Putting together my first SS bike, and am planning on using a 48t x 17t gear ratio. I'd like to simulate that ratio with my current road bike so I can get a feel for what it will be like. I have a mid '80s Panasonic DX-3000 that has a 52/42T ring up front, and a 14-28T freewheel. Is there a gear ratio I can achieve that would closely match the 48t x 17t?

https://sheldonbrown.com/gears/

48/17 is about 75 gear inches.
42/15 will give you 74GI.
52/18 will give you 76GI.

I think those are about as close as you're going to get with your limited chainring sizing. I run 48x17 and have found it to be a very nice ratio for most riding.

Wouldn't it be smarter to find a gear ratio you like using on the Panasonic, and then replicate that on your SS?

Brilliant

True. But go a little bit higher in gear inches if possible, no?
The increased efficiency of a SS/FG supposedly makes a noticable difference. So if you like 44/17 on your geared bike, you may want to do 46/17 on your SS/FG.
Someone correct me if I'm wrong...

I'm doing it this way because the crankset I'm buying comes with a 48T chainring and the wheelset comes with a 17T freewheel. I'm trying to see if I can get away with not buying additional of either, so I want to test out the 48T x 17T ratio.

My two cents: go down a few gear inches if you will be riding mostly around town; go up a few gear inches if you will be riding mostly on the open road. FWIW, 70 g.i. (42x16) is a nice place to start in my experience.

My freewheel is 14 - 16 - 18 - 21 - 24 - 28, so looks like 52/18 is as close as I'll get. Thanks!

I agree. 42/16 is about 70.2" , which is close to the 44/17 (69.3") that I run. It's a nice easy gear but you can still haul some ass if you need to.

Mine is currently 48/17. Hills aren't easy but I haven't had to walk one yet. And I also haven't topped out spinning on a downhill yet. Flats are reasonably comfortable but if I could pick a magic gear for me, I would go up to a 19T or down to a 46chainring. But for now, I deal.
I rode my tri bike this morning and the closest thing I found on there similar was my middle ring paired with my smallest rear cog on a 9 speed. Which for road riding would be way too slow for flats but for in town riding is just a shade too hard(for my liking). But I sure can accelerate fast!

Ah, gotcha.

On FG, you want to use as high of a gear as you can tolerate so you don't explode on downhills. No need to do that if you can coast back down.

I started off with 48x17, then 48x19, and now 46x17. 46x17 is my happy medium for tackling just about any hill and doing longer road rides fixed with a couple of climbs.

My first fixed gear had 46x19 (64GI), it was the best to learn on. I get that everyone starting out wants to look tough and rachet up the highest GIs possible, but don't be coming back to this forum asking why your knees hurt or why you pulled something or other in your leg trying to stop skid. Decent cogs are not that expensive. As far as singlespeed freewheel: the only issue I see in having too high of a gear is that you will be kinda slow on the start

@Broakland - that's such a smart way to do it man. I think Nagrom said the same, or was it Carleton? I forget but it's in the stickied fgss newbie thread. Basically they (and you) said to gear WAY down so you can get the technique. Then work your way back up to whatever gearing you need to. That 64GI combo you mentioned must have been a lot of fun (except on any kind of downhill). But for screwing around and learning to control the bike and how to use leverage for skids/etc and whatnot - perfect advice. Especially since 46/19 has 19 skid patches.

+1 for 46 x 17. I just rode a century with that gearing.