Honda CBR250R Forum : Honda CBR 250 Forums - View Single Post - How FAST can you go?
View Single Post
post #186 of Old 06-21-2012, 12:44 PM
Senior Member
TX_Dj's Avatar
Join Date: May 2012
Location: USA, Texas, Plano
Posts: 1,726
Thanks: 1,001
Thanked 603 Times in 348 Posts
Originally Posted by Rusty Shackleford View Post
I don't know how you guys get anywhere near 90 MPH unless your rolling out 4th and 5th gear really far.


Now keep in mind I'm talking about 6th gear roll on, which stops climbing just about at peak power.
Mechanical advantage is exactly that... advantage. 6th gear is overdrive, it's actually a disadvantage, the transmission input shaft is turning slower than the output shaft.

Now, theoretically, it should not matter which gear you "roll on" (wasn't that a type of deodorant that became less popular years ago? LOL) it should still eventually get there...

But... (posting this again)

This is the chart (stock gearing assumed) I made a few days ago showing what the torque drop/advantage is for each upshift, if the shift is made at a certain RPM.

Theoretically, if you take this bike all the way to redline, you gain a large torque advantage, but that's because the torque drops off rather rapidly at the higher RPM, and the ratios throw you back into the nice flat "sweet spot" of the torque band.

If you shift out most every gear at 8000+ RPM, you gain an advantage in torque (rather than losing torque in the shift).

The bike may only aspire to be a true sport bike, but the engine is designed to be taken up to and kept within the power band.

But, every bike, every rider is different. Depending on your "profile", you'll create more drag. Depending on your weight, it will be harder or easier to pull you up to speed. Depending on your tire inflation/choice, you'll have different rolling resistance. Depending on how well your machine was broken in (that is, how well the piston rings sealed) will determine how much of the compression stroke and power stroke stay confined within the cylinder while the valves are closed. Likewise, any slight tightness to the valve clearances (that is to say, the valves to not close completely) will also rob you of power. Too much oil, windage losses come into play. How well lubed and adjusted your chain is, this also comes into play.

This is why racing is technical... and why I love 250's... every minor thing can be a major setback down the road, you have to give the bike TLC in maintenance, and treat it the way it needs to be treated in order to squeeze every last ounce of power out of it for the advantage.

"I'm No Expert"
Motoring on two wheels since 1983

"This old engine has a nickels-and-dimes sound to it. As if there were a lot of loose change flying around inside. Sounds awful, but it's just normal valve clatter. Once you get used to that sound and learn to expect it, you automatically hear any difference. If you don't hear any, that's good." -- Zen and the Art of Motorcycle Maintenance
TX_Dj is offline  
For the best viewing experience please update your browser to Google Chrome