrating the power at the top end.
08:22 So what we're getting out of a parallel twin that's tuned to be, hey, regular street bike
08:28 plus the influence of Euro 5 is those cam timings that are kind of necessary and they're
08:37 shortened.
08:38 Shortened and getting rid of the valve overlap, which is both valves open at the same time,
08:43 which can really boost the top end, but allows nasty unburned things to get through and out
08:48 the tailpipe and cause problems.
08:50 So all the way to Ann Arbor.
08:53 And it's this really interesting convergence of market desire, simplicity, lightweight,
09:02 rideability, not looking...
09:04 And compliance.
09:05 And compliance.
09:06 It's a pressure from governments and it's a pressure from the market.
09:10 And then now what we've ended up with is you get that beautiful tuned engine that like
09:15 take the Suzuki 800, their 800 and the V-Strom 800DE and the GXS 800.
09:24 And now in the R where the tuning is essentially very much the same.
09:30 They vary a little bit on the dyno, although we haven't dynoed an R yet, but they're very
09:36 much the same.
09:38 And imagine the effort and money that we save as a manufacturer to homologate something
09:44 like that and to just start throwing at the models.
09:48 And that saves the manufacturer money.
09:50 And in turn, that saves me money.
09:53 And the other thing that saves money is on the insurance side, anything that was the
09:57 name sport in its name gets the insurance people moving you to a higher category of
10:05 risk.
10:07 Anything with four cylinders, anything that is advertised as producing high performance
10:13 is likely to push you into a higher risk and therefore higher cost insurance program.
10:20 So it's a three-sided benefit in this way to the consumer because you can insure it,
10:31 you can afford to buy it.
10:33 It's good.
10:35 And I would argue that because it has mid-range now instead of the strong accent on top end
10:45 that was characteristic of sport bikes, nothing, nothing, nothing, you get to 10 or 12,000
10:49 and you're on your way.
10:53 Now whatever RPM you're at, because of the shortened cam timing, it will go, it will
11:00 accelerate strongly no matter what RPM.
11:04 You're not going to have to tap down two gears the way you did in the year 2000.
11:12 So I think these are the reasons why Parallel Twins are succeeding now in the marketplace.
11:25 They provide good motorcycle qualities, which is what people wanted all along.
11:31 They weren't mad for lockable storage.
11:34 That's called a house.
11:39 And it satisfies the regulators.
11:45 And it is a more rideable motorcycle than sport bikes ever were.
11:50 Sport bikes were a thrill, but you had to stir the gearbox.
11:53 You had to be keeping the engine busy in the higher RPM ranges, which are clearly audible
12:00 to some people we'd rather not have a face to face with, namely enforcement.
12:05 Yep.
12:06 Fair point.
12:07 So fun level of engagement.
12:10 I met, it's fun to interact with a sport bike.
12:14 And when you have a 600, a high revving 600, like you take an R6 or something, spectacular
12:20 in its element and fast steering and rock hard suspension and then that top end, but
12:27 very much more of a challenge on a day to day basis, plus the insurance issue.
12:35 I'm not 22 years old, it's a shock, but I'm not 22 years old.
12:40 I went as a real grown adult with no points on my license.
12:46 I took my W, I have a personal WR250R dual sport kind of adventure bike that I built
12:52 up.
12:53 And then I decided to ask my insurance company what it would cost to do a four cylinder leader
12:58 bike.
12:59 And I, because it was a Yamaha that I dual sport, I picked an R1.
13:03 And the R1 was something like $2,800 to $3,000 a year.
13:09 And my WR250 for the same kind of coverage was in the hundreds, it was like $250.
13:14 And it's just, it was, it's the level of risk because, and that's not coming from nowhere.
13:19 You know, people go out and you're going to approach the R1 a much different way.
13:24 And when you get a parallel twin, like I just want to ride around, you know, like that's
13:27 what people, the market has spoken, you know, where the decline of the leader bike, it's
13:32 still there, they're still spectacular.
13:36 Particularly on the, you know, the European side, we're seeing insanely beautiful limited
13:42 productions, M1000Rs and the V4 Panigales are, they're spectacular.
13:48 It's like a completely different kind of motorcycle.
13:52 And it's super satisfying to ride, but man, I just want to, I just want to go out, like
13:57 throw a leg over something like, wait, if I'm just grinding it out, you know, do you
14:01 want to commute on that?
14:02 It's like using fine scotch as paint that are like an M1000 to grind back and forth
14:07 on I-95 or something like, forget it.
