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Old 08-08-2009, 10:58 PM   #1
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Default Shift Point

At what point do you shift for best accelleration? Should you shift just after your peak horsepower or just after peak torque?
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Old 08-09-2009, 04:32 AM   #2
specialsymbol
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Default

Depends on your engine and gearing.

The best point to shift is when you have in the higher gear more power than in the lower gear. Sounds strange, but some bikes are like that. Some will always have more power in the lower gear, so it's useful to accelerate into the limiter.

Check this out:
I stole those gearing diagrams from Norberts Motorradseiten:

First the one from a Ducati 749 R '04:


As you can see, the lower gears end all well above the higher gears. Higher means more power. That means, you'll always have more power in the lower gear than in the higher one. So it's best to rev it into the limiter (or shortly before) and shift then.

But have a look at the 5th gear: At 242km/h it intersects with the 6th gear line. From that point the 6th gear line is higher than the 5th gear line, that means it has more power. So it's best to shift there into 6th instead of staying in fifth.

Let's have a look at the Kawasaki ZX6-R '05 model (ZX636C):


As you can see all gears except first intersect with the next higher one. That means there's always a point where the next higher gear provides more power than the lower gear. This is the best shifting point. Of course the diagram can only relate to speed and not to RPM, but it's still pretty close to the rev limiter though it's not really obvious.

Let's have a look at the gearing diagram of a '06 Yamaha R1:


Here it's really obvious that there is a point (speed) where it's absolutely useful to shift into a higher gear, beginning from first. At 250km/h you'll even have more power in 6th gear than in 4th!

The point of where to shift is with the higher gears a little bit later than with the lower gears, you can see this by drawing a line through the points where they intersect, it's slightly banked (disregard the intersection between 4th and 6th).

However it's such a slight bank that it's practically the same RPM.

All you have to do is find a gearing table for your bike, calculate your gearing diagram, find the intersection points and recalculate the corresponding RPM- then you'll have the perfect shifting point.

I did this for the 05' ZX6R and found the perfect accelerating range to be between 12800 and 14600 RPM (except for first, where it's rev to the max).
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Last edited by specialsymbol; 08-09-2009 at 04:42 AM.
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