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Old 08-15-07, 03:01 PM   #1
bfloyd
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top tube length

This may sound like a silly question but; I normally ride a 23 in. top tube length. I just got a really good deal on a new frame that has a 22.5 in. top tube (though I was told it was a 23 in.). Can I just run a 1/2 in. longer stem to achieve the same results? Thanks.
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Old 08-15-07, 04:09 PM   #2
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More or less.....you could also try a setback seatpost if you have a straight one now. Or just slide your seat back if you have room.....
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Old 08-15-07, 06:03 PM   #3
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Troll

Feel free to ask me to elaborate if you'd like bfloyd.

There are more factors than top tube length in fit, but all else being equal you should have plenty of room for adjustment to make up .5 an inch. Or you could build it up and find that it fits perfectly right off.
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Old 08-15-07, 06:09 PM   #4
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Why don't you try to make yourself useful and help the guy out, troll?
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Old 08-15-07, 07:18 PM   #5
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I think the measurement will vary between manufacturers... I don't think a single number is going to tell you how the bike will be different. It's more complex as small adjustments can mean large comfort or discomfort..
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Old 08-15-07, 08:11 PM   #6
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there are several factors to be involved...but as long as the handlebar/seat ration are ABOUT the same...you shouldnt have a problem...I made a very similar switch recently...went from around 23 effective top tube to 22.5 effective top tube...i was freaked about the change but I actually like it better. Try it out first then you can decide what can be done to change it.
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Old 08-15-07, 08:14 PM   #7
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if pete is a troll i am an ogre
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Old 08-16-07, 05:43 AM   #8
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Thanks everyone. True, I don't want to adjust my seat to pedal ratio as that will cause the knee pain to come back that I finally got rid of by finding the sweet spot where there is no pain.

I'll try the 22.5 as is and see if I feel "cramped" or not. Thanks again.
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Old 08-16-07, 07:09 AM   #9
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Originally Posted by Pete Fagerlin View Post
Hey dipsh|t, I did help the guy out by pointing out that he shouldn't listen to your inane rambling.
But of course you could never, ever provide the "correct" answer. Right, troll?
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Old 08-16-07, 09:55 AM   #10
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troll
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Old 08-16-07, 09:58 AM   #11
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Heck - they should just shut this place down then. No question can have a positive answer because there are too many variables, therefore any answer given is by definition wrong. What's the point of this whole forum? A place for jerks to be jerks I suppose.

The great thing about an internet discussion group is that it promotes healthy discussion and - as Socrates taught us - by way of healthy discussion the pool of collective knowledge becomes richer. Points and counterpoints. Negatives are only negatives and don't positively add to the pool. Of course I wouldn't expect you to have the intelligence and social graces to understand such a concept.

OTOH, Socrates was a prick too......
how can you equate posting incorrect or possibly harmful information on a discussion board in response to a question to creating a pool of knowledge?

Pete is replying, and I replied in another thread, to the OP or whoever is reading the thread, for purposes of letting the readers know that you are fairly clueless.

You should be sipping from the collective pool of knowledge and not peeing in it.
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Old 08-16-07, 10:12 AM   #12
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troll
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Old 08-16-07, 10:18 AM   #13
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Originally Posted by Curt Kurt View Post
how can you equate posting incorrect or possibly harmful information on a discussion board in response to a question to creating a pool of knowledge?

Pete is replying, and I replied in another thread, to the OP or whoever is reading the thread, for purposes of letting the readers know that you are fairly clueless.

You should be sipping from the collective pool of knowledge and not peeing in it.
Nothing I posted was incorrect. Various ways to compensate for a different top tube length include lengthening the stem, moving the seat back by various methods and changing frame angles (too late at this point to do that). I never said "do this and it'll be fixed". What exactly he should do depends on the geometry of his new frame and the geometry of him. Obviously if his seat tube length is the same but the top tube length has changed then the geometry is different somehow. Just how is unknown at this point.He's had enough "fun" with his positioning to know that. I was just adding options. All of which are options. That's why they sell seatposts with different geometries and seats that can be slid forward and back.

I suppose the only foolproof answer would be to say "go pay a fit expert a lot of money". But of course that assumes the fit "expert" really knows what he's doing. Big assumption
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Old 08-16-07, 11:00 AM   #14
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Originally Posted by GV27 View Post
Nothing I posted was incorrect. Various ways to compensate for a different top tube length include lengthening the stem, moving the seat back by various methods and changing frame angles (too late at this point to do that). I never said "do this and it'll be fixed". What exactly he should do depends on the geometry of his new frame and the geometry of him. Obviously if his seat tube length is the same but the top tube length has changed then the geometry is different somehow. Just how is unknown at this point.He's had enough "fun" with his positioning to know that. I was just adding options. All of which are options. That's why they sell seatposts with different geometries and seats that can be slid forward and back.

