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Discussion Starter · #1 ·
Hi folks,

I'm planning to buy a CX bike. I'm not primarily thinking about racing, neither I'll use this bike for commuting.

My plan to ride some of my mountain trails with it (the less technical, "fire-roadish" ones), have a different experience and fun. I would like to get something more nimble, but not too nervous on the downhills.


I'm 5'10" and 32.67" inseam. The bike is a Kona "Jake the Snake" cyclocross. The manufacturer has 2 sizes I think are possible:

56 (21.7" top tube)
58 (22.7 top tube)

In my Titus MTB (Racer-X), I was somewhat between sizes (small 17.5 and medium 19). I
picked the larger (medium) which has a 23.25" TT (590.5mm) and put a 90mm stem on it, resulting in a total reach of 680mm. The slightly larger size TT and wheelbase gives is more stability in the downhills, while the short stem improves handling. For me, it is a perfect combo.

In the CX, if I try to replicate the same total reach (680mm), it could be done:

For the 56 frame (Top tube = 561mm) with a 120mm stem OR
For the 58 frame (Top tube = 576mm) with a 105mm stem

Thus, I wonder if the 58 could be better with a shorter stem, using the same reasoning as my MTB (which may not apply...)

I've run a bunch of body measurements in the road bike fit system of two online sites
www.competitivecyclist.com
www.wrenchscience.com

Both are be pointing towards the size 56. I am almost set on the 56, but I just want more feedback on it.

Last note, the dealer does not have them in stock to try...bummer.

Thanks,

Gui
 

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Don't base your cross fit on your mtb fit atmho.

Ride some road bikes at your dealer. That will give you a reality check when you look at measurements for the cross bike.
 

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Discussion Starter · #3 ·
Thanks for you reply,

Indeed, I believe the fit is rather different...that was just a starting point, given the MTB is my only reference.

The dealer does not have road or CX bikes in stock for me to try (it is a small dealer in Grenoble, France).

Thus I'm trying to get as much feedback as I can. If the doubt remains, I may consider a short trip to a bigger nearby city (Lyon) to try something. The only catch is that I'm leaving in a month and my time is very constrained for something like this...

Gui



it may not apply


pretender said:
Don't base your cross fit on your mtb fit atmho.

Ride some road bikes at your dealer. That will give you a reality check when you look at measurements for the cross bike.
 

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Discussion Starter · #5 ·
So,

The competitive cyclist calculations put me on:

55-56 for the "competitive fit"
56-57 for the "Eddy fit"
58ish for what they call "French fit"

Other than that, all measures point out to 56 too.

Gui


pretender said:
If your "inseam" measurement is floor to pubic bone, the Lemond formula puts you on a 56, too.
 

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You cannot use TT lengths for comparison, as seat tube angles are different. A one degree slacker angle on the seat tube can add upto a centimeter, which means that two bikes with same TT length, but one is 73 degrees and other is 72, the later would fit one centimeter smaller, based in the same position over the bottom bracket.

Given that Competitive Cyclist is basing your sizing on a road bike, and you are purchasing a CX, typically with slacker ST angles, you probably need the larger. This woudl also give you a longer HT. When looking through the gallery of photo's you can see how many bikes have upward facing stems with lots of spacers - all to small.
 

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Discussion Starter · #8 ·
That´s right, I remember reading about this in the Sheldon Brown page.

It just so happens I could try a Kona road bike yesterday. It was a Zing Deluxe (2007 model) in 56 size. One thing I noticed was how much I was crouched when on the drops. Otherwise the reach on the hoods was fine. I did feel a bit wiggly...but take that with a grain of salt, I´m not used with road bike geometry. And there´s just so much you can don in a couple of rides around the block.

I´ll come back to the dealer on monday for another spin...still not sure about the correct size

Thanks you all for the useful feedback !

Gui



shomyoface said:
You cannot use TT lengths for comparison, as seat tube angles are different. A one degree slacker angle on the seat tube can add upto a centimeter, which means that two bikes with same TT length, but one is 73 degrees and other is 72, the later would fit one centimeter smaller, based in the same position over the bottom bracket.

Given that Competitive Cyclist is basing your sizing on a road bike, and you are purchasing a CX, typically with slacker ST angles, you probably need the larger. This woudl also give you a longer HT. When looking through the gallery of photo's you can see how many bikes have upward facing stems with lots of spacers - all to small.
 

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I'm not an expert but

Based on

- my height - 6' 1/2"
- bike inseam - 33.25"
- the fact that I ride a 58" Major Jake (and I replaced the stock stem with one that is 10mm shorter)

I'd think that the 56" is the better size for you.

Good luck.
 

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Discussion Starter · #12 ·
Well, my issue is not really trying to making the bike to fit, but rather to find the correct size. My doubts will apply to any other brand...

If I find to be between sizes, then I might start looking at other offerings.

The Kona JTS costs 1,300 euro here (I know, way more expensive than good ol' USA). I found a Colnago CX at Evans Cycles (UK) with the same components for the same price:

http://www.evanscycles.com/products/colnago/world-cup-cx-105-2009-cyclo-cross-bike-ec017302

And they ship free to France. That is very tempting...given Colnago's reputation. However buying locally have the advantage of having the shop to make all adjustments and fine tuning parts swap I'll need (I'm away from home and cant do this myself here right now)

However the JTS has very good reviews...

Gui


shomyoface said:
Of course, the appropriate thing to do would be to buy a bike that fits you, RATHER than buying a bike, and making it fit you.....there is a difference.

Why not look at other brands............:thumbsup:
 
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