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Frame sizing dilemma

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Frame sizing dilemma

Old 12-30-19, 10:02 AM
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Frame sizing dilemma

Good morning everyone,

I'm struggling to make a decision right now and I was hoping you guys could help me.

So I'm in the process of building a new bike, starting with a vintage frame.
After searching for a while, I've found one incredible frame for sale, full Reynolds 531, in mint condition. It has a classical geometry, with a straight top tube.

The problem is that the seat tube might be too short. I'm 1.78 m, with long legs (inseam is 84 cm) and kind of a short torso. The seat tube is 52 cm, while the top tube is 55 cm ; head tube is 11 cm.
Fit calculators that I've found online suggest that the top tube length would be perfect for me and that a 55 cm seat tube would match me the best.

I'm quite flexible, so I guess I could handle kind of a deep saddle to bars drop, but I'm afraid that setting the saddle to high would push it too far back.

So, what do you guys think? Should I go for it?

Thanks in advance and happy holidays!

PS: I was wondering if I should post this on this section or in the mechanics one. Feel free to move the thread if I'm in the wrong place!
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Old 12-30-19, 10:12 AM
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My guess is that's too small for you. Most useful would be to measure the distance from the center of the crank to the top of the saddle on the bike that fits you the best, and then see where that might be on frames that have a level top tube.
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Old 12-30-19, 10:12 AM
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I think it'll fit pretty well. If the handlebar is too low you can just adjust that a bit with the stem.
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Old 12-30-19, 10:25 AM
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Too small, especially if you have long legs - wait for something that fits.

Been down this road many times and the result will always be a compromise compared to a correctly-sized frame.
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Old 12-30-19, 10:51 AM
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I'm the same height as you and a 52 would be too small. I'd say you want a 56. My inseam is a tiny bit more than yours and I prefer a 57-58 seat tube even, with a 55-57 top tube. I'd prefer to shorten the stem length or run more compact handlebars than need to run a really tall stem to compensate for a too small frame.
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Old 12-30-19, 11:17 AM
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With an 84 cm inseam, way too small. You'd be needing something like a 58-60 cm seat tube .
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Old 12-30-19, 03:22 PM
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Guesstimating 54 to 57 ctr bb-to- top of seat tube on a classic frame with a level top tube.
I'm thinking if you were to go 58 to 60, you might find it too tall, not to mention stand over issues.

56 might be your sweet spot.
Just spit-ballin', tho.

Last edited by chainwhip; 12-30-19 at 05:48 PM.
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Old 12-30-19, 04:05 PM
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If you want something to ride around - as opposed to carrying a bunch of gear, and if you're open to bikes from the 80's or 90's, might want to keep your eyes open for a Crit bike in the 56-ish seat-tube size.
In search of what to search for.
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Old 12-30-19, 07:23 PM
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You need at least a 54 ctc seat tube and many 58s won’t be too big. Keep
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Old 12-30-19, 09:13 PM
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Too many different ways to measure an inseam. Sounds very long for your height but who knows? Vintage sizing is completely different from current era sizing. From not enough information at least 56cm and 60cm is not out of question. Level top tube. 52cm frames are for people 10 and 15cm shorter than you.
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Old 12-31-19, 12:22 PM
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I will agree with much of what is said. At 1.95 m, my first road bike as an adult was a 52cm, given to me by a couple that was moving across the country. I had no idea on sizing, and eventually made it work ok, but it was far from ideal. I learned a lot and now ride 63-65cm frames.

For the English/non-metric among us, 1.78 m is 5'10" and an 84cm inseam is 33". My inseam (for clothes, not cycling) is a, I suppose, slightly short-for-my-height 34-35".

A 58cm frame should be close to ideal, though I wouldn't be surprised if you fit a 60cm. When hunting for bikes, I'd bring your tape measure (or a length/distance measuring device) along and measure seat tube height and top tube length. Top tube length will also be one to keep track of as depending on your arm length, some frames may be a bit long (and thus too hard to "shorten" with a short reach stem, bars, etc). Thankfully, as frames range into the 63cm size, the top tube lengths, in general, increase more slowly. But like I said, bring a tape measure--it will really help to put some concrete numbers in your head for analysis.

Best wishes in your searching!
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Old 12-31-19, 01:12 PM
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do you have one or more bikes that fit you well today ? Usually that is a good guide.

Measure the center of the BB to top of saddle at the projected seat post, and from that point to center of handlebar.

Measure multiple bikes and average them. that's your "magic triangle" of fit that can be used to compare a future or prospective bike.

Online "fit calculators" range from close to total BS. A bike that fits you well is your best guide to what might fit you well.

Mark Petry
Bainbridge Island, WA USA
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