mountain vs road frame
I've been getting by for a few years on different bikes with different set ups for different times of year and conditions. I'd like to make something definitive now that I have a good idea about what would work best for me. I live in Chicago, and my rides are almost all less than 5 miles, flat, and entirely on paved roads which are at least fairly maintained in the winter. I don't ride in deep, fresh snow, but I do in all other conditions. Main purposes are for commuting and errands including groceries. I do have access to a car, so I don't need it for heavy duty hauling. Here are my non-negotiables:
1) Mounts for rack/fenders
2) Spacing wide enough to accept at least 35mm studded winter tires
3) Usable with Shimano Nexus inter-3 rear wheel with coaster brake, for wet/slushy weather (I've considered instead a new fork with disc mounts but ruled it out for various reasons)
4) Ideally a somewhat upright posture, but not dutch-bike-esque
Although buying a new frame and building up from there would be the "best" option, I can't find a way to get this project done for less than $1200 that way--my budget is more like $6-700. What I've done before is bought old, steel bikes and rebuilt them with modern components. I'm thinking that would be my next best option again, but I don't know whether to use a mountain or road frame.
Problems with mountain frame are:
-Typically spacing of rear dropouts is 135mm, which I would need to "cold set" to 126 or so to accept the IG hub I have in mind (it comes spaced to 120mm, can be respaced up to 126).
-Frames are often heavier and often cheap, Taiwan-made and TIG welded.
Problems with road frames are:
-Cannot accept any more than about 35mm max, and I couldn't run wider if I wanted.
-The geometry is less flexible to allow for more upright riding.
-Likely the stock wheels are 27", which means I also need a new front wheel (for 700c tires), whereas I may not need one with a 26" mountain bike frame assuming it's in good condition still.
SO, I'd like your thoughts on whether you think picking up a road or mountain frame would be preferred. Thanks all.