I suppose the only foolproof answer would be to say "go pay a fit expert a lot of money". But of course that assumes the fit "expert" really knows what he's doing. Big assumption
They sell seatposts with different geometries and seats that can be slid fore and aft so that a rider can find his/her correct/comfortable position as it relates to the BB and therefore cranks and pedals. Sliding your seat back to lengthen your theoretical top tube length is horrible advice, as pete pointed out and luckily the OP was aware of.

edit: and what is even funnier about what you post is that you come off a bit arrogant about it. Like in post 4 and 19 in this thread, and your response to me in the 29er thread(that you deleted).

Quote:
Originally Posted by GV27
Feel free to ask me to elaborate if you'd like bfloyd.
Yes any and all, please feel free to tap the vast fountain of knowledge that is GV27. Don't be shy.

Last edited by C Law; 08-16-07 at 12:09 PM.
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Old 08-16-07, 12:08 PM   #15
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Not if the seattube angle is different. It was a list of possibilities. Remember, he's going to a new frame and the only piece of info given is the top tube length. To say that a certain seatpost and certain seat positioning on that seatpost would be the same on any frame for a particular rider is just wrong. If you don't know how the top of his seattube relates to the BB, how can you give such a definite answer?

I'm really surprised that you are advocating giving an rider of an unknown size riding a frame of unknown dimensions an absolute "this will work/this won't" piece of advice.

Last edited by GV27; 08-16-07 at 12:15 PM.
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Old 08-16-07, 12:14 PM   #16
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Originally Posted by GV27 View Post
Not if the seattube angle is different. It was a list of possibilities. Remember, he's going to a new frame and the only piece of info given is the top tube length. To say that a certain seatpost and certain seat positioning on that seatpost would be the same on any frame for a particular rider is just wrong.
who said that?
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Old 08-16-07, 12:15 PM   #17
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Originally Posted by GV27 View Post
Not if the seattube angle is different. It was a list of possibilities. Remember, he's going to a new frame and the only piece of info given is the top tube length. To say that a certain seatpost and certain seat positioning on that seatpost would be the same on any frame for a particular rider is just wrong.
I'm really surprised that you are advocating giving an rider of an unknown size riding a frame of unknown dimensions an absolute "this will work/this won't" piece of advice.
who is doing that?
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Old 08-16-07, 12:18 PM   #18
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You're the one that said he definitely shouldn't slide his seat back relative to how he has it on his current frame. "Horrible advice" is what you said. I didn't say he should or shouldn't just gave it as an option to try. You're the one who said it wasn't an option.
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Old 08-16-07, 12:29 PM   #19
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You're the one that said he definitely shouldn't slide his seat back relative to how he has it on his current frame. "Horrible advice" is what you said. I didn't say he should or shouldn't just gave it as an option to try. You're the one who said it wasn't an option.
I don't think you are understanding me or in general bike fit.

Here is what I had posted.

They sell seatposts with different geometries and seats that can be slid fore and aft so that a rider can find his/her correct/comfortable position as it relates to the BB and therefore cranks and pedals. Sliding your seat back to lengthen your theoretical top tube length is horrible advice, as pete pointed out and luckily the OP was aware of.



He should find his optimal saddle position on his new frame based on his position as it relates to the pedals. He knows this as he points out in post 11.

He should not adjust his saddle positon from there (either with a setback seatpost or sliding his seat back)to increase his theoretical top tube length (especially if he has finnicky knees) as you had advised as an option

Kapish?
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Old 08-16-07, 12:53 PM   #20
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That's exactly what I said. Original post:

Quote:
This may sound like a silly question but; I normally ride a 23 in. top tube length. I just got a really good deal on a new frame that has a 22.5 in. top tube (though I was told it was a 23 in.). Can I just run a 1/2 in. longer stem to achieve the same results? Thanks.
My reply:

Quote:
More or less.....you could also try a setback seatpost if you have a straight one now. Or just slide your seat back if you have room.....
and follow-up:

Quote:
There are more factors than top tube length in fit, but all else being equal you should have plenty of room for adjustment to make up .5 an inch. Or you could build it up and find that it fits perfectly right off.
As you pointed out I was arrogant enough to offer to elaborate and if he had taken me up on this offer I could've talked about angles and such. He didn't. As you said he seems to have a handle on this stuff to some degree. OTOH, if he had it completely in hand he shouldn't have asked the question.

So let me ask you this - assuming his seat-to-bar distance is exactly right now, how do you propose he gets the extra 1/2" he needs? Buy a stem 13mm longer? Most stem manufacturers sell stems in 5mm increments. I suppose if he has riser bars he could get a 10mm or 15mm longer stem and rotate the bars one way or the other to make up the difference. Of course the angle of the stem may make is so that a 10mm or 15mm longer stem doesn't exactly lengthen his position by exactly 10mm or 15mm.....maybe it might all equate out to 13mm..... All of this assumes that the top tube length difference is all due to the headtube angle......you'll notice that I wasn't trying to find him an extra 1/2" in the cockpit of his current frame but rather giving options for finding a good fit on the new one.

