Belt Drive
Mon, 13/02/2012 - 08:23
Text lifted from NC700 thread.
Open for discussion.
Why don't more bikes use belt drive? Here's how I see it.
At first glance, it seems the ideal solution, offering the virtues of chain, without the drawbacks. Also, the virtues of shaft, without the drawbacks. Except it isn't that straightforward. The humble roller chain situation is much like that of the humble telescopic fork. It has drawbacks but, with a bit of evolution, has seen off all competitors as the overall best solution.
Final drive roller chain is the most cost effective solution from a manufacturing point of view, by a long way I would think. And, arguably, also from an ownership point of view. The one big drawback, one which still leaves the door open for other designs, is lubrication. It is messy. It makes a mess of the machine. It makes a mess of the rider (and pillion). If it's not carried out diligently, especially in winter, it will drastically shorten the life of the chain an sprockets. Another, smaller, drawback is adjustment. With the advent of O ring chains, this issue is nowhere near as bad as it used to be. Nowhere near as frequent. The O ring prolongs the life of the chain (and sprockets, indirectly) and prolongs the adjustment period.
What about belt drive? Surely this does everything the chain does, but with no lubrication. It still needs adjusting, but very, very infrequently. In fact I'd not be surprised to learn that modern set ups require no tension adjustment during the life of the belt?
So why aren't they everywhere?
When I say "Belt drive" I mean HTD drive. This seems to be the format that everyone uses, probably because it has the best torque rating (I'll stand correcting on that statement because there maybe recent designs which surpass HTD torque ratings).
IMO:
There are a few drawbacks, which effectively limit the use of belt to relatively low power, relatively low speed machines. There will be exceptions no doubt.
Highest on the list is probably the fact that HTD belts, to work at their best, need quite a high pre tension. Without this pre tension the HTD tooth will not sit into its "groove" properly and will wear or shear off. This pre tension, when added to the tension created when torque is transmitted, places high loads on shatfs, bearings and (rear) pulley mountings. Not to mention the " chassis". Everything therefore has to be "beefier" and therefore more costly. This high pre tension means that, although the belt appears elastic, when installed it offers little shock absorption. So building cushioning into the rear pulley, whilst accommodating the high tension is not so easy.
Next, that pre tension needs to remain fairly uniform as the suspension moves up and down. This means placing shafts and pivot points in precisely the right place. It may mean the use of a jockey pulley. This in turn creates additional heat, wear and probably more important, it saps precious power (we're talking "low" power machines, so we can't afford to throw away another few percent). It adds cost too.
Then we've got the fact that, as we go to higher and higher power machines (resulting in higher rear wheel torque), the belt width is a serious design problem. To keep the belt width manageable, you'd need larger diameter pulleys. This in turn is a serious problem, trying to package the system into a bike rear end. Also larger diameter pulleys mean higher (circumferential) belt speeds. There is a limit on that, so the designer is caught between a rock and a hard place. Wider belt or larger pulley?
Last on the list, but still a problem eventually. How to get the belt out, without dismantling half the bike?
Until we start seeing titanium shaft drives with kryptonite bevel gears, I think the humble roller chain will be around for a good while yet. I think we may yet see a return to the good old chain case! Remember the old Honda Benley and CD185?
Mon, 13/02/2012 - 10:53
#2
Re: Belt Drive
Pittsy - the bottom line, for me, that I prefer chain over anything and everything is the fact that it can be quickly and easily repaired if/when it goes wrong.
My thoughts on the lubing situation are well known and all I will say is that if using ANY automatic chain lube system, from whichever manufacturer and you are seeing oil all over the place, then you are setting the flow rate too high. People think they need to see oil on the outside of the chain, you don't. It needs to be in between the moving elements. Of course there will be some small signs here and there but not any significant amount of fling.
Belts are, in theory a good alternative for some applications but as you say they require major disassembly to replace and that alone has always been a big no no for me.
There is also the fact that when a belt does need replacement you need to get that specific size, tooth pattern etc and that means a bespoke manufacture. I do like going to the local wholesaler here and buying enough chain to do three or four of my bikes, or to carry a spare set when on a journey.
