If the wheels on your kayak trolley become flat quickly, please check and rotate the valve clockwise tightly. If this doesn't fix the problem, there might be a slow leak. You can check it by spraying some soapy water and if it starts bubbling ...
They are not really necessary. They are used to tighten the string (between the footrest and the rudder) so that there is enough tension on the toe piece so that it pulls it forwards. See the attached video showing how to use it.
Rudder Assembly Instructions for 3.6m Pedal Pro Kayak and 2.9m Modular Kayak from Vicking https://workdrive.zohoexternal.com/file/fx2aba8ae1c22a8184c66ae5ea10a2f78f61a
1. Determine exact location of the EVA with issues 2. Make sure location is completely flat with a smooth texture 3. Clean the area where the EVA piece will be placed thoroughly and carefully. Be aware that once the adhesive has bonded to the surface ...