Frustrated over bike sizing - am I wrong?

[Clancy]

I was just looking at a manufacturer’s web-site describing a nicely made steel frame bike. The manufacturer nor the model is important as I have seen the same on virtually all other sites.

The frame is listed at a 54. Very nicely made, typical sloping toptube.

The actual toptube length is 549.9 CTC
The effective toptube length is 565 CTC
The seattube length is 55 CTC

There is nothing “54” in any of those measurements.

I first started riding higher end bicycles in the early 70’s, my first being a Holdsworth. I believe it was a 53, could have been a 54. As we all know, frames had level toptubes and if a bike was labeled as a 53, both the TT and ST were 53cm CTC. The only big difference if my fading memory is correct was that some manufacturers went even in size jumps (48, 52, 54) others odd (51, 53, 55). Some measured the ST both CTC and CTT, but for the most part, one company’s 54 would be the same size as another company’s 54, or extremely close.

Then manufacturers realized they could dramatically reduce inventory by creating a compact frame with a sloping toptube. I have no issues with this concept, it seems to have served the public well. Even if I did, it’s here to stay.

And in the case of lower end bikes that are sized S - M - L - that’s probably just fine.

But was has not served the public well is how the industry is sizing bikes, with the above example not being an outlier but rather the confusing norm.

And I haven’t even mentioned Stack and Reach which is a little bit of a different conversation. But the manufacturer that I’m referring to does not list Stack and Reach, only measurements.

I understand the interplay of ST angles and reach, BB drop and all that stuff. Yet I still have to puzzle over a geometry chart to figure out what the heck is going on. And I’m not saying the industry should go back to making square frames and cookie cutter measurements, but some consistency would be nice. Or at least some relationship between how the frame is labeled and how it measures.

How is the frame I’m using as an example a “54”?

When the industry first started down the sloping TT path, how sizing was measured also changed but there seemed to be some relationship to how frames were previously measured. Now it seems to be much more convoluted, at least to me.

I have always believed that bikes should be measured square, that is where the theoretical horizontal TT would intersect the ST. If that was standard and used in combination of Stack and a Reach, I believe it would eliminate a lot of confusion.

And Stack and Reach was suppose to eliminate confusion and standardize sizing, but in this case, it’s not listed.

We talk about frustration over the lack of standards when it comes to BB designs, axle widths, and headsets and that is confusing. With that said, being more open here can lead to more innovations. However, seems to me the one area that would greatly serve the industry and public well would be to standardize sizing.

I can’t imagine buying shoes this way!

Am I wrong? Set me right.

[oldpotatoe]

Yer not wrong. Bike 'sizing' has made no sense for a long time. That 'number' you see often doesn't really describe anything, kinda like 'S,M,L,XL'...

BUT, 'most' will not buy or ride something without knowing the 'real' dimensions, like seat tube ANGLE and tip tube LENGTH, along with reach and stack...throw in head tube length, angle, etc...Kinda like buying a '44L' suit, rather than a proper sized suit for that 'person'..

[unterhausen]

Kona is really bad at this. Their sizing is almost unrelated to the size of the bike. Obviously, you have to look at the real geometry numbers, but it seems like they should give you a better hint at where to start.

[AngryScientist]

As we all know, frames had level toptubes and if a bike was labeled as a 53, both the TT and ST were 53cm CTC.

i could be wrong, but i dont think this was ever universally true. as far as i know, there never was an accepted standard to numerical frame sizing, and never was a rule that frames were generally built with square geometry as you suggest.

that said, yes - numerical sizing today is all over the place. unless you are familiar with a manufacturer and how they name bike sized, in every case, you need to start from scratch and look at the geometry chart to see what the actual sizing is.

[madsciencenow]

I’m glad to hear that I’m not the only one who has been confused by the seemingly arbitrary sizing that some manufacturers are using. If a geo chart can be found it’s not a big deal but i hope there is more thought being given the design and build of the frame than appears to be the case for the sizing numbers.

Personally, if a bike is labeled with a T-shirt size it’s a clear indicator that it’s not for me. I’m sure there are examples of great frames getting thrown out with the bath water but there are so many great options available these days that I really don’t care.