As for the belt width issue, well I just need to look at the required width of those hideous primary drives that the custom people seem to love so much and that there speaks volumes.
Nope, I am sorry, no one has yet convinced me that there is anything to beat a good ol' chain when everything is taken into consideration.
The CD185 was my first ever road bike and whilst the chain case was a good idea - as also used by the likes of Jawa, it also served to take the drive maintenance issues in to the out of sight, out of mind area of many peoples consciousness.
Mon, 13/02/2012 - 20:51
#3
Re: Belt Drive
Cap'n: "I'm not sure the setup used in the belt driven F800ST is any noticeably "beefier" than that of the F800GS for instance?
Not looked. ........But I will !!
Which one came first? Maybe they designed to suit the toughest version. Maybe the belt bike has a stronger gearbox output bearing and/or shaft, which we can't see from the outside. How do the pulley diameters compare with the chain sprocket diameters?
Cap'n: "And proportionally percentage wise Harley's don't lose any more power from crank to rear wheel on a dyno than a conventional chain-driven big-bore v-twin on face value?"
Do they use a jockey pulley? I'm not sure what the accepted efficiency of an HTD belt drive is. Without a jockey (idler) pulley, close to a chain set up, but I'd guess a little bit worse. Not sure.
Mon, 13/02/2012 - 22:07
#4
Re: Belt Drive
Cap'n: "I'm not sure the setup used in the belt driven F800ST is any noticeably "beefier" than that of the F800GS for instance?
Pittsy: "Not looked. ........But I will !!"
Had a look. Er, it's a bad comparison. There is no comparison! The GS version is double sided swingrm, the ST version is single sided. So they are different animals anyway. The belt pulleys look larger than the chain sprockets to my eyes but not checked spec sheets.
Tue, 14/02/2012 - 05:41
#5
Re: Belt Drive
"I prefer chain over anything and everything is the fact that it can be quickly and easily repaired if/when it goes wrong."
... unless it holes a casing! ;-D I read on an MTS owners site someone's chain snapped (20k I think?) and did a lot of damage to the swing-arm etc, but fortunately didn't hole the casing, although guards can be bought for those concerned. Caveat: I saw pics of his chain and it looked drier than a nuns whatsit and rustier than the Titanic, so looked more user error to me than anything else.
"People think they need to see oil on the outside of the chain, you don't. It needs to be in between the moving elements"
... do you mean between the O-links themselves, or purely between the edges of the chain that are interfacing with the sprocket, or both? Apologies if I can't explain for toffees!
"Nope, I am sorry, no one has yet convinced me that there is anything to beat a good ol' chain when everything is taken into consideration"
... many and the manufactures certainly seem to concur with you.
Pittsy, not sure on all counts, sorry! HD claim 100 hp for the 103 ci and that usually makes 93 at the rear wheel based on dyno charts I've seen. Similar the 86 crank horses produces 77 at the hoop. Percentage wise I can't see a chain drive making more? I'm not suggesting either method is better only that you claimed power loses were greater, which they may be, but based on these numbers that doesn't seem to be the case? I think the GS was released before the GT, but I'm unsure. The belt and pulleys are wider but I wouldn't think the weight difference would be great. the biggest difference is likely to be bearing tolerances and as Shugs says how easy it is (or isn't) for the average guy (that's a 'mechanic' to most these days) to swap one?
Riddle me this then? Why don't kevlar belts have a nice little belt catch. We'll call it a 'link'. When your belt is due renewal, you'd use a kevlar belt link-splitter to break the belt, temporarily link a new one to it, pull it around the pulley's and then re-link it back to the new chain once you've fed the old one through. Sort of like an erm, chain! :-D
So what was wrong with the leather belt drives then? ;-D
Tue, 14/02/2012 - 08:20
#6
Re: Belt Drive
I too wondered about shuggie's comment re oil application. Even with an O ring in place I've always believed it essential to get lubricant down between the links, as Shuggs has said. There's a lot of movement in that area. But surely the roller to sprocket tooth interface needs (light) lubrication too?
