A Short History of Single-Sided Swingarms And Why They’re Dying Out
‘Mono arms’ are a dying breed – here’s why they rose and fell
A Short History of Single-Sided Swingarms And Why They’re Dying Out
- Thread starter Noobie
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Corny
Active member
Interesting article, thanks. Ducati went back to the single sider after the divisive 999/ 749 when they decided it was one of the key design features on the 916 etc. that we all loved, along with the two under seat end cans, vertical exhausts, twin side by side headlights etc. etc. I don't think we've seen the last of them though.
It's form over function for chain drive but for shafts it makes perfect sense. With a chain there's a lot of engineering required to contain the torsional drive forces operating at 90 degrees to the spindle axis, so there's a built-in need for over-engineering. With a shaft you don't have that problem and a twin spar becomes unecessary and would itself constitute over-enginnering.
I can't see single siders ever disappearing from shaft-driven bikes. If they do from chain drives, I can understand it from a cost and engineering standpoint but I would miss the advantages for the owner in cleaning, wheel removal and rear brake servicing.
As a shaft drive owner I must admit I don't miss the chore of chain maintenance and the constant tension adjusting when it starts to wear, but I wouldn't want one on just any bike. Makes absolute sense on the Rocket 3 where a chain would have to be enormous and it's got so much power and torque to start with that the tiny bit absorbed by the shaft is meaningless.
What I don't understand is why more use is not made of belt drive. I experienced it for the first time when I had my Harley and it's a joy to live with. Saps very little power, it's light, quiet, clean and almost maintenance free. Tension and alignment is critical or rapid wear will result. But once set up correctly it's very low maintenance and easy to live with, and would be better for single sided swinging arms as it is lighter and so exerts less inertia and it doesn't doesn't need wide or frequent adjustment.
I see no reason why sports bikes and nakeds couldn't use belts. On track bikes you need to be able to alter the gearing by changing sprockets but the vast majority of sports and nakeds never see track action serious enough to warrant sprocket changes.
I can't see single siders ever disappearing from shaft-driven bikes. If they do from chain drives, I can understand it from a cost and engineering standpoint but I would miss the advantages for the owner in cleaning, wheel removal and rear brake servicing.
As a shaft drive owner I must admit I don't miss the chore of chain maintenance and the constant tension adjusting when it starts to wear, but I wouldn't want one on just any bike. Makes absolute sense on the Rocket 3 where a chain would have to be enormous and it's got so much power and torque to start with that the tiny bit absorbed by the shaft is meaningless.
What I don't understand is why more use is not made of belt drive. I experienced it for the first time when I had my Harley and it's a joy to live with. Saps very little power, it's light, quiet, clean and almost maintenance free. Tension and alignment is critical or rapid wear will result. But once set up correctly it's very low maintenance and easy to live with, and would be better for single sided swinging arms as it is lighter and so exerts less inertia and it doesn't doesn't need wide or frequent adjustment.
I see no reason why sports bikes and nakeds couldn't use belts. On track bikes you need to be able to alter the gearing by changing sprockets but the vast majority of sports and nakeds never see track action serious enough to warrant sprocket changes.
I'd wonder how a belt would deal with the bat shit crazy acceleration on my super Duke
No problem at all. It's a taughtly sprung chassis without super-long suspension travel with lots of lash, which belts don't like, and it would sap less power than a chain so the bike woud feel even more responsive.I'd wonder how a belt would deal with the bat shit crazy acceleration on my super Duke
Big inch Harleys run belt drive up to 200 bhp and 180 ft/lb of torque so it would cope with a Superduke easily. Most switch to chain before they reach those power levels but only because they want to play with final drive ratios which becomes problematic and expensive with belts, but on a stock bike like a high power supernaked they would be ideal.
Those are cam belts. Final drive belts are rather different beasts and slipping and cog jumping won't trash your engine, just as a knackered chain won't (not that you should ever allow either to reach that point). The point is well made though that cam belts on cars are more likely to fail from tooth sheering than actual snapping. A garage who replaced the belts in my car once pointed this out to me. I'd said they looked brand new but they were due for changing based on mileage so I supposed we'd better do it.
He said don't look for cracks on the back of the back of the belt, look at the teeth. He'd just done the belts on a Ford van and he took the old ones out of the bin to show me. They had about six sheered teeth. He said if they'd lost one more that would have been enough for the belt to slip on the crank pulley where it experiences the most torque and that would have caused the cam timing to be thrown out and lunched the engine, but the belt would not have snapped.
Drive belts don't tend to shed teeth if correctly tensioned and they're replaced on schedule (they last a lot longer than chains). They will start to fray at the edges if wheel alignment is out which will wreck the kevlar core. What is catastrophic is a stone getting in between belt and pulley, so they're not suited to dirt bikes and soft-roaders unless fully enclosed. But they dont like going slack under negative tension either, which happens when long travel suspension unloads as the bike leaves the ground. But for many road bikes belts would be an entirely viable option and once you've lived with them chains feel like a PITA.
