mr,grumpy 

The first "nice" road bike that I had as an adult was a 54cm Peugeot, vintage, PR series tat I hapened upon purely by chance. At the time I didn't re;I've that it was "too small" for me and that, acording to the charts and the way that I felt on a bike, at least vintage ones, I was best suited to a 58cm frame, fully two sized larger than what I had. So, I sold it and got a more modern, 58cm Trek 1500. It was, as you can imagine, a much nicer bike than the old Peugeot, if a little more "generic". The problem was that, despite the internet and the 58cm vintage bike I had been riding, telling me that a 58 was the thing, it wasn't and it was too big and got sold. Then, along came my bike now, a Specialized Tricross in 56. It's perfect. No issues. Its set up for general use and I wanted a "race bike" so I got ahold of a Roubaix of a similar vintage, thinking that it was a 56 and i am perfectly comfortable on it and content and it's really a 54. The exact same size that was "too small" for me initially. To test weather or not I've drunk or someting I got a ride on that vintage 58 and it still seems to fit me fine, but going up to a vintage 60cm isn't going to work at all. How can I be so random in what I think "fits" me and wat doesn't?

livedarklions

My two "go-to" bikes are 56 and 52 respectively. They both fit me perfectly, but for slightly different uses. The small one is my "race bike", although I don't actually race, while the big one is more of a relaxed fit. I can and do ride them both for very long distances, but there's no question that I'm a bit faster on the race bike, and more tired after the ride. I also carry more stuff on the bigger bike.

I also like that the bigger bike is my Giant. It certainly looks like one next to my Spesh.

Unca_Sam

Some advice that keeps popping up on the forums here is that the top tube length (virtual TT is better) is more of a final 'bike size' measure as opposed to the seat tube. You have more adjustment in your seatpost than you do with stem length. While seat to pedal is absolutely critical for performance and efficiency, the top tube length is acceptable even if you place too much weight on your hands.

I paid for a bike fitting at a local bike shop, and I believe that the knowledge of recommended frame proportions has paid dividends in my [self destructive addiction] adventure into cycling. You can make some precise measurements at home with some help and use online calculators to approximate what you should look for, and then pay attention to geometry tables when shopping.

'Vintage' road frames were frequently described as 'square' meaning the top tube is parallel with the ground. The top tube length was frequently proportioned (within a size bracket) to the seat tube length. Modern bikes utilizing sloping top tubes still measure center to center for the seat tube, rather than to the imaginary point where a horizontal top tube will join an extended seat tube. The result is that a '52cm' frame might have a 55.5cm virtual top tube, and ride like a 'square' 56cm. I use the geometry charts and the virtual top tube length to figure out a bike's 'true' size, but I only know what sizes to look for because of the bike fitting. To help you evaluate bikes for yourself, compare the geometries of the bikes, with the emphasis on where the saddle is in relation to the bottom bracket and handlebars. A long level is useful when you're top tube is sloping.

Sapperc

Your experience is normal. There is no standard in bicycle sizing, sometimes even within the same brand, especially when comparing frames from different years. What fits really depends on overall geometry of the frame and your riding preferences. You will no doubt continue to discover that you are comfortable on a range of bike “sizes.” Happy cycling!

Wilfred Laurier

There are two issues you are experiencing - (1) Different manufacturers and different eras measure bikes differently, and different manufacturers will build based on different philosophies of fit - even if Trek and Cannondale both intend their 56 cm bike to work for someone 180cm tall, the bike will fit differently. Also, around the turn of the last century, most manufacturers went from traditional 'level top tube' geometry to 'sloping top tube' geometry, and if you try to use the same dimension to identify the size of a bike as you used on a 1980s Peugeot 10 speed to select a 2019 gravel bike, you may be totally out of whack. In 'level top tube' bikes I generally need a 62-64 cm, but the modern 'XL' bikes that I have found that fit me might be called 60cm or 58 cm (or simply 'XL')

And (2) fit charts are usually fine for getting you in the 'ballpark', but all people are different - different thigh/shin length ratio, different leg/torso ratio, different torso/arm ratio, and (just as importantly) different flexibility and expectation of comfort.

Now that you know how you prefer your bike to fit, you never need to look at a fitting chart again, and you can do some simple measurements (or look up the geometry charts for your bike) and compare any potential new bikes to your known-good-fitting bike. In sizing charts, the most important dimensions are 'stack' (vertical distance from bottom bracket to the top of the head tube) and 'reach' (horizontal distance from the bottom bracket to the top of the head tube). If these two0 dimensions are close to those of a bike you know to fit, then it can almost definitely be dialled in to fit you.