HTD belts. It was mainly when there was a jockey used for maintaining final drive tension where I thought it might absorb more power. It just has to. Whether it is such an issue is another thing.....
Re belt weights. I was pondering that one yesterday. I think the pulleys can be aluminium (al ooo minum, if you prefer). Not sure whether a belt would be lighter than a chain to do same power? If I was forced to guess I'd say the belt was lighter. So, maybe belt drive trumps chain in that respect?
Looking for areas where belt offers advantages over chain, (there must be some, otherwise the manufacturers wouldn't bother). We seem to have 2 so far.
Doesn't need lub. Therefore saving on mess and time. Got to be a major plus.
Has lower unsprung weight. (I'm sticking my neck out on that one). Can anyone confirm this? Are pulleys ally?
Any more offers on advantages?
Tue, 14/02/2012 - 09:13
#7
Re: Belt Drive
Gents, what I mean is that people expect to see oil all over the chain and if it is not visibly wet then they crank the flow rate up and then bitch that the stuff gets flung everywhere.
I did not explain it very well as of course the oil needs to be everywhere where mechanical contact takes place, so on the rolling elements, tooth etc too. I kind of took that as a given but did not express it well - sorry.
The optimum rate on a V system is one to two drops per minute though of course that is dependant on conditions but it is a very broad, good bench mark.
Captain - you have me on the holed casings but I will take the side that the foundry was left wanting and the chain was totally innocent :-)
Tue, 14/02/2012 - 20:22
#8
Re: Belt Drive
I used scotoiler systems on all of my many chain driven bikes and they oiled the chain ok BUT to be honest no matter how much time you spend setting up the drips/minute the rate will change with temperature and you will end up with it on the inside face of your rear wheel or a dry chain on cold days.
After a leaky BMW shaft drive I'm happy now with my maintenance free belt drive on my Thunderbird. It's a result for me.
Tue, 14/02/2012 - 22:38
#9
Re: Belt Drive
Hi alanp
Be interested to know how much power the thunderbird kicks out. Just curious to know how much power designers are managing to put through belt drives these days. The thunderbird strikes me as a torquey bike, but I dont know how many ponies we're talking.
Cheers.
Tue, 14/02/2012 - 22:49
#10
Re: Belt Drive
If I've got the right model it looks like 84 bhp. A fair amount.
Is that rear pulley polished ally? Nice bit o kit.
Tue, 14/02/2012 - 23:24
#11
Re: Belt Drive
Looked at the buell models. Bit difficult to access power output specs but seem to be up as high as 100 bhp. The rear pulley looks enormous. Which is what I'd exect!
One benefit of the necessity to use large diameter pulleys is a lower torque applied tension. Which must be a good thing.
Wed, 15/02/2012 - 03:48
#12
Re: Belt Drive
"al ooo minum, if you prefer"
... no more than I prefer Knee-san, Mahz-da, Koo-do, or Hairy Potter! :-D
I think (generalising) the belt advantages (six) over chain are: cleanliness, quietness, lightness, chain cleaner/lube costs, longer adjustment periods, longer life. The 'main' drawback is the replacement costs (item and labour), but having said that chain and sprockets that most people buy (e.g. Regina) and have dealer fitted, is no longer a cheap job either; thankfully it's less frequent nowadays.
"the oil needs to be everywhere where mechanical contact takes place"
... I take that as a given too. Which begs the question, why are 'most' oiler kits sold the single feed type that only oil one side of the sprocket with the majority of the oil presumably going between the sprocket and chain, fling aside only lubricating the cylindrical link aspects that physically mate to the sprocket curvatures and one side of the o-ring chain, but not actually between the links themselves or the other side of the chain. How can that be efficient compared with manual application of lubricant all over the chain following a decent clean? Even the dual feed kits, are they really doing an efficient job, or like VTEC are auto-chain oilers really a solution to a problem that doesn't exist, other than forgetfulness? No slight on Scottoiler, Loobman or Tutoro meant!
Shuggs I've heard of snapped kevlar belts (rare like chains snapping too) holing cases as well, so nothings perfect I guess. I do wonder, in both cases, whether they are the resultant of poor maintenance/adjustment by the owners?
