Originally Posted by
halehankock
Tyres
Continental Grand Prix 700x23c (Specialized: Continental Gatorskins 700x23c)
This is your difference!
And a lighter bike is mostly beneficial on climbs.
So heavier bike more momentum, with less resistance on flat ground and you will fly!
I'd also be interested on which cog your chain is in on that 4 mile section on both bikes. Mostly interested on chain line. If chain is straight that will be even less resistance than a chain bending.