What kind of surface are you running on?

I run mine mostly on Concrete, and I find 1/10th scale Contact Foam Tires are the fastest. I run them on new asphalt every once in a while and they seriously hook up, though they can chunk out when it's hot. I first tried some Duratrax street tires, and they work for bashing, but I did break the drive cup out of one of the wheels sliding into a sand stone flower bed wall! So my fault, but most 12mm Hex drive wheels will fit the Reflex, but I had to make some 1mm shims to keep the Contact Foams wheel from rubbing the hubs. I used 1mm sheet lexan to cut out some hex spacers.