After a leaky BMW shaft drive I'm happy now with my maintenance free belt drive on my Thunderbird. It's a result for me.
... I think we can find pros and cons in all solutions, although Baroness Thatcher probably stretches that theory somewhat! But for my scheckles, so far, I think belt is best in theory. But being a logical bod I know I must be wrong as it's in the minority as a solution, and despite some great points sited by Pittsy, I still don't know why its not the most popular solution both with manufacturers and owners alike. Anyway, I'm glad you like it too. I've ridden the T-Bird, it's a really nice cruiser.
Pittsy, I think the final Buell made 135 hp, but I don't know the torque figure off-hand? I do know that most Harleys are now 103 ci and a claimed 100 lb.ft, equating to about 93 lb/ft at the rear wheel on most people's dyno's. However, they do 110 ci kits and their CVO motors are usually 110 ci. They add about 10 hp and 15 lb.ft more I believe. An output of 115 lb.ft at around 3,000 rpm upwards is not inconsiderable and makes a 300 kilo bike much more sprightly away from the lights than sports bike owners would believe. In fact up to 60 mph they feel effortlessly brilliant. However, when we're only dealing with 75-80 hp, those strong punches are happening less frequently than an inline four could replicate them. Inline fours of the same capacity produce more torque than twins, but it's less accessible. A real test of a kevlar belt would be an S&S 140 ci (2000cc?) engine, making maybe 125 hp and 140 lb.ft. But again there seems to be plenty of bespoke customs doing just that without hearing any snapped belt horror stories. Of course the one's serious about drag racing their bikes convert them to run chain anyway, chains do seem to transmit the most power however small the advantages vs belt might be. Another real test would be make the R3 belt drive and improve the gearbox whilst they are at it, whadya say Triumph?
Wed, 15/02/2012 - 07:54
#13
Re: Belt Drive
Cap'n said: "Hairy Potter"
Hee Hee. I like that one. How about EARS (yes) or NEAR (no).
I think you've probably covered the plus points of belt in a nutshell. It does beg the question doesn't it. What about the plus points f chain next. And shaft. Pros and cons bullet list.
There will be a limit on HP for belts and I'm staggered if buell got 120hp thro one. I don't know which model I was looking at (I think it was on Kev's test archive list) or what HP we're talking, but the pulley was very large. I then noticed Kev's Panigale test was on site (can someone mop him down with a damp towel). Look at the size of the sprocket on that! It's weeny. Aww. I think I know why.
I'm looking forward to Kev's technical rundown on the Panigale. Anyone seen a film called "the couch trip" ?
Wed, 15/02/2012 - 08:45
#14
Re: Belt Drive
Captain - there a dual injectors which will deliver oil to both sides and they are directed against the sprocket. They were developed because people expected to see it more than anything. The oil gets distributed between the moving parts by the movement perfectly efficently courtesy of physics.
The whole notion of spray lube is just so flawed, in my opinion that I would rather have a shaft drive than use that stuff. :-) Well not quite but you get the idea.
Wed, 15/02/2012 - 16:25
#15
Re: Belt Drive
Pits, the other gems I like are 'Hundi' (Hyundai) and orag-ano. Still 'my bad' because, if life was all eggplant and zucchini (aubergine/courgette) then the world would be a boring place doncha fink?
