Clutchless Shifting - K-Bikes.com - Excellence in Motion
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post #1 of 27 (permalink) Old May 7th, 2006, 10:38 am Thread Starter
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Clutchless Shifting

After years of being a cruiser guy, I recently bought a K1200R. Love it, naturally. Could someone please explain the concept and mechanics of clutchless shifting. Is it damaging to the bike?
Thanks,
J
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post #2 of 27 (permalink) Old May 7th, 2006, 12:32 pm
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jdj,

in a motorcycle gearbox, all the gears are rotating with the shafts, but the LOAD transfers thru whatever gear is engaged.

pulling in the clutch on each upshift is to allow a 'cushion' so load can transfer to the next gear without a hard inpact to the engagement dogs on each gear.

the same thing is accomplished by quickly rolling off the throttle and shifting without pulling in the clutch.

my R100-S racebike with 1050 jugs and 'very nice' heads will suffer from clutch slippage in a race IF I use the clutch on upshifts. Clutchless upshifts allow me to finish a race without having overheated and spun the clutch. Of course its a racebike and I don't expect the gearbox to last more than a few weekends.

I have clutchless shifted streetbikes Forever and suffered no damage, but typically save this technique when racing another streetbike or as a matter of convience when I am too lazy to reach for the clutch.

I am sure that if a rider makes clutchless upshifts his normal way of shifting, he is reducing the longterm reliability of his gearbox, when viewed over a multi-hunded thousand mile lifespan one would like to think his BMW is capable of.

Used correctly it will spare the clutch disk and shave 100's of a second off a dragrace or a laptime.

Any harm really depends on if the rider is 'hamfisted/footed' and what level of performance vs. reliability he demands from his machine.
HTH,

Mike Kelly

Triple M Engineering

K12RS

Stanley, NC
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post #3 of 27 (permalink) Old May 7th, 2006, 1:25 pm
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The concept is fairly straight forward but I will over simplify with a conceptual explanation:

Your gearbox has an output shaft connected to your rear drive wheel and a power input shaft connected to your engine via the clutch. The input shaft can be rotating anything from idle at 1K rpm to redline. The output shaft can be rotating anywhere from stop to the maximum speed of the rear wheel through the tranni equivalent to say 155mph. On each of the 2 shaft are gears of different ratios (diameters and teeth) so when you shift you 'connect' the shaft and a gear rotating at engine speed with the shaft and a gear rotating at rear wheel speed.

If you have two gears on two shafts rotating at different speeds you can understand that the chances of getting the gear teeth to mesh together and join up the two shafts whilst moving at different speeds are going to be pretty slim. The purpose of the clutch is to disconnect power drive from the engine so the power input shaft momentarily stops rotating (actually it's slowing down) so you can connect the gears on the input and output shaft. The occasional 'crunch' you hear is the output gear forcing the freewheeling or stopped input shaft to mesh at the same speed. The gears are made to take these 'knocks' provided they are not powered (clutch is in). When you let the clutch out after shifting, the power is connected from the input shaft and gear to the output shaft and gear with the right ratio.

Engines have higher rpms than the rear wheel, so to reduce the ratio you have a smaller gear on the input than the output shaft. When you shift a gear up or down, you change the relative sizes of the gears so for the same engine and road speed before the shift you will not mesh the two new gears, unless the speed of one is changed.

For each shift there will be a road speed and a corresponding engine speed at which the gears on the input and output shaft can mesh without the use of the clutch. Generally the higher the road speed, and smaller the ratio change e.g 5-6, the easier it is to practice the clutchless change because speed differences in the two shafts going 5-6 are going to be similar. That's where you should start.

How do you know when to do the clutchless shift? You have to watch the tacho. and road speed first. Most riders will put a small amount of pressure on the shift lever whilst just backing off the throttle. If you are clutchless shifting up, you are trying to roll off the rpm just enough so the bike will be going at about the same road speed after the shift (but with lower rpm) as before. Going up is easier than coming down, but harder to get right going from shift 2 than 5-6.

Clutchless down shifting is far more difficult and virtually impossible below shift 3 because the ratios (shaft speed differences) are getting greater and you need practice watching the tacho and road speed with light pressure on the shifter to get it right. You can usually with light pressure on the shifter 'feel' when you hit the sweet spot for the shift.

I clutchless upshift all the time mostly 5-6, but generally not below shift 3 or with loads and a pillion. As long as you've developed a sensitivity at the toe and for any reaction or jolt from the bike, and worked to eliminate it, then I don't think you do damage - but it's down to your skill. You certainly save on clutch and hydraulic wear.