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[jtakeda]

I was just looking at a manufacturer’s web-site describing a nicely made steel frame bike. The manufacturer nor the model is important as I have seen the same on virtually all other sites.

The frame is listed at a 54. Very nicely made, typical sloping toptube.

The actual toptube length is 549.9 CTC
The effective toptube length is 565 CTC
The seattube length is 55 CTC

There is nothing “54” in any of those measurements.

I first started riding higher end bicycles in the early 70’s, my first being a Holdsworth. I believe it was a 53, could have been a 54. As we all know, frames had level toptubes and if a bike was labeled as a 53, both the TT and ST were 53cm CTC. The only big difference if my fading memory is correct was that some manufacturers went even in size jumps (48, 52, 54) others odd (51, 53, 55). Some measured the ST both CTC and CTT, but for the most part, one company’s 54 would be the same size as another company’s 54, or extremely close.

Then manufacturers realized they could dramatically reduce inventory by creating a compact frame with a sloping toptube. I have no issues with this concept, it seems to have served the public well. Even if I did, it’s here to stay.

And in the case of lower end bikes that are sized S - M - L - that’s probably just fine.

But was has not served the public well is how the industry is sizing bikes, with the above example not being an outlier but rather the confusing norm.

And I haven’t even mentioned Stack and Reach which is a little bit of a different conversation. But the manufacturer that I’m referring to does not list Stack and Reach, only measurements.

I understand the interplay of ST angles and reach, BB drop and all that stuff. Yet I still have to puzzle over a geometry chart to figure out what the heck is going on. And I’m not saying the industry should go back to making square frames and cookie cutter measurements, but some consistency would be nice. Or at least some relationship between how the frame is labeled and how it measures.

How is the frame I’m using as an example a “54”?

When the industry first started down the sloping TT path, how sizing was measured also changed but there seemed to be some relationship to how frames were previously measured. Now it seems to be much more convoluted, at least to me.

I have always believed that bikes should be measured square, that is where the theoretical horizontal TT would intersect the ST. If that was standard and used in combination of Stack and a Reach, I believe it would eliminate a lot of confusion.

And Stack and Reach was suppose to eliminate confusion and standardize sizing, but in this case, it’s not listed.

We talk about frustration over the lack of standards when it comes to BB designs, axle widths, and headsets and that is confusing. With that said, being more open here can lead to more innovations. However, seems to me the one area that would greatly serve the industry and public well would be to standardize sizing.

I can’t imagine buying shoes this way!

Am I wrong? Set me right.

Your not wrong but you’re also not right.

Without knowing the angles it’s impossible to tell if the bike is designed for long top tube short stem and I could see this geo working depending on bike. That being said, I doubt all the manufacturers you’ve researched designed their frames that way so it’s definitely wonky to size it like that—but I do think on a 1 bike basis it’s possible it will work and fit like a “traditional” 54

[kramnnim]

Unlisted Stack and Reach would be frustrating...

[cmg]

You'll have to create/calculate the stack and reach using online calculators such as https://www.bikegeocalc.com/ and http://www.bikegeo.net/ These will work as long as the Seat tube angle is given. your not wrong it's frustrating. You can't let the shop staff guide you, they'll sell you anything.

[nublar]

Size by stack and reach only

[fmradio516]

What boggles my brain is how current prod frames are labelled XL but have a 56cm seat tube and top tube..

[Dave]

Even without stack and reach, effective TT length should mean the same thing as the former horizontal TT length.

Then look at the head tube length, with the headset. If the headset is integrated, most have a 15mm top on them, that adds to the length. If it's external, then pick a headset and add the appropriate length.

STA is still the same.

Seat tube length could be measured c-c or c-t, but it rarely affects fit, if the TT is sloping.

Any brand not posting the stack and reach is really behind the times.

I've seen resellers adding xxs through xl sizes that are not from the manufacturer and those are meaningless.

Kona road bike charts now have all of the necessary info and their size numbers are the ST length C-T.

[cmbicycles]

What boggles my brain is how current prod frames are labelled XL but have a 56cm seat tube and top tube..

As someone who rides bikes with a 61 eff/horizontal/actual top tube for my road bikes, this doesn't make sense to me either, I would need an XXXL frame I guess. Thankfully, the number of issues with bike sizes pales in comparison to issues with vanity sizing in clothes.

