Shift Point: Peak HP vs Redline - Honda CBR250R Forum : Honda CBR 250 Forums
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post #1 of 51 Old 05-09-2012, 08:49 AM Thread Starter
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Shift Point: Peak HP vs Redline

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?

C'mon, sko sko sko!
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post #2 of 51 Old 05-09-2012, 09:09 AM
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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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post #3 of 51 Old 05-09-2012, 09:09 AM
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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

Last edited by jkv357; 05-17-2012 at 12:51 PM.
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post #4 of 51 Old 05-09-2012, 09:25 AM Thread Starter
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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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post #5 of 51 Old 05-09-2012, 09:31 AM
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Peak power for performance.

Redline/bouncing off the limiter for fun.

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post #6 of 51 Old 05-09-2012, 09:34 AM
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I have my bike for fun, so never really got into it, but I read that for performance you should change when it hits around 8500rpm.

Don't quote me on that though.
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post #7 of 51 Old 05-09-2012, 09:38 AM Thread Starter
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Quote:
Originally Posted by Redline View Post
...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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post #8 of 51 Old 05-09-2012, 09:44 AM
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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.




Last edited by Aufitt; 05-09-2012 at 09:48 AM.
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post #9 of 51 Old 05-10-2012, 09:11 AM
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Garage
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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post #10 of 51 Old 05-10-2012, 09:26 AM
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Here's my Dyno sheet. I shift at 8-8300


2011 CBR250R, Modded 84 honda spree, 2013 CBR500R 2014 Grom


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