Using springs with thicker coils is an option. If you want to try either procedure it would be best to have extra springs on hand. Stretching a spring can also result in a spring with more tension than you need. I have found that with steel springs clipping off a coil or two can be difficult. With the Mega G+ the circuit board with the RFI filter is soldered to the motor terminals, the motor and circuit board will pop out as a unit. That would tend to make those cars more fussy about pickup shoe spring tension and pickup shoe adjustment than with more conventional inline cars that get extra magnetic downforce from the motor magnets. The Mega G+ uses a closed can style motor, so it has no magnetic downforce at the front of the car.
