Ive searched all over the interweb and couldn't find the specific answer i was looking for. so here goes. i plan on putting a 15T front sprocket and 44T rear on my (2012) Ninja 250 because i want to lower highway rpms. i know the 15T is a good choice from what Ive read, but im not sure what size to go with on the rear. if anyone has a better combo to reduce highway (70-80mph) rpms, let me know
Most find that a 15/41 or 15/42 set up is better for what you want to do. You still maintain low end acceleration and reduce top end rpms and better top speed.
With a 15/41 setup, 7.5k rpm will get you approx 72 mph(actual), 75 mph (indicated) in 6th gear. Make sure you shim the needles & remove the snorkel as it makes the bike ride better with the sprocket change.
Blue, its been some time, and i have changed out my sprockets, im running a 15/42 setup. being that i am an idiot when it comes to mechanical stuff, what is shimming the needles and removing the snorkel...what is the purpose and why does it make the bike "better"
Simply put, shimming the carb needles allows a little more fuel in the midrange and removing the snorkel allows a little more air throughout the range. All this equals a little boost and power to the bike, especially in the midrange rpms (7-10k). It also smooths out the acceleration, in other words it will get rid of that flat spot @ 7-7.5k that might be happening in 6th gear.