Buell's last production bike under HD ownership, was the 1125R made 140 hp and 80 lb.ft. It was chain drive (a '520'; Reynolds presumably), but because it was a modern LC, that final drive decision might well have been a marketing lead (sportsbike riders don't do gurlie belts etc) decision, than anything else? http://www.bikez.com/motorcycles/erik_buell_racing_1125r_dsb_2011.php
Buell's last volume bike was the XB12R. It was belt driven. It made about 100 hp and 85 lb.ft, the same but opposite numbers of the current 103 ci Harleys. http://www.bikez.com/motorcycles/buell_firebolt_xb12r_2007.php In terms of HP, it could be the highest of any production bike that has been supplied with belt? The CVO 110 ci's are probably the same, but have about 115 lb.ft
Unlike Harley's, Victory's belts can be replaced without taking half the bike apart it would appear: http://www.jamesrussellpublishing.biz/victory.html
Someone's view: http://motorcycle-intelligence.com/chain-belt-shaft/64/
Shuggs I did mention dual-feeds, but the majority sold are singular, as stated. If you say physics (centrifugal forces, or whatever!) do the business oil distribution wise, then I believe you, coz you know all about that stuff, whereas I struggled to get an O-Level in Mista Singh's class :-D
Oil feeders, particularly auto-consistent feeds like the Scottoiler make logical sense, but I don't think that makes spray lube flawed by default. As long as the chain is clean, well maintained and carefully lubricated as necessary, I fail to see much difference. It's not as thought the oil we apply by hand evaporates is it? :-D
I'm not a fan of 'spray' lube as such. I prefer to use a Scottoil refill tube and direct the feeder in between each link as I lubricate on both sides. In a dry climate a clean and lube every 500 miles is perfectly fine. If I lived in Blighty still and commuted throughout winter then an oil feeder like Scottoiler would be fair mandatory, although if I did that I'd be tempted by an F800ST or Deuxville, neither of which are chain driven bikes but do have reliable drive systems. For dry weather use or in the south of North America a fancy automated feeder is probably a bit overkill, but each to their own. :-D
Wed, 15/02/2012 - 18:01
#16
Re: Belt Drive
Capn - the flaw in spray lube, to me, is that the second you start to move then it is starting to lose its effectiveness as it will begin to get flung off and not replaced. So even if it is replaced every 500 miles then the chain was running a whole lot drier between miles 400-500 than it was 0 to 100.
It's like so much in this little past time we all love, it comes down to self preference and the nice thing in this little corner of biking is that no one falls out over it. Well there was that one ars e, who is thankfully long gone!!
Thu, 16/02/2012 - 08:42
#17
Re: Belt Drive
Roller chain final drive.
Trying to think of negatives..... And there doesn't seem to be too many!
IMO:
Top of the list is lubrication. That falls into two categories. Internal and external.
The internal lubrication problem has already been solved. The humble O ring. This keeps lubricant in between the pins and bushes. Wear here is the cause of stretch, which in turn contributes in large degree to sprocket wear. Solve this problem and you're a long way towards extending the life and adjustment intervals of chain and sprockets.
External lubrication, as a technical problem, you could say has been solved. Drip oil onto the chain or apply a spray. The BIG problem is the mess involved in running an exposed piece of machinery which is whizzing around throwing off all the stuff you've just applied. And, of course, the hassle of having to apply the stuff and clean the chain on a very regular basis. If you're a high mileage, all seasons rider, a real hassle. We can discuss the pros and cons of which type of external lubrication we use. And we should.
That is pretty much it for the cons of chain drive, as far as I can see. There are some other technical issues which don't, as a rule, really show themselves to the rider. There's the chordal effect (polygon effect). Can anyone say they've noticed it? It is probably affecting the life of the chain, but it's just part of how it operates. Maybe you could notice it at speed on a billiard board smooth stretch of road? We're clutching at straws adding it to our list. Going to a finer pitch duplex chain should minimise that phenomenon but would add to the next. Centrifugal speed limitations. As with belt drives there are factors pushing the designer towards larger sprockets to keep down the loads applied to shafts, bearings and chassis, and lessen the chordal effect. But the opposite factor pushes him/her to keep the sprocket small to avoid centrifugal and linear chain speed problems. Like I say, the same issues apply to belts to even larger degree. Similar problems apply to gears, but they're tucked away in a cosy compartment with good lubrication.
Solve the mess and maintenance issue and you're onto a winner.
That brings us back to belts and shafts!
Sun, 22/07/2012 - 23:25
#18
Re: Belt Drive
Boss Hoss uses belt final drive with huge horsepower/torque.
My Victory Kingpin is belt final drive and puts 126 HP and 134 ft-lbs to the tire SAE and there is no place on the tach from 2300-6400 rpm where it doesn't make over 100 ft-lbs (not stock) with no belt issues. It is not true that belts are limited to low HP applications. Buell 1125R comes to mind as a high powered, belt driven machine.
