I'm a older guy in the market for either a hybrid or comfort bike. Early 60's, out of shape and lots of hills here where I live. I'm about 5'11" but with a 31-1/2" inseam. According to Hoyle, I should be looking at mid-sized frames around 17". It seems that the bikes I've tried, just straddling, all come right up to the crotch. Just sampled a Nishiki 17" comfort bike and a Diamondback 17" hybrid (can't recall the model names), and the top tube of each one made contact when I stepped slightly forward off the saddle. The guy at the store (in this case Dick's) said I should have about an inch minimum clearance. A Diamondback Wildwood with a 15" frame gave me good clearance but he said it would be mighty short. Is the old maxim of an inch or so clearance still valid with these new frame styles? Am I going to need a custom frame? Going to check an LBS tomorrow but thought I'd ask here first.
Suspension doesn't always leave a lot of room for clearance. Is 31 1/2" your pants inseam or your biking inseam? At 5' 11", you should probably be looking more towards a 19" frame size, or what most brands would term a size "large".
a sloping top tube, frame type,means the seat tube is shorter,
in relation to the top tube as a horizontal distance..
I encourage you to go to a LBS where you can stand over the frame , and see what clearance is like
I go by top tube length , , but even that there is a range ,
stem length and riding posture influence that part
seatposts are made long , with sloping top tube , more is extended..
I have bikes, several. with a 54 +10 stem .. 56 with a 5 those : trekking bars
57, cross-bike with a 9, road bike with an 8.
and a 60 with upright bars and a big rack in front., short seat post extension..
That's my pants inseam. If I had tried a 19" in those two bikes, I wouldn't want to slip forward off the saddle. The 17" frames were just barely clearing, if that. I was wearing jogging shoes. I understand what you're saying about height and how it affects what length frame you need. It's just odd that I'm riding the rails, so to speak. Hence my initial question of maybe I am looking at this the wrong way. If these were, say, road bikes with a straight top tube geometry, I would have had little to no clearance.
When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking. — Arthur Conan Doyle