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# Geometry question

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# Geometry question

01-10-23, 10:50 PM
#1
Senior Member

Join Date: Feb 2007
Location: Tariffville, CT
Posts: 15,407

Bikes: Tsunami road bikes, Dolan DF4 track

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Geometry question

I have unusually short legs and a long torso. My road bike is an equivalent 50 cm level TT frame (but with a 40 cm c-c seat tube and a sloping top tube). So the main specs are:

Effective seat tube: 50 cm
Effective TT: 56.5 cm
STA: 75.5 deg
HT height, with headset: 12 cm.

Based on those dimensions the bike will fit.

I got the Dolan DF4 because it almost mirrors that fit (I got the 57 cm frame).
Effective seat tube: 50 cm
Effective TT: 57cm
STA: 74.5 deg (so it's shallower, so I need a longer top tube for same reach)
HT height: 12 cm.

I was poking around for another frame, partially because I want one, partially because I want a second bike in case something happens to the first (I have two identically set up road bikes for the same reason). The DSP cool-front-end bike caught my eye, but some of the numbers seem weird. So for the Med..

Effective seat tube: 54 cm (which is really really high for me)
Effective TT: 55.6 cm
STA: 74.5 deg
HT height: 12.5 cm

So if I can straddle the thing, it might be a bit short in length.

In order to compare apples to apples, I decided to check the stack and reach of the Dolan and the DSP
Dolan stack: 49.8 cm (just a touch below the 50 cm effective seat tube length, so it makes sense)
Dolan reach: 43.4 cm (about 14 cm less than the effective TT length, which makes sense due to seat tube set back).

DSP stack: 41.3 cm (????)
DSP reach: 51.6 cm (????)
The DSP stack doesn't make senes - if it's a 54 cm seat tube to the top of the top tube, the stack should be about 53 cm. Ditto the reach - if the top tube is 55.6cm, reach should be in the 41 cm range (since seat tube angle and seat tube length is same as Dolan, it should be about 14 cm shorter than effective top tube).

I wrote DSP and they simply replied with "this is the geometry chart from the factory" which has the same numbers.

Am I missing something? (I just realized, maybe they got stack and reach reversed?)

Charts for Dolan and DSP attached

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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson
01-11-23, 08:50 AM
#2
aka mattio

Join Date: May 2005
Posts: 6,586

Bikes: yes

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Looks to me like they have the Stack and Reach columns mixed up. The Stack values look like reaches, and the Reach values look like stacks.
01-11-23, 07:12 PM
#3
Senior Member

Join Date: Feb 2007
Location: Tariffville, CT
Posts: 15,407

Bikes: Tsunami road bikes, Dolan DF4 track

Liked 183 Times in 104 Posts
Thanks. I wanted to do a sanity check.
__________________
"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson

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