Belt final drive is super light weight, maintenance free, quiet, and efficient. If a belt breaks it won't take out an engine case like a chain can. Chains and sprokets are expensive too.
Yes, on a Harley the belt replacement is a chore, but right side drive machines (custom HD clones and Victory) are easy to change the belt on. I can do it in 1/2 an hour.
Sun, 22/07/2012 - 07:48
#19
Re: Belt Drive
Half crazy said: "It is not true that belts are limited to low HP applications."
I guess you're right. I think my comment is out of date. Things have moved on. Belt ratings have gone higher.
Although I did say "relatively" low hp and "relatively" low speed. Compared to, say, a panigale, 120 hp is still "relatively" low. But, still, it is a brilliant achievement. Both on the part of the bike builder and the belt designer/manufacturer. If the belt didn't have the rating, no amount of engineering ability could make it last.
Thanks.
Sun, 22/07/2012 - 10:18
#20
Re: Belt Drive
Re belt weights. I was pondering that one yesterday. I think the pulleys can be aluminium (al ooo minum, if you prefer). Not sure whether a belt would be lighter than a chain to do same power? If I was forced to guess I'd say the belt was lighter. So, maybe belt drive trumps chain in that respect?
My gut feeling was that belts might offer less unsprung weight but I was speaking with someone at Triumph about this and they say the weight of the pulley more than offsets the lightness of the belt itself, and you end up with greater unsprung weight than a sprocket and chain. So no performance gain there.
A belt drive is also slightly less efficient than a good condition chain, although chains do of course go off much more if they're not maintained well.
The issues that I've heard over the years in discussions with bike engineers come down to two main points. One is bulk as much as weight, it can be difficult fitting the sprockets into the space you have both at the rear wheel and also at the crankcase end.
The second is tolerance of everyday conditions - a belt is intolerant of such things as stones getting caught in the sprocket and incorrect tension, where a chain withstands this kind of thing much better. You can't have a belt on an off-load bike at all, it simply wouldn't last half a mile with mud and debris being caught up in it, and while that's less of a problem on road bikes it's still an issue to some extent.
Also power transmission is still a limitation, 120bhp seems to be the current limit with modern Kevlar belts, more than that and they become too bulky to fit on a motorcycle. But it's rear wheel torque that matters really, and while a lot of cruisers like Victorys have higher power, they also have very tall gearing which means the rear wheel torque is quite low.
There are other design issues too, the Buell Firebolt became well known for breaking its belts (and lots of other things...), it turned out because the engine oil stored in the swingarm was causing it to heat up and expand (I reckoned by about 1.5mm) and that was enough to over-tension the belt, which duly snapped regularly.
An advantage of belts not mentioned though is noise, they're much quieter than chains and with noise emissions becomes increasingly strict, that's starting to matter more.
But not only do chains work very well in all kinds of conditions at any power level, they're cheap too. A belt itself is costly - Kevlar ain't cheap - and the pulleys need much more accurate machining than a sprocket, which is also expensive.
Sun, 22/07/2012 - 13:45
#21
Re: Belt Drive
power transmission is still a limitation, 120bhp seems to be the current limit with modern Kevlar belts, more than that and they become too bulky to fit on a motorcycle. But it's rear wheel torque that matters really, and while a lot of cruisers like Victorys have higher power, they also have very tall gearing which means the rear wheel torque is quite low.
700+ HP motorcycles with belt final drive:
http://www.youtube.com/watch?v=BcZ6r1Vq9Qg
This black bagger has a 1" wide final drive belt and is geared down 7% (2 teeth smaller than stock front pulley):
http://www.youtube.com/watch?v=cWzsVUClbC8&feature=g-upl
http://www.youtube.com/watch?v=a12v2li-qpQ&feature=context-gau
Good thing it's low torque:
http://i177.photobucket.com/albums/w225/half_crazy-01/DYNOGRAPHSAELARRY.jpg
Sun, 22/07/2012 - 22:07
#22
Re: Belt Drive
Kevin, thanks for the input. It's appreciated and I find it very helpful.
