Bicycle Mechanics - rear rack mount inside dropouts?

the title says it all. strange question, no? of course the rack
struts should mount outside of the dropouts to avoid interference
with the chain.

but is there any other reason NOT to mount inside the dropouts?

i'm moving old piece parts to a new frame (BMC alpenchallenge AC01).
outside mounting is not happy. a ridge along the dropout prevents
the strut fitting on the upper eyelet. lower eyelet is too close to
the skewer to mount the rack.

i suppose i could try cutting/trimming the rack strut, or make a
triangular aluminum spacer. perhaps bending the strut to get the
approach angle different. however i'm living in a small town in china
with NOTHING. everything must be mail-ordered....tires, tubes, nuts
and bolts....everything. want to keep it simple and not make any
changes i can't unmake.

aluminum racks are generally spaced about the same as a bike frame, so
must spread the struts out a bit to mount. or in my case squeeze them
together about the same distance.

so. other than avoiding chain rub, and the fact that it's traditional....
everyone mounts a rack on the outside of the dropouts.....is there
any reason NOT to attach the struts inside the frame? the upper
eyelets are high enough to provide ample chain clearance.

There are two good reasons to mount racks, fenders, etc. outside the dropouts.

First of all, few bikes, and no derailleur bikes I've ever seen have enough clearance between the inside of the right dropout and the outer sprocket. That distance is kept to a bare minimum so as to have the minimum asymmetry in rear hubs.

On IGH bikes there probably be enough room, but one argument against mounting inside the dropout is safety related. If a screw fails, and a brace gets loose, outside mounting somewhat reduces the chance of the now free leg jamming into the wheel. It's no guaranty, (I speak from experience), but at least it should help.

If the brazeon is high enough or your gears are small enough,I see know reason not to do it.If the chain clears,it clears.

I would try to get a stovehead or some type of round headed bolt to use,just in case your chain tries to jump up,it doesn't hang on the bolt head.

Mount the bolt head in.If the brazeon is threaded,use a jam nut on the outside,so it doesn't come loose.If it's not threaded,use a nylock nut,double nut or some type of Loctite on the nut.

Chances of it causing a problem if it comes loose are slim......unless your backpedaling at the time and run it thru the cassette.Guess you could rip the brazeon off if you tried.

It's going to be close quarters in there,I think you'll here plenty of rubbing going on if it comes loose before something bad happens

I had a lock nut inside the dropout one time to keep my rack on as the threads seemed stripped on the eyelet (or at least the bolt kept working it's way out easily, I don't really remember). It cleared the chain, but I had a couple of times when the chain got dropped outside the small cog (bent hanger) and it got wedged but good between the nut and the cog. Was a real bear to get out as I couldn't get my wrench on the nut enough to turn it with the chain wedged there and the wheel didn't want to come out of the dropouts with everything all wedged up. Got real greasy that day before I made it home.