Depends on the track surface...

My local track is older carpet that shares a building with an off-road track. The combination of dust from the off-road track and sauce causes the foam tires to develop a peculiar glaze to them, if we don't have a lot of on-road entries on a given day. Removing this glaze requires a little bit of scrubbing, using a rag/shop-towel with Paragon or motor spray. Ive seen some people using lighter fluid on occasion, but I have personally never used it.