Depends what losses there are in the cables supplying the heating wire and hence the voltage applied to the heating wire.
2.5-3.0 ohms of heater resistance will give you 57.6-48.0W respectively at 12.0v, Since P = V*V/R in a DC system.
When the bike is running, the nominal battery voltage will be 14.4v (possibly more), so 2.5-3 ohms will dissipate a maximum of 82.9-69.1W respectively of power.
The thicker the cable leading up to the heating wire is, the higher the voltage applied to the heater will be and hence more power will be dissipated as heat in the wire.
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