Clutchless changes

[kenr]

So I gotta confess I have been giving it a go (using the advice in the thread from Motomonster and Janusz - thanks guys) and I have to admit it really does make sense to me - not at all from the point of going fast but the gearchanges are extremely slick, much more so than its possible to achieve with the clutch.

 

If you think it mught be for you I recommend at least giving it a try.

 

Ken

[Janusz]

Five....

 

Seven stubborn to go...

 

Practice will make you believer.

[Guest Jeff Kelland]

Janusz, maybe you should learn how a constant mesh transmission works. Just because the gear teeth remain in constant mesh, doesn't mean everything else does. Power is transfered through dogs on the side of the gears which engage slots in the mating gear. When the clutch is disengaged, it is impossible to transmit a shock load from mismatched engine and driveline speeds, if it isn't disengaged, it can transmit mismatched speeds. This beats the hell out of the dogs and slots which eventually causes the transmission to jump out of gear. If the rider is experienced and gets the timing right, shifts up or down without the clutch are harmless. If the rider gets a little bit off, CLUNK!! Thats the sound of your engines torque being used as a hammer on the dogs and slots! I can shift mine without the clutch. I have to pay constant attention to that task. I prefer to use that attention for other things on the street. Is it faster, probably by a few thousands of a second a shift, big deal! Real racing bikes are shifted sometimes without the clutch, but they are equipped with a sensor on the shift lever that kills the ignition for a split second while the shift is made, no engine, no torque load transmitted during the shift. I bet Valentino can shift without this device a lot better than you or I. He's got it so his attention can be somewhere else, like on the corner rushing up at him at 190 mph. As to the experience of the members here, the advice I read was thought out and given with honest consideration for all the members at all levels of experience. Probably not a good idea to tell a relatively new rider to shift his expensive Italian motorcycle without the clutch.

[Guest ratchethack]

Nicely stated, Jeff. Anyone who has dismantled a constant-mesh motocross transmission that has been raced (read shifted constantly without the clutch under combat conditions) for the purpose of replacing worn shift dogs (I have) understands the principles involved. There's no way around the fact that clutchless shifting causes the sharp 90-degree "corners" of the shift dogs to become rounded off, eventually followed by a "ramping" wear pattern on the mating faces of the dogs. This causes the trans to start to jump out of gear, followed by rapidly accelerated wear as the bike becomes unrideable until it gets a trans rebuild (with new or re-cut shift dogs). It's pretty obvious that overall, habitual clutchless shifting contributes to this wear significantly faster than using the clutch.

 

Just my personal habit, but while I will occasionally shift sans clutch on my dual-sport thumper (only when I know I can get a "clean" shift), as a rule I never do it with the Guz. My reasoning is that there's a whole lot more risk on the Guzzi when you don't get it exactly right. By comparison with a motocrosser (and many other bikes for that matter), the heavy flywheel effect and relatively huge drive train mass of the Guzzi would tend to greatly enhance the effects of wear and damage to the shift dogs due to the "heavier hammering" of clutchless shifting - far more than on a racing bike with a very significantly lighter crank and flywheel, and a VERY significantly lower-mass chain drive.

 

Ratchethack

[dlaing]

I don't think anyone is advocating using racing technique.

Using racing technique you would bang the engine into the drive train to increase accelleration....this is a bad idea, unless you have money to burn.

 

Upshifting without the clutch can produce smoother shifts that are easier on the drive train.

 

I am not sure exactly what is going on inside the gearbox, but I suspect a clutched shift works because it nearly neutralizes the force coming from the engine.

This allows the gears to find there way home with the prompting of the gear shifter.

It is not the perfect way to shift because the engine side of the gear box does not know how fast to go. It is free spinning and is at the will of the tire side of the gear box and its deccellerating forces. Hang on to the shift for too long and you can be in gear box pergatory.

 

PROPERLY executed clutchless shift produces less wear and stress because the force is not completey neutralized, but rather the engine runs just a hair faster(presumably the engine runs faster, but a hair slower would work too.)

The perfect speed difference allows the gears to find there way home.

 

How reliably can one execute clutchless shifts, I don't know.

But as Jeff suggested, if you get it wrong, you can do expensive damage...

[Janusz]

Just try it guys.

Try it on Guzzi without prejudice and THEN tell us what you think.

 

My Guzzi for instance has over 40,000 km and approx. 90% of upshift starting from gear 2 up were done clutchless.

