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Twins Have Teeth?


johnnyrod
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Usual apologies if this has been covered or is in the wrong place, I've tried to make sure that isn't so...

 

There is a lot of guff in the m/c press for sure but how much truth is there in the difference in grip that a twin has driving out of a corner compared to a four? I ride a SV650 V-twin, but have previously also ridden fours. I don't know if it's just a feeling, but to me it feels like when you get on the throttle to exit a bend, with a twin the back tyre seems to bite more than with a four. I am using proper throttle control rather than just on/off (years of riding rubbish old bikes makes you smooth) and had no problem with this at level 1. Twins tend to rev lower than fours, mine redlines at about 10k although sometimes I'll be coming out of a bend at as much as 7k, which is in inline four territory, although it'll still make half the number of power pulses as a four of course.

 

So, what do you think? This has had me wondering for a while. That and I'm thinking about getting a new bike...

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Usual apologies if this has been covered or is in the wrong place, I've tried to make sure that isn't so...

 

There is a lot of guff in the m/c press for sure but how much truth is there in the difference in grip that a twin has driving out of a corner compared to a four? I ride a SV650 V-twin, but have previously also ridden fours. I don't know if it's just a feeling, but to me it feels like when you get on the throttle to exit a bend, with a twin the back tyre seems to bite more than with a four. I am using proper throttle control rather than just on/off (years of riding rubbish old bikes makes you smooth) and had no problem with this at level 1. Twins tend to rev lower than fours, mine redlines at about 10k although sometimes I'll be coming out of a bend at as much as 7k, which is in inline four territory, although it'll still make half the number of power pulses as a four of course.

 

So, what do you think? This has had me wondering for a while. That and I'm thinking about getting a new bike...

 

The difference is really in the fact that the engine pulses are further apart so the tyre can recover from the explosion that fires the piston down and creates the drive. With a normal inline 4 cyclinder engine, the pulses are every 90 degrees of crank revolution, on a twin (typically), they're longer, say 180 degree's. This of course, depends on many factors, like V Angle, crankshaft spacing, but as an overall principle, that's why it's said to be the case.

 

This another of the reasons MotoGP bikes and Yamaha's R1 road bike sound a bit like a twin. Although they're all 4 cylinder engines, they have unevenly spaced firing orders to aid the tyre to re-gain traction.

 

This is typically only of benefit on larger capacity bikes that have an abundance of power and torque to overwhelm the rear contact patch, and is one of the reasons you really don't see the need on say a 600CC bike as it generally doesn't overwhelm the tyre contact patch unless lean angle is added to the equation.

 

Hope that makes sense..?

 

Bullet

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Jasonzilla, twins don't rev as high as fours so they produce less power. Same torque at higher revs means more power. The SV produces around the same (peak) torque as a 600/4 but they rev to 14k+

 

Bullet thanks for the info. The SV certainly doesn't have enough power to spin up out of bends unless you're being a tool. If I was looking to jump on a GSXR750 do you reckon that's still not so powerful that the twin/four thing makes a difference? A lot of it is about feel and confidence and I do like the way a twin seems to drive out of bends, I've never ridden a four as hard as I have the SV though.

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Is the firing also what causes such a difference in HP? I'd also think that the drop in power toward the top of the RPM's would cause the secure feeling also versus the increase of power 600's have.

 

Hi Jase,

No the thing that causes the difference in horsepower is a combo of a few things. No.1 the more cylinders you have, the more horsepower you can generate, i think it's to do with the amount of surface area you have, so if you think 2 big pistons and the surface area they have, against 4 smaller ones. Additionally because each of the pistons is smaller, they weigh less and can be this rev'ed harder. Horsepower is an equation of Torque x rpm.

 

Bullet

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The SV certainly doesn't have enough power to spin up out of bends unless you're being a tool. If I was looking to jump on a GSXR750 do you reckon that's still not so powerful that the twin/four thing makes a difference? A lot of it is about feel and confidence and I do like the way a twin seems to drive out of bends, I've never ridden a four as hard as I have the SV though.

 

The SV would spin up certainly if you had loads of lean angle on, and also in the rain it could as well. The GSXr750 develops about as much horspower as a 1000cc Twin like an Aprilia RSV, or Duacti 999, but not quite as much power as the 1000 cc fours, or the 1200's Twins. They're lovely bikes GSXr750, a really good half way house in performance and make tremendous road bikes, enough power, but not too much as you frighten yourself silly.