Going 5-6 is quick and lazy so I do it a lot. Lower gears need time to get the right rpm/road speed balance so I'd say it's slower to do if you are really pacing the bike and virtually impossible under hard acceleration without risking damage. The other lazy saving technique is double shifting up or down with clutch, but not under hard acceleration or perhaps fully loaded with pillion. The K has bags of torque and clutchless shifts get better with practice. Most of what I posted is memory and whilst I can do it successfully, getting all the details right when not riding is a tall order. So only practice 5-6 6-5 first, until you get no sharp decel reactions from the bike.

I started by reducing my clutch pull before shifting on higher gears to the extent I'm now hardly separating the clutch at all - that's good for clutches, bearings and you're well on towards clutchless changing.



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post #4 of 27 (permalink) Old May 7th, 2006, 3:39 pm
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no clutch/bucks

I read a report somewhere on an oil company web site. General advice to motor cylists. The writer advocated clutchless shifting on the up change.

I proceeded to ride that way

Until club service day.

A rider there had just spent $5000 on a gearbox. All because of clutchless shifting.

Now if had have been any one else, I would have thought, riders fault. But this guy has done 400,000 on his current late model bike, has featured on TV commercials in the jungle of South America.

Back to using the clutch. Incidently, sold my last bike at 130,000. Clutch on the new bike and the old bike feel the same.

Some old truck drivers do not use a clutch either shifting up or down. I have also done it, especially in a battle tank. But I am the guy paying for this K so I shall declutch with care.
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post #5 of 27 (permalink) Old May 7th, 2006, 4:55 pm
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Riders spend a fortune after burning their clutch splines out and they're not clutchless shifting, same is true of oilseals. I get the impression at the moment these are going to get you first!



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post #6 of 27 (permalink) Old May 7th, 2006, 6:03 pm
 
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Quote:
Originally Posted by MikeK
jdj,

the same thing is accomplished by quickly rolling off the throttle and shifting without pulling in the clutch.


HTH,
I have pretty good luck with clutchless upshifting on my K12RS but not on my R11R. Any idea why?
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post #7 of 27 (permalink) Old May 7th, 2006, 6:45 pm
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Yes.. it will damage your bike if done improperly.. any bike.. and don't listen to those advocating it...They are in need of meds. ;-)

Bottom line... the clutch is there for a reason.. VERY smart enginneers designed it to be used for shifting ... why on earth would anyone choose NOT to use it when it's virtually an effortless, no-brainer action??.. You'll NOT be any faster...or smoother.. or sexier.. racers don't do it.. Sure you'll be able to brag to your friends that you don't need no stinkin clutch.. the smart ones will think you are a moron.. the uninformed mght think you are cool..

I'm baffled every time this comes up...

Just my opinion, but it oughta be yours.. "Shift with the force, Luke"

and that's all I've got to say about that..

Jerry D. Finley ("Danger" is my middle name)
"I speed, therefore I am. "

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post #8 of 27 (permalink) Old May 7th, 2006, 6:50 pm
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I have clutchless shifted for years up and DOWN!. 6th to 1st
I also will use the clutch. depends how I feel.
But you will get better performance with-out the clutch. "faster shifts"
I spoke to my BMW mechanic about this and he said " tranny is built like a rock crusher, I won't hurt it"

I also have a big rig with a 600HP eng. and 15 speed trans. I NEVER use the clutch up or down shifting.
You can not speed shift!! Big truck transmissions don't have Synchromesh gears.

When the engine reachs the top RPM say 2,000 you fully lift of the throttle and wait for the engine to lower it's RPM so that when you shift the trans. it will smoothly go in to the next higher gear. The gears will match up. maybe 300 RPM lower.
It will depend on the Trans gear ratio's. A close ratio Trans. will have 300 Rpms between shifts. A wide ratio may have 500 RPM drop.

Now this is for Advanced Truck Drivers Only. You know that big trucks have engine brakes right? No, Ok
It changes the engine into an air compressor, so it will slow down the truck. On big engines it can make 600 HP for braking. That's the BDDDDDUUU noise you hear when some trucks slow down.

So, you can use this engine brake to slow the engine down faster so you can shift faster.
NOW YOU Know how to speed shift a big rig!!!

HAPPY MOTORING
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post #9 of 27 (permalink) Old May 7th, 2006, 7:07 pm
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Transmissions with straight-cut gears will shift themselves when you pre-load the shifter and simply release the throttle for a split-second. The K1200RS will do it. You don't have to pull the shifter, just pre-load it. The transmission simply changes gears the moment you unload the tranny (by releasing the throttle). Race car transmissions are built this way and racers use clutchless shifts all the time.

Bill

'04 K1200RS Alpine White/Orient Blue
'05 R1200GS Red
'07 KTM 950 Super Enduro
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post #10 of 27 (permalink) Old May 7th, 2006, 7:30 pm
 
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Quote:
Originally Posted by Pirate
racers don't do it..
We'll need to let Kevin Schwantz know this. He is still teaching it at his Road Atlanta school.
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