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Bike size

Old 08-12-20, 07:28 PM
  #1  
Ramshackle
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Bike size

I have a question about bike size. Iím 170 cm (5'7") with an inseam of 71 cm (28"). My bike is a 54 cm Domane 4.3 (carbon frame) that Iíve modified in the following way: 165 mm crank, zero offset seatpost, 40 mm stem (although Iím now using a 100mm Redshift suspension stem). I converted the bike to a flat bar so reaching the brakes and shifter is no problem. The standover height isnít a problem given the sloped top bar. Based on my size, I probably should be riding a 52 or even 51 cm bike, but I donít want to lose money selling my bike unless there is a compelling reason to do that. Despite the modifications I made, is there some geometry in the design of a smaller frame that would make the bike handle better or be more stable that would justify
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Old 08-13-20, 01:07 AM
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Originally Posted by Ramshackle View Post
Despite the modifications I made, is there some geometry in the design of a smaller frame that would make the bike handle better or be more stable that would justify
None. You can simply adjust the seat forward and to a much smaller degree, increase height to compensate for the bigger size.
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Old 08-13-20, 05:58 AM
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Being able to go back to drop bars would be compelling enough for most folks You have an inappropriately sized bike that you've kludged to make more or less rideable. If that's all you need for how you ride, I wouldn't worry about it.
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Old 08-13-20, 09:05 AM
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Caveat: you can fit a range of sizes. The traditional range is: French, Race and Eddie. I use the LeMond-Guimard method of determining size. Basically, convert your inseam to metric and multiply by .665. That will give you a rough approximation. My inseam puts me at a 54/55 frame although I've ridden a 58 well. But, my current bikes are in the 54/55 niche. As to the geometry of the bikes...and, this is a generalization....a smaller bike will be lighter. It will also have a shorter wheel base. All other things being roughly equal, the smaller frame will feel more nimble or "twitchy" depending on who is evaluating it. The larger frame, with it's longer wheel base, will feel more stable and turn less quickly. Will the difference be significant enough for a recreational rider to notice or be affected? I don't know. I guess it depends on who you are and your experience. FWIW when I mentioned my method of determining frame size, I was referring to a traditional frame and not a sloping TT. In order to fit the latter you will have to establish a virtual TT and measure from the virtual intersection of the seat tube and virtual TT.

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Old 08-13-20, 11:43 AM
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Funny thing is, the switch to sloping top tubes that allows a shorter person to straddle a bike usually means you would ride a frame with a smaller size number than with older 'level top tube' bikes. I ride a 62 or 64cm in the old geometry, but I can fit on many 58cm frames that are called 'XL' by the manufacturer.

The fact that you weren't comfortable with the drop handlebars says to me that the bike is too big. Frames designed for drop bars usually have very short top tubes compared to bikes designed for flat bars, so if you feel the need for a short stem with flat bars then the bike is possibly much too big for you.

However, if the bike is comfortable for the riding you do, then that's really all that matters. Many folks like drop handlebars for the multiple hand positions they allow, but lots of people don't like them. Only you can say what's right for you. And how can you tell if it's 'right'? When you ride the bike, do you feel like you would be more comfortable on a slightly shorter or lower frame? If the answer is 'yes' and you already have zero-setback seatpost and a short stem, then, yes, you should get a smaller frame.

As for losing money, you could sell the used frame you have and find a replacement used frame in a more appropriate size and then you are theoretically only out whatever it costs you to have the parts all switched from one to the other. Moving to a smaller frame will also often allow you to re-use cable housing and maybe even cables, while moving to a larger frame will usually necessitate replacing cables and housing. If you are paying someone else (a bike shop) to swap the parts then it might make economic sense to get new cables and/or housing as re-using the old ones can take a bit more time and effort.
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Old 08-14-20, 12:59 PM
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Thanks for the replies. They have been very helpful. I may try to swap my frame for a shorter one that is equivalent.
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Old 08-14-20, 01:22 PM
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Hmmm....the reach on a 54cm Domane 4.3 appears to only be 374mm and the stack is 575mm.

I'm your size and my bike is 380mm reach, 545mm stack and I use a 120mm stem. I don't consider myself to be overly "flexible".

Have you been fitted?

edit: Never adjust your seat for a reach problem.
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Old 08-14-20, 01:27 PM
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Originally Posted by jadocs View Post
I use a 120mm stem.
Interesting! Plus, if you need a 120mm stem you probably could/should be on a bike even one size larger.
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Old 08-14-20, 01:29 PM
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Originally Posted by shelbyfv View Post
Interesting! Plus, if you need a 120mm stem you probably could/should be on a bike even one size larger.
Ha!
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Old 08-14-20, 01:37 PM
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[Test] How is your stand over clearance in Inches or CM? stand flatfooted straddling the top tube. lift the front wheel off the ground,

how far up can you get it? (you did not say)






/....
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Old 08-14-20, 05:03 PM
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Ramshackle
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I agree about not moving the seat forward to shorten reach since you lose the suspension of the seat rails. Tried it once and the ride was brutal. Stack was never a problem since I compensated with spacers. The big problem was reach, and in particular, where my knee was in relationship to the crank. I've got a bad knee and a too long reach hurt my patella. When I shortened the reach with a zero seatpost, my knee was lined up with the center of the BB and the pain eased.
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