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Old 04-08-2010, 11:18 PM   #1
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Question Calculating shift point

What variables are necessary to calculate how to make an ideal clutchless shift? (bike or car)

Is engine speed (RPM), wheel speed (speedometer) and gear ratio enough?

What is the equation?

for example - shifting from 3rd gear to 4th gear on my bike what should my RPM and speedo indicate to allow for the "ideal" clutchless shift?

Thanks!
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Old 04-08-2010, 11:50 PM   #2
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Mechanically you can shift at any point. To get maximum drive at the rear wheel, shift at the point where the calculated driving force applied to the rear wheel in the next gear becomes greater that what it is in the current gear based on the torque/horspower curve for your engine. Engine power multiplied by the total gear ratio working on the rear wheel.

Torque is more important in lower gears and hp is more important in higher gears.

http://www.sportrider.com/tech/146_0402_art/index.html
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Old 04-09-2010, 07:11 AM   #3
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Quote:
Originally Posted by bioGuru View Post
What variables are necessary to calculate how to make an ideal clutchless shift? (bike or car)

Is engine speed (RPM), wheel speed (speedometer) and gear ratio enough?

What is the equation?

for example - shifting from 3rd gear to 4th gear on my bike what should my RPM and speedo indicate to allow for the "ideal" clutchless shift?

Thanks!
Define "ideal"
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Old 04-09-2010, 08:11 AM   #4
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Quote:
Originally Posted by Dave C View Post
i dont know the specifics but i know when shifting clutchless will be rough or very smooth... so i stick to when it's smooth. seems like lower rpms on my bike and its only when i'm cruising and too lazy to put my hand on the clutch since my hand is on my hip leg ... go ahead and judge me its okay i wont get upset
+1. Never really understood the point of clutchless shifting on the street (unless, like you, I'm just being lazy at the moment).
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Old 04-09-2010, 08:22 AM   #5
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Quote:
Originally Posted by Challen View Post
+1. Never really understood the point of clutchless shifting on the street (unless, like you, I'm just being lazy at the moment).
Extends the life of your clutch cable (if you have one )
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Old 04-09-2010, 08:22 AM   #6
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Quote:
Originally Posted by Dave C View Post
i dont know the specifics but i know when shifting clutchless will be rough or very smooth... so i stick to when it's smooth. seems like lower rpms on my bike and its only when i'm cruising and too lazy to put my hand on the clutch since my hand is on my hip leg ... go ahead and judge me its okay i wont get upset
actually dave, on our 650's i find clutchless upshifting to be way smoother at higher RPM's. i clutch up from 1st to 2nd, then clutchless from there. like i said higher RPM's, so if i'm going slow i use the clutch. at the track its clutchless all the way ('cept from 1st to 2nd again). just put some pressure on the shift lever, then let off the gas for a split second so it can shift, then back on the gas!

i always us the clutch for downshifts though.
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Old 04-09-2010, 10:05 AM   #7
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Quote:
Originally Posted by Challen View Post
+1. Never really understood the point of clutchless shifting on the street (unless, like you, I'm just being lazy at the moment).
It is really more a theoretical geeky/nerdy mathematical question than an applied question.

In theory one should be able to make every shift without the clutch if the speeds of the transmission and gears (or engine side vs. wheel side if you like) are matched exactly. So there should be a formula to determine how to match those.

The ideal shift for the purposes of this discussion is one that minimizes the strain on the entire drive train.
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Old 04-09-2010, 10:13 AM   #8
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Quote:
Originally Posted by bioGuru View Post

The ideal shift for the purposes of this discussion is one that minimizes the strain on the entire drive train.
I think that would be more about load than RPMs or wheel speed
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Old 04-09-2010, 10:19 AM   #9
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Quote:
Originally Posted by Bevo View Post
I think that would be more about load than RPMs or wheel speed
Minimize the strain on the drive train during the shift.

Maintaining a consistent load will minimize the strain. A bad shift even at low speeds/RPMs will strain the drive train more than a smooth shift at higher speeds.
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Old 04-09-2010, 10:39 AM   #10
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Quote:
Originally Posted by bioGuru View Post
Minimize the strain on the drive train during the shift.

Maintaining a consistent load will minimize the strain. A bad shift even at low speeds/RPMs will strain the drive train more than a smooth shift at higher speeds.
I don't think so. I am pretty sure you want to drop the load. As was stated apply pressure on the shifter and cut the throttle momentarily. This allows the friction forces keeping it in one gear to reduce and it will shift. This is how the pressure sensitive auto shift devices work. They read your pressure on the shifter and cut of the injectors to cut power and then reapply when the gear has shifted. This is faster than hand control. My .02 could be totally wrong, so don't hold me to it.

Also the RPMs of one gear to the next is a set ratio no mater what RPM the engine is cranking. The only optimization would be for power delivery and engine brake efficiency (how the load cut off takes effect on the tranny).
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