14:09 You know,
14:10 There's also this, buying a sport bike is like buying a service automatic pistol for
14:18 home defense.
14:21 Ownership is not mastery, is not skill.
14:26 You will come closer to feeling competent on a motorcycle that has broad power band
14:34 than you will on a motorcycle that suddenly threatens to just shoot out from under you
14:40 when it gets to 11,000 RPM.
14:41 Which again, is a great feeling, don't get me wrong.
14:46 It is a great feeling.
14:49 Even though we're not them young fellers that Don Tilley talked about, there is a thrill
14:57 at seeing this, this thing right here makes 214 horsepower, which implies this thing right
15:05 here makes 214 horsepower.
15:10 But with the motorcycle, you need to work on your skills, just as if you, if you're
15:17 one of these home defense enthusiasts, you'd better get down to the pop-up target place
15:22 and see that you can distinguish in low light level between family members and others.
15:30 Yes.
15:31 Skills make all the difference and you can get them more easily, I would argue, on a
15:37 motorcycle with a broader power band.
15:40 Yeah, absolutely.
15:41 And these new motorcycles benefit from all the rapidly accumulating knowledge about suspension
15:48 and tires and so forth.
15:50 So they're on a further generation of cycle parts, they used to call them, than the sport
15:59 bikes were 15 years ago.
16:02 Yeah.
16:03 Let's talk about packaging of the Parallel Twin because V-Twins have been, continue to
16:09 be really popular.
16:10 I know you still have Ducati making V-Twins and how many, how many millions of Harley
16:17 Davidsons V-Twins are there, you know, potatoing around?
16:20 I mean, just unbelievable numbers.
16:22 So they continue to be popular and they, but they present, you know, some packaging challenges
16:28 that, you know, the narrowness is nice, but a Parallel Twin, particularly a Parallel Twin
16:33 that has to meet emissions regulations, you're going to have a reduced bore more than likely,
16:39 something that isn't going to be a cylinder bore like a Panigale.
16:43 I mean, even when Panigale is on a V-Twin, they were going for something specific and
16:47 they did a hundred and-
16:48 116.
16:49 16 millimeter bore, four something inches, massive bore, hard to get to pass emissions,
16:57 plus a ring air.
16:58 Bigger than a big block Chevy.
17:01 Yeah.
17:02 And this is going to be, this is, this is weed stuff here, folks, you know, but ride
17:07 along because this is, these are like, this is fundamental stuff that's influencing your
17:14 motorcycle that is unseen that we, I think, benefit from because when you shrink the bore
17:21 and you raise, particularly if you raise the piston rings towards the top of the piston,
17:25 the place for unburned hydrocarbons, the ability to light the fire, if the, if the bore is
17:31 this big, you can light the fire in one place and it's got a very short path to burn and
17:36 it happens quick.
17:38 And tell us why that's good, Kevin.
17:40 Well, the thing is the piston ring crevice space is out at the cylinder wall.
17:48 So as the piston comes up on compression, some unburned mixture is forced into the ring
17:55 crevice and then the spark plug makes it worse because now we have an expanding flame front
18:01 in the middle of the cylinder that is shoving quite a lot more mixture into the piston ring
18:09 crevice space, as much as one to 2%.
18:14 And then peak pressure occurs maybe 10 or 11 degrees after top dead center.
18:21 And after that it's expansion.
18:23 And I watched a movie that was made at MIT with a square cylinder with a transparent
18:30 side.
18:31 It's a Schlieren movie.
18:32 And it shows that N-gas, that unburned hydrocarbon streaming up out of the piston ring crevice
18:40 space all the way into the next intake stroke.
18:45 So the people up in Ann Arbor are, I smell something illegal here.
18:51 Yeah.
18:52 What the hell is a Schlieren movie though?
18:57 It's a wonderful thing.
18:58 It makes use of differences in density to make an image of what's happening in the gas.
19:08 So you can see like those shock diamonds in a jet exhaust.
19:14 That's a sort of a natural occurring version.
19:18 But this is why production automobiles have completely given up that four inch bore, two
19:26 and a half inch stroke that we all were so enthusiastic about it 40 years ago, while
19:32 I was.
19:34 And now they're making the bores as small as possible in order to get rid of as much
19:40 of that piston ring crevice volume as possible.
19:44 And they're also trying to improve the cooling of the very top of the cylinder bore by going
19:48 to open deck in some cases.