[prototoast]

As someone who rides bikes with a 61 eff/horizontal/actual top tube for my road bikes, this doesn't make sense to me either, I would need an XXXL frame I guess. Thankfully, the number of issues with bike sizes pales in comparison to issues with vanity sizing in clothes.

Where's the manufacturer located? The average male height in the Netherlands is about 5 inches more than the average height in China. I'm 5'11 and typically ride a 56-57. In a Northern European country, I probably belong in the "medium" bucket, in an East Asian country, "large" or "extra large" makes a lot more sense. With global supply chains, not every brand recalibrates their sizing charts for each market.

[HTupolev]

As we all know, frames had level toptubes and if a bike was labeled as a 53, both the TT and ST were 53cm CTC.
Not necessarily. In any given road bike model there was usually a size where the ST and TT lengths were about the same, and this was usually somewhere in the mid-50s. But ST and TT lengths could be very different on the same model in the more extreme sizes: typically, seat tubes would change with frame size more than top tubes did (this is still true of modern bikes).

I have always believed that bikes should be measured square, that is where the theoretical horizontal TT would intersect the ST. If that was standard and used in combination of Stack and a Reach, I believe it would eliminate a lot of confusion.
I understand the interplay of ST angles and reach, BB drop and all that stuff. Yet I still have to puzzle over a geometry chart to figure out what the heck is going on. And I’m not saying the industry should go back to making square frames and cookie cutter measurements, but some consistency would be nice. Or at least some relationship between how the frame is labeled and how it measures.
The issue is that virtual seat tube length doesn't actually correlate to a bike's overall sizing very tightly. For instance, if a frameset uses a taller head tube because it's intended to be fit more upright, this will tend to make the virtual seat tube longer, even though the bike isn't intended to fit bigger riders.

Today's "frame size numbers" try to solve this by representing the intent. It's often nebulous how they relate to a bike's sizing, but I think from most manufacturers it probably maps better to the old-school seat tube sizing than you'd think. Especially since that old-school seat tube sizing had multiple centimeters of slop in it anyway, due to different manufacturers using CTT or CTC or whatever.

I can’t imagine buying shoes this way!
A bicycle frameset has far more geometric considerations than a pair of shoes. It needs to accommodate the shape of the entire body, not just the feet. And it will vary by use case, both due to posture and contact point selection (a bicycle intended for a lower-reach handlebar will usually have a longer top tube, for instance).
There's nothing strange about multiple numbers being not only needed - but desirable to have - when selecting a bicycle frame.

Also, if you only care about a single-number "shoe size" when buying shoes, congrats on the average-shaped feet. Many of us need to also worry about width, and different brands have different interpretations of how these things scale. It gets messy.

And Stack and Reach was suppose to eliminate confusion and standardize sizing, but in this case, it’s not listed.
Stack and reach does reduce confusion. If a bike manufacturer isn't listing it on production models in 2019, run the other way.

[ToonaBP]

I have always ridden a size 54 or medium. When I purchased my C-Dale Topstone I needed a size SMALL.
Horizontal TT is 54.4 on the small and 56.1 on the medium....

[prototoast]

I can’t imagine buying shoes this way!


Shoes are sized by completely arbitrary numbers that aren't standardized across brands, countries, or genders. Most people find shoes that fit through trial and error.

[Dave]

I have always ridden a size 54 or medium. When I purchased my C-Dale Topstone I needed a size SMALL.
Horizontal TT is 54.4 on the small and 56.1 on the medium....

That's a example where reach helps make the correct decision. The TT may be 54.4, but due to the slack STA, the reach is short at only 37.7cm. My Colnago C-RS has a much shorter TT length of 52.7cm, but the reach is about the same, after subtracting 6mm to correct for the lower stack height. The difference is because the STA on is 74.6 on the Colnago, compared to 73.1 on the topstone. The tall stack on the topstone tells you that it's an endurance bike, intended to have a more upright position.

I corrected the above because I forgot that the reach of two frames with different stack heights cannot be compared directly. The reach of the frame with the shorter stack should be reduced by 3mm for each 10mm of stack height difference.