I am riding a flip/flop hub, 18T both sides. My chain ring is 46T. My commute is 50% steep grades. Would going to 42T ring make enough difference? Or should I consider something different in the hub?

50% grades ? You'll need a winch.

But seriously folks.

It depends on how hard you're pushing now, how hard you want to be pushing, how fast you can spin on the downhill, and about a hundred other factors, all of which are entirely personal. Short answer: try it out. If it helps you save a couple bucks, going up a tooth in the back will give you about the same effect.

I interpreted this as 50% of the roads he rides are steep uphill. Which would be true so long as the other 50% is equally steep downhill.
Going from 46T to 42T in this instance would be a huge difference, maybe overkill depending on how steep we're talking. 42-18 is pretty low. However a 42T chainring may get you into the range you need, then you can experiment with smaller cogs (much cheaper) to find the ideal gear for you. For FG with downhills I would hesitate to go so low that you are in the optimal gear for climbing, one speed is always a compromise.

Okay, okay.... you're funny.

But anyway, to put things in perspective, on my Tourist I have a 30/42/52 triple and a 11-32 (9 speed) cassette in the rear. I can spend an easy third of my commute in the 30T chain ring and my lowest two gears in the back. I know this isn't a fair comparison to SS. I could become a stronger rider, but right now, I ain't!!

For now, I will switch to the free-wheel side. My FG skills need work!! (like getting into the toe clips!!!)

The laws of physics don't change when you switch from geared to SS to FG. It takes the same amount of work to climb a hill, regardless of the drivetrain type. If you are riding your geared bike with the 30T chainring and assuming your second lowest cog is a 26T, then that is a granny gear in the low 30 gear inch (gi) range, whereas a 46 x 18 is upper 60s gi. Even assuming that you are standing up the whole time and pulling on the upstrokes with 100% foot retention, it will be near impossible to ride up any hill more than a few hundred feet long. If I were in your situation, I wouldn't even attempt to ride a single gear bike.

S3X, FTW.

It's a suck it an see situation. I face a long, steep climp (3 km and on my geared bike, ride it in 30x32) and know what you're facing. Whatever gear you're using, you've got to ride it both up the hill and down so yes, you need to learn to spin, learn to control your leg speed using brakes and back pressure, and learn to climb efficiency. I've just gone to the S3X ... and then got a really bad flu so I haven't settled in to using it yet.

There are two ways of using your S3X. The first is to use top gear as your around town gear which gives you two lower gears for getting up hills. This isn't a bad option because the downhills are only restricted by your ability to spin.
The second way is to use 2nd gear as your around town gear. I've gone this way because my downhill run is in heavy traffic with a dodgy shoulder so I really need to run at traffic speed so 1st gear is my high speed gear (I top 60km/hr every day). Unfortunately, the drop from 2nd to 3rd isn't that great so my lowest gear isn't a climbing gear, it's merely less horrid trying to get up that sodding hill.

You will get a lot stronger as you ride more fg - if you have gears, you tend to use them. If you're young and fit, you may wind up climbing your hills. At my age, it's not likely to happen so I spend a lot of time using the 24inch gear (two feet).

How long have you been riding? I say stick with it and eventually you'll get used to it if you haven't been riding long

I originally started at 52/16 on an old '80s Schwinn conversion that still had a Biopace chainring on it . Then I built my Pake up with a 46/16 ratio and it was alright but I felt my form and my spin needed some work so today I finally got my 18T cog in the mail and I'm in LOVE. 46/18, in my opinion, is the way to go. It's not too intense on the climbs and you can still work on your spin and form.

So just keep to it and eventually it'll become second nature. There's only one way to get stronger - keep pushing!... safely of course... don't hurt yourself.

For what it's worth, 46/18 is about 70 gear inches, depending on tire size. That gearing is pretty much what everyone would advise as a starting point. All of my fixed gear bikes have run between about 68 and 71 gear inches, depending on the particulars of the equipment I had on hand and pesky integer-based mathematics.

A small variety of cogs and chainrings will never go amiss. Get another chainring and a couple of cogs and play around with different gear ratios.

Thanks for the replies. I think I will buy another ring plus maybe two more free-wheels and play with ratios a bit.

I take it that all 5-hole rings are a standard size? Or are they brand specific??

Yes 42T would definitely help. If you end up still finding it difficult you can get a larger cog after that.

I LOL'd

Neither. You need to know the bolt circle diameter (BCD). They can be 144mm or 130mm or even 110mm BCD. If your cranks can mount the chainring on either the inside or outside of the spider, then they are probably 130mm BCD. If the chainring mounts on the outside only, then it's probably 144mm BCD. Brand doesn't matter, but avoid chainrings with shifting ramps for derailleur usage. Also, if you're using a 3/32" singlespeed chain, then you need to use a 3/32" chainring. If your chain is 1/8", then it doesn't matter and either a 1/8" or 3/32" chainring will work.

Thanks for the excellent help!!!