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Chuey wrote:Are you asking why we don't double clutch the bikes?

Chuey

No, not really. Up-shifts in sequentially shifted race car boxes are simply cluthless, downshifts mandated a clutch and matching (or coming close) the speed of the motor and the drive-train by heel and toe technique (as is mentioned, "blipping the throttle") to select each lower gear.

I am truly only aware of having to actually "double-clutch" transmissions that are not sequential, both straight cut (think a semi tractor) or a synchronized box that has no synchronizers left. I do not know how you would double clutch a sequential as you need a neutral to truly do it.

1) Clutch in.
2) Select neutral.
3) Clutch out.
4) Hit the gas (optional; depends on why you are doing it and in what; may not be needed in a broken synchronized transmission...)
5) Clutch in.
6) Downshift.

This would truly be double-clutching. Ask any trucker, they know all about it.

robtg wrote: When upshifting or downshifting you , with the throttle, you match the speed of the input shaft with the output shaft of the gearbox to allow the shift dogs to slide together without trauma.
Trying to understand your question is difficult because of all the extra wording getting in the way.

No, you don't match the speeds on upshifts to speak of really, only when the dogs hammer themselves together. Yeah, they are matched when you hear the "big-bang" but I know the engines were never paused in the least for the 3-4,000 RPM you dropped on an up-shift. Grab, preload, burp-engine -> ram into gear. It only takes "slack" in the drive train on upshifts. That is why the electronic shifters work so well. They simply shut the spark down for a few cycles to allow for the slack; its mere milliseconds... This is called "shift-no-lift" and you don't lift in the least. We could do it by setting the rev-limiter and yanking the lever when the engine choked...

Apparently it was not wordy enough if the majority of the posts here keep telling me why not to do it. That was never the question at all. (Everyone must have gotten tired of reading before the end...)

Perhaps the design difference I don't see is the answer - there is not much of a difference.

I suppose if one operated these bikes in this manner, you might expect the transmission to last 3 or 4 thousand miles before failure? Not too good for street use, but that is likely the top end before something was out of spec and needed replacement on the competition boxes.

I still don't understand why we don't HAVE TO spin the transmissions up on downshifts, but it would appear no one else does either...

I believe, the only difference that could make such things necessary on the car and not on the motorcycle would be the size and inertia of the components.

dougie wrote:

Zombie Master wrote: Could you explain non sequential shifting please?

Non-sequential shifting cannot be done with a sequential gearbox. To shift from 1st to 4th you must shift through 2nd and 3rd (and vice versa). The basic manual gearbox in cars can go from any gear to any other gear. World Rally Championship cars, F1 cars, shift sequentially, as do passenger cars with paddle shifters.

Zombie Master wrote: Can't understand why guys want try and go fast on these old Merecedes like bikes.

Not "go fast" ZM.
"A rather brisk pace."

Always a brisk pace indeed! Airheads were designed to run continuously near their red line. I like to use machinery the way they were designed to be used!

Major Softie wrote:I believe, the only difference that could make such things necessary on the car and not on the motorcycle would be the size and inertia of the components.

Pretty good thinking; far too obvious a notion for me to have entertained prior to asking. Indeed, this could be "it" for the designs really differ little.

I have only once performed such a threshold stop type deal as I would in a high performance car and likely could not tell you if I ground the box kicking it through the gears as I was slumped over the bars so far that my head nearly was hitting the front fender... (Don't let anyone tell you these [or any for that matter...] drum brakes are inadequate!)

I know as well, if anyone asked me to hit every stop on a bike as one would on a track in a four-wheeler - with the tires rotating slightly slower than the pavement, it would not take me long to crash.

Thanks for posting Major.

Zombie Master wrote:Always a brisk pace indeed! Airheads were designed to run continuously near their red line. I like to use machinery the way they were designed to be used!

I remember (1971?) picking up a VW Super Beetle at the factory in Germany (European delivery plan).
I asked the technician what was the top speed? He said "81 mph".
I asked the technician what was the cruising speed? He said "81 mph".
All boxers are good boxers!

Of course, you have to spin the engine up to match when dropping down on the tranny. It is not science to match these two gears to allow the gears to MESH.. without a crash.. but it takes practice and experience. (still never easy or without mechanical stress)

So the question is how many times can you miss before the tranny gives up and say's, "NO More."

If you think machinery is expendable.. then do this over and over.

I like the clutch lever.
jim , Ketchikan

gertiektn wrote:Of course, you have to spin the engine up to match when dropping down on the tranny. It is not science to match these two gears to allow the gears to MESH..

I would guess if you polled a bunch of riders, the majority of them (not simply "us here" - BMW fanatics...) would tell you they don't race the engine up to match on downshifts like heel and toe down shifting in a race car.

Thanks, but you "don't get it..."

With the industrial "racing types" it was not just "mechanically friendly" to spin them up on downshifts, like an 18-wheeler's transmission, it is required. Without doing so, such transmissions don't merely "clunk" or wear out more quickly, they SIMPLY DO NOT GO INTO GEAR AT ALL - JUST GRIND, GRIND, GRIND and the sequentially shifted type will stay in the "false neutral" between gears...

Have you never heard a semi downshifting for a hill before??? They don't spin them up for the fun of it, or to make the transmission last, as mentioned above, one must; the question was, why is it not necessary on our BMW transmissions? I thought it possible the ability to freely shift up without a clutch might likely be related to the notion that with such a system, one MUST spin it up to go down (in gear ratio.)

It is unclear if they are related, but I see no one either knows the answer beyond any doubt, nor have most really read what is here. One thoughtful post of the lot of them - possible cause, higher spinning (transmission) inertia as well as traveling inertia of said vehicle (car vs motorcycle) hence more loading from the output end on deceleration.

gertiektn wrote:If you think machinery is expendable.. then do this over and over.

Can I say "never-mind" now???

Incidentally, since you did not notice and apparently don't already know, the downshifts for which I speak of ONE USES THE CLUTCH AND STILL MUST SPIN UP THE TRANSMISSION. Only up-shifts were performed "sans-clutch."

I think the reason we can down shift our airhead transmissioms without very close matching of engine rpm, is the size of the holes the shift dogs engage to lock the respective gears to their shafts. The holes are close to one and one half times the width of the dogs that slides into the holes to engage the gear. There are four dogs and four holes so it is a pretty coarse situation compared to the spacing on synchronizers. Any crashing/grinding heard from an airhead trans is the dogs banging the edges of the holes, not the gear teeth themselves. The dogs will and do break off of the slider that moves between the meshed gears as we shift.