What make/type of tyre is it? Some a much much worse than others for seating the bead. Also bad storage practice such as storing tyres on their sides for long periods, or buying old stock (always check the date branding) can lead to the beads being distorted and difficult to seat.

If it's a stubborn tyre, then a 12V tankless compressor won't do the job. They can meet the pressure needed, but without a tank they just can provide the volume of air anywhere near quick enough. To pop the bead on you generally need the full volume of the tube to reach at least 50 - 60psi almost immediately and use plenty of tyre soap. As Brian says - "shock it on".

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