 

Riding Four's and Twin's is different really one you ride on top end power (four), Twins on flexible grunt. Both tremendous, though I have to say, I'm a Twin man through and through (which is why I love the new R1 so much), but that said, I race in line 4's. :lol:

 

As long as it's got wheels and an engine, who cares.

 

Bullet

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Riding Four's and Twin's is different really one you ride on top end power (four), Twins on flexible grunt.

 

Actually, I've found that twins have less "flexible" engines than inline-four's. On my old R6, I could effectively use the upper 1/2 of the revs, while on a friends SV650, I needed to be in the top 1/3 to make it go fast (and hence many more gear changes).

 

As long as it's got wheels and an engine, who cares.

 

And enough horsepower :D

 

Kai

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Riding Four's and Twin's is different really one you ride on top end power (four), Twins on flexible grunt.

 

Actually, I've found that twins have less "flexible" engines than inline-four's. On my old R6, I could effectively use the upper 1/2 of the revs, while on a friends SV650, I needed to be in the top 1/3 to make it go fast (and hence many more gear changes).

 

Perhaps I should have said Big twins. My RSV has a wonderful engine, though it's terrible at low speed stuff.

 

Amen on the power! :lol:

 

Bullet

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My perception of it was that the pulsing power of the twins (and the I4's with the uneven firing sequence) would make it more forgiving when powering out of turns on the edge of traction, not that it would actually give it more traction. But it could still be a big advantage because that could certainly translate into better drive out of the turns. Dirt bikes are usually singles, even the 4 strokes, so their down to 1 ignition per 2 whole engine revolutions (I think it's funny that this works at all!). Imagine an I4 dirt bike and how hard it would be to keep the rear tire under the bike under hard acceleration on loose surfaces)

 

" With a normal inline 4 cyclinder engine, the pulses are every 90 degrees of crank revolution, on a twin (typically), they're longer, say 180 degree's. "

 

Bullet, isn't it more like one ignition per 180 degrees for the I4, and one whole turn per ignition for a twin? Think about it, 90 degrees, implies that all the cylinders are firing for every revolution. True for a 2 stroke, but not a 4 stroke.

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From what I have gathered, the "eggsperts" doesn't fully understand why lesser firing pulses gives more traction. At 10-15000 rpm, the pauses between each firing must be considered infinitesimal at best. 12000 rpm = 200rps and whether you fire them evenly spaced at 400 puffs per second or in one big whack and 100 bangs per second, it still seems unlikely that you could have the tyre grip between the slips before the next power burst hits.

 

In theory, having many cylinders and even firing spacing should provide the most tractable and flexible power because the crank speed will not vary nearly as much as if you have a single cylinder. But in real life, fewer throbs seems to work better than many thuds when it comes to traction.

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...isn't it more like one ignition per 180 degrees for the I4, and one whole turn per ignition for a twin? Think about it, 90 degrees, implies that all the cylinders are firing for every revolution. True for a 2 stroke, but not a 4 stroke.

 

 

I think he's got a point

 

From what I have gathered, the "eggsperts" doesn't fully understand why lesser firing pulses gives more traction. At 10-15000 rpm, the pauses between each firing must be considered infinitesimal at best. 12000 rpm = 200rps and whether you fire them evenly spaced at 400 puffs per second or in one big whack and 100 bangs per second, it still seems unlikely that you could have the tyre grip between the slips before the next power burst hits.

 

In theory, having many cylinders and even firing spacing should provide the most tractable and flexible power because the crank speed will not vary nearly as much as if you have a single cylinder. But in real life, fewer throbs seems to work better than many thuds when it comes to traction.

 

 

Too bad engines aren't as simple as the theory. The pistons actually come to a dead stop during the stroke, valves float and cams lobes don't exactly do the job that visual inspection suggests. Inside the explosion container (cylinder) are supersonic pressure waves and other disturbances that engineers must tune after the prototypes are built.

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...isn't it more like one ignition per 180 degrees for the I4, and one whole turn per ignition for a twin? Think about it, 90 degrees, implies that all the cylinders are firing for every revolution. True for a 2 stroke, but not a 4 stroke.

 

 

I think he's got a point

 

From what I have gathered, the "eggsperts" doesn't fully understand why lesser firing pulses gives more traction. At 10-15000 rpm, the pauses between each firing must be considered infinitesimal at best. 12000 rpm = 200rps and whether you fire them evenly spaced at 400 puffs per second or in one big whack and 100 bangs per second, it still seems unlikely that you could have the tyre grip between the slips before the next power burst hits.

