I have a 2012 250 racing and my dad has a 2004 300 gasser will the wheels fit my 2012????

hmm probably-phone gasgas uk for sure!

Just try, you will soon see.

Steeling parts from pop's bike? did you break something??

I think the wheel dimensions are the same but not positive. Like the others said phone call or try it and you will find out.

I use wheels from a 2003 gasser in my 2012 250 Pro. As long as your racing model uses same wheels as the pro there should be no problem:-

Back wheel fits without modification.

You need to replace the bearings and spacer in the front wheel. You can get a conversion kit from GG.