The frame is designed for a front wheel of size 50-355 (18" Any wider 355 tire would fit, but currently there are none on the market...) and a rear wheel of size 50-559 (26") but you might be able to squeeze in 60-559 in the rear. The frame can be used with Kojak/Durano racing tires (32-355/32-559) but it will sit very low then. If you hear the steering rod scrape the ground in a left turn take it easy. It will still tilt up by some degree but when it hits the frame the front wheel loses ground contact. Marathon tires in 40-355/40-559 are a good compromize between sportiness and everyday use. A white front tire is currently available in limited numbers.