I installed a SpeedoDRD from 12 O'Clock Labs to correct the highly 'optimistic' reading from the speedometer of my Zongshen RX3.
I like this speedometer corrector very much, and I am pleased I purchased it.
If you like, you can read my installation thread at the following link.
http://www.chinariders.net/showthread.php?t=14756
__________________
Spud
"Never argue with an idiot. He will drag you down to his level, and beat you with experience."
Mark Twain
2015 Zongshen ZS250GY-3 (RX3)
2006 Zongshen ZS200GY-2 (Sierra 200)
2005 Honda XR650L
2004 Honda CRF250X
1998 Kawasaki KDX220
Mods made to my Zongshen ZS200GY-2:
http://www.chinariders.net/showthread.php?t=6894