Going down in frame size?

Discuss light weight issues concerning road bikes & parts.
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by Brandonnie

Currently i am riding a size 54 caad10 which has a 54.5 cm top tube. I am using a 120 mm stem with the frame size. I want to upgrade to a evo soon but was hoping to get a smaler size such as a 52cm or a 50 even. Other than getting a longer stem what else would have to be done to achive the current fit on my caad10? Im fine with a greater saddle to bar drop but am wondering if i would need any different setback seatpost.

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by DJT21

Well, looking at the geo, the 52 has a steeper seat tube angle so you would need to move the saddle back slightly to achieve the same position relative to the BB.

But with a longer stem and lower front end, its hard to say, maybe the saddle will stay in the same place? Maybe it'll move forwards?

Just wondering why you want to go down a frame size? If your current frame fits, why change it? It seems to be a bit of a fashion led thing in my opinion...

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by nathanong87

your stack will be immediately like an inch lower and the reach you could adjust with another stem, but like that other guy said your saddle will need to go back alot becuase the st angle is steeper.... and why are u looking to go down 2 sizes? 120mm stem on ur current size is probably a decent indication of things working well for you currently.

also toe overlap will be a future concern for you. i switched from a 52 to a 50 and like life though. im short.


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As you can see from the reach numbers, you would only need a longer stem if you corrected for the stack difference with spacers, and even then; you're looking at a .7cm difference in reach(.1cm difference between sizes; and .3cm for each 1cm of spacers.)

Cannondale's 52-54cm sizing is pretty weird in regard to how similar it really is in the reach; and the 50 and 52 are pretty similar as well. However, as someone else pointed out there are other concerns like toe overlap, wheelbase, headtube angle, trail that will all effect the "feel" of the bike as well.

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by WMW

Is your saddle all the way back now? Based on the chart posted above, going from a 54 to a 52, you would need to move it ~5mm back. Your reach with the same stem would be ~1mm less, and the bars would be ~17mm lower.
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by Brandonnie

Im looking to get a greater saddle to bar drop since i feel i could get even more areoo. And yea its partly for looks. Right now my saddle has a whole lot of room to move back since im pretty much in the middle if the saddle rails. I also want to get a smaller frame size since the seatpost i use is a pro stealth evo which flattens out at one point. I was barley able to get it low enough which hides all the seatposts beauty. Looks like the biggest thing i need to worry about is toe overlap.

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by AllAboutTheEngine

as others have said, sizing down will most likely be a mistake. sounds like your bike fits as is.

you wont necessarily get more aero from a greater saddle-bar drop if that number is already high.

are you slammed to the max?

-17 deg stem?

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by DJT21

One thing to be wary of is power output in this new "lower" profile. Will it be the same? Do you have the means to check?

A -17 degree stem would be a good starting point, aswell as removing any stem spacers/headset top caps.

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by Brandonnie

Currently slammed down with the slam that stem headset cover. Im using a zipp sl145 which i think is a -12. Hmm... I dont have a way to measure my power. Looks like ill just get the same frame size then when i get my evo.

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by 11.4

It's not quite as simple as some are portraying it here, and you may have more position improvement than some see here.

Consider what's happening here. You drop your front end and end up more aerodynamic. But in the process, you are changing both two critical measures, the angle of your hips to your thighs and your weight distribution. On the angle of your hips, this change will in practical measures change the power you deliver, for better or worse. Because it will demand a bit more flexibility in your hamstrings and glutes and lower back muscles, you may not see the improvement right away but be able to find significant improvement as you adapt to the position. That new position will change your saddle height (rotating your hips does that), potentially change your cleat position, and likely change your foot angle at the pedal. For what it's worth, you'll also change your rib cage position with regard to your diaphragm (which changes your lung capacity), and you'll change your shoulder angle (which can improve or worsen shoulder discomfort and also affect how you transition from seated to standing position).

On that last point, note that everyone has two completely different positions, one standing and one sitting. Because standing typically moves you forward, it changes your weight distribution significantly and when you are dropping your bars at the same time, it further accentuates this change. It may be an improvement, may not, depending on how well positioned you are already. Nobody writing a post on this thread is going to know, so don't let anyone dissuade you unless they have data to work with. Even just looking at the standing position, going lower in front will change the center of gravity of your upper body without changing the center of gravity of your lower mass (your hips don't really change location significantly with lower bars). Then three things happen (ignoring aero changes for the moment): First, you have more weight on the front wheel, which generally stabilizes your front wheel at speed and allows you to turn faster; second, you are using your upper body more to support your body, which affects how well your lower body can deliver power to the pedals (again, for better or worse, but only you will be able to test that); and third, you will have changed the position of your diaphragm relative to your thighs and rib cage, and may either improve or diminish effective lung capacity. Typically to maintain your sense of control over the bike, lowering the bars is helped by lengthening the reach (either long stem or greater handlebar reach); this has the added advantage of stretching out your torso slightly, which raises your rib cage and gives your lungs more capacity. There's a limit to this, but most of us aren't at that limit yet. This, by the way, is one reason why pros ride longer than usual stems and also slam them -- I've seen 10-20% improvements in vO2max just from the positional change (at least on the track where I've measured it).

Bottom line? You know yourself, or need to. If you think a smaller frame will work better, then absolutely take it seriously. Just understand that it will lead to a number of positional changes, some of which you'll have to acclimate to, but which can all improve your performance.

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by edesigner

Great advice. Ill add that nobody can really accurately help also unless we see your position.

Also it depends on how you like your bike the handle. Most of us want the best of both worlds.. response and stability. If you go down too far you will loose the latter for sure.

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by WMW

Brandonnie wrote:Looks like ill just get the same frame size then when i get my evo.

I would most definitely get a 52 if I was you, since you are at the low end of your 54 and wish to go lower. If you decide you don't like it, it is easy to go higher on your 52 via stem and spacers.

Aero will almost certainly improve. If you want to go fast, you have to learn to ride bent over. Power might drop a little, but it might not. Stability and handling will *not* be harmed. Toe overlap is essentially the same on the two. The 52 will be lighter... etc.
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by em3

Here is some required reading you need to engage in order to understand stack and reach, and how it effects fit on your bike:

http://velonews.competitor.com/2012/05/ ... lly_216035" onclick="window.open(this.href);return false;

http://www.cervelo.com/en/engineering/t ... d-fit.html" onclick="window.open(this.href);return false;

viewtopic.php?f=3&t=29177&start=0" onclick="window.open(this.href);return false;

...and here is a little something extra on how position effects power output:




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by MagnusH

Frankly I'd take the Cervelo speech about geometry with a grain of salt.
The world’s most demanding athletes ride stock Cervélo frames.

Yeah sure. With the saddle slammed way forwards on zero setback posts (here) and without headset bearing covers combined with 17 degree stems (here)

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by Dbfire

If your looking to save some money on an evo I know that they are discounting the 2012 dura ace more than 30%. An they only have size 54 left.
I think if I was just racing it then I could live with the aggressive fit of a 52. I'm not sure I would want to do many long training rides on it, but I'm old.

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