Compact frame

[bumperjohn]

Could someone please help me understand about compact frames please? I do not understand how a compact frame would equate to me and am looking for some help here.

According to the Competitive Cyclist fit calculator, I should ride a 56 cm seat tube, c-t, and a 56.2 - 56.7 top tube. How would the measurements change on a compact frame and what different riding and handling characteristics would I notice between a regular and a compact frame. Thanks.

John

[Dave]

A "compact" frame merely means that the top tube (TT) is sloping rather than horizontal. Despite the slope, all brands still list a horizontal TT length that may be referred to as "virtual" or "effective". This value is the one to use if you're trying to compare a compact frame to one with a horizontal TT. I see no reason for any company to list the actual sloping TT length, but some do.

The Competitive Cyclist fitting information is well intended, but incomplete. The recommendation for a 56cm c-t seat tube is not of much value these days, with so few horizontal TT frames being made and those that are made may not be measured c-t. The head tube length (with the headset) is a better indicator of vertical frame size, but even the HTL gets confusing, because many frames use an integrated headset with only a 15mm height, while others use a coventional (pressed-in) headset with a 25-30mm height. You must take this into consideration when trying to compare frame size based on the HTL.

The other huge mistake with the CC fitting information is the lack of a seat tube angle (STA). A top tube length without a STA means nothing. With a different STA, a 54 or a 58cm TT length could fit the same as the recommended 56cm (an extreme example of a 2 degree difference, but possible).

As for ride or handling characteristics, those are very difficult to substantiate. One well-known builder claims that a sloping TT frame climbs much better. Could be, but I haven't noticed it, alternating between a conventional frame and a sloping one, riding in the Colorado mountains. The compact's ride might actually be better, but that could be due to many other differences in the frame's construction, particularly carbon frames, where tube sizes and shapes can vary by large amounts. All I can say is I've owned several compact frames, including an aluminum frame with CF stays that looked like it might be a rough ride, but wasn't (Fondriest MDC). Uless I buy a nostalgic lugged steel frame just for kicks, I don't expect to ever own a horizontal top tubed frame again.

[3chordwonder]

all brands still list a horizontal TT length that may be referred to as "virtual" or "effective". This value is the one to use

- from what I can tell, that's indeed the one overriding key measurement you can really work with between all the varying geo numbers listed on websites.
At least it gives a relatively reliable indication of whether it'll fit you.

The other measurements (saddle height, handlebar height) can all be adjusted anyway.

imho etc

[Peter P.]

You shouldn't notice any important difference between a traditional frame and a compact frame of the same dimensions. Think of it like this: manufacturers take a traditional frame and shorten the seat tube, POOF!, compact frame!

Some manufacturers take it a little further. They recognize that, with the advent of threadless and integrated headsets, there is less "stuff" like headset stack height, above the head tube so handlebars can't be raised to a level equivalent to a traditional frame. So they take the head tube of a compact frame and stretch it a little bit, and shorten the seat tube a little bit more to keep the standover height the same, yet help you get the bars to a comfortable level. You merely use a longer seatpost.

Now, some claim a compact frame, due to the shorter seat tube, is stiffer. Stiffer is not always better, and today's frames are plenty efficient enough that it's not worth considering this.

A compact frame will "feel" lighter because the center of gravity is lowered a bit, due to the dropped top tube. It will "feel" lighter because the bike will toss around easier left-right if you're out of the saddle. It's merely a feeling, and I don't think this perception is even worth considering. Consider all the Tours de France Lance won on a traditional frame and I think you'll get my point.

In some people's eyes, a compact frame has a cool, racy aesthetic.

If you look at the geometry chart of DeSalvo Cycles, you'll see the compact and traditional frames both have the same size headtubes. Since traditional frames are limited in their headtube length by the frame size/horizontal top tube, this length is the standard. The compact frames duplicate this dimension to achieve the same position on the bike.

http://www.desalvocycles.com/?p=steel_road

Also, Tom Kellogg has a great article which demystifies the compact frame.

http://spectrum-cycles.com/616.htm

[bumperjohn]

Thanks for the replies! I really appreciate the help.

John