drmacgyver said:
Just found this link on the forum: http://electricscooterparts.com/tires.html
Haven't browsed too much, but seems like they have lots of stuff.
Hope this helps!
Nah, unfortunately they only sell 6" as the smallest and fairly narrow at 1 1/4" too, no 5" tires/tubes...most likely won't find in the States through scooter parts suppliers but the large scale RC airplane market (for tail wheels, etc) seem to sell a variety of small size pneumatics here, lastly try Chinese suppliers through alibaba or sellers of the Skike off road roller blades in Europe or elsewhere but I assume you've tried that avenue thoroughly already, great design by the way!!
Here's one seller of a full wheel 6x1.25 (elecricscooterparts only sells tire and tube, no hub...):
http://www.ebay.com/itm/Air-150mm-Pneumatic-Wheels-6-X-1-1-4-Inches-Scooter-2-Pieces-/231378509696?pt=AU_Skateboarding&var=&hash=item7b8ca60d92
Medical supply store: (always only grey color, uggh)
http://www.caremedicalsource.com/Shop/Wheelchair-Parts/Wheelchair-Casters/6-Wheelchair-Casters
5" and 6" + sizes tire, tube, hubs, whole wheels...
http://nordicskater.com/rolski/access.html#aerowheels
6" Airplane Nose Wheel, Tire, Tube, alu hub:
http://www.matcomfg.com/TAILWHEEL6PNEUMATIC-idv-3373-13.html
5" & 6" Wheels:
http://skike.com/
http://skike.com/shop.php?l=pl&c=PL&page=5&cat=3&sub=478&aid=303
Avoid this product, it looks good and the tire is great (6x1.25") but the hub will crack and fall apart as soon as you ride over 5mph or go off the the curb or bump into anything (I know from experience and from others on this forum...):
http://apollocaster.com/store/6-x-114-swivel-caster-with-a-pneumatic-black-wheel-threaded-stem-connector-and-ball-brng-66554-p-66554.html