Mon, 23/07/2012 - 03:21
#23
Re: Belt Drive
Buell's last production bike under HD ownership, was the 1125R made 140 hp and 80 lb.ft. It was chain drive (a '520'; Reynolds presumably
The 1125R was belt final drive. I have that belt on my bike right now because I needed a 2-teeth shorter belt. The 1125R belt is a 1" wide Goodyear belt with 145 teeth.
1125R picture:
http://coolbikepictures.info/wp-content/uploads/2011/06/Buell-1125R-Side...
My belt:
http://sphotos-a.xx.fbcdn.net/hphotos-ash4/425864_155485227904899_170537...
On the Buell the belt is tensioned by a spring loaded idler pulley. This causes premature belt failure (around 12K miles) because it stresses the belt in both directions.
Mon, 23/07/2012 - 07:48
#24
Re: Belt Drive
Hi half_crazy.
The buell in the photo has a lot of nice design touches. The idler pulley is clearly seen mounted on the footrest bracket. Very neat. How is it spring tensioned? On the photo it looks concentric with its mounting bolt. It is positioned very close to the driving pulley, which you would expect as this is where the least movement occurs. An inch wide belt sounds incredibly narrow, given the power. Having said that, the driven pulley is enormous, so that will keep torque applied tension down, at the risk of excessive circumferencial speed. Is the tooth profile HTD? Or another, more advanced version? I assume the swingarm doesn't pivot concentric with the driving pulley, or there wouldn't be a need for an idler pulley?
I'll stick my neck out and suggest that the belt width was deliberately kept narrow to a) make it reasonably easy to package onto the bike and b)more importantly, to keep the shaft overhung loads down, avoiding bulky gearbox shaft sizes and bearing sizes and/or exotic shaft materials. Go on, shoot me down in flames!
Just a thought... You say the idler pulley is the cause of premature failure. Could it be reasoned that excess power (fully used!) is the cause. Put less horsepower through the exact same set up and would you not achieve a much higher working life? Depends on how you want to look at things I suppose.
Cheers.
Mon, 23/07/2012 - 12:28
#25
Re: Belt Drive
Hi half_crazy.
The buell in the photo has a lot of nice design touches. The idler pulley is clearly seen mounted on the footrest bracket. Very neat. How is it spring tensioned? On the photo it looks concentric with its mounting bolt.
Not sure how the idler is tensioned, as I don't own a Buell 1125R. I assume it IS the belt tension adjustment... since there is no fore/aft adjustment at the rear axle. It appears to be behind the peg bracket, not bolted to it.
It is positioned very close to the driving pulley, which you would expect as this is where the least movement occurs. An inch wide belt sounds incredibly narrow, given the power. Having said that, the driven pulley is enormous, so that will keep torque applied tension down, at the risk of excessive circumferencial speed.
What about the small pulley up front? As soon as it makes the sharp bend around the small pulley it gets bent the opposite way it was designed to bend by the idler. This stresses the chords in the belt in both directions, where any other belt drive only bends the belt in one direction... the direction the belt was designed to bend.
The Buell belt is the same 14mm pitch and the same tooth profile as Harley and Victory OEM belts (Gates).
There is a nice Buell forum online. The members there were very helpful.
Mon, 23/07/2012 - 17:46
#26
Re: Belt Drive
The 1125R was belt final drive
... yes. If you look at my post I said it was chain drive. And I said it was belt drive too. I like to edge my bets! Whatyamean, missinformation?!?! ;-D
How does the F800ST or Yamaha 530 TMax kevlar belt systems work compared with the Buell?
Would no maint chain in bath, like the new BMW scooter be suitable for larger capacity machines?
HAs anyone tried a Choinkwich, and is it as good as they say?
Mon, 23/07/2012 - 18:07
#27
Re: Belt Drive
Half_crazy said: "What about the small pulley up front? As soon as it makes the sharp bend around the small pulley it gets bent the opposite way it was designed to bend by the idler. This stresses the chords in the belt in both directions, where any other belt drive only bends the belt in one direction... the direction the belt was designed to bend."
