ltxi

Not helpful perhaps but for me the answer is when it feels right. I adult cycling grew up before god invented fit gurus...for the better in my case. Last bike I purchased took me about a minute's ride in the LBS parking lot to determine it was a right/good choice. Knowing my u&c frame size for the application helps immensely. On the hunt for a new primary road bike myself at the moment. Suspect it's not going to an agonizing, drawn out experience.

garysol1 

Heel on the pedal-leg stretched may get you in the neighborhood for saddle height but it has nothing to do with KOPS or saddle fore and aft adjustment.

Gege-Bubu

Let me clarify,
I set my saddle height using "heel on pedal" - only as STARTING point for further adjustments.

This is my basic setup, plus saddle in the middle and leveled to the ground. Once I set myself at this position I can start playing with my adjustments.

exime

I'm exactly 172 cm (5' 7.75"). My inseam is about 31".

I just purchased my first real road bike and it's a Trek SL5 in a 54. Seat a little bit forward and spacers half-way down.

Wheever

+1

I'm 5'9" and I ride a 52 because I have 33 inseam, and therefore a short torso. if you're 5'5+" with a 30" inseam, you're also short of torso, and would probably be happiest with a 50, although you could make a 52 work.

Having been put on 54s (supposedly correct for my height) the first time I tried a 52 Domane, I knew it was perfect. As someone said above, it fit like a glove.

I recommend you try a 50 before you settle on a bike. (And the 54 is RIGHT OUT. Trust me. )

dim

there is also the Eddy Bike Fit Calculator. Use the first result (the Eddy fit). I find this to be pretty accurate with only a few minor adjustments needed:

Bike Fit Calculator | Find Your Bike Size | Competitive Cyclist

over the past several months, I have owned several bikes of different sizes. (I buy a bargain, ride it for a few weeks then sell for profit and buy better)

My 2 current bikes are 50cm frames, and I fly on these. When you get a bike that fits like a glove, you can corner faster aswell and you become very confident. I rode a 56cm road bike for a few weeks and whenever I stopped at a traffic light, I had to lean the bike 45 degrees so as to put one foot on the ground. The saddle was less than an inch from the top bar.

lightspree

Geometry charts are usually available on the web. There is quite a bit of variation.

If I were you, I would go more with feel and less with intellect. You can pick up a lot of ideas that get in the way. Actual experience unwarped by prejudicial ideas will guide you better. Best is what someone above called a "magic" ride.

I can't adequately describe the value of that sort of magical ride quality. It is analogous to relationships. There might be one that is okay -- no real problems, you get along alright, etc. There might be another that is a step up. You feel like buddies, and it's pretty good.

There might be another in which there is something else. You laugh more, there's some spark....

And then there's head-over-heals dynamite. It changes your experience of life in a major way, and changes the level on which you are living.

There are rides that are analogous. Someone said of this that most people, even among longtime cyclists, never get to experience that sort of ride.

I really think it's worth looking around and finding something like that. It can be done. Life is short, years go by, why waste them.

lightspree

Test riding a bunch of different bikes can be very useful.

joejack951

Trek uses C-T (center to top) for their seat tube-based frame sizes. Most other companies use C-C. Because of this measuring style difference, in my experience one needs to 'size-up' on a Trek. YMMV.

Wheever

Seat tube means literally nothing. It's all about the top-tube.

joejack951

When everyone is throwing out seat tube-based sizes for frame and telling the OP he should be on a such-and-such seat tube-based size frame, then seat tubes matter. Unfortunately the bike industry continues to use seat tube-based sizing so we're stuck somewhat caring about an otherwise irrelevant measurement.

lightspree

effective top tube....

and seat tube....

Reynolds 

There are many "scientific" fit calculators, but an experienced eye is as good or better IMO. Here you can see the opinions (and sizing chart) of a master frame builder:
https://https://davesbikeblog.squarespace.com/

rmfnla

Agreed.

Feel too cramped? Bars are too close to the seat.

Feel too stretched out? Opposite of above.

Hips rocking when you pedal? Seat's too high.

Etc., etc., etc...

dim

exactly .... I've recently fitted a Brooks B15 professional saddle to my daily commuter. The previous saddle was a cheapie, but I had it set perfect

when I mounted the brooks, I measured the distance from the centre of the bars to the foront of the previous saddle, and made sure that the brooks was in the exact same position .... aswell as the distance from the centre of the crank to the top of the saddle

3 days later, and I'm still adjusting and tweaking .... moved the saddle half an inch forward tonight, but I think I'm nearly there now

so.... moral of the story .... keep tweaking till it feels right...,. nothing worse than riding a bike that feels uncomfortable... if it does not feel right, something needs adjusting

rmfnla

I went through the exact same thing when I went to my Brooks Flyer; maybe 20 or 30 stops and tweaks until it was "Ahhhh"...

StanSeven

Seat tube is as good a designation as anything. No one measurement describes a frame. I see at least three different ways top tube is measured which is the same as seat tube. Stack and reach probably comes closest. But when you get down to it, choose the frame and pick it out with the seat tube size or however the manufacturer labels it

Wheever

That's nice. Listen, how does the seat tube sizing tell you anything about reach? It doesn't. The height of the saddle can be changed via the seat post, with a huge range of variability to cover a lot of leg sizes with no impact on function of the bike; the top tube, and hence the reach, not so much. Because stem length can, and usually does, impact handling, you have at most 2cm of decreasing reach, and maybe another 2cm to increase the reach. However, depending on the bike and the trail of the fork, etc, either of those could have a negative impact on handling.

Seat height is easily adjustable, with no impact on handling; reach is not. Ergo, the more important dimension is top tube length or reach.

StanSeven

Let me try again. I don't disagree with what you said except maybe there's now a lot more agreement that stem length has minimal impact on handling. What I'm saying is non custom sizes have labels to designate size. It can be tt length, seat post length, small/medium/large or whatever. Many manufacturers keeping the old size designation of seat post is fine. They can use tt length as well.

My point is someone finds the size frame they want from using all the dimensions. That includes reach and stack, sta and hta, chain stays, head tube height, etc. It might be what Specialized calls a size 56 which happens to be sestpost size

Reynolds 

Don't forget that the seat tube isn't vertical, so changes in saddle height also affects fore-aft position, which in turn cause weight distribution and hip angle changes.

lightspree

+1 -- there are many important factors.

The OP might find it useful to know what to look for when test riding, or how exactly to get the best information you can from test rides. I'm interested in this as well, and am starting a thread on the subject.

joejack951

Back to the context of my original post, though, someone saying 'you should be on a 50cm frame' is a worthless comment. Agreed?

lightspree

No, I don't think it's worthless at all. Maybe it would be better to suggest test riding something smaller, and seeing how it goes, rather than "you should"; but no, I think it would be quite useful for the OP to try different sizes, including 50cm, and gain some experiences and insights in doing so.

I know from riding a number of different bikes and sizes that 50cm is an excellent starting point for me.

If I notice a longish top tube, that's information too. More important, for me, is knowing the frame size. YMMV, but why try to impose it on others. I will continue with the approach that is more useful to me. I know the top tube lengths that work best for me, and how chainstay lengths affect the ride, head tube angles and seat tube angles, bottom bracket drop, rake and trail, etc. It all factors in.

lightspree

I would also suggest that the OP try 49cm and 48cm sizes, with an open mind, just to gain some more data points and experience. When I went down in sizes beyond what the shops thought advisable, I found some delightful rides -- far better than what they were putting me on.

StanSeven

Yep. The only way that comment makes sense is everyone talking about the same manufacturers model.