We’re all sick of the repetitive posts asking this question, can someone make this a sticky? Check www.thumperfaq.com for great information, especially on how to “YZ a WR” etc. WR more suited for trails and YZ more suited for track. You can modify either bike to make it more like the other. If you only ride tracks it is a no-brainer to get the YZ. For trail riding a lot of folks prefer the light weight of the YZ, but there are a lot of differences besides just the weight. Here’s the differences, make up your own mind. YZ is 29.3 lbs lighter, as of 2007: more maneuverable, quicker acceleration. That means the WR is 14% heavier than the YZ. WR: Heavier flywheel: slower acceleration, but less likely to stall in tight/technical sections. Many YZ riders put on heavier flywheel or Rekluse clutch for trail/technical riding to compensate. Suspension: set up more for trail riding, not as stiff as YZ. Not as good on track for jumping as YZ, but YZ suspension may be too stiff on trails. Either one will do the other job OK, but are set up to be best at what they are made for. Overflow for radiator: Saves rad fluid if you overheat on slow/technical trails. Radiators themselves are same size (same part # for ’05 models at any rate). On YZ the fluid will be dumped on the ground and lost if you overheat. Overheating not much of an issue on tracks. 18” Rear wheel: thicker rubber for better shock absorption on rocks/roots, less likely to get pinch flats (YZ has 19” rim, but same outer diameter of tire). Somewhat heavier which would slow down acceleration (similar to heavy flywheel). I think it would also give a bigger contact patch if you are running low air pressure in sand etc. (more flex in the tire). Motor: WR is detuned in stock form, but basically identical once you do the free mods. The cam timing on the YZ is a little different (different part #’s for YZ v. WR exhaust cam as of 2005). Supposedly it is intentional on the WR to make the motor “hit” a little less hard so you are less likely to break traction when you don’t want to (same with the grey wire in the “free mods” Exhaust: WR comes with more restrictive exhaust to make it quieter. Can be uncorked (see free mods) or replaced with a YZ can for more power. YZ exhaust does not have spark arrestor and is ILLEGAL on most national forest land, so a YZ would need a new exhaust or spark arrestor insert for trail riding. E-START: Man this is huge. If you stall out on some crazy hill climb or in a precarious position, the e-start is a god-send. 4-strokes harder to re-start after you drop them (which you’re more likely to do on trails) and the e-start is really, really, really nice. Has a kick start as a back-up. Lights: Can ride at night/dusk, either intentionally or if something happens and your ride runs longer than expected. In some states you can get it plated for dual sport (street legal). Wide Ratio Tranny: Lower 1st gear, so less likely to stall it out in tough, technical sections. Higher 5th gear, faster top speed. Some say the WR is almost 20mph faster than the YZ at max speed. Bigger fuel tank: 1.8 gal for YZ v. 2.1 gal for WR. Gives longer range (16% more fuel). Aluminum frame: If looking for a used one, the YZ’s went aluminum in ’06 but you need to get an ’07 WR for the Al frame. Green sticker: If you live in CA, the WR is a green sticker bike (for most years, anyway) and YZ is not. Check the details on this as I don’t live in CA... [EDIT]: sounds like the '03, '04 and '05 WR's are red sticker Did I forget anything?