Winter is coming. I have a 3x6 old MTB as a winter bike. Had shifters freeze. I was thinking, could I remove rear derailleur, shorten the chain and just place it in a straight line from middle chainring to the rear cog directly in line with it? Will it work as a single speed? The frame has horizontal dropouts for the rear wheel.

This is SOP in the ghetto, but is easier to set up with a horizontal dropout, so you can adjust the chain slack. There's a risk to this approach in that of the chain for some reason deflects and engages a larger sprocket it'll bend or break your axle (if you're lucky) or worse.

A better approach which also offers more versatility is to leave the RD on as a guide, and set it for the gear of your choice using a straight pill spoke or a cut down gear wire, running from adjuster to pinch bolt .

Of course, you could always leave it as a 6s, an not shift when it's too cold to.

shouldn't be a problem. using the middle chainring will result in a very limited (probably two) choices for a cog, given that a workable chainline is necessary and consequently limit gearing, but if you like single speeding, in the future you can remove the freewheel and purchase in inexpensive single speed freewheel for about 20 dollars and expand your gearing possibilities.

don't forget you have a big ring and a middle ring, at least, that may be able to swap positions. the big ring in the middle position could cause chainstay clearance issues though. but, if workable, will give you a couple more gearing choices for zero cash outlay. good luck.

+1) _ horizontal slot dropouts help .. thereby you can shorten the chain.
verticals.. 8 speed .. there are 3/32nd half links to maybe get the length closer since axle wont move.
Or leave the RD on, maybe just a short cage .. substitute for MTB &shorten chain..

It is quite likely that your plan will work without a hitch. Getting good chain line is very important, though, if not using a derailleur.

This is what we did for my SS winter bike - it has vertical dropouts.


We used the Origin8 conversion kit: Amazon.com : Origin8 Single Speed Conversion Kit : Bike Hubs : Sports & Outdoors

I'm going to my third winter on this set up; no complaints. I made the SS conversion after freezing the derailleurs one too many times. The only thing that can get tricky in the cold is the freehub; at temps below 0F the grease isn't happy.

BTW the chainring and cranks are brand new this winter cause the original chainring was shot.