Quote Originally Posted by barnone View Post
I don't know how you can say the size of the 13 tooth front sprocket is way too small when the size of the front sprocket by it self means nothing. It is the combination of the two sprockets that matters.
I'm running a 13/30 right now on my 2012 DF with a top speed of about 65 MPH indicated at about 7k RPM now that I have an air filter that flows enough air to stop the cutting out. BTW, I am sitting upright and not tucked under.

Maybe you should start a different thread for the DF250RTC-B which looks like a neat bike. Also send an email to the seller to correct the 250cc to 229cc in their ad.
It's a common error for those engines...
I guess they're meeting the emission standards for a 250cc engine, but not for the 229cc.

Concerning the gear ratio, you're still 1000RPM above the optimal setting, meaning for every 200-300cc bike, there's an optimal 100:1 RPM over MPH ratio, meaning at 60MPH you should be doing 6k RPM, not 7K. That way you can go another 5MPH faster.
Your gear ratio is about the same as my 150cc scooter with CVT, and that one accelerates like a beast, and also tops out at 62MPH. I can only imagine with 1/3rd more cc's! (CVT eats upto 10% of power compared to geared bike).
I'm saying the front sprocket is too small, because it is. You can't go much lower on the rear without having the chain eat up the rear fork. You need to increase the front if you want to make your ratio a bit higher.

From the numbers you told me, optimal gear setting for your bike (best acceleration/MPG/top speed) would be a 15/31 sprocket setup. 15/30 is bad because of the rear sprocket teeth being a multiplier of the front sprocket teeth, causing uneven tooth wear.
It would drop RPM from 7k to 6k, which is a lot better for the engine.

If I would have geared your bike, from the numbers I see, I would have equipped it with a 17/30 setup. It would not be a dragster, but it would be rideable in traffic, accelerate just fine, do 5,5k RPM at top speed, perhaps suffer some top speed, but it would be in the 110-125MPG range.

But should I sell that bike as a dealer, I would equip it with a 17/36T setup, which is about the same as a 15/31 or a 13/27.5T (yeah, just between 27 and 28T on the rear)
With that sprocket you'll not only lower RPM, and increase MPG, but you hit top speed right in the torque band, allowing you to go even faster (at least 5MPH faster, perhaps 70-72MPH tops).

No wonder top speed figures didn't make sense to me!

I can't believe they actually equipped those bikes with a 13/41 (or 13/43 for the RTD, which is a rebel type) stock.
I don't know what front sprocket the RTC series have, but the RTC racing bike has a 46-48T rear sprocket, which is just insane, but at least it has a lot of room for improvement on the rear!