Hi
You cant have your cake and eat it. : ) You put an idler pulley in there, that's what you get. When I said place of least movement i was referring to the varying movement of swingarm going up and down. I took the view that where the idler pulley is situated it will minimise the implications to the belt tension of that movement. I don't know the first thing about Kevlar, as a material. I suppose, like most materials, repeatedly bending it in rapidly alternating directions will eventually fatigue it. Although the Kevlar is wound into chords and so I think this type of rope like construction is as suited to alternating directions as any. My own stab would be that the varying belt tension due to swingarm movement is at least as much the cause.
You mentioned premature belt failures. I assume these are the belt literally snapping and not teeth shearing off?
Gates do a variety of synchronous belt tooth profiles. HTD used to be the highest torque rating but I would imagine things have moved on a lot.
Interesting stuff. Keep it coming.
I'd love to know how the belt for the bike in the photo is tensioned and whether the idler pulley is locked in place once tension has been achieved. A bit like the old Honda 400 four cam chain principle? ie: release lock nut, a spring applies the tension, re tighten
lock nut. Or does a spring constantly fluctuate? I don't like the latter, not unless a damper is also involved. Difficult to be sure, but a second look at the photo and it looks to me for all the world like the idler pulley is mounted on the footrest bracket, but it is very difficult to tell. Maybe eccentric adjustment?
Cheers.
Mon, 23/07/2012 - 18:16
#28
Re: Belt Drive
Captain scarlet said: "Would no maint chain in bath, like the new BMW scooter be suitable for larger capacity machines?"
Hi cap'n. I asked myself the exact same question. My answer to myself was "probably, but what about the unsprung weight? As well as the physical bulk. The street cred (lack of)....."
To my eyes there are two aspects of the big Beemer scooter chain drive which are definite plus points. One is the fact it is enclosed, but also the fact that the driving sprocket is concentric with the swingarm pivot ( I'm going from memory so I hope that last bit is right!)
Mon, 23/07/2012 - 19:17
#29
Re: Belt Drive
This is interesting...
http://www.motorcycledaily.com/2008/05/08may08_chainsvbelt
Mon, 23/07/2012 - 20:01
#30
Re: Belt Drive
"This is interesting..."
It certainly is! Thanks very much for that.
The text doesn't explicitly say this, but I think I can glean that the idler pulley on the buell concerned is concentric, fixed and non adjustable. It doesn't have to be adjustable as long as a few components are made within reasonable tolerance of each other. So how is the belt tensioned? By the suspension i reckon. Remove the shock, lift up the swingarm high enough and the idler pulley will be relieved of tension. As long as the " give" in the belt is reasonable, that will work. The big issue, and this is not to sniffed at, is that a not inconsiderable amount of pre tension will be applied. This will place load on to all the components concerned and is additional to the torque induced tension. That sound reasonable?
The other thing I noted from the text was that the author said that chains can operate on ridiculously small sprockets. Yes they can but with drawbacks. The chordal effect will be more pronounced, unless fine pitch duplex or triplex sprockets are used. These have their own drawbacks. Also, using small rear sprockets increases torque induced tension. Having said all that, the sprocket on the panigale looks incredibly small, given the power, so there are obviously ways around it.
Also, the text refers to "rectangular" shaped teeth. The first generation synchronous toothed belts had teeth similar to a rack, but not involute I don't think. The later HTD tooth profile is round and smooths out the stress "squeeze" as the imaginary stress lines are squeezed over into the narrow part of the belt between teeth. Meaning higher torque (hence power) can be transmitted for a given belt width and pulley diameter. I think the flat sided teeth are more suited to applications requiring a higher degree of synchronisation as their teeth don't deflect as much. All the more reason to use HTD profile on a rear drive. Anyone back me up on this?
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Addendum.
Because HTD belts are wide compared to a roller chain, the side load on a shaft and bearing, (which is already higher due to pre tension), is further exaggerated by the belt width. The side load is taken from the middle of the belt (or chain), so the extra width moves the point of load further out, placing higher loads on the shaft, bearing and whatever is supporting them.