Compact Frame

[madscot13]

i've noticed a lot of compact frames lately. I like them because I can finally reach a stand over clearance! Does anyone ride one? What are your thoughts on the rest of the bike fit/ riding stability?

[rij73]

Mine is compact. It's my first road bike, though, so I have nothing to compare it too. All I can say is that I love my bike, and I absolutely needed a sloping top tube to accommodate my short legs/long torso body.

[geekgirl]

I also ride compact or semi-compact frames -- a Salsa Casseroll as a daily commuter and a Klein Quantum as a go-fast fun bike. I have a bit of a longer torso (at least compared to most women, I guess) and short legs, so I feel more comfortable on compact frames.

You just have to be careful if your proportions are different, though, and pay attention to the "effective top tube" measurement. People get into trouble on compact frames when they think that just because they can stand over the top tube with clearance, then the bike will fit -- often times I think the reach will be too long, unless you have a longer torso.

The only way to really find out what fits is to go and try out a whole bunch of different bikes -- you'll figure out which brand's geometry works for you, and which ones don't.

[7rider]

My bike has - I think - 12 degrees of slope to the top tube. It's very compact - looks tiny...feels big. I love it. It's very sure-footed, tracks like it's on rails, and fits me like a glove.

Here's Seven's take on sloping top tubes/compact frames from their Custom Kit booklet:
http://www.sevencycles.com/buildingbike/customization/customkit.php
(see page 6 of the pdf on that page for a graphic illustration of the benes of it).

Why Incorporate a Sloping Top Tube?
About 85% of the road frames Seven builds have some degree of slope to their top tube. We incorporate top tube slope into most designs for one primary reason: Optimal fit.
A sloping top tube allows us to accomplish three goals:
1. Top tube slope allows us to properly set the handlebar height relative to the saddle height—we call this dimension the "Handlebar Differential"—to provide optimal comfort and proper weight distribution on the front wheel for ideal handling. As we increase the length of the head tube, the bar height begins at a greater height relative to the saddle top.
2. With a taller head tube length, top tube slope allows us to provide an optimal Handlebar Differential without the use of excess spacers under the stem. This in turn allows for greater bar height adjustability in the future.
3. Finally, with a taller head tube, sloping the top tube allows for sufficient standover clearance at the mid-point of the effective top tube.

[Zen]

Exactly what qualifies a frame as compact?

[geekgirl]

Compact geometry means the bike has a sloping top tube, whereas a traditional geomety bike has a completely level top tube. I believe Giant may have been the first to come out with compact frames for road bikes -- here is a link (http://www.giant-bicycles.com/en-US/technology/compactroad_new/) to the Giant website with more info.

[Zen]

Heh.
I've just always called it "a sloping top tube":p

[wannaduacentury]

I have a compact and love it. I feel too stretched out w/ the diamond frames. Jenn

[madscot13]

I kind of don't get how they measure top tube lengths. shouldn't the effective length be shorter than the actual top tube length? where do they measure standover height since it actually does matter where they measure it on a sloping tube?

[Zen]

all very good questions.
Where is our resident LBS owner?

[VeloVT]

I kind of don't get how they measure top tube lengths. shouldn't the effective length be shorter than the actual top tube length? where do they measure standover height since it actually does matter where they measure it on a sloping tube?

I'll take a crack at it (someone correct me if I'm egregiously wrong).

1) top tube is measured from where it meets head tube to where it WOULD meet seat tube if it were horizontal

2) the reason this effective length is LONGER than actual length is that BOTH the down tube AND the seat tube have slope. Put more clearly (I hope :eek:), if the downtube had slope but the seat tube were perfectly vertical, the actual tt length on a bike with a sloping tt would be longer. But while the down tube slopes away from an imaginary vertical line bisecting the bottom bracket, the seat tube also slopes away, in the opposite direction, so as you move UP the seat tube (=as the tt gets more and more horizontal), you are effectively stretching the tt out (b/c the sloping seat tube moves farther and farther away from the imaginary vertical bisecting the bottom bracket as it goes up). I checked this out on my new compact frame and I think it's true. But I'm not mathy (my verbal SAT score was several hundred points higher than my math score :eek:), so someone go ahead and lay in if this doesn't hold water.

3) standover -- I wonder if this varies by manufacturer? I just measured my new bike, and standover ranges from 71cm at the seat tube to 75 at the head tube. The Scott website lists it at 73 cm. This seems to be the median? If you look at the geometry diagram here http://www.scottusa.com/us_en/category/72/contessa_road (you may have to click on the "geometry" tab), it appears they take the measurement somewhere in between. :confused::confused::confused:

Hope that helps, and hope someone can correct any major errors I may have made :rolleyes:...

[madscot13]

err, I'm not great at trigonometry. let's talk real life value. do I use the effective or actual top tube value?

do you actually stand at the midline or do you stand closer to the seat making the standover an estimation?

[VeloVT]

Well, the standover and the top tube measurement are separate issues... and I think the standover is much less important than tt (though I'm tall enough at 5'6" that standover on frames that otherwise fit me is rarely an issue, so maybe I"m a little biased on this point). But in terms of reach, you definitely want to use effective top tube length, NOT the actual length.

To give some comparison on standover values, my compact frame standover ranges from 71 cm to 75 cm right at the head tube. By contrast, my old 54 cm traditional geometry frame had a standover height of 77cm, and I had at least a half inch of clearance (probably more, I've sold it so I can't check and I don't remember precisely, but it was never an issue).

I think it's possible to overthink these things -- exactly where you'll stand over the frame and whether you'll have enough clearance, given an abstract number on a page -- maybe better to just go try a few :rolleyes:...

[madscot13]

you are absolutely right; I should go stand over a few. the bikes that I am actually thinking of are just frames though. And I'm not really looking to buy this exact moment.

I'm just sort of curious with what they are doing with the frame and if that means they would fit me. Stand over is always an issue with me. My inseam is about 26" and so that is the first thing I look at when I am looking at frames.