help with racing

[yfzrider124]

Hey ive rode atvs all my life and ive had my yfz for about a year now. I have parts put on my 4wheeler like pipe, jetted, filter, nerf bars and all the parts like that that most people have. I still need to get flat track tires and widen and lower my atv. but once i get done setting it up for racing what class would i enter if i have never raced before with my yfz450?