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Frame up or frame down???

Old 07-20-17, 04:50 PM
  #1  
canflyboy 
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Frame up or frame down???

Here's my dilemma. Looking at building up a gravel bike and I'm trying to determine what frame size I should use.

I took a couple of my road bikes and cross bike and using squares, levels, rulers, etc plotted their overlapping geometries and discovered my "sweet spot" which I was happy to say is within a couple of centimeters from one bike to another.

To replicate this "sweet spot" geometry on the new build I have two options. Smaller frame with longer stem and longer headset spacers OR larger frame with shorter stem and shorter headset spacers.

So is there any advantage to one over the other? Yes, I realize the larger frame with the slightly longer wheelbase should give a more compliant ride. Anything else?

Thanks

canflyboy
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Old 07-20-17, 05:13 PM
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You don't offer details, so it's hard to give specific advice.

So, here are some considerations.

You get better strength and rigidity with shorter post and less stack height. But it really only matters near the extremes, so avoid going with much more than 1" in spacers below the stem.

Longer stems offer improved steering feel and control. Try not to go with a stem shorter than 90mm.

Things can change over time, so try to have the "ideal"position centered with room for adjustment in both directions.

Those are some things to consider, then use your best judgment, since it sounds like either will do anyway.
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Old 07-20-17, 05:23 PM
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The company offers a 54 and a 57 cm frame. After mapping the geometries on my other bikes and reverse engineering I came up with a 54 frame with a 120mm stem with a 25 mm spacer under the stem OR a 57 frame with a 95 mm stem and a 10mm spacer under the stem.

Probably overthinking this and should just flip a coin.

Thanks
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Old 07-20-17, 05:33 PM
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I went from a 100 stem to an 80 stem and it definately changed the handling. It is more twitchy with the shorter stem.
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Old 07-20-17, 05:40 PM
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Would the 57 have a much longer wheelbase?

If you're not locked in to that brand, why not see if there's an ideal stack and reach gravel frame out there for you?

Give me those numbers and I could give you some options.
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Old 07-20-17, 05:43 PM
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Originally Posted by canflyboy View Post
Here's my dilemma. Looking at building up a gravel bike and I'm trying to determine what frame size I should use.

I took a couple of my road bikes and cross bike and using squares, levels, rulers, etc plotted their overlapping geometries and discovered my "sweet spot" which I was happy to say is within a couple of centimeters from one bike to another.

To replicate this "sweet spot" geometry on the new build I have two options. Smaller frame with longer stem and longer headset spacers OR larger frame with shorter stem and shorter headset spacers.

So is there any advantage to one over the other? Yes, I realize the larger frame with the slightly longer wheelbase should give a more compliant ride. Anything else?

Thanks

canflyboy
Forget about all of the science. You are making this WAY more complicated than it has to be. Go out, ride some bikes, buy the one that seems right.
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Old 07-20-17, 05:47 PM
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I'll nearly always go for the smaller of the two. 120 isn't that long of a stem.
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Old 07-20-17, 06:03 PM
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I'm 5'10" with a 33 inch inseam. I have a Specialized Diverge gravel bike, and I got a 54cm because of the long stack height. I swapped on a 120mm stem and it fits fine.

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Old 07-20-17, 06:13 PM
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Originally Posted by canflyboy View Post
The company offers a 54 and a 57 cm frame. After mapping the geometries on my other bikes and reverse engineering I came up with a 54 frame with a 120mm stem with a 25 mm spacer under the stem OR a 57 frame with a 95 mm stem and a 10mm spacer under the stem.

Probably overthinking this and should just flip a coin.

Thanks
Based on your info, it is a coin toss, though I like more extension with drop bars, so everything else being equal, that would tip it toward the smaller frame.
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Old 07-20-17, 06:17 PM
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Nice Bike Lazyass (we could be related). I'm long in the torso - short in the leg - 5 11" with a 32 inseam.
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Old 07-21-17, 05:11 AM
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It's easier to make a bike 'bigger' than it is to make it 'smaller'. In other words, a small frame can live with the saddle further out of the seat post and a longer neck. If you try to take a large frame and lower the saddle too far, you may run into strife and as the neck gets shorter, the steering gets twitchier.

I don't know the details but based solely on what you say, take the smaller frame and for heaven's sake, don't let them cut the steerer tube, do that after the bar height is finalised.

One of the best frames I've owned was, unfortunately, too big. I made it fit and it was a lovely bike but after about 3,000km, I had to admit that it was too big.
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Old 07-21-17, 07:14 PM
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Thanks all for the input - Going with the smaller frame
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