Some rubbers will swell and be ruined with WD40 but probably not tires as they have to withstand all kinds of glop on the roads. I would still make an effort to keep the WD off any part of the tires. My worry would be making the tires a little bit slippery on the road surface. Not a big worry mind you but take it easy when starting out on a ride to get a feel for if your traction is OK.