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| KnightsFall |
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KnightsFall
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Triton Thrasher
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| stinkwheel |
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stinkwheel
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 Posted: 20:08 - 15 Jun 2015  Post subject: |
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Sounds like an excuse for poor slow riding skills.
Although many BMW clutches are single plate and dry unlike most other motorcycle clutches which are multi-plate and wet.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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Kickstart
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| KnightsFall |
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KnightsFall
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KnightsFall
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Albigularis
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Kickstart
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Rogerborg
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| KnightsFall |
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KnightsFall
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| Rogerborg |
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Rogerborg
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Posted: 21:31 - 15 Jun 2015  Post subject: |
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A 1200GS probably isn't a great choice for urban commuting, because of the clutch but also because it'll be collecting hubcaps on the cylinder heads. 
If it turns out that he's got a 650 or 800 then he's just making excuses.
There's nothing wrong with using a scooter for urban commuting - that's what they're for. It's just dreadfully dull.
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GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike |
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KnightsFall
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Rogerborg
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Northern Monkey
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KnightsFall
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Northern Monkey
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Rogerborg
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Northern Monkey
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| Teflon-Mike |
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Teflon-Mike
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Posted: 14:59 - 16 Jun 2015  Post subject: Re: Rush hour bad for the gear box? |
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| KnightsFall wrote: | At the risk of asking a silly question, is the amount of clutch slipping on a typical rush hour commute especially bad for the gear box? |
"Clutch slipping"  Lets make a motorcycle go slower than it's gearing and stall speed will allow, by revving the knackers off it; slipping the clutch and holding it back on the back brake and call it 'good slow Speed control'... it's not.. and it really annoys me that it's now vaunted as not only the only way to go slow but actually essential! Again, its not!
Luckily as has been mentioned, most modern motorcycles have whats called a 'unit construction gearbox', which is to say that the gearbox shafts live in the same 'unitary' casing as the crank-shaft and pistons of the engine. In days of antiquity; the engine used to be one 'lump' and the gearbox another; (Most Moto-Guzzi's & BMW's still are) Connecting the engine to the gearbox, was a 'primary drive'; usually a chain and sprockets, with a clutch on the gearbox input shaft; living 'outside' either engine or gearbox and its lubricating oil, the clutch was what is now termed 'dry' to differentiate it from the 'wet' clutches of modern machines, that with the gearbox and engine sharing a common casing, usually had the drive between them, most often by gear rather than chain, and the clutch inside that casing all splashing about in the oil lubricating the moving parts.
So we have two types of clutch; 'wet' and 'dry'. But as a device for engaging or disengaging 'drive' between rotating shafts; There's also a number of different arrangements of clutch design; but most are essentially like a wheel-brake working backwards; a pad or shoe gripping a spinning plate or drum, or not.
Most common type of clutch, as used on cars (& shaft drive BMW & Moto-Guzzis) is the single plate, diaphragm' clutch. A cork disk, mounted on the gearbox input shaft is sandwiched between a leaf-spring 'diaphragm' and the engine's flywheel. Diaphragm normally holds the cork pressed against the flywheel; pull in the release lever, and it relieves pressure on the diaphragm, and the plate can slip. This type of clutch usually runs 'dry' in it's own chamber or free air, not oil.
More common on motorcycles, is the 'compound' clutch; rather than having one cork plate between a pressure plate and flywheel, you have maybe five or more 'friction' plates, in a stack, between 'driven' plates; the friction plates keyed to a drum, the driven plates keyed into a hub; clamped in 'drive' by coil springs, which the release mechanism relieve tension on when the lever is pressed.
The compound clutch, with multiple plates in a drum, can be much smaller in diameter and offer a much larger friction area between friction & driven plates, hence afford a higher power transmission in a more compact component; it better 'suits' a compact motorcycle engine.
And the larger possible friction area can be used to compensate for running the clutch 'wet' lubricating oil robbing a lot of the friction between plates.
However, not having friction robbing oil between the plates; a 'dry' multi-plate clutch can be made smaller and lighter than a wet one for the same power transmission; and will 'tend' to have a lighter action. But dry clutches tend to be less 'progressive' and have a much harsher take up in 'slip' between the initial bite point and 'locked' in drive.
Consequently, where a light action, and weight and high power transmission is more important than a progressive take up, like in racing, the 'dry' multi-plate clutch has retained favor.. but they are easily 'cooked'; the plates getting very hot in 'slip'; where a single-plate clutch, the flywheel provides a large metal 'heat-sink' and a very short thermal path to soak the heat out of the clutch; or a wet-clutch, where the lower friction of lubricated plates tends not to generate so much heat to begin with, and the oil offers some cooling by both conduction and convection into the rest of the engine.
