Both modified and stock trials bikes have pros and cons: Modified (20" wheels) Pros: ~Superb standover clearance ~Easily manueverable in most every circumstance, especially anything rear wheel ~Less expensive ~Less parts to break ~Nearly impossible to bend the rim of a well-built 19" rear mod wheel running enough tire pressure ~Learn to sidehop up to both sides without worrying about a rear derailleur ~Lighter Cons: ~Some people may think it's a BMX bike ~A pain to ride more than a mile or two on ~May be harder to find parts for it ~Harder to roll down things ~Easier to go over the handlebars (but less scary when you do) ~Doing wedge or wheelbase moves is less comfortable Stock (26" wheels) Pros: ~More stable ~Bigger wheels = roll everything easier ~Easier to do wedge or wheelbase moves ~Easier to pedal-kick on odd surfaces because of the larger diameter wheel ~You can ride to your riding spot easily (if you have a seat and working gears) ~Looks more like a mountain bike ~People won't ask you to "grind" stuff or think you do BMX vert or street Cons: ~Bigger bike = less standover clearance = pain if you fall on the bike ~Easy to hit knees on top-tube of most bikes ~Less room to work with for bending down before sidehopping, bunnyhopping, etc. or when absorbing landings ~More expensive because of greater frequency of breakage and more parts to break ~Rear derailleurs - easy to smash into things (though most bikes have replaceable derailleur hangers that will bend before the derailleur is broken) ~Wheels - 26" size = easier to get out of true or taco (20" wheels are extremely hard to ruin when built and used properly) ~Chain can slip down or up a gear while you ride if your chain is too loose, or you smack your derailleur in section and break it ~Heavier