I recently bought a LIFAN LF 250 B and I'm really enjoying the ride but it runs out of steam at around 90kpm/55mph. I've checked all the mechanical so my only option is gearing.

Standard the bike comes with 16/45 sprocket set up and what I'm trying to do is perhaps go 17 or 18 on the front sprocket but I'm not sure about back sprocket or where to find the sprockets for front and rear that fit.

Help is much appreciated and if there is an earlier thread on this please direct me to it.

Thanks for the help