GSAP Question

tanneman said:
Yes, this is what happens in a synchromesh. Even though there is no synhromesh in the dog box you still have to match shaft speeds so you either cut ignition or dip the clutch to move up a gear and speed up the input shaft when when going down a gear. By loading the ring gear to the next gear you are trying to match the gears and a momentarily pause in power transmission aids the selection to move the gear over to a new ratio.

The function of a gearbox is to convert the input rpm to either lower or higher output rpm. In the case of motorised vehicles it usually is a lower rpm which has the effect of increasing torque and thus affecting the power output for a given rpm. As confusing as it may sound to some but the gearbox input and output shaft speeds are indeed a product of the engine rpm and reduction ratio of the gear set and has nothing to do with road speed. For shifting gears in a gearbox the shaft speeds are the concern, not road speed.

Technical gobblygook.
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Yes - but input and output shafts link rear wheel rotation and engine rotation speeds via a pair of gears, so at the end of the day engine speed, via an engaged clutch, is locked to road speed via the whole transmission, with the ratio between the two controlled by which pair of gears are engaged.

Change which pair of gears are engaged and you change the ratio, thereby potentially introducing a mismatch between engine speed and road speed. This makes changing ratios difficult, hence technologies like synchromesh to help gears turning at different speeds to engage. However just successfully engaging a different ratio does not eliminate the mismatch, it just moves the problem elsewhere. The mismatch therefore has to be eliminated one way or another, normally by allowing momentary slippage between the clutch plates, otherwise you would have wheelspin, forced clutch slip or something like the drive shaft or gearbox could break.

So, when you change gear, road speed and engine speed cannot both remained unchanged - the mismatch has to be eliminated one way or another. Either your road speed has to change or your engine speed has to change, or a bit of both. By operating the clutch during a gear change you are allowing slippage between the engine and transmission clutch plates until both sides are rotating at the same speed and the clutch can grip again.

If you don't use the clutch, and do nothing else to help equalise engine and transmission/road speeds, then on a downchange due to the new ratio you will get a chirp from the rear tyre as it tries to instantaneously make the engine turn faster to match the unchanged road speed. On an upchange you will get a lurch as what is now an unsuitably high engine speed for the current road speed tries to instantaneously accelerate the bike to a road speed which would match the engine speed.

In other words either the engines tries to make the rear wheel rotate faster, or the rear wheel tries to make the engine spin faster to suit the new ratio between them. GSAP attempts to smooth out clutchless changes by cutting engine torque on up changes to make it easier for the engine speed to drop and so minimise the lurch, and blipping the throttle on downchanges to speed the engine to avoid the rear wheel momentarily under-rotating.

Fred
 
tanneman said:
Yes, this is what happens in a synchromesh. Even though there is no synhromesh in the dog box you still have to match shaft speeds so you either cut ignition or dip the clutch to move up a gear and speed up the input shaft when when going down a gear. By loading the ring gear to the next gear you are trying to match the gears and a momentarily pause in power transmission aids the selection to move the gear over to a new ratio.

The function of a gearbox is to convert the input rpm to either lower or higher output rpm. In the case of motorised vehicles it usually is a lower rpm which has the effect of increasing torque and thus affecting the power output for a given rpm. As confusing as it may sound to some but the gearbox input and output shaft speeds are indeed a product of the engine rpm and reduction ratio of the gear set and has nothing to do with road speed. For shifting gears in a gearbox the shaft speeds are the concern, not road speed.

Technical gobblygook.
Click to expand...

The reason you have to cut ignition or dip the clutch is to unload the dogs, which allows them to disengage. The difference in shaft speeds is taken up by the engine, this is why the revs of the engine change when a gear is changed.
 
Fred and Andrew. I concur. I'm just pointing out the misunderstanding of the technical terms. Road speed is the reference to the speed the centre of the wheel hub moves in any linear direction at a moment in time. In fact the difference in speed between the tyre contact patch and the road surface is 0 because there is no distance travelled by any particular point of contact between the tyre or road surface unless there is slippage or spinning (like locking the wheel or doing a burnout) where Speed = Distance/Time. The effect the rear wheel will have on the clutchless shift (call it that or GSAP) will depend on the radius from the centre of the hub to the contact patch on the road and the final drive ratio. So in effect the bigger the radius the more strain will be on the gear selection. Bla, Bla, Bla, Bla you know what you are talking about. We all say the same thing.

