It is impossible to test any significant number of bike models for compatibility with front and rear mounted child seats. There is a standard set of dimensions that a bike must have for a seat to be safely attached. All measurements and dimensions are also listed in the installation and user manual for each bike seat.
Front Child Bike Seats
RideAlong Lite, Yepp Mini, Yepp Nexxt Mini
All models of Thule front mounted bike seats need to be attached to bikes with handlebar stem lengths of at least 21 mm, or .83 in, in to provide a secure fit. The stem must also be between 20 mm and 28 mm, or .79 in to 1.10 in, in diameter, as shown in the diagram below.
Carbon frame bikes are not compatible with child bike seats due to possible crushing hazards.
Rear Child Bike Seats
Thule produces two styles of rear-mounted bike seat; Frame Mounts and Rack Mounts. The RideAlong is only available as a Frame Mount. The Yepp Maxi and Yepp Nexxt Maxi are available as either a Frame or Rack Mount, but cannot be converted between the two.
Frame Mount bike seats attach to the seat tube of the bike frame. This frame tube must be either circular or oval and have a diameter between 28 mm and 40 mm, or 1.10 in to 1.57 in. Triangular and square frames do not provide a safe fit.
Full suspension bikes and some styles of step-through bike are also not compatible.
Beyond matching the shape of the seat post, the bike seat must also be balanced over the rear wheel. The "mid-point" marker on the seat, as shown below, must be positioned no more than 100 mm, or 3.94 in, behind the rear axle.
The seat should also be positioned high enough over the tire to allow for enough clearance so the seat does not make contact with the tire when going over a bump in the road. The bottom of the seat should be positioned 120 mm above the tire, including 40 mm of clearance above any rear rack accessories between it and the wheel.
Child bike seats must be mounted to rear racks with a minimum load capacity of 25 kg, or 55 lbs. It also must comply with the ISO11243 requirements. The top of the rack must be between 110 mm and 170 mm, or 4.33 in to 6.69 in, across and must have a thickness between 11 mm and 16 mm, or .43 in to .63 in.
Similar to Frame Mount rear bike seats, the mid-point of the seat must be positioned as close to the rear axle as possible and no more than 100 mm, or 3.49 in, to the rear of it.