How do I know when my frame is too small?

When it's too big, it's obvious. If it's too big, I can't stand over the top tube and I can't lower the seat enough to reach the pedals comfortably. But what if it's too small? What problems are there which can't be rectified by a longer seatpost, increased setback and a longer stem?

The reason why I'm asking is that I can get a good deal on a used road bike frame. Right now my seat tube 47 cm is C-C, top tube is 51.5 cm C-C, wheelbase is 102 cm. I'm 5'6" with 29" inseam. The frame I'm looking at will be smaller, I don't have the exact measurements yet but it's 650c and most likely I'm looking at a 49 cm top tube and 92-93 cm wheelbase.

I'm wondering if I can adjust it to fit me, and if I'm going to run into any problems because of the shorter wheelbase.

that seems small but you can make it work. What is making you want to go to a 49cm?

As a comparison I'm a generous 5'5" and I ride a 49cm. However some bikes run a little bigger so a 49 could work depending on the bike

Took the measurements. Top tube 49 cm center to center, seat tube 46, head tube 13, wheelbase 97. Looks like an OK fit, at first sight.
No specific reason to go with this size, except that I can get it relatively cheap, it's an old carbon frame that needs a paint job.

I'd skip it, I ride a 650 TT bike and finding good tires is a *****, and latex tubes simply don't exist. Plus the wheelsets suck compared to what you can get in 700c these days.

By the way, I've been watching Tour de France the last few days and it struck me that most competitors were riding bikes that looked much smaller (with respect to their physiques) than mine. Just look at the size of that seat post:

https://i.telegraph.co.uk/multimedia/...o_2254972b.jpg

Or to take a guy whose height is closer to mine (5'7"):

https://www.cyclingnews.com/news/phot...ur-stage/79290

Measuring his frame in the picture, I get a 49.5 cm top tube and a 40.5 cm seat tube. He has a small frame and he has to raise the seat way up to accommodate his legs. On my bike, there's barely enough room for a bag and a rear light between the saddle and the frame, I had to ditch the reflector because there was no room for it.

if you measured effective top tube on both bikes you would have some idea about how much longer stem you'll need on the smaller one. but I can tell you that if you're already riding a 120+mm stem on your current bike it's very unlikely that smaller one is going to work.

a bike is too small when you can't get the proper fit on a 140mm stem, or can't get proper saddle setback according to your femur length using a setback seatpost. either of those makes a frame too small. BOTH of them make a frame "way too farking small".

btw seat tube length and seat post extension mean nothing at all as long as you can standover the top tube and the seatpost isn't beyond the minimum insertion. aero road or TT bikes with integrated seatposts / seat masts are especially prone to issues with long-legged riders or riders on the wrong frame size.

Sorry, I changed my mind....

Both bikes have horizontal top tubes. So, effective top tube = measured top tube. I have a 110 mm stem, which is mounted at the top of the steerer tube, and spacers below the stem effectively subtract about 40 mm from the horizontal distance between the saddle and the handlebars.

wheelbase of 102 for a frame that small???

Just remeasured it. 102 give or take 0.5 cm.

I don't get it...are you saying these two pics show guys with small bikes and looooong seatposts? If so, I wouldn't agree at all.

I'm running with far more extension that these guys...Oscar for sure looks like he could even go down a size.

What am I missing?

Just google "Ryan Trebon Felt" for a pic pic of a massive seatpost...

All I know is that my seatpost looks like this https://i50.tinypic.com/16jlnva.jpg

Slam it.

I presume you've got short legs and a long torso, proportional to your overall height. Otherwise that saddle would be way low.

the 650 wheels make it a big NO! for me...

Look at your top tube. It is horizontal. Many frames have downward sloping toptubes, so by the time they are at the seatpost they are quite a bit lower than horizontal top tube bikes - resulting in more exposed seat post.

In addition to that, many professionals will often use a bike that is slightly smaller, and just put a longer stem on and move the saddle up and back to keep the same fit. You can get more drop this way, and it's said the frame is stiffer as well.

We're very similar (height and inseam) but ride a 53.5 ETT with a 90mm stem (common for anything for any frame which is 52 and below).

I had a bike which had a 52 ETT and I felt too cramped. I tried to fix the issue with a slammed 110mm stem which alleviated the issue a little bit. I needed more set back on my seat post and too bad I had a "stream" post which was very limited. Thank god I won't be riding that frame anymore.

That must be the case, because the saddle is just right. I'm not 100% about the stem, but the saddle has been in that spot for close to 1500 miles and it is fine.

True. But if I got the top tube length right, it's still smaller than mine. So hard to find pro riders' bike specs.

why the hell does the bike have 650 tires? Even my 49 has 700 tires..

I bet it's a geometry problem, trying to avoid making the HTA way slack and making the STA too forward...? Also maybe for aerodynamics, smaller wheels, less drag?

Because it was a triathlon specific frame.

In any case, it is gone, someone else made a better offer.