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I am no expert but I have read that belts are not suited to the sport bike world duw to the relationship between the output shaft, the swingarm piviot and the rear axel. Again I am not an expert and dont claim to be right, this is just how I understand what I have read. Modern sportbikes use the chain, during acceleration to raise the rear of the bike. The raising of the rear causes the wheel base to shorten slightly and raises the center of gravity and is essential in the proper setup of a race or sport bike to handel properly. Belts must be kept tighter not to slip on the pullies but chains with teeth can be set much looser and therefore work much better over the larger amounts of suspension movement. Shaft drive effects this much less than belts so we see shaft drive on some higher performance bikes but not on the full blown supersport or super bikes. Again, I am not an expert and I may not be remembering it correctly as I read about this many years ago but there must be a reason we dont have a belt drive super bike. if I recall all the racing Harleys from the 60s thru 90s were chain final drive
There's a lot of conflicting information about belts and why they're not more commonly used. On race bikes, whether they're Harley baggers or GP bikes, teams go with the lightest chain possible for minimum power loss and replace them very frequently. They also need to change final drive ratios to suit the track they're racing on. That is expensive and awkward with belt drive because for one thing, as they can't be tensioned as tightly as chains they need a counterbalance pulley which limits gearing ratio options, and replacement usually involves removing the swinging arm, so belts would be a nightmare in the pits. There may be some truth in the point that belts don't taughten the rear suspension and cause the bike to sit up and favour the front end under power, though that can be overcome by swinging arm pivot geometry. KTM did this with the latest generation of 1290 Superduke, as previous generations had the opposite problem and tended to squat at the rear under power, unloading the front end and causing weaves and shimmying. The Gen 1 was the worst (I know, I had one). It would dance and squirm under power in fast bends. It was predictable and fun if you like a lively ride but it isn't much good if you want to win races. The effect was exacerbated by the upright semi-supermoto riding position and the lack of wind protection which causes the rider's body to act like a sail, compressing the rear and unloading the front, which led to high speed weaves. KTM overcame this with the latest version by some clever redesigning of the swingingarm and rear suspension geometry which kept the chassis level under power. Whether the same would be possible with a belt drive I don't know, but race teams undoubtedly operate with the philosophy of if it ain't broke don't fix it, and what they do carries over into sporty road bikes.
On power drain there are opposing views out there. Some maintain a belt saps more power than a chain due to softer tension and the counterbalance pulley; others that it saps less because it is lighter than a chain. Certainly they soften the transmission and make the power delivery less immediate (though this would barely be noticeable to the rider) which might be undesirable on a race bike but is a positive benefit on a high torque, low revving engines producing big power pulses, like a Harley. Though Harley do not use belts on their Pan-America Adv bike because of the risk of debris damage when going off-raod.
What isn't in doubt is that belts are cheaper per mile in use than chains, as while they're more expensive to replace, they last vastly longer (they can last up to 100,000 miles in some applications) and they don't require ongoing maintenance nor lubrication and cleaning products.
And the motorcycle industry and its customer base tend to be very conservative. They like to keep things familiar. USD fork technology was available long before it became the norm. I remember when they were showing up in the late '80's/early '90's people were dubious, saying they didn't "look" right and they suspected the stanchions would get dammged being nearer the road, would rust quicker and all the oil would run out. All nonsense of course, but generally the biking world is suspicious of radical change. Look at the ribbing Exige gets over the funny front end on his Tesi. And which BMWs still get for their Telelever/Paralever system.
All that said, I still think there are many more applications where belt drive would be of great benefit. Mid-weight roadsters and commuters ridden all year round in particular. They'd be great on retro twins as well from a practical point of view, but again, buyers would say they didn't look right and weren't inkeeping with the trad spirit of the bike even though most people wouldn't notice they were there.
Which brings us back to the SSSA. It's notable that people love them for the looks more than anything. That's true of the bike on its side stand showing off a shapely wheel on the offside. It's not so true when you walk round and take a look from the other side where they present a massive shaft-drive-like lump of metal.
Anyway, it's an interesting topic and sorry for the thread derailment.
On power drain there are opposing views out there. Some maintain a belt saps more power than a chain due to softer tension and the counterbalance pulley; others that it saps less because it is lighter than a chain. Certainly they soften the transmission and make the power delivery less immediate (though this would barely be noticeable to the rider) which might be undesirable on a race bike but is a positive benefit on a high torque, low revving engines producing big power pulses, like a Harley. Though Harley do not use belts on their Pan-America Adv bike because of the risk of debris damage when going off-raod.
What isn't in doubt is that belts are cheaper per mile in use than chains, as while they're more expensive to replace, they last vastly longer (they can last up to 100,000 miles in some applications) and they don't require ongoing maintenance nor lubrication and cleaning products.
And the motorcycle industry and its customer base tend to be very conservative. They like to keep things familiar. USD fork technology was available long before it became the norm. I remember when they were showing up in the late '80's/early '90's people were dubious, saying they didn't "look" right and they suspected the stanchions would get dammged being nearer the road, would rust quicker and all the oil would run out. All nonsense of course, but generally the biking world is suspicious of radical change. Look at the ribbing Exige gets over the funny front end on his Tesi. And which BMWs still get for their Telelever/Paralever system.
All that said, I still think there are many more applications where belt drive would be of great benefit. Mid-weight roadsters and commuters ridden all year round in particular. They'd be great on retro twins as well from a practical point of view, but again, buyers would say they didn't look right and weren't inkeeping with the trad spirit of the bike even though most people wouldn't notice they were there.
Which brings us back to the SSSA. It's notable that people love them for the looks more than anything. That's true of the bike on its side stand showing off a shapely wheel on the offside. It's not so true when you walk round and take a look from the other side where they present a massive shaft-drive-like lump of metal.
Anyway, it's an interesting topic and sorry for the thread derailment.