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  #16  
Old 09-01-2019, 02:10 PM
ultraman6970 ultraman6970 is offline
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THanks for the picture. Im just perplexed... even if he is off like 5 cm from what lemond says, clearly the frame is off for a lot.

I do not know what to think... this dude is one of those points in that spreadsheet linear regression to calculate the saddle height which needs to be excluded from the sample data... totally off...

Trek and spech have tall front tubes right?
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  #17  
Old 09-04-2019, 01:58 PM
rigged rigged is offline
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Been thinking on this topic a little more, reading up on bike fit and interested to know if the following is logic holds.

The recent trend is around reach and stack rather than seat tube length. Leaving reach aside, since stack is comparable across bikes, can I use stack to determine if the bike will fit well vertically?

For example, if I require BB to saddle length of 82 cm, and I assume 20 mm in spacers under the stem and a saddle rise relative to handlebars of 8 cm, then I would subtract 10 (cm) from 82(cm) to get the desired stack i.e. I would need a stack of 72 cm.

Does this figure? The stack seems way too hi and I cannot figure out why.
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  #18  
Old 09-04-2019, 08:38 PM
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fa63 fa63 is offline
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You are measuring saddle height along the seat tube, but stack is a vertical measurement. For example, at a saddle height of 82 cm and a STA of 73 degrees, the vertical measurement would be 78.4 cm. Using your simplistic approach, you would then need a stack of ~68 cm, which is still quite tall. Trek Domane in a 58 cm frame has a stack of 61 cm. Throw on 30 mm of spacers and a flipped up stem, and you are probably getting close.

Quote:
Originally Posted by rigged View Post
Been thinking on this topic a little more, reading up on bike fit and interested to know if the following is logic holds.

The recent trend is around reach and stack rather than seat tube length. Leaving reach aside, since stack is comparable across bikes, can I use stack to determine if the bike will fit well vertically?

For example, if I require BB to saddle length of 82 cm, and I assume 20 mm in spacers under the stem and a saddle rise relative to handlebars of 8 cm, then I would subtract 10 (cm) from 82(cm) to get the desired stack i.e. I would need a stack of 72 cm.

Does this figure? The stack seems way too hi and I cannot figure out why.
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  #19  
Old 09-04-2019, 08:45 PM
rigged rigged is offline
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Quote:
Originally Posted by fa63 View Post
You are measuring saddle height along the seat tube, but stack is a vertical measurement. For example, at a saddle height of 82 cm and a STA of 73 degrees, the vertical measurement would be 78.4 cm. Using your simplistic approach, you would then need a stack of ~68 cm, which is still quite tall. Trek Domane in a 58 cm frame has a stack of 61 cm. Throw on 30 mm of spacers and a flipped up stem, and you are probably getting close.
Excellent point fa63. I wasnt factoring in the angle of the seat tube. Thanks very much clearing that up..
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  #20  
Old 10-08-2019, 08:13 AM
rigged rigged is offline
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Detailed Bike Calculator

If anyone is interested I found this very detailed bike geometry calculator on the intertubes: https://www.bikegeocalc.com/

I find it really useful for gauging prospective bike fit if you know your personal measurements, and you have the geo chart for any bike. The difference in vertical fit for two 56 labeled bikes can be significant based on differences in geometry-- notably stack and seat tube angles.
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  #21  
Old 10-10-2019, 07:10 PM
ultraman6970 ultraman6970 is offline
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THanks for the link, really interesting idea, now compare would be easier.
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  #22  
Old 10-10-2019, 07:32 PM
rigged rigged is offline
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Quote:
Originally Posted by ultraman6970 View Post
THanks for the link, really interesting idea, now compare would be easier.
For sure. Now you can tell if what you are buying should fit if you can't actually put your leg over it.
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  #23  
Old 07-30-2020, 11:13 AM
520arachnid 520arachnid is offline
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Thanks!
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  #24  
Old 07-30-2020, 12:30 PM
robt57 robt57 is offline
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looking that 56, and just IMO, you be better suited on a 58 with shorter reach handlebars.

For example; my longest and shortest TT for bikes I am comfortable on are TT 577&603mm. 577mmTT has 12CM stem and 92mm reach bars, 603mmTT 11.5CM Stem and 69mm reach bars. The reach is actually slightly shorter on the 603mm TT bike. That is my workable window none the less, and of bikes I have and ride. Always 'start' with your know saddle setback FWIW.

IMO. the 109% of inseam for saddle height always works. Pedal to saddle top. If you are like me and do not employ an ankling pedaling style, Add little for pedal/cleat/shoe stack. Otherwise add all that pedal/cleat/shoe stack [maybe more] into your toe down preference.
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  #25  
Old 07-30-2020, 05:09 PM
cph cph is offline
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Looking at the picture of your bike, I think you should maybe split the difference and get a larger frame. I think you might even be in the custom frame category. I think the super long seat post would influence your ride (maybe more compliant, but you will negatively impact some power transfer).


I would look for a frame with a horizontal (or sloping to the front TT) in your case.

p.
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  #26  
Old 07-30-2020, 05:17 PM
robt57 robt57 is offline
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I have found this Gunnar online app very prospective enhancing.

http://gunnarbikes.com/site/my-gunnar/

It is keyed to their specific frames/geoms. But easily ascertained and compensated for in the app for comparison.
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  #27  
Old 08-04-2020, 03:34 PM
rigged rigged is offline
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Quote:
Originally Posted by cph View Post
Looking at the picture of your bike, I think you should maybe split the difference and get a larger frame. I think you might even be in the custom frame category. I think the super long seat post would influence your ride (maybe more compliant, but you will negatively impact some power transfer).


I would look for a frame with a horizontal (or sloping to the front TT) in your case.

p.
Thanks for the feedback. I lucked out and found a custom frame on this forum a few months back with a geo that matched my needs. It measures 808 mm center to top of saddle and 568mm top tube length. (671mm of stack measured to the center of stem). The fit is so much more comfortable than the 56 cm stock that I was riding. So you are absolutely correct.
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