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Modern Bike Frame Size vs Vintage Bike Frame Size

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Modern Bike Frame Size vs Vintage Bike Frame Size

Old 03-24-19, 09:26 AM
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FordTrax
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Modern Bike Frame Size vs Vintage Bike Frame Size

I have a couple of modern road bikes but I would like to find a nice vintage steel frame and restore it or update it a bit depending on what I find. I want something like a sport tour or touring frame that I can run 32 or 35mm tire on it. I may use it as a winter bike.

I am just over 6' tall and at that size it seems like I take about a 58cm frame most of the time in a modern road style frame. Something around a 580 stack and 385 or so reach. At 56 I ride with the saddle and bars about the same height.

From looking at vintage frames for a while on c/l and the BAY I get the feeling that sizing was measured different then. I don't mean just the fact that they used inches vs cm.

Can you folks give me some assistance in how I know what size vintage sport tour/touring frame I need to be looking for? What measurement do I need from the seller? It seems like many of the sellers don't really understand bike sizing or know for certain what size their bike is.

BTW: Any suggestion on brand/models to keep a look out for would be appreciated.
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Old 03-24-19, 09:39 AM
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I always tell people to look at old Peugeots and Raleighs. Nearly any road bike made before the early 1980's will have pretty generous tire clearance capable of runnig a 32 at least, if not a 35 mm tire.

A 58 cm frame is a 58 cm frame, provided it's measured center to center and not center to top. Sellers of used bikes almost always list the wrong size, I pay more attention to the size of head tubes than to advertised size. Where are you located? Someone on the board who lives near you might be able to make you an offer on something in your size.
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Old 03-24-19, 10:15 AM
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I live near Harrisburg, PA.

When you say "center to center" I assume you mean center of the crank (spindle) to the point on the seat tube which intersects the center of the top tube. However, I think my modern bikes (where I ride a 58cm) are measuring effective top tube length.

For example my Salsa Casseroll is a 58cm the effective top tube length is 580mm but the seat tube length is 600mm. My other bike is like a 575mm top tube and 560 seat tube length.

I seems to me that seat tube length could very by a few cms and you could just expose more or less seat post. But you cannot really change the top tube length - well I guess you can change stem length to some degree.

I guess this is where I am getting confused. I might be making this harder than it has to be but I am having a hard time reconciling the two.

Last edited by FordTrax; 03-24-19 at 10:16 AM. Reason: typo
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Old 03-24-19, 10:27 AM
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If you look at the differences between various frame sizes, the top tube length does not change that much. So I would not worry about that being a limiting factor, the main thing is that your legs can clear the frame when you're standing over it.

It seems as though tall people have most of their height in the legs, while torso length remains relatively constant. There are lots of frames too "tall" for me, on which I would have no problems with the amount of "reach".
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Old 03-24-19, 10:43 AM
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In ye olden days, say the mid to late 70s, you were sized by being asked to stand over the bike. Then you grabbed the bike and pulled it up lifting both wheels off the ground. At that point the space between the floor and the wheels was measured - usually eyeballed. The standard was typically 1 inch to 1.5 inches. 1 inch was more touring; 1.5 more sporty. That gave you the frame size. With that in mind you picked from one of the several bike lines sold at a shop to find one with a top tube length and general layout suited to you. There was a tendency for everyone to want to get on the biggest bike possible. During the 80s there was a general trend to ride smaller frames. Thank Greg Lemond for this.

As a very very rough rule of thumb, I usually figure add about 5cm to your modern sloping TT bike size to get your vintage size. Obviously it depends on many factors.

BTW 99% of bikes sold in bike shops BITD were measured center to top. Only a few exotic Italians used CTC.

Last edited by Salamandrine; 03-24-19 at 11:01 AM.
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Old 03-24-19, 11:37 AM
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As previously mentioned, one straddled the bike standing straight up. The general rule of thumb was you wanted 1-2 inches of top tube clearance in case you came off the saddle, you didn't land on the family jewels. Thinking was much different 20-30 years ago. Case in point--I have a 36 inch inseam and ride a 25 inch frame (the tallest Peugeot made). I bought that bike new 35 years ago. It's my one and only bike and it still fits and is comfortable to ride all day long.
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Old 03-24-19, 11:48 AM
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As you are aware, vintage bikes had true horizontal (level to the ground) top tubes while most new geometries have sloped tubes. Generally top tube length refers to actual length of the tube centre to centre, but it is not uncommon on Geometry charts to see "effective" top tube length, which is also level to the ground.

Many of the on line frame size calculators seam to use effective top tube length and generate a recommend frame size as a the seat tube length similar to vintage geometry. I have used this one before and it seamed to generate the right size for me. https://www.competitivecyclist.com/S...ulatorBike.jsp
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Old 03-24-19, 03:06 PM
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Okay. So just focus on my inseam for vintage bikes because that is the way they were sized back then. So if I have a 33" inseam no shoes I am probably goood with a bike around 32.5" max since my shoes probably add about 3/4". If I look at the vintage size charts they say about a 57 or 58 max then. I also saw something about bikes not being made proportional to size until the mid-80s. Before that the bike companies did not change the lenght of the top tube as the bikes got bigger. That adjusting of the top tube (proportional sizing) for long reach on bigger sizes did not start happening till the mid-80s from what I just read. Do I have that correct?

