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How are you guys eyeballing frame sizes?

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How are you guys eyeballing frame sizes?

Old 11-13-20, 05:42 PM
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How are you guys eyeballing frame sizes?

I see a lot of posts here where someone will post a picture of a bike or a frame without saying what size it is, and other people will say something like "Oh, I'd buy that if it were a little bigger/smaller," or they'll just somehow just know the size outright. How are you doing that - is it just experience?

If I'm browsing through pictures on Craigslist or eBay, I look at how much space there is between where the top and down tubes join the head tube, but other than that I have no clue how to estimate the size. Are there other tips/tricks?
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Old 11-13-20, 05:47 PM
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Head tube size. I know roughly what a 56 cm (my ideal frame size) head tube looks like, so that's my visual target.
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Old 11-13-20, 05:49 PM
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Yeah, for traditional diamond frames, head tube length is an excellent indicator but there are always exceptions.
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Old 11-13-20, 05:50 PM
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Me too, head tube is the first place I look. With the classic geometry from the mid- to late-20th century, that's a good rule of thumb since it was fairly consistent from one bike type to another.
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Old 11-13-20, 05:52 PM
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I focus on frames that are roughly my size while I'm browsing eBay and have had enough of my own, so that I can rather quickly tell the proportions between the main tubes to figure things out approximately. What throws me for a loop are larger or smaller frames with awkward proportions that sometimes make them seem to mirror what I usually see in my size range, which is between 60-62cm. It most frequently happens with slightly smaller frames that have high bottom brackets and longer-than-usual head tubes to compensate for the rise.

It's just a matter of looking at bicycles way too much, really... That's all!

-Gregory
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Old 11-13-20, 05:58 PM
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Originally Posted by nlerner View Post
Yeah, for traditional diamond frames, head tube length is an excellent indicator but there are always exceptions.
In general older bikes have shorter head tubes, as a result of bigger clearances. Early nineties Giants have also fooled me, because of their slightly forward-sloping top tube.
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Old 11-13-20, 06:54 PM
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Yeah, if the head tube looks like my bike, i know we're in the 58-60 range, and i kinda extrapolate from there.

Obviously we base these guesses on a bunch of assumptions that we may not recognize. So when I bought a 1940 Schwinn New World on ebay some years ago, i failed to consider that it had 26“ wheels. Sadly it proved to be a much smaller frame than I'd expected. Doh!
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Old 11-13-20, 07:09 PM
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Originally Posted by ScottRiqui View Post
I see a lot of posts here where someone will post a picture of a bike or a frame without saying what size it is, and other people will say something like "Oh, I'd buy that if it were a little bigger/smaller," or they'll just somehow just know the size outright. How are you doing that - is it just experience?

If I'm browsing through pictures on Craigslist or eBay, I look at how much space there is between where the top and down tubes join the head tube, but other than that I have no clue how to estimate the size. Are there other tips/tricks?
...I once drove all the way to Merced and back to look at a 58cm Paramount that turned out to be a 21" frame, even after I asked the guy to measure it. So I always ask the current owner, and then I don't count on getting correct information. I want to measure the top tube length and the stem to saddle distance as currently configured anyway, so while I can sort of get a feeling from a photo, I don't count on my feeling being correct either.

The tip is to bring along a tape measure.
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Old 11-13-20, 07:24 PM
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If the head tube has a pump peg, it's placement will give you some indication. 56cm frames generally look square or close to it. 58cm and up the TT looks shorter than the rest of the triangle. 54 and down, the TT generally looks longer than the rest of the triangle. Buy yourself one of the small 6ft. tape measures and put it somewhere in the vehicle you go to look at bikes in.
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Old 11-13-20, 11:16 PM
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Like everyone has said: head tube length (on traditional frames). But you gotta combine that with a lot of time spent looking at pictures of bikes. After getting into the hobby I realized that after a month or so I was starting to eyeball frame sizes, not long after that I was a natural.

