I've a very old Specialized Rockhopper that was built with horizontal dropouts. I've used it as a fixie for winters and as a townie for years. Because the frame has 135mm dropouts and the flip/flop hub axle can only go to 130mm, I've been using a quick release. I don't like the QR because the hub can slip when climbing a tough hill under torque and just because it is much harder to adjust chain tension. With a QR, I can not tighten bolts on either side one at a time to "walk" the hub into place. Does anyone have any experience with swapping out an axle that takes a QR and substituting a solid bolt-on axle? If I can do that swap, I can cold set the dropouts down to 130mm to make it work. If relevant, the hub is a Sovos cup and cone type.

It shouldn't be a problem. Wheels Mfg. has a selection of axles to choose from, e.g.:


https://wheelsmfg.com/products/hub-p...s/axle-06.html

Use a Surly Tugnut to hold it in place. It comes with washers so it will work with a skewer.

Or if you can find a disc rear wheel, you could put a bolt-on cog. Although it would change your chainline a bit.

This is what you want and what you really need:
https://www.paulcomp.com/shop/compon...bs/fixed-word/
Bolt on 135 fixed/free and you are golden my friend.

Paul has been doing single speed and fixed gear MTB stuff for quite a while and certainly has kept his business going so he can continue making awesome parts that aren't just for SSMTB.

Good call. Or get Surly's version, with thread-in bolts and a hollow axle, should you ever want to go back to QR.

just do this. Then go for a ride.