I want to add a layer over my bike tights for warmth. Leg or knee warmers seem like a nice versatile option. I am just wondering if there is any issue with wearing these over tights as opposed to over bare skin with shorts.
I've worn my knee warmers under my tights, it worked well to keep me warm and they stayed in place well. However, the tights were the kind that went over top of my standard bib shorts, not the kind of tights with integrated chamois.
If you want to try and wear them over your tights, you might need to get a larger size kneee warmer, depending on the thickness of our tights. You might also have trouble with them staying put, since they tend to be held up partially by the bottom of your cycling shorts.
Personally, If it's colder than my comfort zone with just tights, I'll usually wear a pair of stretchy synthetic knickers on warmer days (like chrome telegraph knickers) or some breathable shell pants (north face resolve) on colder days over top of my tights to help kill the wind and retain more heat.
The only thing that I could expect to be different may be that the rubber like band that is included in their ends to prevent them from slipping might work not so well on your tights than on skin. But this surely will depend on the materials involved, so just give it a try.
Everything else should not change, besides the fact, that you have two layers of fabric, i.e. more isolation, less heat transport, a bit less breatheability... but that is the reason why you want to wear two layers, right?
I'm surprised no one's mentioned slipperiness.
I wear an elastic knee brace because my knees are the first thing to complain on a long ride. I wear the brace over my tights for comfort. The repeated action of pedaling slowly works them down, so after a couple of hours the brace is around the top of the calf muscle and my knee is complaining.
So your warmers might slip down easier, which is good if you're pushing them down intentionally.