# Schwinn Lightweight Frame Geometry



## momo608

How does Schwinn lightweight frame geometry differ from model to model and why?


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## Eric Amlie

I'm going to go get some popcorn, sit back, and enjoy this!


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## Metacortex

1963 and later electro-forged lightweight frames such as the Varsity, Suburban, and Continental had very "layed-back" 70 degree head and seat tube angles, a 2" fork rake and a relatively long wheelbase. The '60-'62 models had even more layed-back 69 degree HT/ST angles.

Fillet-brazed lightweights (e.g. Superior, Super Sport, S/S Tourer and Sports Tourer) and Paramounts had more upright 73 degree HT/ST angles and a shorter wheelbase than the EF models. The fork rake was 2" (same as the EF bikes) on all except the '72 and later P13, where the rake was reduced to 1-3/4".

Paramount P14 track frames had even more upright 74 degree HT/ST angles, a fork rake of only 1-3/8", and an even shorter wheelbase than the other Paramounts.

More "layed-back" HT/ST angles and longer wheelbases contribute to stability (for example making it very easy to ride no-handed) but also make a bike slower to respond and corner. As the angles increase and the wheelbase shortens the bike becomes more nimble and quicker handling. 

All of the above had parallel head and seat tubes, meaning they were both at the same angle. There were exceptions to this. One very notable exception was the '74-'77 Sprint, which had the same 70 degree layed-back head tube as other EF bikes, however this was combined with a more upright 73 degree seat tube that was also bent or curved to significantly shorten the wheelbase. This would create a bike much more responsive and quicker handling as compared to the other EF frame lightweights.

There are other items contributing to a given frame geometry such as top tube length, bottom bracket height and of course the overall size (seat tube height) of the frame, but the above points out the basic differences in geometry between the EF, FB, and Paramount models.


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## Dale Alan

Great info,and easy to understand explanation in the differences .Thanks


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## Eric Amlie

Something that was started long ago either on the original Schwinn Forums, or perhaps the later SchwinnBikeForums was a discussion of the frame sizes. Early on(mid sixties or so and back), Schwinn called two of the frame sizes 21" & 23" on the electroforged lightweights. At some point these changed to 22" & 24". The question was, did the actual frames change, or just method of measuring? I don't think the question ever was completely answered. I started measuring frames on my many fifties & sixties lightweights and found so many differences(like how far the seat tube extends above the top tube) that I gave up, hoping to get back to it sometime when I had more time(that hasn't happened yet).
Does anyone have any thoughts on this?


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## momo608

Well I can say this. I just now measured again my 1960 Continental 23" and my 1982 Continental 28", the only two bikes I keep in the house. They were both advertised in these frame sizes and they both measure that way from the center of the bottom bracket to the top of the seat tube.

I measured quite a few bikes and I have never seen a deviation from the advertised frame size and the actual frame size, Schwinn lightweights anyway.


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## Eric Amlie

I remember the advertising(for the '63 Superior I think) talking about the new more upright geometry. I only have '62 Superiors, so am not able to confirm any difference between the '62 & '63, but years ago I bought a '62 Varsity frameset and built it up with 27" wheels. Last summer I brought home both that  bike and a '64 Varsity(my last recently completed project) and had them parked next to each other. I figured that with the 27" wheels on both bikes that they would stand the same. Not so. I didn't do any measuring, but the '64 model has a higher bottom bracket and sits noticeably higher, presumably from the steeper geometry that Metacortex mentioned. Both frames are 21".


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## momo608

Eric Amlie said:


> I remember the advertising(for the '63 Superior I think) talking about the new more upright geometry. I only have '62 Superiors, so am not able to confirm any difference between the '62 & '63, but years ago I bought a '62 Varsity frameset and built it up with 27" wheels. Last summer I brought home both that  bike and a '64 Varsity(my last recently completed project) and had them parked next to each other. I figured that with the 27" wheels on both bikes that they would stand the same. Not so. I didn't do any measuring, but the '64 model has a higher bottom bracket and sits noticeably higher, presumably from the steeper geometry that Metacortex mentioned. Both frames are 21".




That makes sense. We can assume by that that Schwinn and I suspect the industry norm, was to cite frame sizes measured from the center of the bottom bracket to the top of the seat tube. Obviously there is a disconnect when considering geometrical differences and advertised frame sizes. I always thought the stand over height should have been the one advertised. At least you would know if you could ride the damn thing by measuring your inseam.


