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Have an old (16 years) road bike frame which is a little too big for me. Its old geometry so the top tube and seat tube are the same length at 53cm. Newer road bikes have much shorter seat tubes than their top tubes. A few brands specify a size but none of the tubes are actually that size. For example, Trek say I need a 52 bassed in my height and inseam, but none of the measurements on that size are 52. Not even the effective top tube. So, what does the 52 relate to?
Folk tend to go with top tube size especially with sloping frames. I'm 56 in old skool frames (30 years ago), but a 54 on newer (horizontal TT) although just got a 52 cx bike (horizontal TT).
I'd try some different bikes (even if not the one you want). You ideally need both effective top tube length and effective seat tube height
I'm more upright on the CX bike than the old skool bikes, but all fit fine.
They're probably just using old fashioned sizing to be applied to modern sizes. I was always a 62 but that's now often a 58 as seat tubes have become more compact.
It's like how MTBs used to be sized according to seat tube length but in inches rather than cm.
Most road bike gemometries will quote stack and reach. Pretty good explainer here:
https://www.cyclist.co.uk/in-depth/how-to-measure-stack-and-reach
Sounds like you could find a frame you lke that matches your stack/reach and then look at the next size down.
Newer road bikes have much shorter seat tubes than their top tubes.
Unless they don't. My frame is 54/54 as it has a horizontal top tube. The only measurements I look for are the effective top tube length and the head tube length (so pretty much reach and stack) and the length of the seat tube is irrelevant seeing that 10-20cm of seat post is sticking out of it.
Define “too large”. Only effective top tube matters. And you can adjust stem length for overall position. Generally stems of 80-120 will get a decent fit on a bike that is a size too big to one a size too small. If a frame is really too small, then a 130-140 stem is used. Pros love those because it gives a lower front end and more weight on the front wheel.
The 52 will be the parallel effective top tube and you’d get the same effect on your old bike with a 1cm shorter stem if head and seat tube angles are the same. Smaller frames tend to have slacker head angles (72-72.5 degrees) to reduce toe overlap that makes for a shorter top tube (about 1cm per degree)
Define “too large”.
Feels a little too long with an 80mm stem. And too tall with only about 10cm of seatpost exposed. Im always sliding my hand back on the hoods to get comfortable.
What’s the saddle set back (nose behind BB) measurement. 10 cm of seatpost is not unreasonable for a traditional frame. Stem does sound a little on the short side, but that might be saddle position. 5-6cm behind BB# is a good starting position. The other important measurement is crotch clearance. Stand over the bike. Lift the frame up until it impacts the crotch. You need at least an inch of clearance. Less than that and the bike IS too big.
#back the bike up against a wall and measure the horizontal distance from wall to BB and wall to saddle nose. Subtract the smaller from the larger.
If you have an 80cm stem and it still appears to be too long (sliding hands back from hoods) then it sounds too big. Would need to go down on effective top tube by at least 2cms. The thing to then watch out for is bar height being reduced IF the 52 has a shorter head tube (which is likely).
You can also change the bars to a set with shorter reach. Some bars are 100mm reach while others are 75 (and even 70 for specific short reach models). If you are on 100 then a 75 would make all the difference.
If the bars are currently the correct height then how many spacers do you have and therefore how many would you need if the head tube was reduced. Nothing wrong with having spacers but not great to have 5cm of them really.
Without seeing you on riding on the bike we are all just clearly guessing though...
If you have an 80mm stem then a size down (based on ETT) would almost certainly be fine. When I started riding I was advised to buy a 56cm based on my height but it never felt right. Sized down and put a longer stem on (110mm) and it felt much better. Better control/felt more stable and my position was much more aerodynamic. Still nearly always end up with a smaller road/cx bike and a longer stem. My only trouble is long legs and shorter torso so I am at the limit of seatpost length, particularly as seta tubes seem to be getting shorter every year. Weirdly I tend to size up in mtb but that's probably because I want the opposite - long reach and short stem?
Its relatively straight forward to measure the ETT on a bike. Look for some pictures. You'll be near enough and then you can compare. The other option is to sit on some bikes. You'll be able to find geometry for more modern bikes, particularly new ones so this will let you compare.
Look at Specialised, Giant and Trek specifically at their size guides and take note of the geometry. Then use those numbers for manufacturers than don’t offer a size guide - it’ll put you in the right ballpark.
The difficulty usually comes if you’re in between sizes. For this, I tend to size down for road bikes as opposed to up for MTBs. Too short a stem on a road bike is twitchy and being too stretched out makes it hard to use all the hand positions offered by drop bars.
Giant says im right at the bottom end of a size small. Trek and speciallized sat the lower end of a 52.
Ill have a measure of my frame and compare.
So, what does the 52 relate to?
It's a nominal size, might as well say "medium" for all the relevance it actually has to any measurable physical characteristic of the frame.
Giant says im right at the bottom end of a size small.
Probably not far off if you need to use a tiny stem and low(ish) saddle on a 53 and still find it too big.
Unless you have mobility issues, or are trying to sit bolt upright.
Trek’s 52cm size will refer to the seat-tube length for a frame where a virtual horizontal top tube would meet the seat tube. If your old bike is 53cm top-tube length, then you’re getting towards smaller frame sizes, more so if you’re finding an 80mm stem with only 10cm of seatpost showing a touch too large.
The OP sounds similar stature to me based on bike frame size and I’d be looking at no bigger than a 50cm in Trek - a 52cm frame would be too big.
Lots of dealers would offer you a bike fit sizing session effectively for free if you were to buy a bike from them.
Im 164cm if that helps. Fairly flexible.
Again, without seeing you I am guessing but for someone 164 high a 53 definitely would sound way too big.
I prefer a 53cm top tube and I am 177.
Just took some measurements and got the following:
Effective top tube = 540
Seat tube = 510
Head tube = 145
Saddle set back = 25
Bar reach = 80
Stem = 80
Stem spacers = 20
The hoods of the levers are about 25mm lower than the top of the bars. Ive noticed most new road bikes have the hoods and bars level. So a shorter head tube wont be an issue.
I'd quite like the saddle to hoods about 25 - 30mm shorter.
Just ignore "sizing". All they do is compare one size of bike of a particular model to a bigger or smaller one. You can't even rely on that always being consistent through a manufacturers range. In the good old days of horizontal tubing we used to say that the frame size (thats seat tube) should be 10" less than your inside leg. Not your trews size but floor to balls. It isn't far off even with modern geometry.
To be sure check top tube, stack etc and ideally try for size.