New to the forum, I apologize if this is not the right place for this thread. I recently purchased a 02 CBR600 F4i from a private seller. He had a number of mods on the bike including a leo vince exhaust, custom headlights, and near gear ratio. After riding I find that I am only getting about 90 miles per tank at best and my speedo is always off by alot, at 30mph it shows 41mph, at 70mph it reads 95mph!! I checked the FPR, air filter, plugs, tire pressure, everything looks good. So I'm guessing the new gear ratio is causing this? The rear sprocket is quite large 54T, not sure what the front sprocket is? Will going back to stock sprockets help? Any other suggestions? Thanks

 

Sounds like your bike is running fine, the problem is definitely the sprocket. Any sprocket change will affect how the bike reads miles. When I went -1/+1 mine was reading an extra .1 miles per 10 I actually rode. So basically you're not actually getting 20 mpg the odometer needs to be recalibrated with a speedohealer or speedoDRD. That being said a ridiculous rear sprocket like that will still cause you to get worse mileage than you will with a stock set up.

 

Using the Gearing Commander website (very useful, definitely check it out) I found that the stock rear sprocket for an '02 F4i (same as my bike) is 46T so if yours if 54T that is quite a difference.

Also on the website it says that if, in fact, your front sprocket is stock (16T), that to go true 70 with that sprocket combination you would be turning about 6900 RPMs, which would definitely eat up gas faster. But I'm not sure if it would be THAT much faster... So maybe the front is even down a tooth???

Does the bike seem to want to pull the front wheel off the ground a little TOO easy? I wonder if it was set up for some sort of stunting or wheelie'ing...

Either way, I know at a -1/+2, where my bike is now, I use more gas than I want... (about 32 mpg) I have already ordered my OEM sprocket and chain set to go back to stock... which was claimed to be around 44mpg I think.

So hopefully there is some useful info in there somewhere for you. Good luck getting things set up to your taste, now that she's your bike Welcome to CBRs and to the Forum...

 

Thanks for the warm welcome and the advice, that kinda confirms what I suspected. Just wanted to make sure I wasn't missing something?? Yea the guy I purchased it from said he put the larger sprocket on the back so he could get more low end torque. The acceleration is great, but I'd rather have better gas mileage. I contacted my local repair shop and they said it will cost about $250 for the parts and labor to put the stock sprockets and chain back on the bike. I'll probably do that. Thanks again!

 

If your bike thinks its going alot faster then it is then it hasn't gone the miles its showing when you run out of gas.