So it sounds like you’re on the right track, you just maybe haven’t looked through countless thousands of photos of bicycles like the rest of us

Last edited by polymorphself; 11-13-20 at 11:21 PM.
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Old 11-14-20, 04:59 AM
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It's also important to note that you are only looking for 2 sizes.

Size 1: "Thats my size. I can ride that."
Size 2: "I better list that one in the Looking
For/Ebay thread so someone else can see it."

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Old 11-14-20, 06:06 AM
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As others already mentioned, the length of the head tube gives a good clue on the frame size.

I also pay attention to the location of a pump peg (if present of course) and the distance from the peg to the top and the down tubes.

If the distance between the peg and down tube is roughly double of the distance between the peg and the top tube then that's a good indication of a 56cm frame:




If the distances from the peg to the top tube and the bottom tube are about the same - its 54 cm. Important note here: the distance should be roughly equal to the top tube to peg distance on 56cm frame (about 1"). On 52 cm frames the distances from the peg to top/down tubes are about the same too but they are much smaller (about 1/2").
Example of 54 cm frame:


if the peg to down tube distance is about 2.5-3 times greater than the peg to top tube distance then it could be 57-58 cm frame. But it's much harder to eyeball the frames that are larger than 56cm (in my experience). Here's an example of a 57 cm frame:



As far as I remember, the 50cm frames and smaller will not have the pump peg.

Hope this helps.

And yes, I am showing off my bikes ... cause i love them and they are pretty
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Old 11-14-20, 10:15 AM
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Originally Posted by 3alarmer View Post
...I once drove all the way to Merced and back to look at a 58cm Paramount that turned out to be a 21" frame, even after I asked the guy to measure it. So I always ask the current owner, and then I don't count on getting correct information. I want to measure the top tube length and the stem to saddle distance as currently configured anyway, so while I can sort of get a feeling from a photo, I don't count on my feeling being correct either.

The tip is to bring along a tape measure.
If the camera position is good, you can take a ruler or caliper and scale the TT length against the wheel diameter, and come up pretty close to an in-person measurement. Of course it's possible to mess up an in-person measurement as well.
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Old 11-14-20, 05:36 PM
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Originally Posted by t1k View Post

And yes, I am showing off my bikes ... cause i love them and they are pretty
Thanks for that! And the pictures were particularly helpful, since I just recently got my first vintage bike, and it's a Miyata 1400!
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Old 11-14-20, 06:44 PM
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Head tube size. I know roughly what a 56 cm (my ideal frame size) head tube looks like, so that's my visual target.
And that is exactly what works for me until I got this Quintanna Roo which I though to be way too big, due to the length of the head tube. Turns out the bike, fitted with 650a wheels, was a perfect fit for me...
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Old 11-14-20, 07:39 PM
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Originally Posted by ScottRiqui View Post
Thanks for that! And the pictures were particularly helpful, since I just recently got my first vintage bike, and it's a Miyata 1400!
Miyata 1400 is an awesome bike. What year is your bike? Looks like Miyata was selling 1400 only for two years. In 1989 the bike had a steel frame, in 1990 - aluminum. They are fairly high end bikes. Second from the top of the Miyata steel bikes lineup (step down from Team Miyata).

Post pictures of your Miyata. I'd love to see it.

Another thing that helps identifying the frame size is looking into manufacturers catalog and finding out what sizes were available for the given model. For example, Miyata's touring models (600, 615, 618 and 1000) were available in 54 and 57cm, but the rest of their road bikes had 56 cm option.

Here's a link to the Miyata catalogs: https://www.ragandbone.ca/Miyata/miyata_selector.html
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Old 11-14-20, 11:17 PM
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Headtube length is reasonable with these modifiers-
frame era- 60’s bikes will most often have more generous clearances, and often a longer top tube- making for a shorter headtube verses
an 80’s bike with tight clearances for only smaller tires and a short reach brake in front.
One gets a visual Ref. After a while.

