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What are the important numbers in bike geometry

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What are the important numbers in bike geometry

Old 09-11-14, 11:08 AM
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What are the important numbers in bike geometry

I've been looking for a road bike to supplement my tri bike. Went to a fitter to see what bike would be best for me. He came up with a Kestrel Rt-1000 and Trek Domane. I'm more of an endurance fit than race fit. I'm trying to keep cost down and have been looking online at different bikes and some on ebay.
I've taken down the frame dimensions of a half dozen bikes. All are slightly different than the Domane. Are there any critical dimensions I should be looking at.

I've got some that the Effective TT length and reach are almost exact to the Domane but the stack is shorter.

Some where the Effective TT length and reach are longer but stack is shorter.

Others with longer Efffective TT but almost the same stack & reach.

Trying to figure out which numbers I should be looking at?
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Old 09-11-14, 11:51 AM
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I'm confused. I thought the art and science of fitting a bike was to get you the best fit for the bike you wanted. I mean... the fitter said the best bike for you is a $2,000 Kestrel? Can they do that? Do you have to listen? Nor do I think the lesson is to go out and try to find whatever other bikes out there that fit like the Kestrel! Even the Kestrel can be made to fit like something else given substitutions of stem, bars even crankset. As I understood it, the assignment of the fitter was to collect as much dimensional data on the client as possible and distill that into a set of bike fit parameters that allow the client to then get comfortable, or aero or efficient on whatever make or model of bike (or BSO) that their tastes and/or budget allow them to consider.

Did your fitter give you the measurments he took? I would plug them into the Competititve Cyclist fit calculator and see what kinds of frame, stem and seatpost dimensions it recommends. Then I'd shop for a bike based only on intrinsics of what grabs your eye and heart and component group level, etc. And of course what you can afford. Then you get the frame size that CC recommends, if it isn't in stock they should be able to order it. If the bike simply isn't made in that size then get the next smaller size and get a correspondingly longer stem. Its that simple.

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Old 10-17-14, 12:19 PM
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I bought my latest bike online. I compared stack and reach values to my existing bike with Bikegeo.net. I would say that reach is most important number. Stack can be adjusted with spacers without effect to riding performance.
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Old 10-17-14, 04:58 PM
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One reason you will see frame reach and effective top tube vary independently is that frame angles (particularly head tube and seat tube angles) vary from frame to frame. Two frames with identical reach and stack can have different ETTs because of angle differences.

For endurance riding, I would think you'd want a fairly high frame stack for a given frame size. Otherwise you will be using a stem with a large positive rise. ETT and reach may also be important depending on whether your fitter indicated you should have a shorter reach or longer.

So, for example, the racing Trek Madone in 56cm size with H1 racing fit has a 546mm frame stack and a 400mm reach. The endurance Domane in the same 56cm size has a stack of 591 and a reach of 377. The ETTs are close - about 10mm different - but the stack on the endurance bike is 45mm greater (and frame reach is 23mm shorter).

Of course, within limits some things can be adjusted with saddle and handlebar positioning and stem, seatpost and handlebar changes.
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Old 10-20-14, 11:16 PM
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You Hiring one Custom ? the builder is who you should be talking to..
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