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## Dale Alan

I agree momo608,I have never understood the lack of standover height . With all the variables like angles,lengths,BB drop,etc. , the first concern should be if you actually ride the thing.


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## Eric Amlie

Yes, agree with both of you on the standover height. When I buy bikes on ebay I always ask about that. Unfortunately, often, the sellers don't know what it means and I have to explain it to them. Even then some of them get it wrong. I've bought at least two bikes that are too big for me after the sellers assured me that the standover was no more than 32"(my preferred max.).


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## schwinnbikebobb

Meta will know but I'm sure Schwinn changed the way they measured the frame size at some point.  Early 60"s maybe. Seem to recall they did not measure to the top of the seat tube.


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## momo608

Girls bikes. There is a reason bike frames are measured the way they are and it has nothing to do with men's road bikes. We need more info from old dusty history books. Back in the old days, they apparently didn't care how hard it was to get up on one those contraptions or how far you could fall getting off. Inseam as it relates to the distance from your butt to the pedals. Must just have been a relic from the past that no one thought it worth the effort to change.


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## Metacortex

Eric Amlie said:


> Something that was started long ago either on the original Schwinn Forums, or perhaps the later SchwinnBikeForums was a discussion of the frame sizes. Early on(mid sixties or so and back), Schwinn called two of the frame sizes 21" & 23" on the electroforged lightweights. At some point these changed to 22" & 24". The question was, did the actual frames change, or just method of measuring?




Both! Schwinn dealer News Flash 1971 #5 (dated 2/25/71) stated:

LIGHTWEIGHT FRAME SIZES - A number of dealers have asked about the differences in lightweight frame changes in 1971 compared to 1970. Actually, the 19" and 20" frames and the 21" and 22" frames are identical in size for both years. We simply changed the size designation to conform more accurately to the actual frame size (center of crank hanger to top of seat mast). However, the 23" frame has been dropped and replaced by the 24" frame this year. Therefore, the spread is 2" in all three frame sizes and they are essentially true measurements.​
So to summarize, starting in 1971 the 19" and 21" frames were simply re-labeled as 20" and 22" without an actual change in size (they were 20" and 22" all along). However at the same time the 23" size was increased to 24".

But wait, there's more!  That News Flash doesn't address the 25" to 26" size change, but I would assume like the 23" to 24" that it was also a real change. More details: In 1970 Schwinn offered a 25" size Continental that according to another News Flash bulletin was "hand-brazed" (fillet-brazed like the 28" Conti for '82 and '83), which led to problems filling orders. The 25" size was dropped for '71, then a new 26" size was offered starting in '72. But according to another bulletin that also ran into early production problems as they were initially fillet-brazed as well. Production of 26" frames was shut down until the 2nd quarter when EF frame head tooling for the 26" size was available.


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## Metacortex

Eric Amlie said:


> I remember the advertising(for the '63 Superior I think) talking about the new more upright geometry...




You are thinking about an article in the Dec. 1963 Reporter which stated: _The Sierra, along with all other derailleur equipped models, now has a shorter upright frame design to give finer balance, maneuverability and "cornering" qualities._

While it said "all other derailleur equipped models" I believe it was only referring to the EF bikes, which changed from 69 to 70 degree HT/ST angles at that time (which would result in the handling change described). I believe that the FB bikes were always 73 degrees.


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## Eric Amlie

Metacortex said:


> The FB bikes were always 73 degrees.




Ahh!...so that explains why there is no discernible difference between the '62 & '63 Superior in these photos.

You da Man, Metacortex!


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## momo608

Here is the article that went along with that illustration I used. Quite good!

*Bicycle Frame Geometry*




Frame geometry, loosely defined, is all about the lengths and angles of a bicycle frame. It’s important because it determines how the bicycle will perform as well as how it will fit you. Sometimes it’s easy to look at the most obvious aspects of frame geometry (how long is the top tube and what is the standover height) and forget about the rest. Understandable, because we (the manufacturers) don’t always do a good job of explaining the rest to you and what it means. This gets a little dry, but bear with me.





So let’s start with frame angles: the seat angle and the head angle. The seat angle is the angle between the top tube and the seat tube. The head angle is the angle between the top tube and the head tube. For typical road bicycles, the head angle is between 71 and 74 degrees. The head angle, in combination with the rake, determines how the bicycle handles. Steeper head angles, like 74 degrees, are usually reserved for bikes that are very manuverable, like criterium bikes. On the opposite end, shallower head angles are found on touring bikes where, in combination with a long rake, they provide stable handling.

