Gauge

Hello all! I am about to do a century for the Tour de Cure. When it was first mentioned, my father challenged me to do the century on my track bike. I am more than capable than doing so, so I considered it. He then, calls me up one day and tells me that he will join me and ride along, on his track bike as well. My father and I have been avid cyclists for a good 25 years.

Moving on, now that he is joining me for the ride, I came across on old tandem and it really got my gears turning in my head. I acquired the tandem, which originally had a 3 speed coaster brake hub, and I am now in the process of rebuilding it; to make sure it is up to par for such ride.

I ditched the original wheels (26"), in favor for 700c. No worries, the conversion fit w/ plenty of room and I even have caliper brakes that complete the conversion. I'll post pics as soon as I can get some. The gearing on this bike is as follows; the synch chain has 39t chainrings and the drive chain has a 50t chainring and I will be using a single speed freewheel.

On to my question... Both my father and I run anywhere from a 46t to a 53t chainring on our fixies along w/ a 14t to 16t cog. Those are great gears for really cruising along. I am wondering about the gear inches, if our synch gears are 39t and the drive chainring is 50t w/ a 16t freewheel, would that be the same as pedaling a solo bike w/ a 39x16 or more like pedaling a solo bike with 50x16?

i hope this isn't too confusing and don't think I missed anything. And I really appreciate any input, advice and help in advance. The ride we are doing is in Florida, so hills are not a concern. And, I want to make sure I get the gearing right as we don't want to be spinning out nor pushing so hard and not getting anywhere. I estimate to run anywhere from 18-23mph, preferably between 80-90rpms.