Forgive me, I'm big bike n00bish. I'm buying my first set of tires (606/908)for the 990, and the website from which I purchase tires warns that UHD (or even HD) tubes should not be used on the street. While I often ride the road between dirt destinations, I've been using UHD tubes on the 525 for years without event. Is there some reason about which I'm ignorant that the UHD tubes are a hazard on the big bike, on the street? I'm sure "heat" is one possible explanation. Thanks.