Do you know what cadence you are running at?

As an example: Spinning the wheels at 60 RPM is not as efficient as spinning at 90PRM. This is due to the fact that at a slower spinning rate the muscle has more time to contract and does not give you the most performance. Typically 90RPM +/-5 is the sweet spot for spinning the wheels with maximum efficiency (this is unles you are racing or Lance @ 120RPM).

I would recommengd using the smaller gerars but spinning faster every once in a while.

I used to be all into spinning big gears @ 65RPM but I've slowly realized the power of higher cadence.