Unca_Sam

Hooray for consensus!

You're not drunk, what you have experienced is normal!

Wildwood 

Different saddles, posts and bars are often overlooked as contributors to an unexpected outcome with fit and deserve scrutiny when evaluating a change in bikes or cockpit components.

modern saddles may be longer and narrower than vintage.
posts = setback or not?
bars have different reach, drop, bends, etc

edit: I comfortably ride many bikes ranging from 58 - 63cm frame sizes.

CliffordK

That is more or less how I consider sizing. One might also look at the headtube length (stack height).

But, in general, the length of the top tube seems to be the most representative.

However, one can look at riding the bicycle as 3 contact points.

Pedals (bottom bracket), Saddle, and handlebars.

You can make a bunch of adjustments. Stem length, stem height, saddle height, saddle fore & aft, crank length, etc.

The OP didn't mention his height. I'm not convinced a high top tube is a major problem, at least for riding on the road. Unless, ou are trying to do a top-tube descent.

At stop lights, I take one foot off the pedals, and sit one cheek on the top tube, and it is nice to have it a bit high. But, riding, you're not on the top tube.

Stack Height will affect bar drop if that is a concern.

cyccommute 

I would posit a third issue...habit. People get "used" to the way a bike fits and have trouble changing. I've had to fight that problem for more than 40 years. Not me...I fit any 58cm road and any 19" mountain bike that is made without issue...but my wife. My wife is a very tiny 5' tall. Her first bike was a Sears "10 speed" and was a 27" (in other words it had 27" wheels). The frame was closer to my size or about a 23". She figured out how to ride it as a kid and when we got into bicycling, we got something closer to her size (still too big) and it didn't feel right. She was used to riding a huge bike.

As we upgraded, the bikes she could get were still to big...the smallest sizes up until a few years ago was a 49cm. When manufacturers finally got enlightened and started making smaller bikes, her "actual" size of 43cm felt far to small. She has the proper sized bike now and it feels "normal" but it was a long road to get her to actually accept what was right.

mr,grumpy 

Thanks guys. I'm glad to know that my imagination isn't playing tricks on me! I was OK in the 56-58 "range" thing but when my latest new-to-me turned out to be a 54 (by my measurements, not a manufacturer's sticker) it left me bewildered. Now I need to ride more and obsess less and i'll be good to go.

Wilfred Laurier

Thanks for that. I would go as far as to say it is possible that a person can get used to a very ill-fitting bike, and feel like what most of us would call a 'good' fitting bike is uncomfortable.... kind of like when a casual cyclist expects to be able to put both feet flat on the ground when astride the saddle, and are uneasy with the suggestion that they should not be able to.

The way the OP described their attempts with different size and manufacturers, though, I don't think this is the case here.

alcjphil

I can provide a very good example: I own 3 Look bikes, a 595 size large, a 481SL size 54 cm and a 496 TT/TRI in size small. They all fit very well even though they are supposedly different sizes. I previously owned a 55 cm Look KG381(the predecessor to the 481SL) and the 57cm top tube was just too long for me. It is also important to remember that the bike that fit you 20 or even 30 years ago may no longer suit you. My first good bike was a 23 1/2" (58 cm) Raleigh Professional back in 1973. I thought that it was a perfect fit even with a 130 mm stem. That was then and this is now. I would not be able to ride it today. I currently own a 1980's 54 cm Limongi steel road bike that is very similar in road feel to my old Raleigh Pro as well as being almost as good looking. I have only ridden it a few times, just enough to know that it is a very good fit. we used to look at standover height as a good starting point for bike fit. That is no longer the case

bruce19

With the advent of SST it's a bit harder to know what a designated size really is. I just bought a CAAD12 in size 52. After 40 yrs. of cycling I know I can ride 54-56. But, the CAAD12 fits perfectly. How can that be? Well, using a level and tape measure I "leveled" the TT (virtually) and measured the frame again......54 actual.

DaveSSS 

Getting the right frame size is much easier, now that most brands publish the stack and reach. Those two values tell the story. It makes no difference what the size number is.

The only other thing to pay attention to is the seat tube angle. I ride smaller sizes that nearly always have a 74 to 74.5 degree STA and either one will work with a 25mm setback post. If the bike has a steeper 75 degree STA, I'd need a 32mm setback and I avoid that.