19:51 So there's water behind the top of the cylinder bore where sometimes on full throttle for
19:58 a long period of time, you could get lubricant boil off.
20:04 We don't want any of that nasty business.
20:06 Well, yeah.
20:07 And that's a very, you know, that's an interesting topic like on its own.
20:11 I know this is not like engine builders podcast, but open deck, there are those advantages
20:18 to open deck.
20:19 If you start, if you start turboing and you start doing other things that would challenge
20:23 the ceiling, you've got to support that top.
20:26 So you might lose that little bit of cooling.
20:28 But I've actually seen at an engine builder shop, they machine rings that have holes in
20:36 them and they close the deck.
20:38 So they put that into that open area to support it so they can, they can crank the boost up.
20:43 It was just something I saw recently closing the deck with an insert on, you know, some
20:49 Ford engines where they can just crank up the boost then and get, you know, 400 horse
20:52 out of a little tiny teapot.
20:54 Well, here's the argument for open deck, which is if you can make the top of the ring travel
20:59 cooler, then you can move the rings up higher on the piston and thus reduce further the
21:07 ring crevice volume.
21:10 So you're, yep, you're keeping, yeah, go ahead.
21:13 So you're minimizing, you're minimizing unburned hydrocarbon going out the exhaust by a series
21:21 of, huh, well, how does that work kind of steps.
21:27 And I think, I think it's grand and we love the short stroke era because of the high RPM
21:34 and all the rest of it.
21:36 But now we're having to do things a little bit differently and I think we can still have
21:40 a hell of a good time.
21:43 And for most riders and even motorcycle testers, you know, when you get on a good running parallel
21:51 twin and it's just good times, you know, the, the Yamaha Tenere 700, MT07, FZ07, that motorcycle,
22:02 the MT07 came out and man, you're just like, is this, how perfect is this?
22:10 It's really just spectacular.
22:11 And it's been applied to all these other bikes and it does a phenomenal job, you know, at
22:18 its displacement level and how it runs.
22:20 Suzuki finally came out with their, their parallel twin in the eight hundreds.
22:24 And there's something, there's something else about that engine.
22:28 Like even it has a displacement advantage over the Yamaha, but there's something else
22:35 that they've done a really spectacular job in the way that it runs.
22:40 And I think a lot of that is, it's the combustion chamber size, it's the combustion chamber
22:45 shape and it's the, it's just got a real lively, happy feeling, free revving.
22:52 And it's this, again, it's this convergent, it's convergence of real nerd stuff about,
23:00 you know, the piston rings are shorter, the circumference is smaller and all that stuff,
23:04 all that nerdy business.
23:05 But what happens is you get on it and, and it's, it's got snap.
23:10 You can feel it.
23:11 You can feel it.
23:12 Well, they're happy.
23:13 You know, like a Norton Commando has a great combustion chamber and you know that because
23:18 the ignition timing at max advance for pinned full speed lighting the fire early.
23:25 So if the engine is rotating and the fire has enough time to reach peak pressure when
23:29 the cylinder goes after top dead center.
23:32 So at max it's 28 degrees.
23:35 That's a very impressive number.
23:36 Right.
23:37 You know, and this is again, super nerd stuff.
23:41 I'd love to know what the max ignition timing is on some of these bikes, but they, a lot
23:45 of times are very secretive about that stuff.
23:47 Now it was 45 degrees on, on what FCR 750.
23:54 Yeah.
23:55 It was a bunch of, it was a bunch of advance back in those days.
23:59 Here's another point.
24:00 And that is the fewer cylinders an engine has, the better the ratio of cylinder volume
24:08 to heat rejection surface.
24:12 Because I first noticed this years and years ago, the Ducatis at Daytona had smaller radiators
24:18 than the Yamaha's.
24:19 The Yamaha fours had radiators that made me think about the glorious days of sale at this
24:26 huge thing.
24:27 Yeah.
24:28 That's a great analogy because they were massive and they had that huge curve in them and they
24:33 were just going all the way to the front.
24:35 You know, they were really like zipping around the front wheel sort of.
24:38 Wonderful stuff.
24:39 Yeah.
24:40 Yeah.
24:41 And the Ducatis didn't need as big a radiator because they didn't have as much, they weren't
24:48 losing as much heat in the engine, losing it to cool.
24:52 So the same thing with making the bore smaller and the stroke a bit longer.
24:59 If this is an era where we're going to be paying $4 for gas, that's one way to save
25:06 a penny here and there.
