Dragon Chopper (3/4 chopper)

[Kingdiamond20]

Here’s an update I tested the bike today with the new 17T drive sprocket and bad news the top end speed did not change. What do I need to do from here?

[culcune]

You probably didn't realize it, but your RPMs were probably a bit lower. That happens with some members on dual-sports and rear sprockets; they don't get higher top speed, but the bike cruises without all the vibration and the engine at redline. The next step is rear sprocket.

[Kingdiamond20]

Where would I look for the rear sprocket??

[franque]

Get dimensions, then send an email with the dimensions to JT sprockets' website.

[Kingdiamond20]

What dimensions do I need to get I need to know specifics

[franque]

Look at this photo so you have an idea of what measurements are needed:



You want to know the diameter of the inner hole on the sprocket as it mounts to the hub, the diameter of mounting bolts, and the diameter of the circle that the bolts form as they're mounted. The picture's pretty self-explanatory, the last measurement is analogous to the bolt pattern used on wheels. Also, metric is king, if you don't have some calipers, get some cheap harbor freight plastic ones.

[JerryHawk250]

Not sure but i think your sprocket will be the same as on mu X22R from looking at the pictures. See if the dimenision match up with the JTR242 If it does then you will need to have one
custom made as the JTR242 only comes in 50 and 53 tooth. I provided a link earlier on where to order from.

[Megadan]

So I did a little math with various sprockets and the 205/40-14 rear tire.

All figures are the mechanical speed at 8000rpm in 5th gear and a 17 tooth front sprocket.

50 rear = 52mph
45 rear = 58mph
40 rear = 65mph

Just for comparison sake, a stock Hawk 15 front 50 rear and 110/100-18 tire has a mechanical top speed of 67mph at 8000rpm in 5th gear.

To match a 17 front 50 rear on a Hawk this bike would need to run a 34 tooth rear sprocket.

That combination would likely give a realistic top speed of around 65mph. That 14 inch rear tire is just too small to effectively gear very high.

[Kingdiamond20]

I’m actually not hitting 50mph after I installed that 17T drive sprocket, I’m hitting about 47-48 top speed now. Why did my top end speed decrease??

[franque]

Is your top speed GPS verified, or is it by the gauge? Also, do you have a tachometer, is it revving as high as it was? How is your clutch adjustment, is it slipping, are your brakes dragging? There's about a million variables in play, I'd verify all of those.

[Kingdiamond20]

Top speed is gauge, I have no tach, yes it’s revving about the same, an no slipping , brakes are not dragging

[franque]

Chinese speedometers are notoriously inaccurate. I would verify with a GPS. Having a lower top speed is physically impossible for the same RPM with the changes you've made (as your top speed isn't limited by HP), short of something slipping in a way, some of the ways having been mentioned. I would verify clutch adjustment and make 100% certain that it's not slipping.

[Kingdiamond20]

Ok

[Kingdiamond20]

How notorious would you say?

[franque]

They're all inaccurate. Without using a GPS, your readings are effectively useless.