I have been fooled, but not often.
worst was a reportedly 57 center to top frame that looked “right”. It arrived and was a 54!
even marked as such on the bottom bracket.
the image was distorted- very strange.
referencing the images later it still looked like a 57 in the seller’s sale image set.
seller went awol after.
Vanished.
fortunately it was a good size for my son later.
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Old 11-15-20, 03:05 AM
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I bought this Marinoni off of Kijiji. The bike was listed as a 52cm, a perfect size for my one of my grand daughters. I did not even question the bike's size until a bit later...


When I got the bike home, something did not jive. The lady who owned the bike was the same approximate height as I am. With that in mind, I straddled the bike? Got off and snapped up the measuring tape. Not a 52, but a 56cm machine. No good for my grand daughter but perfect for you know who. Yup, me and the Marinoni is now my daily rider, when I can actually ride (been off the bike for a couple of months now with worn out hands that cannot pull a brake lever).

I got fooled by the over sized tubing which make the head tube appear to be short and proper for a 52cm size. I was wrong but still tend to look at head tube to approximate a vintage road bicycle's size.
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Old 11-15-20, 06:29 AM
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You tell by lookin' from the dorsal to the tail.
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Old 11-15-20, 06:57 AM
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It's really top tube length that's most important, but fortunately, it doesn't vary as much as seat tube length, and can usually be corrected with the right length stem.

I had a 59.5 cm frame that was perfect in the "reach" department, but I just couldn't clear the top tube standing over it. Why a taller person needs to have the top tube right under their crotch when the reach is already fine ... I will never know. I prefer the smaller frame sizes anyway, most 58 cm and larger steel frames flex like crazy for me, why anyone taller than me would want that, if they could use a smaller stiffer frame size ... also a mystery.
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Old 11-15-20, 09:20 AM
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Originally Posted by Lemond1985 View Post
Why a taller person needs to have the top tube right under their crotch when the reach is already fine ... I will never know. I prefer the smaller frame sizes anyway, most 58 cm and larger steel frames flex like crazy for me, why anyone taller than me would want that, if they could use a smaller stiffer frame size ... also a mystery.
Mostly because seat post lengths tend to top out at 250-300mm. I'm already at the maximum safe length for my 64cm frame's seat post. And I can ride taller bikes than that.
But most taller frames often use stiffer tubing (less butting or oversized) to compensate for the flex.

As for OP, practice and looking at head tubes.


57cm Koga-Miyata WorldTraveller


66cm Koga-Miyata WorldTraveller
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Old 11-15-20, 09:39 AM
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I have a couple of un-butted "plain gauge" frames, and really like them for their stiffness. I do think butting causes unnecessary flex in many frames, maybe that's why Miyaya and others went to "triple butting" their frame tubes, to try to minimize this.

Beautiful bikes, BTW.
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Old 11-15-20, 09:55 AM
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Originally Posted by JaccoW View Post
Mostly because seat post lengths tend to top out at 250-300mm. I'm already at the maximum safe length for my 64cm frame's seat post. And I can ride taller bikes than that.
But most taller frames often use stiffer tubing (less butting or oversized) to compensate for the flex.

As for OP, practice and looking at head tubes.


57cm Koga-Miyata WorldTraveller


66cm Koga-Miyata WorldTraveller
Is that just a normal dt braze-on mounted on the back of the seattube for fd duty? I may have to find someone to do that to one or more of my frames. All the contortioning of a suicide shifter, but lighter and easier setup.

Actually I've got a sscx frame that I've put a chain tensioner with a rd hanger to make into a 1x. That would be the best way to add a multispeed crank.
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Old 11-15-20, 10:28 AM
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On horizontal top tube frames, you can also look at the distance between the rear tire and the top of the seat cluster.
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Old 11-15-20, 10:36 AM
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Originally Posted by Dylansbob View Post
Is that just a normal dt braze-on mounted on the back of the seattube for fd duty? I may have to find someone to do that to one or more of my frames. All the contortioning of a suicide shifter, but lighter and easier setup.

Actually I've got a sscx frame that I've put a chain tensioner with a rd hanger to make into a 1x. That would be the best way to add a multispeed crank.
Bottom bracket dynamo.

But if I weren't going for bar ends that would be a pretty sweet option.
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