Well I own both the 450 and 500 foreman so i will try to help. Both atvs have been problem free (450 has 400 miles) and the (500 has 500 miles). The foreman 500 has a better suspension, ride, and bigger seat than the foreman 450. The foreman 500 also has a gear indicator on the pod to remind you what gear you are in (nice feature). The foreman 500 seems to start easier and warm up quicker than the foreman 450. Both atvs have stock exhaust and the foreman 500 is quiter than than the foreman 450. I can not comment on bigger tires since both atvs are running the stock tires. Hope this helps.