What the f**k you say? you may ask. Yes, the speed is zero at the point of contact between the tyre and tarmac because there is no displacement or a relative distance travelled between these 2 points. Like 2 mates walking toward each other and standing still having a chat and walking off while the earth is rotating. This also means that when that particular point reaches the very top of the rotation of the tyre (180deg from the contact patch) it would be travelling twice as fast as the centre of the axle where it matched the the speed of the axle at a 90deg angle relative to the contact patch. Physics eh? What about the ABS and speed sensors etc. Basically the angular velocity stays the same for the same gear ratio and engine speed unless you change the gear ratio or engine speed. For any point on the tyre circumference (or any object that rotates) there will be a displacement for a given period of time and this is measure in angles. The ABS sensor (position sensors, speed sensors etc) measures the intervals in how often theses angles passes a specific point hence you have a ring with precisely machined gaps and spokes and a magnetic pickup to induce an electrical signal which can then converted to a readout on the speedometer.
 
fred_jb said:
You are only supposed to use it on downshifts with the throttle fully closed, so if you don't it is quite likely to be clunky. I've noticed this myself in the lower gears when you can sometimes get too much engine braking if you close the throttle completely, so I often don't, but GSAP doesn't like that so I tend to only use it down to third.
Click to expand...

The manual says that you can downshift with an open throttle, well my 2018 manual does :)
 
Mr Bean said:
Good luck with that one...
Click to expand...

When I say open I mean held steady but not closed - should work as the the manual says as long as the load is removed from the dogs by the computer subtracting just a smidgen of throttle.
 
Engineer said:
When I say open I mean held steady but not closed - should work as the the manual says as long as the load is removed from the dogs by the computer subtracting just a smidgen of throttle.
Click to expand...

Mine will not work smoothly with any load on the gearbox - unload it and all is well.
 
Engineer said:
I haven’t delved into how this works yet but I have a simple question.

Does the GSAP influence the clutch engagement in anyway on downshifts?
Click to expand...

For someone as technically able and clever as you I would have thought you would have immediately understood how GSAP works. It’s actually very simple and involves electronics.

I don’t think fuses play a part though apart from protecting the whole electronic circuit!
 
tanneman said:
Fred and Andrew. I concur. I'm just pointing out the misunderstanding of the technical terms. Road speed is the reference to the speed the centre of the wheel hub moves in any linear direction at a moment in time. In fact the difference in speed between the tyre contact patch and the road surface is 0 because there is no distance travelled by any particular point of contact between the tyre or road surface unless there is slippage or spinning (like locking the wheel or doing a burnout) where Speed = Distance/Time. The effect the rear wheel will have on the clutchless shift (call it that or GSAP) will depend on the radius from the centre of the hub to the contact patch on the road and the final drive ratio. So in effect the bigger the radius the more strain will be on the gear selection. Bla, Bla, Bla, Bla you know what you are talking about. We all say the same thing.
Click to expand...

OK - strictly speaking maybe I should refer to engine speed (rpm) and rear wheel rotational speed when saying that these are in a fixed relationship for each gear ratio. However in this context road speed is proportional to rear wheel rotational speed, and the wheel radius is not a variable, so I think this is an acceptable and commonly used shorthand.
 
Engineer said:
When I say open I mean held steady but not closed - should work as the the manual says as long as the load is removed from the dogs by the computer subtracting just a smidgen of throttle.
Click to expand...

Does the LC have a slipper clutch, that may offer enough slip when the GSP (isn’t that a dog) unsympathetically drops it down a gear?

Part of the fun of biking is blipping on down changes and the older the bike and the heavier the flywheel the better :D

Just got a manual car after years of auto's - I don’t need to toe&heel, mainly because I’m just going with the flow but when the opportunity arises it’s wonderful to be the person responsible for that mechanical sympathy and maintained balance
 
Think I’ll stick with clutch and manual blipping, it’s by far the most smooth and mechanically sympathetic way to change gear - clutches are cheaper to replace than gearboxes too.
 
Giles will have to take notes.

The future is whatever colour you want.
 
Engineer said:
Think I’ll stick with clutch and manual blipping, it’s by far the most smooth and mechanically sympathetic way to change gear - clutches are cheaper to replace than gearboxes too.
Click to expand...

What a load of old tosh. MY GSAP is seamless and instant. No human hand and foot could make it more mechanically sympathetic........
Utter Tosh !
 
Onahi said:
What a load of old tosh. MY GSAP is seamless and instant. No human hand and foot could make it more mechanically sympathetic........
Utter Tosh !
Click to expand...

At the end of the day if you don't use the clutch to allow some slip between engine and transmission, then the mismatch in their speeds when you change gear has to be absorbed somewhere else in the drivechain, putting more stress on it than when the clutch is used. Maybe those with all the sensitivity and mechanical sympathy of a rhino don't feel a thing, but it is still happening! :)
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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