I'm trying to figure out this frame size. From the pic, I'm assuming it's a 54cm. Any help would be appreciated. Thanks.

If measured from the bb-I'd say 52cm. I can tell easier by the size of the headtube/haha. Pic of the entire bike would be appreciated.

Is this a trick question? That's a tape measure. 2.54 cm to an inch.

Does this help? Website info says bike was offered in 52cm and 54cm.

Not a trick question. I'm curious about correct measurement. 21 inches = 53.34cm. Wondering if anyone else is seeing 21 inches....little more or less???

Robbie could tell you for sure.

My guess is 54. Looks like the tape is sort of positioned to the front of the ST, which might be giving a slightly inaccurate reading.

I see 20.5"

Depends on which convention Centurion followed.

Looks like a little less than 21 to the top of the top tube so 53 cm c-to-t unless the angle of the photo is playing tricks on me or the bottom of the tape is not centered on the spindle.

That is a 52cm frame (20.5 inches center to center).

Some companies measured to the top of the seat tube, most or many measured to the center of the tube intersections including for the seat tube.

Of course this difference in measuring is confusing, some might call that a 21 inch frame, and the thing is, it does not matter what we call it, either way it is the same frame, does it fit or does it not?

Yeah, it is a 52 cm/20.5 inch frame.

The top tube length is more telling to me, as long as I can get a seat post that will adjust out to my needs, I go by the top tube length as the more important when I compare bicycles to one another for size.

J

Thanks Loose Chain,

The angle may be off on the photo. I did a better job with this one. You are stating that center of BB to center of top tube is the correct way to measure?

This is what I'm thinking, too. And from the second pic, it's looks like a relatively long top tube. You should measure that, @Foghat, and compare it to other bikes that fit you well. There isn't a universally accepted "correct" way to measure, but most of us and most manufacturers use C-t-C.

Zero end is the center axis point the BB spindle rotates around..

top end can be center to center, center to top or center to the highest point, you have to specify, for clarity..



...

If you do a google search for 'how are centurion frames measured' you will find a lot of c-top answers. Just sayin. I agree with the concept that the frame size is what it is, but the question posed (I think) is do I have here a 52 or 54 Centurion?

Not shown, the bottom end of the tape.

Bottom end of the tape is in the center of the BB spindle.

Why does it matter which size the frame is? Are you able to get your needed fit with it? Most riders can set their seat height to the same amount with a range of frame sizes. BUT it's the reach forward to the bars (and their relative "height" compared to the seat) that is often the trickier issue. Andy

That appears to be an '89.
Centurion used the c-t convention, according to their 1987 catalog, and it seems unlikely they changed their approach in '89?

As it is ~21.25" c-t, it is a 54 cm by Centurion's measure.

(Italian convention was c-c, while English was c-t.)

Thanks Machinist! That is some solid information.

I don't know why it matters to the OP, but one reason might be if the current frame size isn't ideal and one wants to determine what size to look for. Or for a person of short stature it might be useful to understand whether the present frame is the smallest they made, or whether there is still another size down.

Center to top of seat tube is a legitimate way to compare within the same brand of cycles or even type but since many manufactures leave the seat tube as much as an inch above the top tube or even more this can prove frustrating when trying to compare bicycles. The effective top tube length c/c is the best way, I suppose but failing that, measuring c/c of the seat tube is useful.

It does not mater what Centurion says the size is, what matters is how it fits the OP and how it compares to other bicycles he has in his/her fleet or experience.

J