Saddle height
 

I like to ride upright on commutes and tours. Mtb with smooth tires. Riser bars, tall stem.

I picked up a new old mtb with flat bars that sweep back 13-15 degrees. This bike frame is much larger than my regular bike mentioned above. The previous owner had the saddle on this flat-bar bike way above the bars. It looks much cooler that way, but for me my feet wouldn't touch the floor. Is that okay? I can stand over the top bar just fine with both feet flat on the ground.

Yes, it's fine. You also look cooler with a better saddle height.

Heel on pedals, Inseam x 0.883, 109% of inseam, inseam (in CM) less 10cm, 25 degree at the knee...all produce results that are within 15mm of each other for me. All of these methods are good for finding a starting point, but in the end you will need to explore a bit to find the saddle height that helps you produce the most power, keeps parts from getting numb, and (most importantly) is the most comfortable.

Don't rush the process, it takes time.

Yep, it depends on a how big your feet are and how high the bottom bracket on the bike is. I can get my toes down on my road bike, my full suspension mountain bike has a much higher bottom bracket and there's no way.

To the OP: Think about it this way. At the bottom of the pedal stroke, your leg should have a slight bend, but the pedal is still 3in off the ground. If you were to straighten your leg the whole way your heel probably can't touch the ground, but your toes might.

Cyclists deal with this issue a variety of ways. Most simply come forward off the saddle when they stop. If you lean the bike to one side, you can put a foot down. You'll also see cyclists with a foot on the curb, which is the right height to reach while seated.

Or they do like I did when first using clipless pedals and come to a stop light, try to put their foot out without unclipping and fall over to the side. :lol:

For me the most important issue is to find the point where knee pain does not occur and where my toes don't feel like my foot is trying to drive through the top of the pedal at bottom dead center. Heel on pedal is not far from the correct spot. Usually when I rediscover this point if I go even a little lower I get some front/side of knee pain, and if I go much higher I feel stretching in the hamstrings and back of knee, and some clunking from my left foot gently leaving the pedal. Historically that's how my legs work. I also need to think about if I'm on the metal cantle plate or cushioned on the tensioned leather surface.