I have disc brakes.

If I want a second wheel set so I can easily switch between road and gravel tires in 2 minutes rather than 20....is it simple to get a second set of wheels where the disc rotors line up to the calipers?

As in, will the rotor always be X distance from the center of the wheel hub? Or do I need wheels with the exact same hub to make sure both rotors are in the exact same place?

(See what happens when it rains for 5 straight days? I can't burn off my energy riding my bike so I burn it off coming up with creative ways to spend more money on the bike)

The rotor spec is 10.5mm (15.5mm for boost) from the end of the axle to the face of the 6 bolt rotor mount. It depends on how finicky your disc setup is and the hub manufacturer's tolerances but generally if you are going with name brand stuff, you should be fine.

Thank you!

Realistically, you should expect to need to make minor adjustments to your brakes and derailleur, even when swapping like for like, due to manufacturing and assembly tolerances.Your consistency in positioning the wheel will be a factor as well.

You may get lucky and it'll work, but the tolerances for the pads are really tight so it might not. You can shim the rotor of whichever hub has the rotor more inboard to make it match if you really need to be able to swap without adjustment. Also if you have a rotor with considerably more wear you'll have to reset the pads somewhat when moving to the rotor with less wear.

Oh good point. I wouldn't have thought about that.

Speaking of rotors...

One of my rotors is a little out of true. Can those be trued? Or is it easier to just get a new one and bolt it on?

(It's not terrible. I just get a slight rub once per rotation and can see it wobble slightly as it spins. It still stops the bike though)

Truing rotors is routine work. There's a tool for it but a small adjustable wrench or knipex wrench pliars works fine for the occasional home mechanic. I like to true with the wheel installed and use the brake pads as a guide. Go really slow at first until you get a feel for how much deflection you need to make a small change to the rotors—this varies a lot. You may never get out a major overcorrection.

Yes. Rotors can be trued by hand. There are undoubtedly tutorials on YouTube on the subject. There's a special tool that isn't necessary if you have a small crescent wrench and a steady hand. You do it with the wheel mounted. Work slowly and carefully, thinking about where you place the wrench jaws, the deflection that you'd like, and how much/what direction the force of the wrench. Re-measure often. It's not hard.

I think this rotor and the pads are glazed too so I'm going to take the whole thing apart tonight and work on it. It stops, just not nearly as well at the front brake. So I'll take it all out, clean it, sand it, and true up the rotor.

Thanks for all your input. I wasn't sure if trying to true the rotor was likely to snap it in half so I didn't want to just go experimenting.

I bough this bike used and it needs a little TLC.

I'm sure the rest of you understand...the TLC on a used bike is part of the fun!

Super basic spare wheels, at a good price, come thru my local shop,
built, boxed and shipped, by the wholesale distributors they buy parts through..

hand checked in the shop, before delivery, to you..

I have two carbon wheelsets with disc brakes for my Culprit. No issues swapping back and forth. The 55mm tall aero Token rims that came on the bike developed a rear hub bearing problem, and I got a set of Reynolds carbon 41mm for half price from the bike mfr. The mfr then put in a warranty claim and Token replaced the rear bearings and freehub on the original set, so now I have two sets. The tall 55s are tricky on windy days, so I have a set of 41s to fall back on that are much more wind friendly. Two different wheel makes with disc brakes, no issues swapping back and forth. I do have TRP mechanical disc calipers which have a spring to maintain pad clearance from the rotors, if that makes any difference from hydro systens.

If I were upgrading wheels I would say get new wheels if I was downgrading to avoid doing a quick tire swap, I would probably not do it. Save the money and just swap tires, maybe take some time and practice a bit, Also having a good tire lever will help, I like the Crank Bros Speedier Lever.

Now If I were to upgrade wheels I would probably do some measuring on the hubs and calculate the distances between the rotor mounting and maybe shim it out as needed (Syntace makes some that work just fine) so both work equally.

One can fine-tune any new wheel using axle-spacing tweeks to match an existing wheel on one side or the other (cassette or disc side), but the separation distnce across the hubshell could still be another variable that might require a different cassette spacer or disc shimming.

This is why I have several bikes (at least this is one of the reasons why I have several bikes).

Even on non-disc bikes, it's a hassle making sure that the indexing and limit screws are adjusted just right (and that the brake calipers are adjusted just right) when changing wheels.
Add to that the two cassettes which might have different levels of wear but which must work with the same worn chain and these are irritating little grievances I have with frequent wheel swaps.

Just get another bike in lieu of each additional pair of wheels. If it's just a once-per-season swap then I guess one bike might suffice, but there can be serious issues with misadjusted rear derailers including cable breakage (over-tight limit screw) or chain into the spokes. I often deal with broken cables where the owner has adjusted their cable tension without bothering to revisit their low-limit screw adjustment.