25:08 Yeah.
25:09 Welcome to the...
25:10 I know we didn't become, we did not become motorcycles to save a penny here and there.
25:16 But when those who know us best complain about our favorite activity, now we have something
25:23 to tell them.
25:25 Yeah.
25:27 Home defense.
25:29 So packaging, let's talk about packaging.
25:32 So we've covered the ways that all the things came together to make the power and the way
25:39 the engine runs rideable.
25:41 We have a low parts count, therefore probably lighter, cheaper to make.
25:47 We aren't looking for astronomical RPM, so we don't need fantastically expensive connecting
25:52 rods and we don't need titanium valves and all the things that would drive the cost up.
25:58 And yet we will get incredible lifetimes out of these engines for reliability.
26:03 So all of that is making an engine that is pleasing to ride, easy to maintain, easier
26:10 to buy, lower cost to build, et cetera.
26:15 Packaging, we have improved suspension components over time.
26:20 Very interesting new frame designs, controlled fill castings and shifting to steel frames
26:28 because of the cost.
26:31 Retracing our historical steps in some cases.
26:35 I remember that that first 600 Honda had a steel frame and it was reviewed very positively
26:43 because they said, "This is a motorcycle that you can afford because it's not pretending
26:48 to be a super bike, a race bike with an aluminum frame."
26:53 Well, they fixed that pretty quick.
26:56 Well, yeah, the Hurricane was interesting because they enclosed everything in its bodywork.
27:04 It was fairing all the way up to the tank, like you couldn't see the frame.
27:10 And it was square tubes.
27:11 It was like, "Wow, this is interestingly industrial."
27:15 You mentioned packaging.
27:17 If you have this much space for an engine, you can put a V-twin in it.
27:23 But if you don't have that much space, a parallel twin will fit.
27:30 Which is a zero degree V, right?
27:32 Yes, it is a zero degree V, just as Max Fruese's first BMW is a 180 degree V. A special case.
27:46 Right, it's easy to put that in the...
27:48 It's easy to package and you can give it a long wheelbase and you can do all the things,
27:53 like if you want to make room for a passenger and you want to put a great big fuel tank
27:58 down behind the engine and do whatever you want to do.
28:01 But you have the room and flexibility.
28:05 You can go very short wheelbase if you want because you can pack the whole thing up.
28:09 If you stack the gearbox shafts, like gearboxes used to be like this, and now we have them
28:13 like this.
28:14 And the clutch is way up here.
28:17 Way up high, packaging this beautiful, tight little thing.
28:20 And imagine being a designer and being able to work with something like that from a, certainly
28:26 from a technical perspective of partying the engineering house again, where we can put
28:31 the center of gravity and how much weight can we get on the front wheel so the bike
28:35 turns better and all those things, feels better in corners and all that.
28:39 So packaging advantage is significant.
28:44 It gives more freedom to the designer, yes.
28:48 So I've often thought, wouldn't it be wonderful if we had this little black cube with nothing
28:58 leading into it.
28:59 It just has a sprocket sticking out and you hook the chain onto there and you're all set.
29:06 Okay.
29:07 So this is where you've called yourself a soulless technician.
29:11 Nobody wants to look at a black cube, man.
29:13 We want to see machine cut cylinder fins.
29:16 Yes, we do.
29:17 We want to have the suggestion of the internals on the outside with cover.
29:22 Shrink wrap packaging.
29:24 Yes.
29:25 Fins that look like their guts.
29:28 Yep.
29:30 Well?
29:31 Well, these are a lot of good reasons that the Parallel Twin would be taking over the
29:36 world.
29:37 You know, it's packaging, it's cost, and we've really benefited from a really beautiful broad
29:43 selection of what I would call especially big middleweights.
29:47 You know, we get these sort of 600 to 900 CC Parallel Twins and they're in high performance
29:54 adventure bikes and commuters and all these things and the world is better for them.
30:00 Yeah.
30:01 Yeah.
30:02 That's it for today's Parallel Twins are taking over the world.
30:08 If you like what we're doing, please like, comment, and subscribe.
30:12 Particularly comments.
30:13 We'd love to hear from you about topics that we can discuss on the show.
30:17 You can please drop down in the comments and communicate with us.
30:22 We'll see what's going on.
30:24 We'll do a show on something that the readers, you guys have questions.
30:28 I'd love to hear what Kevin Cameron has to say about it.
30:30 So jump in there and get going.