i had a 4" marlin pack. i took out the top 2 leafs and replaced them with the top 2 leafs from a toy rear pack. its only a 5 leaf pack cause i left out that really small leaf that sits on the bottom. there so flexy/soft that if i throw it in reverse and slam on the brake front DL will pop out. yes its a bit short but still the whole truck will shoot high in to the sky in reverse or slam down easy when on the brakes. id really recommend this pack, but keep it 6 leaf.