The answer to his original question is "it depends". You and troll seem to be giving him a "yes" answer. Of course neither of you have bothered to try to actually answer his question, just to attack me. I essentially gave him the "it depends" answer. Y'all said that was wrong.

Quote:
Originally Posted by Curt Kurt View Post
He should find his optimal saddle position on his new frame based on his position as it relates to the pedals. He knows this as he points out in post 11.
Yes - which may well involve sliding his seat back in the post. If he doesn't have room to slide it far enough he may have to go with a setback seatpost if he doesn't already have one. There is some (slim) chance that this could make up the 1/2" without the need for a new stem. For all I know he may need to slide it back more than 1/2" and go for a shorter stem. I doubt it, but who knows?

Last edited by GV27; 08-16-07 at 01:06 PM.
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Old 08-16-07, 01:24 PM   #21
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Originally Posted by GV27 View Post
Yes - which may well involve sliding his seat back in the post. If he doesn't have room to slide it far enough he may have to go with a setback seatpost if he doesn't already have one. There is some (slim) chance that this could make up the 1/2" without the need for a new stem. For all I know he may need to slide it back more than 1/2" and go for a shorter stem. I doubt it, but who knows?
Since you keep bringing up the setback seatpost in this and other threads, are you under the assumption that most bikes sold today are specd with strait post's and zero offset clamps? Or did you have a certain seatpost in mind that offered more offset than the standard strait post with offset clamp?
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Old 08-16-07, 01:30 PM   #22
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Or did you have a certain seatpost in mind that offered more offset than the standard strait post with offset clamp?
I was wondering this too.
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Old 08-16-07, 01:47 PM   #23
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Old 08-16-07, 04:14 PM   #24
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Wow, this thread sure caused some controversey. Sorry 'bout that.

Back to the original, I don't think the seat tube length matters as long as the seat tube angle is the same. Regardless of the length of the seat tube, if the angle is the same the seat height and fore/aft position will be the same as the old frame. The seat tube angle pivots about the bottom bracket.

I agree that by sliding the saddle back on the rails, or getting a more layed back seat post (I'm already using a 1.5 in. set back) will make the effective top tube longer but this will affect pedal stroke more than using a longer stem to achieve a longer top tube length.
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Old 08-17-07, 06:31 AM   #25
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That's exactly what I said. Original post:



My reply:



and follow-up:



As you pointed out I was arrogant enough to offer to elaborate and if he had taken me up on this offer I could've talked about angles and such. He didn't. As you said he seems to have a handle on this stuff to some degree. OTOH, if he had it completely in hand he shouldn't have asked the question.

So let me ask you this - assuming his seat-to-bar distance is exactly right now, how do you propose he gets the extra 1/2" he needs? Buy a stem 13mm longer? Most stem manufacturers sell stems in 5mm increments. I suppose if he has riser bars he could get a 10mm or 15mm longer stem and rotate the bars one way or the other to make up the difference. Of course the angle of the stem may make is so that a 10mm or 15mm longer stem doesn't exactly lengthen his position by exactly 10mm or 15mm.....maybe it might all equate out to 13mm.....
All of this assumes that the top tube length difference is all due to the headtube angle......you'll notice that I wasn't trying to find him an extra 1/2" in the cockpit of his current frame but rather giving options for finding a good fit on the new one.

The answer to his original question is "it depends". You and troll seem to be giving him a "yes" answer. Of course neither of you have bothered to try to actually answer his question, just to attack me. I essentially gave him the "it depends" answer. Y'all said that was wrong.



Yes - which may well involve sliding his seat back in the post. If he doesn't have room to slide it far enough he may have to go with a setback seatpost if he doesn't already have one. There is some (slim) chance that this could make up the 1/2" without the need for a new stem. For all I know he may need to slide it back more than 1/2" and go for a shorter stem. I doubt it, but who knows

Oh, I get it now.

You are saying that your advice only applies if the only difference in the two frames is top tube length and that the reason the top tube is shorter on the new frame is because the head tube angle is different? What, did he buy a chopper bike or something with a 50 degree HT angle?

And you wanted to know what I would have advised the OP?

Build up the bike , dial in his saddle position, and ride it a bit to see if he really notices the 1/2 inch. Or if he notices it, maybe he likes that feeling on his new frame. If he doesn't, then add 10mm to his stem if he feels he needs it.

And above all else, make sure he doesn't adjust his saddle position, as it relates to the BB, to compensate for the shorter top tube.

Last edited by C Law; 08-17-07 at 07:26 AM.
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