Marin San Quentin 20" JR Bike Real Mountain Bike. Real Kid. Young riders who are ready to hit actual singletrack and dirt jumps deserve a bike that was designed for them. The San Quentin JR 20" draws its DNA directly from the Alcatraz dirt jump platform and the full-size San Quentin lineup, scaled down to fit a smaller rider without watering anything down. The Series 2 aluminum frame carries a tapered head tube, 3D forged dropouts, IS brake mounts, and semi-internal cable routing, the same construction details you find on bikes built for adults. A Manitou J-Unit air suspension fork puts 80mm of travel up front and gives parents and young riders a real tune point rather than a coil spring with no adjustment. The geometry paired directly from the adult San Quentin a slack head tube angle for high-speed stability through rough patches and a steep seat tube angle that keeps the rider's weight forward for efficient climbing. The drivetrain is a 1x 8-speed Micro Shift Acolyte setup with a clutch-equipped rear derailleur, so the chain stays put when the trail gets rowdy. Kid-specific hydraulic disc brakes provide consistent stopping power that a smaller rider can actually modulate, and tubeless-compatible tires on double-wall alloy rims mean fewer mid-ride flats cutting the session short. A one-piece seatpost and saddle unit drops the standover lower so younger riders can get a foot down with confidence. This is a purpose-designed trail bike for kids, not a department-store bike with trail-worthy stickers. Features Series 2 aluminum frame with tapered head tube, 3D forged dropouts, IS brake mounts, and semi-internal cable routing built to the same standard as the adult San Quentin lineup Manitou J-Unit Sport 80mm air suspension fork fully adjustable and air-sprung for a lighter rider's weight range, with a 15x110mm thru-axle for front-end stiffness1x 8-speed Micro Shift Acolyte drivetrain with clutch rear derailleur keeps the chain secured on rough terrain and simplifies shifting for younger riders Kid-specific hydraulic disc brakes deliver consistent, modulation-friendly stopping power sized for smaller hands Tubeless-compatible double-wall alloy rims 26mm internal width, ready to run tubeless for fewer flats and better traction on the trail One-piece seatpost and saddle unit lowers standover and ride height so riders can get a foot down confidently Specifications Frame Series 2 6061 Aluminum, 20" Wheels, Disc Specific, 27. 2mm Post and Dropper Compatible Fork Manitou Junit Sport, 20", 80mm Travel, Air Sprung, Adjustable Rebound, Tapered Steerer, 15x110mm Axle Rear Shock N/A (Hardtail)Headset FSA No. 57EShifters Micro Shift Acolyte, Short-Reach, 8-Speed Front Derailleur N/A (1x Drivetrain)Rear Derailleur Micro Shift Acolyte, 8-Speed, Super Short Cage, Clutch Crankset Forged Alloy, Narrow Wide 30T, 127mm Bottom Bracket Sealed Cartridge Bearings, Square Taper Chain KMC Z8Cassette Micro Shift Acolyte, 8-Speed, 11-38TBrakes Tektro HD-J285, Kid's Specific Hydraulic Disc (Front & Rear)Wheelset Marin Double Wall Alloy Rims, 26mm Internal, Tubeless Compatible; Forged Aluminum Hubs, 32H, Disc Specific; 14g Stainless Steel Spokes Tires Delium Versatile, 20"x2. 4", Light Construction, Wire Bead Handlebar Marin Riser, 31. 8mm Clamp, 30mm Rise, 580mm Width, 19mm OD Grip Section Stem Marin Alloy, 40mm Grips/Bar Tape Marin MTB, Small Diameter Seatpost Integrated with Saddle, 27. 2mm Alloy Post Seatclamp Saddle Marin One-Piece Saddle/Post Combo Pedals Kids Specific Nylon Pedal Intended Use Trail, Dirt Jump Note: Components are subject to change without notice. METRICINCHMarin San Quentin 20" JRSize One Size A: Seat Tube Length280B: Effective Top Tube426. 1C: Stack433D: Reach310E: BB Height260F: BB Drop10G: Head Tube Length90H: Head Tube Angle65degI: Seat Tube Angle75degJ: Standover Height534K: Chainstay Length340L: Wheelbase922Crank Arm Length127 mm Stem Length35 mm Handlebar Width580 mm Suggested Rider Height Frame Size One Size Rider Height Marin San Quentin 20" JRSize One Size A: Seat Tube Length11. 0B: Effective Top Tube16. 8C: Stack17. 0D: Reach12. 2E: BB Height10. 2F: BB Drop0. 4G: Head Tube Length3. 5H: Head Tube Angle65degI: Seat Tube Angle75degJ: Standover Height21. 0K: Chainstay Length13. 4L: Wheelbase36. 3Crank Arm Length127 mm Stem Length35 mm Handlebar Width580 mm Suggested Rider Height Frame Size One Size Rider Height | Marin Bikes | San Quentin 20" Jr Bike Yellow Orange | Nylon