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Plus or minus suggested size

Old 02-10-24, 02:51 PM
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Plus or minus suggested size

Hello I've been building bikes for kin and myself for years. just recently I've got into knowing about sizes of bikes. Before I used to set up the handle bars seat height and angle to positions that I thought just looked cool but not anymore.


I believe I'm putting this in the correct section because I'm not asking about components or techniques. I've measured my inseam length to be just under 33" so about 83cm


Some road bike size calculators suggest me a frame size of 55 to 55.5cm


As I am still building and shopping for bikes or frames to build. My question is how far higher or lower can I go from my suggested size. Considering I am 6ft tall and probably won't grow anymore at my 35 years of age.

​​​​

my theory is that I can go a bit lower and find the sweet spot by raising the seat post incrementally but I shouldn't go higher bc I can't do the opposite if it's too high.
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Old 02-10-24, 03:10 PM
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How important is standover height to you? It's more important to some people, but I say don't build a bike for standing over, build it for riding. Not to the extreme where you actually can't stand over it without injuring yourself, but I bet you can lift your current bike while straddling it, right? Lift both wheels off the ground and see how high it goes before getting uncomfortable. That's how much larger you can go.

Handlebar height is the main reason for "frame size" (seat tube length) anyway, for traditional level-toptube frames. If you like the bars higher than a racer, you can get it on a small frame with a long up-jutting stem, but those are structurally inefficient and look ugly. Designing the top of the head tube based on desired handlebar height, and the top of the seat tube by standover, you might end up with a sloping toptube. That used to be something bikies shunned because their favorite racer had a level TT, but nowadays practically all the pros have a sloping TT.

So design the frame around the contact points with your body: hbars, saddle and pedals, maybe middle of the TT if standover clearance is a must. I recommend drawing a frame full-size on paper, at least until you get a handle on the process. Or do it on the computer if you're an expert CAD-jockey. I haven't drawn a frame on paper since the '70s but I'm glad I did, it taught me stuff.

Framebuilders shouldn't be paying any attention to what someone else "recommends" as your frame size. Try different things until you know what works for you. Generalizing that to other people is tricky and can take years or decades to get good at even for a full-timer, so getting ideas from other brands is acceptable, but don't be afraid to diverge from the designs others are using. Definitely don't slavishly follow what racers are doing. Unless you're actually pinning a number on your jersey, you probably shouldn't be riding in that position.

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Old 02-10-24, 07:11 PM
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Thank you. I'm not a frame builder but I did want a frame builders perspective.
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Old 02-10-24, 07:30 PM
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I found my sweet spot for bicycle size by trail and error. Over the years it has slowly changed so I now keep detailed specs on what feels comfortable for me. If you have been riding regularly you should be able to find your sweet spot pretty easy. Once found take those measurements and keep them close.

Note that at 70 years my bikes are not set up anything like they were 50 years ago... Ha
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Old 02-11-24, 01:42 PM
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Originally Posted by Bike jambalaya
Thank you. I'm not a frame builder but I did want a frame builders perspective.
Ah right, sorry, you said "bike builder". I would call that a bike assembler, but of course I am a framebuilder snob who looks down on anyone who doesn't build their own frames <jk>
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Old 02-12-24, 10:03 AM
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There is a forum about fitting.
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Old 02-12-24, 06:12 PM
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Originally Posted by unterhausen
There is a forum about fitting.


There it is. Between Fifty Plus and Folding Bikes... Who Knew?
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