Coleman SK100
 

Does anyone know if there is a wheel hub or adapter that will allow me to run a larger wheel and tire combo on a Coleman SK100 ?

Welcome
What's your skill level? reason I ask is I doubt anyone has an adapter as the style wheel isn't designed for much of a load.I'm betting this uses foreign parts since they advertise "USA designed" and not "made in the USA". You'll need to measure the shaft to know the I.D. diameter of the bearing.If it's close to 5/8"=.625" or 15.88MM you could order 8" riding mower wheel/ tire combo's pretty cheap. If the shaft size is smaller then you'd need to order bearings to fit whatever wheel you come up with, still very cheap. The other alternative is finding a hub + wheel/tire w/matching bolt pattern- If the rear axle has a keyed slot or splines that adds more measuring & calculations! I'd confirm what I have- then search other Chinese ATV/UTV/kart models/parts for a match as most of them use the same parts.