cycling/running tights

I don't think there really is a correct answer, but a number of "it depends". So it's more the rationale for making decisions that you may be looking for.

For my previous response, the rationale is that the bike shorts are made to go right up against you. Some tights might work, they might not (unpadded here, remember). I know mine don't (they don't have a pad), so I put the shorts on first. There is a seam on the tights. It's not that big, but I know it's there. The bike shorts help to absorb this. If the tights moved around, I would try to find out how to get them not to. Or replace them. I know this type won't work going under the shorts, so I don't do that.

If both have a pad, then I'm not sure it makes that much difference. Go with whatever feels best. Largely, that will mean whichever way keeps everything in place best and is the more comfortable.

Both padded would be too much material for me, which is one reason I intentionally picked out a pair of tights without the pad (the other being I didn't want to run with one). I can replace the shorts (bibs now, actually) easily enough.

I have no real answer to which way is better for style. I don't really care. It mostly needs to work for me. Remember, you're wearing near full-body spandex in a bent over position.

Running

Compression tights?  Generally you wear just those, no shorts, no underwear - even if it doesn't have a chamois.  You could wear regular shorts over them if you feel like it.  You'll see plenty of people either way.

Regular tights?  You can wear them over compression shorts, or under regular shorts. 

If you are wearing regular tights over regular shorts, then chances are the tights are too big.  You're not supposed to be running in parachute pants.

Cycling

If they have a pad, they're designed to be worn alone.  If they don't have a pad, you wear them over regular bike shorts.

Never two pads.

I usually wear them under, but today I climbed Mt Lemmon and started without them on. On the way back down I had no place to change so I just wore them over the top.  I really could not tell a difference.  

9

Michael9% of the time I wear my tights under my bibs.  Reason is I like storing my ride food under the leg bands on my bibs for quick and easy access during rides - don't have to dig it out of my rear pockets....as well as throw my trash there as well.  Digging into my full rear pockets with winter gloves while riding is somewhat of a PITA. Tights don't usually have any storage pockets.

Michael

You got it.  I find that I chafe less with my running tights on the outside but whatever works for you.  

Yup, either way.

I always assumed that it was better to have chamois-on-skin as it is what they were made for, but after some issues with pressure sores along one of my sitbones on a bike bib (good Assos one no less), I tried experimenting with compression no-chamois running shorts UNDER the bib, and it actually cured the spot. Probably because it allowed more gliding there. 

At the same time, I could see this sensation being annoying to some, so it's whatever works for you.