Originally Posted by
akohekohe
A lot of not getting tired over a distance is actually technique and pacing, not fitness per se. One thing new riders often do is use too high a gear and that wears you out very fast. Try to press more lightly on the pedals but move your legs a bit faster to go the same speed by putting the bike in a lower gear. And don't try to go fast - go slowly enough so you can easily talk while you are riding. You didn't mention if it is hilly where you ride but if it is you need to make sure the gears on your bike are low enough so you can make it up the hills without getting out of breath. Start slowly and you will get faster very quickly as your technique and fitness improve.
I think this depends a lot on which 'part of you' is in shape, which part of you is not, and the general strengths and weakness of your body type. I'm 6'6", and weigh 220# or so. My whole lungs/cardio system has been a limiting factor for me athletically my whole life. No matter what shape I'm in, I will usually be struggling for air before my muscles give out. I play basketball and people will ask me if I'm okay, because my face will be bright red and I will be huffing and puffing... but my legs will be fine. I'm never going to keep up by spinning the pedals fast, but I can use my long legs, a longer crank, and my strength to move along in a higher gear. I agree that you want to get your pace up the best you can, but that pace is different for different people, and whether to gear down or grind it out is not a "one size fits all" decision.