im pretty sure i know the answer , but wanted to make sure . im turning my 93 xr600r into a dual sport . i plan on ordering bridgestone bt45s for the front and rear . FRONT : 90 90h 21 REAR: 130 80v 18 these are going on a totally separate set of rims so i can swap rim/tire combos from street to dirt easier . i need to buy tubes for the tubeless street tires . will any 21" and 18" tubes work? i found a 130/80x18 tube on ebay as well as a 90/90x21 ... these will fit ok right? i just was worried about having the tube match the rim width rather than the tire. thanks !