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Old 05-17-12, 08:37 PM   #1
gamedic
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Question about a frame that is to small for me.

I'm 6 ft. tall with a long torso and 32 inch pants inseam. I normally ride a 56cm bike, but I have a 50cm Motobecane Grand Sprint frame sitting around. I really like the frame and would like to build it up. I know it is way to small. Could it be made to work with a head tube extension and a tall seat post without looking like an elephant on a tricycle.
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Old 05-17-12, 08:59 PM   #2
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No. I bet your bicycle inseam is even longer.
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Old 05-17-12, 09:33 PM   #3
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6cm=a little over 2", so you have a seat post and stem that much longer. You could also get a stem with positive rise so that would cut down on exposed quill. You already have the frame, build it up(ideally with parts you have, you might borrow a few items from your 56cm so you can ride the 50cm without spending much) and ride it. If you really like it build up to keep as another in your stable. I'm a very big guy, my bikes are huge, and I could care less if they don't look "normal/typical", I love to ride them. You might look at some of the rides in the pro peletons, way more seat post than "normal".

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Old 05-17-12, 10:18 PM   #4
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Given the pretty generic way manufacturers tend to size bikes these days (roll eyes) as calstar says it may be about 6 cm shorter in the seat tube.

So if your 56 has a whole lot of exposed seat post you might be in a little strife...but if you're running a pretty small seat to bar drop on the 56 the 50 might be doable with a longer seat post and longer stem. You may even need to flip the stem over to angle up (shudder)...
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Old 05-17-12, 10:40 PM   #5
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Yes, you can get a long seat post and tall stem, but I think you've forgotten about top tube length. I'm 5' 9", have a 31 inch inseam, fit best on a 56 cm frame, but can ride 58 or 54 cm. On my 54 cm frame I'm already using a 130mm stem. If you'd go to a 50 cm frame I'd guess (don't really know for sure) you'd need a 160 - 170mm stem (I've never seen or heard of one that long), and you state you have a long torso, so may need one even longer. If such a thing even exists it would look weird and possibly be so long as to affect bike handling.

Last edited by tcarl; 05-18-12 at 03:21 PM.
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Old 05-17-12, 11:49 PM   #6
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If such a thing even exists it would look weird and possibly be so long as to affect bike handling.
Good point...you'd be pretty far over the front wheel...could get somewhat twitchy!
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Old 05-18-12, 03:49 AM   #7
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Yes, you can get a long seat post and tall stem, but I think you've forgotten about top tube length. I'm 5' 9", have a 31 inch inseam, fit best on a 56 cm frame, but can ride 58 or 54 cm. On my 54 cm frame I'm already using a 130mm stem. If you'd go to a 50 cm stem I'd guess (don't really know for sure) you'd need a 160 - 170mm stem (I've never seen or heard of one that long), and you state you have a long torso, so may need one even longer. If such a thing even exists it would look weird and possibly be so long as to affect bike handling.
How about a tandem stoker's stem facing forward like a normal stem?
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Old 05-18-12, 07:10 AM   #8
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You are wasting your time and money on a frame that is much too small. It's like you wear a size 10 shoe and someone offered you a super bargain on a pair of size 8.

Put the frame on Craigs List and use the money to buy the right size.
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Old 05-18-12, 07:21 AM   #9
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That's about my size and I'm 5'7" with stumpy legs. Even with a long seatpost and stem, I expect you would feel scrunched up on it like it was a little kid's bike. I rode a 48 cm frame for a little while that came from a relative (she was convinced to buy a road bike when a hybrid or cruiser would have been best), I hated it. Way too small, even with a long stem. This match would be even worse for you.
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Old 05-18-12, 07:22 AM   #10
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You can get a long seat post and tall stem, you can ride 58 or 56 cm for best comfort.