 

In theory, having many cylinders and even firing spacing should provide the most tractable and flexible power because the crank speed will not vary nearly as much as if you have a single cylinder. But in real life, fewer throbs seems to work better than many thuds when it comes to traction.

 

 

Too bad engines aren't as simple as the theory. The pistons actually come to a dead stop during the stroke, valves float and cams lobes don't exactly do the job that visual inspection suggests. Inside the explosion container (cylinder) are supersonic pressure waves and other disturbances that engineers must tune after the prototypes are built.

 

You're right, I'm not an engine designer nor coach, I'm a riding coach, who knows a bit or two about stuff on other things. This is part of the challenge of no trying to get deeply intricately lost in deep technical discussion sometimes, you try and simplify something as an overall concept rather than the intrciate details.

 

You're right the firing of the pistons isn't every 90 degree's its the crank pin themselves that are on things like the new r1. If you want to reread more about R1 crank, why it's designed the way it is, http://www.yamaha-motor-europe.com/designc...ageTitle=Yamaha Technology 2009: Crossplane crankshaft&pageNum=2 Read this.

 

There is a good article on i4's v Twins here. http://motorcyclebloggers.com/tech-talk-ar...s-inline-fours/

 

It's really deeply technical for those that really need to know in that much depth.

 

The fact stil remains, regardless of rev's/engine speed though, a twin fire's half as much of the time as a i4, hence the tyre gets that little bit better of a break. You can believe it, or not elirik, but that's one of the main reasons they're trying to create offset crank and firing orders for MotoGP bikes. and i quote "Current performance 4 stroke engines utilize the big bang firing order to create a recovery gap during which the rear tire regains traction" on wikipedia, so it must be true right..? ;)http://en.wikipedia.org/wiki/Big-bang_firing_order

 

Bullet

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I believe - as I wrote - that fewer power pulses and/or crowded power pulses improve grip. In fact, there is no denying that. What I tried to get through is that nobody has fully understood WHY it is so, that it is down to using logic and speculation and not objective science.

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I believe - as I wrote - that fewer power pulses and/or crowded power pulses improve grip. In fact, there is no denying that. What I tried to get through is that nobody has fully understood WHY it is so, that it is down to using logic and speculation and not objective science.

 

Perhaps we're at cross purposes?

 

I think you'll probably find the engine designers know what/why. We only can go from what we're told and the understanding of why. I can't say as it makes much difference the engine type to me personally, and I've much experience of all variants, but I expect there must be some solid science in it at the very top level, otherwise they wouldn't be doing what they're doing.

 

I can tell you, from riding the 2009 R1 a lot, it has an incredible feeling of connection from the twist grip to the rear tyre, even though it's an electronic throttle, and in reality you have no connection to it whatsoever. You can lay the power down incredibly well even in the rain, it's simply wonderful.

 

If I ever get the chance to ride a top level GP bike, (highly unlikely), I'll tell you what it's like, but in the meantime, I guess we just have to go from what we're informed by the powers that be.

 

Bullet

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My perception of it was that the pulsing power of the twins (and the I4's with the uneven firing sequence) would make it more forgiving when powering out of turns on the edge of traction, not that it would actually give it more traction.

What I meant to say, just not as well put as Harnois.

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My perception of it was that the pulsing power of the twins (and the I4's with the uneven firing sequence) would make it more forgiving when powering out of turns on the edge of traction, not that it would actually give it more traction.

What I meant to say, just not as well put as Harnois.

 

It's not a perception though, it's a fact. :lol:

 

Bullet

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From what I have gathered, the "eggsperts" doesn't fully understand why lesser firing pulses gives more traction. At 10-15000 rpm, the pauses between each firing must be considered infinitesimal at best. 12000 rpm = 200rps and whether you fire them evenly spaced at 400 puffs per second or in one big whack and 100 bangs per second, it still seems unlikely that you could have the tyre grip between the slips before the next power burst hits.

 

[...]

