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Discussion Starter #1
Since we don't have a "physics" forum, I'm assuming "performance" is the best place to put this. BTW, I'm aware this has been posted on other forums on the web, but there's the typical mixed responses, and none of them apply to our bikes, which have a different weight, are built for a different purpose, etc. In any event, Here's the question: Which of the two practices below do you do when you need/want to lay into the CBR250R? If both, then under which conditions? If neither, no response is necessary.

1. Some people shift at redline. The perceived pro/con is...
PRO: Takes advantage of gearing.
CON: Up-shifts into downward slope of the power band.

2. Some people shift right after peak horsepower. The perceived pro/con is...
PRO: Up-shifts into an RPM range straddling the peak of the power band.
CON: Loses gearing advantage by shifting into a taller gear.

Thoughts?
 

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If Im really trying to get on it, Ill typically shift right before redline, 9-10k area. Try and take advantage of as much gear without sloping off of the powerband too much.
 

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#2 is closest.

EDIT: Based on an engine dyno curve alone, #2 may be correct, but if you factor-in the transmission (as you should...) things change. Allen pointed this out in post#22 and added an informative link with more info.

Redline is only the safe max the engine can spin at for any length of time, and doesn't tell you anything about where your peak power is.

BTW - optimum shift point is different for every gear.

Some more info - Shift Points - Sport Rider


Jay
 

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Discussion Starter #4
I tend to shift straddling the power-band peak as well, so at about 9k. I really didn't see a point in taking advantage of gearing to rev faster into what, declining torque/horsepower and putting unnecessary stress on the engine? Whenever I need the power, it's for passing or re-accelerating while already moving, so there's not exactly that drag-race momentum going either.
 

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Discussion Starter #7
...for performance you should change when it hits around 8500rpm.

Don't quote me on that though. :)
Pun intended ;) Anyhow, 8,500 is about peak HP, so I can see that being about right. I choose increasing power over gearing torque as well. In real-world driving it's necessary to fluctuate in how much throttle is applied to compensate for traffic. Most of my navigating the upper RPMs is for staying out of dangerous spots on the interstate. Riding in someone's blind spot on a bike gives me the heebiest of jeebies.
 

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All depends upon the load you will be dumping on the next gear, ie uphill/downhill, sweeping corner, setting up for a series of corners etc.
With the std gearing so high and the gaps between the gears so big with such little power sometimes have to run it all the way to the limiter (which is 10,800 I think?)

However If I was having a flat straight road drag with someone, I would not look at the tacho and just go by feel. 9500-10000 seems good, any less and you bog, any more is a waste.

It will drop about 1500 into the next gear so you want that in the fat part of the powerband which is about 8-8500.
 

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Shift point calculator based on eyeballing a 250R dyno chart says the best hp area under curve shift point is just before redline for all shifts.

1->2 @ 10497 (to 6670)
2->3 @ 10497 (to 7785)
3->4 @ 10350 (to 8595)
4->5 @ 10408 (to 8900)
5->6 @ 10405 (to 8985)

Don't have real dyno data to go on though, just had to measure on a chart and take a guess.

Shift points for HP matching in corners and whatnot are 10308, 9843, 9032, 8946, 8917.
 

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Do you have the actual data that generated that chart in a CSV or something? Would make it easier to come up with shift points that aren't just approximate guesses.. ;)

Shifting that low isn't going to hurt anything, but if you're going for maximum acceleration, wait longer. Shifting at 8 is dropping you down around 6 or so in the next gear, so you're spending a lot of time making under 20hp that you don't need to.
 

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i love the sound of the bike after 8000 rpm so usually i shift around 10,000 rpm.
But i think shifting at 9000 rpm is the best
 

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I shift when the engine goes crazy and to get it go smoothly. Noticed that I shift at around 8000 rpm in the first three gears and at even lower rpms in higher gears.
 

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This engine loves revs!

I think we have to beware of inertia dyno graphs. These tend to look unstable at high r.p.m. but when you ride the bike on the road the revs will happily creep over 9000 and approach 9500 on a level road. Unfortunately because the spacing between 5th and 6th is too big you can be at 9500 in 5th on a hill or into a headwind but changing up will slow the bike down because the revs drop to just over 8000 and it falls out of the power band.

By the way my rev counter over reads by 200-300 rpm across the range so I'm actually talking about indicated rpm.

I enjoy the challenge of getting the most out of a small engine so I tend to use 9500 when conditions allow.

Regards Roadster
 

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I shift when the engine goes crazy and to get it go smoothly. Noticed that I shift at around 8000 rpm in the first three gears and at even lower rpms in higher gears.
If you're just having fun on the street, the lower gears are seemingly so narrow and the higher gears so widely apart that plus the output of the engine and what you're describing seems like a natural tendency.

It wants to wind up fast on the lower gears...and I'm a sucker so I happily oblige.
 

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When I want to blast it I noticed I shift at 9000 rpm just off of feel. 9-10k shift doesnt feel right for max acceleration. Seems like others feel the same way.
 

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getting on to highway I max it out 9500 to 10000. in the city or blasting around I take it as it comes anywhere around 8000 to 10000. engine sounds like crap below 7000 anyway so I let her sing.
 

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When I want to blast it I noticed I shift at 9000 rpm just off of feel. 9-10k shift doesnt feel right for max acceleration. Seems like others feel the same way.
How it feels is subjective. The math isn't, and neither would an accelerometer, g-tech, or other such device. Unless you've significantly modded your bike, fastest acceleration is achieved by shifting @ redline.
 
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