So the seat tube size give a good indication of the standover clearance I will have on a vintage bike because the top tubes were flat. But the real tell is the standover height needs to be about 1" less then my inseam so around 32.5" of stand over.

Is that it in a nut shell?
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Old 03-24-19, 03:46 PM
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Modern Bike Frame Size vs Vintage Bike Frame Size

Sizing is the same across the market spectrum.
Inconsistent.

Fitting methods are the same across the market spectrum.
Inconsistent.

I've used Colorado Cyclist's chart for modern fits, the "Merckx Fit."
Otherwise, it's hit or miss, and has cost me a few stems and a couple of seat posts.

Once you have the fit, it's like a new bike.

Last edited by RobbieTunes; 03-24-19 at 03:49 PM.
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Old 03-24-19, 03:54 PM
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Hereís some info from one of Greg Lemondís books. Keep in mind the old adage YMMV depending on the type of riding you do and your overall flexibility. According to his recommendations I should be on a ~58cm, but I tend to prefer my two larger bikes (59 & 60cm), both with 130mm stems.. so go figure. Anyway, hereís the book, and the charts

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Old 03-24-19, 04:13 PM
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Originally Posted by RobbieTunes View Post

I've used Colorado Cyclist's chart for modern fits, the "Merckx Fit."
Otherwise, it's hit or miss, and has cost me a few stems and a couple of seat posts.

Once you have the fit, it's like a new bike.
I like their write-up, it explains the methodology thatís behind the charts from Lemondís book
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Old 03-24-19, 05:37 PM
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Originally Posted by shoff535 View Post
Hereís some info from one of Greg Lemondís books. Keep in mind the old adage YMMV depending on the type of riding you do and your overall flexibility. According to his recommendations I should be on a ~58cm, but I tend to prefer my two larger bikes (59 & 60cm), both with 130mm stems.. so go figure. Anyway, hereís the book, and the charts
I should be noted that the Lemond method was a new and pretty radical approach at the time. The size recommendations are about 4cm less than what were conventional fitting methods at that time. They slowly caught on over the course of the decade. I took a lot of heat from the old timers circa early 80s for riding a "too small" frame. The obvious benefit was that the bike was stiffer and lighter, which was no small thing during that pre OS era. Comfort was not even a consideration. You will be in a slammed stem position. Now that I'm a middle aged recreational rider, I'm much happier with the older traditional fitting with a bigger frame.
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Old 03-24-19, 06:28 PM
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Originally Posted by Salamandrine View Post
...Comfort was not even a consideration. You will be in a slammed stem position. Now that I'm a middle aged recreational rider, I'm much happier with the older traditional fitting with a bigger frame.
Note that with a horizontal TT vintage bike, the smaller the frame, the harder it is to get the bars up near saddle height. Nitto Technomic, and the slightly less tall Soma Sutro stems help, but youíve got to be close to the low stand-over clearances mentioned in other posts. And some would say that that stand-over clearance is not really needed. Iím fine with an inch or less.
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Old 03-24-19, 06:46 PM
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Also note that often the riding position where you were expected to spend the majority of the time was usually the tops. A slack head tube also put the bars closer since if it was rotated about the tt/ht junction. The slacker head tube also gave the bike more stable handling when reaching for downtube shifters. So it was done for good reason. So bar height & reach was different back in the day. A 58cm top tube put the bars closer in reach more on par like a modern 54.

Modern bars are, in general, in a more agressive riding (longer/lower) position owing to better ergonomics of brake levers & the expected riding position of being on the hoods near the shifter/brakes.

These are just broad stroke generalities. I claim no actual expertise, just observations of various bikes I have come across. I ride a 57-58 effective top tube bikes usually, but have found vintage bikes that fit are usually 60-ish top tube & still need 130mm stems to be passable.

Last edited by base2; 03-24-19 at 07:51 PM.
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Old 03-24-19, 06:48 PM
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Originally Posted by Dfrost View Post

Note that with a horizontal TT vintage bike, the smaller the frame, the harder it is to get the bars up near saddle height. Nitto Technomic, and the slightly less tall Soma Sutro stems help, but youíve got to be close to the low stand-over clearances mentioned in other posts. And some would say that that stand-over clearance is not really needed. Iím fine with an inch or less.
This is an interesting thread - lot of good info. I am glad I asked. I have also noticed the above is also often true on modern frames. But definitely worth me remembering since I ride saddle and handle bars about even - so a bigger frame would help me out there. Thanks DF.
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Old 03-24-19, 07:08 PM
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"Reach and stack" are useful - and would be more useful if all the current brands used the same conventions.

the dimensions can be transferred to lugged steel level top tube bikes but some drawing is required.
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Old 03-25-19, 11:11 AM
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I was measured for a 54" frame by my LBS but can ride a 56 to 58" vintage bike comfortably with just a small adjustment in saddle height. I actually feel more stretched out on the smaller modern frame and find the vintage geometry way more comfortable for my vintage body.
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