 

Good point but it still seems like a reasonable theory to me. The inline 4 with an even firing sequence has one ignition stroke per 1/2 a crank turn, and each ignition stroke lasts about half a crank turn, so it is basically always "on" with practically no pause between. Whereas the twin would be "on" for half a turn then "off" for half a turn. A single would be on for half a turn then off for 1.5 turns. I guess one would have to dig into the intricacies of tire technology to know if that is enough time to regain any traction, but if it's enough time to lose it in the first place... Plus the strength of the pulses is still controlled by the riders throttle hand. Plus on top of all that, riding a twin you can feel each individual pulse (vibration) except maybe at high rpms, so how fast is that really? I was trying to figure out how many pulses there would be per revolution of the tire, depending on gear ratios, thinking this might give a better perception than the "bangs per second."

 

It seems similar to anti-lock brakes. Per wikipedia, "A typical anti-lock system can apply and release braking pressure up to 20 times a second" and "ABS-equipped cars are able to attain braking distances better (i.e. shorter) than those that would be easily possible without the benefit of ABS." The use of the phrase "easily possible" is interesting - just like we're saying here, that the pulsing throttle is more forgiving.

 

Thanks for the interesting links, Bullet. And I wasn't try'n to be a smart alec there, just say'n. Like you said, the concept is the same either way.

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Thanks for the interesting links, Bullet. And I wasn't try'n to be a smart alec there, just say'n. Like you said, the concept is the same either way.

 

Wasn't taken as such, I assure you fella. ;)

 

Bullet

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Interesting discussion, especially what Bullet thinks about the new R1 and its traction. I'm pretty bad at feeling for the edge of grip so I can't say much about that, but to me it feels a bit like when you feed in the power, on the SV and other twins I've ridden (mainly smaller ones) that the back tyre almost grows little teeth and drives you out, whereas on fours that doesn't seem to happen, they just punt you forwards. Probably sounds like a daft explanation but that's the way it feels to me!

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Usual apologies if this has been covered or is in the wrong place, I've tried to make sure that isn't so...

 

There is a lot of guff in the m/c press for sure but how much truth is there in the difference in grip that a twin has driving out of a corner compared to a four? I ride a SV650 V-twin, but have previously also ridden fours. I don't know if it's just a feeling, but to me it feels like when you get on the throttle to exit a bend, with a twin the back tyre seems to bite more than with a four. I am using proper throttle control rather than just on/off (years of riding rubbish old bikes makes you smooth) and had no problem with this at level 1. Twins tend to rev lower than fours, mine redlines at about 10k although sometimes I'll be coming out of a bend at as much as 7k, which is in inline four territory, although it'll still make half the number of power pulses as a four of course.

 

So, what do you think? This has had me wondering for a while. That and I'm thinking about getting a new bike...

 

Not sure we can see it from the engine design approach--

Why use 4 cylinders instead of 1 for the same engine size? A piston will accelerate faster if it has less mass, and when the ratio of connecting rod length (L) to the crank arm radius ( R ) is larger. Acceleration can be faster by making R smaller. However, small crank arm radius also means less torque, so the engine needs more cylinders to compensate for torque requirement. Same reason for building a 12-cylinder engine for racing car and only 4 cylinders for Civic. A big-banger trail bike needs torque and therefore uses large crank arm radius R but compromises the piston acceleration, and needs only 1 cylinder.

In short, a multi-cylinder engine will accelerate faster by design. Wondering whether what you are feeling, is partially in fact due to the faster acceleration of the in-line 4 engine compares with a V-twin that has only 2 cylinders.

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  • 3 months later...

Finally - an explanation that made sense cool.gif It's not the big bangs or closely set firing pulses that give the extra grip, but the smoothness of the crank rotation!

 

Excempt from the July 2010 Cycle World issue, by Kevin Cameron:

 

The 90 degree crank (in the R1 and M1 Yamah fours) is useful at full lean in turns, when the bike has little extra grip and the rider first begins to feed power. With a 180-degree crank, all pistons stop at either top or bottom dead center every 180 degrees of rotation... The crank responds with an equally rapid rpm flutter, which is transmitted to the rear tire. The energy in each of these pulses (at 10,000 rpm) is equal to the weight of a service automatic pistol falling 7 stories. The rider is trying to feed the power, but this crank speed flutter is messing with traction in a rapid series of snatchy yanks, making the rear tyre 'feel squirrely'. so he waits (for the bike to stand up some).

 

Now look at a 90 degree twin. When one piston is stopped, the other is at its max velocity. 180 degrees later, the situation is reversed. The pistons are trading energy, not with the crank, but with each other. As a result, the crank rotates more smoothly, and the rear tyre is undisturbed by piston stop and start. The same is true of any V-engine and also of a 120 degree triple.

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