I have just bought a YZ 250 and I was wondering what is the biggest rear sprocket they make for the rear and the littlest for the front.
I do trail riding and I want to be geared low I want it to creep in 1st gear. Please reply back.

 

SprocketSpecialties will have any sprocket you want regarding size. The only limit will be clearance issues on the bike.

You may also want to look at putting on a flywheel weight. Steahly makes them. Cost about $100 and will be the biggest improvement you will make to help you out on the trail. Nearly every GNCC racer in the bike classes run these.

The flywheel on the Cannondales can't have a weight added, but Steahly modified mine by adding weight to the flywheel itself without making it larger.
It is the single best improvement I have made. Makes it nearly impossible to stall and will pull one and sometimes two gears taller in an area that usually had me in 2nd. It does keep it from revving as fast as it did before but not by much.

 

similar question

Does Yamaha make a 15 tooth counter shaft sprocket? that will fit the YZ450F or YZ250F?