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Old 07-09-08, 11:53 PM   #1
Aspiring_Rider
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Top Tube too tall

I'm 5'3" and after much online research on the finding the correct frame size for my height, I found people recommending a 48cm. I recently got this road bike frame off ebay that is 46cm. after putting on 700c wheels, i found the bike to be too tall. I need to stand on my toes and cannot plant both feet firmly on the ground. if the top tube was just 3 inches shorter, the bike would have been perfect. what is wrong with the online measurements? multiple people of my height have said they fit a 48cm perfectly. how come that isn't the case for me?
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Old 07-10-08, 12:03 AM   #2
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You may have short legs.
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Old 07-10-08, 12:10 AM   #3
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Then u measure your inseam. Rule of thumb is, bike size = inseam x 0.65.
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Old 07-10-08, 12:32 AM   #4
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According to the bike size = inseam x 0.65 calculation, my frame size should be a little over 46 cm, which is what I have. Is it important to be able to stand over my bike comfortably with both feet on the ground?
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Old 07-10-08, 12:47 AM   #5
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Ur standing with your standard bike shoes right. Yes it's important. So get a smaller frame then.
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Old 07-10-08, 05:33 AM   #6
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The other solution is to get a "compact" frame, that slopes down as it nears the seat post. It seems like about half the road bikes out there use compact frames. Still, what you're saying doesn't quite add up. The online methods aren't foolproof, but a 3 inch discrepancy is still a lot.

What is your inseam and your height?
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Old 07-10-08, 05:35 AM   #7
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Old 07-10-08, 06:38 AM   #8
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Go to a bike shop and they can help you find the size you need.

Not all frames of the same size (as shown on the sticker on the seat tube) are the same. Frame sizes vary between brands.
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Old 07-10-08, 08:08 AM   #9
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Are you SURE the frame is really 46cm? One that size should always clear someone your height, even if your legs are short. Measure it to see if it is mismarked or plain wrong. From your description of needing 3" (7-8 cm) more clearance it wouldn't surprise me to find out the frame is really 56 cm.

It's not as if E-bay sellers are always correct.
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Old 07-10-08, 08:10 AM   #10
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You don't need to touch both feet to the ground. Leave one clipped in, and stand on the other. Stand over height means nothing.

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Old 07-10-08, 09:50 AM   #11
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+1 on the measurement. Even manufacturers differ widely in measurements, much like clothing. Truly the only way to tell if a bike fits is to ride it. For a person in your position (AKA the hard-to-find-a-bike position), EBay is not a good idea. But you've figured that out. You should be able to resell and then find something you can ride.
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Old 07-10-08, 10:04 AM   #12
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Older bikes tended to have relatively high top tubes. The top tube length is more important. How do you feel riding on the bike--stretched out, cramped, just right? Some of that can be accommodated with a different stem, but the top tube length needs to be in the right ballpark.

It's nice to have a bike you can stand over comfortably, but for road riding, I'm more concerned about how I feel riding it.
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Old 07-10-08, 10:38 AM   #13
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Aspirin Did you ask Willy Wonka 1st ???
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Old 07-10-08, 10:49 AM   #14
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The problem may be the way the frame is measured. The difference between a c-c measurement and a c-t measurement may be as much as 3 cm for a frame with a level top tube. Also for a good fit you need to measure the effective top tube length. It sounds as if someone took advantage of you.

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Old 07-10-08, 11:06 AM   #15
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Quote:
Originally Posted by Aspiring_Rider View Post
...what is wrong with the online measurements?...
Probably nothing. However the measurement that was not taken into account is the height of the bottom bracket off the ground. Often with smaller frames the bottom bracket height is raised higher than with larger frames.

SB has something about his I believe on his site.

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Old 07-10-08, 11:06 AM   #16
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Also, certain bikes with the same size seat tube, even if measured center to center may have different stand-over heights due to differences in BB drop. For an extreme example, many cyclocross bikes have high bottom brackets, so you typically need a shorter seat tube to ge tthe same stand-over as a standard road frame.
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Old 07-10-08, 11:10 AM   #17
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Quote:
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You don't need to touch both feet to the ground. Leave one clipped in, and stand on the other. Stand over height means nothing.

... Brad
+1 on this one. THe BB heigh varies from bike to bike so for example a track bike usually has a BB that is like 2 - 4 cms higher than a road bike, so the TT is higher also. So that darn idea abotu hte standing over doesnt work. As a contrast, if you have a bike with a super low BB, that frame will end up being a lot bigger than what u might need for sure because the TT will be lower also. When people will stop using the stading over rule, that thing doesnt work... as a guide yes, as a rule, nope.

Theguy that gave the rule of thumb of inseam times a factor is right. I think the OP is expecting someting else I guess....

Do the OP put the seat and seat tube in the bike already??? It would be nice to see the bike with him seated in the bike to start with.

Secondly what bike are we talking about?? brand or something?? Probably this guy got a track frame.

Whats the TT lenght center to center of the frame??

Thanks...
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Old 07-10-08, 11:26 AM   #18
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To the OP: Are you trying to plant your feet on the ground while on the seat or while standing over the top tube? You should not be able to reach the ground with the former, and it's not even necessary with the latter, but it is nice to be able to. When it comes to traditional frames, my long torso and short legs require a size where I am sitting on the top tube while my feet are flat on the ground. Most importantly, does the bike feel huge while riding it? If so, you might want to try a bike with 650c wheels.

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Probably nothing. However the measurement that was not taken into account is the height of the bottom bracket off the ground. Often with smaller frames the bottom bracket height is raised higher than with larger frames.
That makes no sense to me. The smaller bikes are likely to have shorter cranks, so you should be able to have the bottom bracket lower and still have clearance. Is there a reason they do this that I'm not realizing?
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Old 07-10-08, 11:32 AM   #19
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...That makes no sense to me. The smaller bikes are likely to have shorter cranks, so you should be able to have the bottom bracket lower and still have clearance. Is there a reason they do this that I'm not realizing?
You're right--it makes no sense that they don't put shorter cranks on (which they don't). Try finding anything shorter than a 170mm crank on a production adult bike.

Steve
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Old 07-10-08, 11:39 AM   #20
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That makes no sense to me. The smaller bikes are likely to have shorter cranks, so you should be able to have the bottom bracket lower and still have clearance. Is there a reason they do this that I'm not realizing?
I have seen older frames where the BB seemed high on a small frame, and it looked to have been built that way to keep the top tube level. Folks didn't go for all that slope-y business before about 1987 or so for mountain bikes and 1997 or so for road bikes. Some still don't. Sales floor quotes: "Why was it built that way?" "Is it bent?" "Was it made on a Friday?"
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Old 07-10-08, 02:30 PM   #21
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???? if you lower the BB and keep the WHEELS the same size building a super small frame u'll have problems with the FRONT TUBE, and then with the lenght of the tt... Jezzzzz.
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Old 07-10-08, 02:46 PM   #22
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That makes sense. I forgot that people thought sloping top tubes were the devil only 20 years ago.
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