need gearing help!!

[caliking]

hello there new to the thread, I have owned my fair share of bikes and due to finances a 2009 ninja 250 is what I found for what I had at the time, I spend a lot of time on long flat straight roads where I live and am looking to get the RPM's down a little while holding speed or greater , right now at 80 im at 9,200 rpm's, I want to try to bring it down to atleast 7k or less, on my big bikes for wheelies I mess with the sprockets down in the front for more torque, so for more top end you would go up but will this help rpms or just top end, if that makes sence.......please help

[Alex]

/moved to new-gen tech

[Alex]

Here's a decent thread that covers this:

https://www.ninjette.org/forums/showthread.php?t=57813

You can use the www.gearingcommander.com site to play with the sprocket ratios and estimate the effects.

[Yakaru]

You can do a front and rear sprocket swap to lower your RPMs, but you'll start to bog the engine/lose acceleration really fast if you want big decreases while cruising of the type you describe.

Take a look at this: https://www.ninjette.org/wiki/Sprock..._Chain_Options

But the Ninjette is designed as a high revving engine -- many people here run them at 10k all day every day and the engine has no issue with it. I'd say maybe do one step in each direction on the front and rear and just ride it at whatever RPM range the bike ends up with after that.

Edit: addendum -- Generally dropping below (and I'm going from memories over a year old here) 6k RPMs is where things start to bog down -- just as a point of reference for just how high revving the 250 is.

[DaBlue1]

Originally Posted by caliking

....I spend a lot of time on long flat straight roads where I live and am looking to get the RPM's down a little while holding speed or greater , right now at 80 im at 9,200 rpm's, I want to try to bring it down to at least 7k or less, ...

The Ninja 250 lacks much torque so don't expect any big changes there by just changing sprockets. However, the Ninja does rev high enough and has enough HP to make proper use of most sprocket changes, especially when you want to reduce your Hwy RPM speed even further. 80 mph @ 9,200 rpms would indicate you already have a 15 tooth front sprocket.

The some modest modifications (shimming, plugs, oil, snorkel delete) you can effectively reduce your RPM speed and still have enough decent power and torque for city and hwy use.

Those who ride freeway like to reduce the RPM speed as much as possible and still be able to have passing power in the top gear if need be. As a frequent Hwy rider I use 15/41 and still outpace most traffic easy. I weigh about 235 fully loaded.

15/41 @ 8k = 76.3 mph in 6th gear
15/42 @ 8k = 74.5 mph in 6th gear
15/43 @ 8k = 72.8 mph in 6th gear
15/44 @ 8k = 71.1 mph in 6th gear
15/45 @ 8k = 69.6 mph in 6th gear

Some have used a 15/38 setup because they long flat ride hwys frequently, however the downside is there is a great reduction of power available in 6th gear, the bikes engine will not go past 10.5k in 6th, the chain length needs to be reduced, low end torque decreases and downshifts become the norm when going up inclines
Although the 38 tooth rear sprocket is the smallest rear sprocket recommended for the bike, it still not get you to your target of 7k rpms or less for cruising @ 80 mph.

[InvisiBill]

http://gearingcommander.com/ will quickly show the math for playing around with different sprockets.

[rojoracing53]

God forbid you ever hit a headwind. I run 15-41 and that's tall enough that in my last two long distance trips I spent a lot of time in 4th and 5th just to do the speed limit because it got really windy. There's nothing wrong with me running 4th or 5th gear, hell my 4th is almost as tall as 6th with stock gearing so when I'm stuck in 4th I'd be no differnt then someone else using 6th.