I recently converted an old mtb frame to fixed, and yes- dreaded vertical dropouts. I'm trying to find the magic gear, and I'm using a half link chain. I'm currently running 43x16 it's slack, and doesn't fall off when I ride, but if I remove half a link it becomes WAY tight and I don't want it to damage my bb. Any advice? I want to know if you guys think that replacing the 43 tooth with a 44 would tighten it up or not?

With horizontal dropouts, each tooth added or subtracted results in a 1/8th inch movement of the axle. Maybe you can use that info the estimate the effects of an added tooth.

Or, you could buy an eccentric bottom bracket to gain the ability to adjust chain slack.

so do you think something more like a 46tooth maybe?

Is there sentimental value to this frame or serious budget contstraints?
No offense but I'd start with more approriate frame. I built and rode much worse contraptions so here are my 2 cents
- Get another frame designed for 700c wheels, either vintage with horizontal drop outs or vintage/modern with track fork ends
- Lose half link chain
- Enjoy your new FG

If you insist on using this frame - start reading, oldie but goodie Fixed Gear Conversions

It's math. Do it. Go to your bike and make some visual estimations.

Or, borrow some chain rings and experiment.

I did maths! I'll be sure to let you guys know how it turns out when the parts come in!

I DID IT YES THE TENSION IS PERFECT!!! ITS COMPLETELY SILENT AND HAS NO VISUAL SLACK YESSSS. Thank you all if you helped, the right combo was 16x44

I didn't die face down in the jungles of 'Nam to come home to people trying to do a fixed gear with no way to properly adjust chain tension. If you must has a MTB find an old Bianchi B.A.S.S. which has track ends (horizontal) or one of the modern SS MTBs. If not get a dedicated single speed/FG frame with track ends and be much happier over time or at least some Eccentric hubs and BB so you have a little adjustment in your chain!

It's not about a mountain bike frame, it's about THIS frame... It has history. It's a bike that's been through hell and back with me, so I'm going to stick with it.

Until the chain stretches a little and you're right back in the boat you originally set sail in. Those half-link chains are notorious for stretching like a mother****er.

I'm going to switch over to 17x44 soon anyway, that should pick up the slack and I doubt it would stretch too much more, if so, I guess I'll just buy cheepo chains and replace them every once in a while.

I get that the fame has sentimental value and you want to keep it, nothing wrong with that. But seriously, why not follow the advice you were given from the beginning and invest in an eccentric hub or bb and just be done with all this foolishness of magic ratios, swapping cogs because your chain stretches, and buying cheap crappy chains for the rest of your life? It seems like you made this way more complicated than it should have been. Just my $0.02

Have fun with it.

That's cool but run it as a SS MTB so you can have a tensioner and not have to deal with a loose chain in a short time. You can then go out and get a frame that you can actually properly run fixed and tension the chain and such. You don't have to get rid of an old bike but trying to repurpose it for something it cannot really do well and certainly wasn't meant to do seems silly.

I probably would've measured the area, went to a hardware store and gotten a plate of steel to be welded on the flat inner part of the drop out and fabricated a track end for it ? Would've been a little work, might've cost a little more to weld it, but it would've probably worked without dealing with chain links and eventual chain stretch.

Exactly. My beater SS MTB for this winter's commute had vertical drop outs (CL trade, not great). Chain tension was perfect w/ regular chain at the start of winter. I was taking links out and replacing w/ half & whole links every month to take up slack... that and increasing cog size. Not fun.

That saying has always bugged me. If you are a motherf*****r, then you are doing the stretching and not being stretched....

Just a thought...

Now, back to the normal programming in which someone gets to buy and endless supply of chains in place of an eccentric BB. Please do tell me the brand, in case it is a company that has stocks.

All you would need to do with these is cut the original dropouts and find a welder to attach these. Paint the new dropouts.

Custom Fixie Track Ends Track Dropouts Campagnolo Style Frame Build Sale | eBay

You have stockholm syndrome. Buy another frame.

i need a welder now, I will find it. And I shall learn. And yeah, I wouldn't call it Stockholm syndrome. But I do think inanimate objects have feelings... *twitch*

So now instead of just using another frame - or an eccentric BB as others have mentioned if the frame means something to you - you're going to buy a welder, learn how to weld and replace the dropouts instead?

Seem like a lot of bother for little reward.

No, you can go to a Midas muffler shop or any place in the industrial section of town and they'll probably do it for a reasonable fee ? Would it cost what a new frame or used one runs even off ebay ?

That's if you have to have this frame ? It most likely can be done for what a low end track frame from China would cost delivered ?

What is the primary downside to an eccentric, just less convenient to adjust? Less durable?

The horizontal end does seem like the most elegant straightforward solution.

I use an eccentric on my MTB that regularly sees black diamond trails. And, no problems to report.