And yet, as I said before, there is no wear.

Also, for approx. last 25 years I shifted clutchless, nice and easy, on any bike I owned provided it (the bike I mean) liked it. Some had 150,000 km plus.

I would not clutchless upshift Guzzi 5 speed. But the new 6 speed just LOVES clutchless upshift. Not even one CLUNK Jeff.

Forget why, forget how the box is built. The fact remains that the proof is in the pudding.

 

That's all.

[Janusz]

 

How reliably can one execute clutchless shifts, I don't know.

39202[/snapback]

 

I do know.

With some practice, positive attitude and common sense: very reliably.

[dlaing]

Ok, I gave it a try.

Maybe I am a spaz, but I gave it a try and found that although it works, the clutch shifts are still smoother to the feel of my foot.

I tried today to find a timing that was smoother than clutched shifting.

 

Breaking the time down into theoretical time segments:

A. cut throttle 100 milliseconds

B. bring back throttle 100 milliseconds

 

 

I tried preloading the shifter and quickly cutting the throttle and bringing it back.

This seemed to produce a fairly smooth shift, but my concern was that preloading would cause strain on the dogs or whatever they are called. Plus the shift was not as smooth as a proper clutch shift.

 

Trying to simultaneously cut throttle and upshift I found that if I was to early with the shift, there was too much resistance at my foot.

If the shift was within the first few milliseconds of the throttle cut, the shift was optimal and nearly as smooth as a clutch shift.

If I was too late with the upshift, I found false neutrals.

 

The shift had to take place within the first 100 milliseconds.

Probably the smoothest shifts were between 10 and 50 milliseconds.

In order to get the timing right the shifts had to be unrelaxingly quick and I had to be accellerating not just cruising and upshifting for the heck of it.

 

I still reserve judgement and will practice more as conditions dictate, but I am not ready to shift in the twisties with this technique, shift while cruising, down shift, shift when full throttled close to red line, shift at low rpms, or shift from first to second.

 

Meanwhile the clutched shifts allowed for a lighter touch of the foot.

On the good side, I think the exercise(experiment) improved my clutched shifting.

 

Granted that I am not the most coordinated.

I have white mans dance feet. I have been bowling once per week for six years and still throw a gutterball or two on the lead shot, on average more than once per night.

AND I am still in the top one percent of sporting riders in terms of chicken strip size.

Got passed by a grey haired guy on a Kawasaki Dual Purpose today <_>

So maybe Janusz can constantly be in clutchless nirvana, I don't want to take the chance except under ideal conditions like accellerating onto the freeway.

 

My humble opinion only, your mileage will vary.

[helicopterjim R.I.P.]

I think Moto Guzzi anticipated this discussion when they came out with their automatic transmission. I just don't know why the MGS doesn't have an automatic transmission? It would accelerate so much faster and never stall off the line!

 

P.S. My favourite post so far!! I hope it never ends!!!!

[dlaing]

What we need is a continuously variable transmission and a really peaky engine to go with it.

Oh yah and belt drive!

And! a hybrid gas/electric power system.

And self adjusting multi-valves.

And liquid cooling.

And pneumatic tires!

But seriously, one thing I did notice today was how wonderfully spaced the gearing is on our bikes. Bellisimo!

[kenr]

Can someone explain (just because I am interested to know) why clutchless changes in the low gears don't work so well ?

[pete roper]

Can someone explain (just because I am interested to know) why clutchless changes in the low gears don't work so well ?

39264[/snapback]

 

The difference, the *gap* between lower gears is bigger. This means that the various shafts, dogs and the rotating mass of the crank have to *adjust* more, essentially travel through a greater arc, before the dogs can slide into engagement and it's also happening a lot quicker in lower gears so there is less chance for the slow, human motivated, engagement to take place.

 

I do agree that you have to understand how a constant mesh box works before you can fully grasp what you are trying to achieve with a gear change, clutched or clutchless. It's intersting to note that in an attempt to improve, ie, speed up changing on the 5 speed box the Carb Sports and some of the early i's had only 3 dog engagement on the pinions. This, aong with the lack of a rear wheel cush drive is responsible for almost all Carb Sport gearboxes going tits-up at low mileages.

 

A gearbox, any gearbox, in this sort of application is a huge series of compromises. Whether you change clutching or clutchless won't make wear and strain go away, but both can be used if you know wha youre doing!!!!

 

Pete