The seat angle isn’t quite as sacred as the head tube angle, but it sure has important implications for fit because it determines whether or not you’re going to be able to get in the right position relative to the pedals. Seat angles range from 72 to 74 degrees with 73 degrees being the most typical. Note that by moving the saddle back and forth on the rails, you can effectively change the seat tube angle a couple of degres. Once the seat angle is greater than 74 degrees, the geometry really puts the rider in an awkward position relative to the pedals. Unfortunately, some designers manipulate the seat angle to make the top tube shorter. To easily visualize this, imagine a bike with a 90 degree seat angle (i.e., the seat tube is vertical). Yes, the top tube is really short, but at the expense of a good fit. Steep seat angles also tend to give a rougher ride: imagine sitting on a pile driver.

Another dimension most geometry charts mention is the bottom bracket height. This is the distance from the ground to the center of the bottom bracket. You’ll find higher heights on bikes where pedaling through corners is important (like bikes used in criterium races) and lower heights on bikes where a low center of gravity is important for maintaining stability (like touring bikes). Because the bb height can vary a little depending on the tires, some manufacturers also publish the “drop”. This is the vertical distance from the wheel axle to the center of the bottom bracket. It’s a fixed number, so in manufacturing, bicycle frames are built to drop, not to bottom bracket height.

No geometry chart would be complete without rake, which describes how much the end of the fork blades deviates from a straight line drawn through the head tube. Rake is usually in the 2 to 6 cm range. Rake doesn’t mean a lot by itself, but when manipulated in a trigonometric relationship with the head angle and the circumference of the front rail, you can derive the trail and the caster angle of the bike. When all bikes had 700c front wheels, trail used to be a hallowed indicator of how the bike would handle, but with the advent of 650c and 24″ wheels, it’s lost its luster. Caster angle is probably a better measure; caster angles in the 80 to 82 degree range give neutral steering regardless of the wheel size.

Finally, there’s the chainstay length. You’ll find them in the 39 – 40 cm range on racing bikes, since this makes for a stiffer rear end that won’t twist under explosive acceleration. Bikes made for touring usually have the longest chainstays (43 cm +) for better shifting with wide range gearing and heel clearance for panniers.

Hopefully this has given you a little more cycle savvy about frame geometry!

Tailwinds,

http://community.terrybicycles.com/...y-eletter/bicycle-frame-geometry#.Vsca1PkrK71


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## Eric94TA

Metacortex said:


> 1963 and later electro-forged lightweight frames such as the Varsity, Suburban, and Continental had very "layed-back" 70 degree head and seat tube angles, a 2" fork rake and a relatively long wheelbase. The '60-'62 models had even more layed-back 69 degree HT/ST angles.
> 
> Fillet-brazed lightweights (e.g. Superior, Super Sport, S/S Tourer and Sports Tourer) and Paramounts had more upright 73 degree HT/ST angles and a shorter wheelbase than the EF models. The fork rake was 2" (same as the EF bikes) on all except the '72 and later P13, where the rake was reduced to 1-3/4".
> 
> Paramount P14 track frames had even more upright 74 degree HT/ST angles, a fork rake of only 1-3/8", and an even shorter wheelbase than the other Paramounts.
> 
> More "layed-back" HT/ST angles and longer wheelbases contribute to stability (for example making it very easy to ride no-handed) but also make a bike slower to respond and corner. As the angles increase and the wheelbase shortens the bike becomes more nimble and quicker handling.
> 
> All of the above had parallel head and seat tubes, meaning they were both at the same angle. There were exceptions to this. One very notable exception was the '74-'77 Sprint, which had the same 70 degree layed-back head tube as other EF bikes, however this was combined with a more upright 73 degree seat tube that was also bent or curved to significantly shorten the wheelbase. This would create a bike much more responsive and quicker handling as compared to the other EF frame lightweights.
> 
> There are other items contributing to a given frame geometry such as top tube length, bottom bracket height and of course the overall size (seat tube height) of the frame, but the above points out the basic differences in geometry between the EF, FB, and Paramount models.



This is the information I've been looking for, many thanks. The layed-back geometry not only affects stability and handling, it plays a significant factor in comfort. The more upright the geometry, the less the bike is suited for "tourist" configurations in my experience. The electro-forged trio are great for easy riding in tourist config without messing with my knees. Kudos for this info.


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## Eric94TA

Anyone know about the Japanese models, specifically the LeTour II and III?


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