When I first got my 421 serval I had stock swinger. If I was drag racing on dirt, It was a handful to keep the front down. Hell at one of the BHQ play days everyone saw me launch and my front tire came down on top of the tire of the guy next to me and my bike and I went rolling. I went to a +4 and had no more problems in the dirt at all and no issues in the trails either. I would go +4 if I were you