I'm reading an MTBR thread that says 4in tires might fit as long as you use 50mm or less rims
Anyone Have One of Those Gravity Knockout Frames?- Mtbr.com
The frame is cheap and available in more colors if anyone wants to adopt a project. Comes with fork, headset, stem, and seat post clamp for $150
BikeIsland.com - Bicycle Parts, Accessories and Clothing at Affordable Prices with Free Shipping But considering the frame + wheel set is about the same price as the complete bike maybe don't bother.
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."