Last edited by centralpark; 05-25-12 at 05:22 AM.
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Old 05-18-12, 07:45 AM   #11
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I think that's just too much, you'll end up feeling like one of those circus clowns on a tiny bike. I ride down a size on my tourer, and MTB, but the top tube length isn't all that far off and I can still get a decent KOPS position. But 56cm to 50cm, that's a huge difference regardless of the geo on the Motobecane, and 56cm might be a size down for you anyway. I think you are just buying trouble. Perhaps you can trade the frame?
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Old 05-18-12, 01:25 PM   #12
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Heck, I'm 5'5" and ride a 54cm with 120mm stem. I like to have plenty of top-tube clearance for a flat back with my head a hip-level, plenty of breathing space and no knee-to-elbow interference.
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Old 05-18-12, 02:44 PM   #13
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If it is an older bike with a level top tube then it is waaay too small. No matter what you do the bike will never feel quite right. If it is a more modern frame with a sloping top tube then 50cm may only be two sizes too small.

However, if it is a modern motobecane (bikes direct) it is not really worth any effort to make it right - it is a cookie-cutter asian frame that can be replaced with a new one of similar quality for $200 - $300 or so. Older ones have a little more style. But yours would be best saved for someone 5'6" or so who can enjoy it properly.

FWIW, the 'quality' of a bike, the frame material, the components, the name on the frame decals... all are less important than proper fit for the rider... a 50 cm frame simply is the wrong size for you. THe comment above about getting a great deal on shoes that are 2 sizes too small is perfect..
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Old 05-19-12, 05:40 AM   #14
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If it is an older bike with a level top tube then it is waaay too small. No matter what you do the bike will never feel quite right. If it is a more modern frame with a sloping top tube then 50cm may only be two sizes too small.
Which perfectly illustrates why not sizing bikes by effective top tube length is bloody stupid. It f**king s**ts me to bloody tears, dammit.

I can only imagine the OP's bikes are compact frames, cause I'm 5'10" and I take a traditional 57. Actually, my current bike is square (most 57s have a 55-56cm top tube, IIRC) and I prefer it.

Anyway, my advice to the OP (and everyone else, for that matter) is to forget about bloody useless seat tube lengths and figure out what effective top tube length suits you. Then you can ignore the length of a tube that only determines the height of a clamp, and inquire about a dimension that actually matters a damn.
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Old 05-19-12, 05:48 AM   #15
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Originally Posted by gamedic View Post
I'm 6 ft. tall with a long torso and 32 inch pants inseam. I normally ride a 56cm bike, but I have a 50cm Motobecane Grand Sprint frame sitting around. I really like the frame and would like to build it up. I know it is way to small. Could it be made to work with a head tube extension and a tall seat post without looking like an elephant on a tricycle.
You should be able to make it fit.

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Old 05-19-12, 06:53 AM   #16
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Old 05-19-12, 07:18 AM   #17
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Which perfectly illustrates why not sizing bikes by effective top tube length is bloody stupid. It f**king s**ts me to bloody tears, dammit.

I can only imagine the OP's bikes are compact frames, cause I'm 5'10" and I take a traditional 57. Actually, my current bike is square (most 57s have a 55-56cm top tube, IIRC) and I prefer it.

Anyway, my advice to the OP (and everyone else, for that matter) is to forget about bloody useless seat tube lengths and figure out what effective top tube length suits you. Then you can ignore the length of a tube that only determines the height of a clamp, and inquire about a dimension that actually matters a damn.
Your point is well taken but in this case the frame does indeed have a nearly level top tube so the nominal sizing correctly implies the top tube length. From Bikes Direct web site's geometry table this 50 cm frame has an effective top tube length of 52.1 cm which should be far too short for the OP.
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Old 05-19-12, 10:40 AM   #18
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If you decide to go through with it I have a 160mm 1" stem, 5-ish degree rise, 25.4mm clamp, I haven't tried fitting drop bars in it, however.

Yours for $11 shipped.

I'll be out on tour for a bit over a week, so can't ship for a while.
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Old 05-19-12, 12:42 PM   #19
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54 cm, sure . My inseam is 31 or 32, and I have a 54cm bike on which I use a long quill stem and a seatpost with a lot of setback, and it's fine.

50cm is really pushing it I think. But everyone is different and there is no right or wrong, just what seems to work.
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