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Position changes with new bike/geometry question.
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This is coming from someone who races 15 or so tt's a year and one tri. I am now riding a 56cm toptube with a 75 degree STA and 14.2cm head tube length. The bike I'm looking at is a 54cm toptube with a 74 degree STA and 12.5cm headtube length. What accomodations would be needed to fit the same on this bike? Easy as a 1cm shorter/longer stem, or is the geometry way off? I know there's going to be a bit more drop in front, but I was concerned about length and going with such a slack STA. I have been advised to not go with a 74 degree bike. but is the difference between 74 and 75 THAT big?

Thanks for any insight. This is driving me crazy.

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HEDmafia.com
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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Are you 100% sure your current position is optimal? If so then, what is your motivation for switching bikes? If not then, what is your motivation for keeping the identical position?

The best way to determine if the new bike will match your current bike is to put them side by side. If you are looking for position adjustability, aerodynamics and comfort... then consider a TitanFlex.
Last edited by: NYSLIM: Jan 22, 08 18:00
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Re: Position changes with new bike/geometry question. [NYSLIM] [ In reply to ]
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I have been fitted by a pro, Bob Duncan of Wheelie Fun in Lebanon, Oh. My reasoning for changing bikes is a sponsorship frame available to me. I am comfy on my current frame, and would ideally like to have a very similar position.

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HEDmafia.com
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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Any chance Bob Duncan can fit you again to this frame? Any chance of your new sponsor going custom? If not, what you are considering sounds within the ball park of possible adjustments with seatposts and stems. Perhaps your sponsor will throw in the appropriate stem/seatpost? Keep in mind that the bike may ride differently - maybe good or bad. What are the bikes?
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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tell me which frames we're talking about and I'll give you an exact comparison
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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Unless you are placing the saddle at the extreme ends of the adjustment spectrum, the difference in ST angle between 74 and 75 degree ST frames is easily within the range of compensation afforded by the rails of a standard saddle (if you have a ST length consistent with that usually found on a 54cm frame. The geometry is a little less forgiving with really, really long STs.)



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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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It's the Fort Komet, size M. 54 seat tube, 75 STA, 56.4 tt, 14.2 headtube.
vs the HED Vo4, size M, 54 toptube, 12.5 headtube and 74 degree STA

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HEDmafia.com
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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Are they both the same headset configurations? External will add 2cm over internal.
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Re: Position changes with new bike/geometry question. [NYSLIM] [ In reply to ]
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Yep, both internal. I'm running zero spacers right now, with a slightly down turned stem, so I'm thinking the 2cm difference in HT length won't be an issue.

So I guess my question is, when comparing bikes with 2 different STA's, what does that do to the toptube measurement? The fitter told me he likes me on a 56 square bike. I then called him and gave him the measurements of this current frame and he okayed it. I never though to ask what the STA meant in terms of fit from bike to bike.

Here's my situation:
We have two frame sponsors, HED and Fuji. So depending on lead times, my choices are an Aloha CF2, which is 73.5 degrees, a HED Vo4 at 74 degrees or an Aloha 1.0 at 77 degrees. If my "proper" toptube length is a 56cm with 110 stem on a 75 degree bike, what changes as the seat tube gets steeper or more shallow? i.e. do I order one size down Aloha 1.0 because the STA is steeper by 3 degrees than my current bike?

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HEDmafia.com
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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"So I guess my question is, when comparing bikes with 2 different STA's, what does that do to the toptube measurement?"

It does nothing independent of the saddle position. What you are trying to figure out is the effective reach, and you aren't factoring in the most important variables, which are where you actually sit on the bike, and where you place the bars.

Go read the stack and reach articles on the main site, and then go measure your existing bike, and then get back to us.


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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/
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Re: Position changes with new bike/geometry question. [fredly] [ In reply to ]
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Awesome, will do. I have this site bookmarked and always forget about the main page.

Thanks.

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HEDmafia.com
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Re: Position changes with new bike/geometry question. [cslone] [ In reply to ]
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Shows what would be required to shift from Komet. I don't know your stem specs - just add the differences shown above to whatever you have
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