Ducati's, trading on their 'racing heritage', commonly employ a 'dry' multi-plate clutch.. and yup.. as many owners have discovered, as the marque gained popularity, they don't tend to fare well, in a city environment, being over-worked, making lots of changes and used against their nature for 'slip & drag' slow speed riding, getting little cooling air-flow to stop them frying, and so can be consequently short lived.
BMW's & Guzzis, with their dry diaphragm clutch tend not to suffer so badly; but again; they are dry clutches; they tend to have a less progressive take up, while they also have a quirk in the 'leaf spring' of the diaphragm that clamps the plates; designed to put maximum pressure on the plate when in 'drive' the spring tends to be pretty stiff, but the spring 'over centers' when you pull in the release lever, so that it 'should' be quite light to hold disengaged... in the middle though.. where you would be trying to 'slip' it.. it can be horrible! Its lacking progression and feel, and offering a gross amount of resistance wanting to be either in or out, NOT in the slip zone.
Its not that city traffic is particularly problematic; BUT they don't respond or fare well to modern 'slip & drag' riding habits. Wet multi-plate clutches, ARE 'better' suited to that style of riding; and have helped promote it as a legitimate technique, unfortunately.
But in any case; it's the 'Drag & Slip' riding habit that's the issue; you shouldn't HAVE to drag and slip on the road; wet-clutch bikes might tolerate it 'better' and dry clutch bikes little or not at all; but the answer, if you are worried about clutch life is to simply NOT do it! If you cant 'filter' at trickle speed clutch 'out'.. DON'T filter! Be more decisive and either stop, or go; don't half and half and wear your clutch out in the neither nor of 'dithering'.
Meanwhile, the centrifugal clutch used in Twist and Go's is basically a drum brake working backwards; the back-plate spun by the engine, often at crank-speed, centrifugal force throwing the 'brake shoes' out against the drum to grip as hard as the centrifugal force throws them, and 'automatically' released by a light spring, when the forces are too low to make them grip.
Usually 'dry'; the centrifugal clutch has a slightly more progressive 'take up' than a dry single-plate clutch, but only for relatively small power transmissions; They also tend to be 'tuned' to offer a fairly large amount of slip; in a direct drive transmission, (or a centrifugal variator transmission, that only offers a relatively small amount of ratio variation, compared to a conventional gearbox) and that fixed (or almost) gear ratio has to be a compromise for top speed and acceleration and launch, so, mimicking 'slip & drag', a taller overall drive ratio can be selected that will naturally mimick 'drag' and the clutch can be set up to give a large degree of 'slip' to help the engine drive it from a faster crank-speed without stalling.
So, its actually an irony, that centrifugal clutch twist and go's are so vaunted for city stop start traffic... their clutch and transmission actually is the less suitable for it, 'technically'; but, for limited power transmission, and a very simple transmission, as a 'compromise' it's probably a better one, more often, than a dry racing clutch in a Ducati, or a dry single plate clutch in a Guzzi or Beemer, ridden by a Drag & slip devotee.
So, as has been offered, NO, the clutch slipping wouldn't be bad for the gear-box... it would be bad for the clutch
There maybe 'some' merit in the suggestion a T&G is probably 'better' for rush-hour commuting; and a T&G's centrifugal clutch is likely to survive longer, through not having so much power put through it in 'slip' than a bigger bike, whatever kind of clutch it got. AND not really having much of a gearbox to be damaged!
But, bikes with gearboxes.... if you change gear, you will move bits of metal in the gearbox, that's going to wear stuff out.. If I get on my bike, I engage 1st, launch, ride to the end of the street.. if I turn left, I'm heading into town... two miles to ASDA, I'll likely have to stop at least half a dozen times for roundabouts or traffic lights... so I'll make quite a few gear-changes, probably all between first and second, in that short journey... IF I had turned right, though? Be heading out of town, couple of miles of 40 limit to the NSL could be five miles before I have to make a down shift... and on the 'open' road, many many miles where I possibly don't have to shift at all. And as far as wear and tear goes; its not just the number of shifts, but the loading, and in the lower gears used round town, the loading are high.. that's what the gears are for; lower gears multiply force, so in the loading's will be high, and changing a lot between accelerating and braking, which will all add to 'wear and tear'.. so city bikes do often develop gearbox 'niggles' or problems, often in the selector mechanism or the actual engagement 'dogs' from so much high-load gear changing, and usually on the 'most used' 2nd gear, at high miles or if sorely abused or neglected.
BUT that is from the nature of city riding, not the design of the machine; which is either aggravated or alleviated by the rider, working with or against the strengths and weaknesses of a specific bike.
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
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| Rogerborg |
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Rogerborg
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| Posted: 19:39 - 16 Jun 2015 Post subject: |
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Mike's right, a modern supersports 600 would be ideal.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike |
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Northern Monkey
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| Jewlio Iglesias |
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Jewlio Iglesias
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Rogerborg
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ferrisio
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Old Thread Alert!
The last post was made 10 years, 246 days ago. Instead of replying here, would creating a new thread be more useful? |
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