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  #31  
Old 06-17-2016, 11:00 AM
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David Kirk David Kirk is offline
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Originally Posted by Happy F View Post
What about time and gravity. Your spine can compress as much as 2.5 centimeters over the course of a day. Your arch can also collapsed shortening one or both leg length and not necessarily symmetrically. We spent far too much time worrying about the numbers not about our posture and position course of the day. Someone brings their numbers to a fit first question I ask is what time a day was it taken. Second question I ask numbers are so good why you are getting another fit. It’s not about the numbers. It’s about a position on your bike. It has to be sustainable for the distances you want to ride. Gravity and time affect a fit as much as changing the saddle or frame. When I get numbers I explained they are carved in Jello. To understand what I’m talking about try this experiment. Take a person to a bike fit on them first thing in the morning. Have someone else Record numbers. Put them away. Don’t look repeat the dwarf all BB eight fit 8 to 10 hours later. Compare the numbers. I agree it’s nice to replicate someone’s position on the bike. But we get too caught up in the numbers. They are any more variables .
I think we might be talking apples-and-oranges here.

I'm not in any way talking about how a person should be measured to get a proper fit....I am only talking about how to replicate the fit of one bike to another so that they fit exactly the same. The fit might be good and it might be bad but it will be the same from bike to bike.

dave
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  #32  
Old 06-17-2016, 11:17 AM
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David Kirk David Kirk is offline
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Originally Posted by sacwolf View Post
This is an older post, but I have had the same dilemma and I am trying to follow the logic:
1. why wouldn't top tube length, etc make a difference in the contact points? Is it because if they are, they would require different components? Example- If I am setting up bike A with a 52cm TT, but bike B has a 54cm top tube- wouldn't this difference impact the measurements to the wall, floor, saddle position? If the bike A contact point measurement at handle bars is transferred to bike B, couldn't that affect bike B's pedal stroke angle?

I guess what I am trying to figure out is if you use these three points, bike A may fit really well, but bike B may not and could require major adjustments to stem length, crank length, etc. If that's what you already said in your post, then thanks for the insight. Either way, I am going to give it a shot- no longer does my "ride it and figure it out method" really work effectively, at least initially
Hey there -

I'm not sure I fully understand your question - that said I'll try to answer the question I think you are asking.

What we are doing here is defining the three contact points in space. It gives a relationship between the three points so that we can then replicate that same relationship on other bikes.

So....actual top tube length or other frame dimensions have no effect as long as one can pick a stem (or seat post) that will allow those 3 points to be replicated. So if bike A has a shorter TT than bike B then it will no doubt get a longer stem to allow that same saddle to bar reach.

In the end the technique will give you saddle height, saddle setback, saddle to bar reach, and saddle to bar drop of bike A and then one can take those numbers and adjust (or replace components like the stem or seat post) to get bike B to be set up the same way. One should never need to adjust crank length for any of this. It just doesn't factor in whatsoever.

I did have one person write me very confused and they thought that to replicate the fit from one bike to the another that they should make the measurements to the floor and wall the same from bike A to bike B. This is not the case. Due to differences in chainstay length and BB drop this will not work. The measuring gives you a proper relationship of the three contact points to one another and not to the floor or the wall which are irrelevant.

I hope that helps.


dave
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  #33  
Old 06-17-2016, 05:12 PM
giordana93 giordana93 is offline
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Quote:
Originally Posted by sacwolf View Post
This is an older post, but I have had the same dilemma and I am trying to follow the logic:
1. why wouldn't top tube length, etc make a difference in the contact points? Is it because if they are, they would require different components? Example- If I am setting up bike A with a 52cm TT, but bike B has a 54cm top tube- wouldn't this difference impact the measurements to the wall, floor, saddle position? If the bike A contact point measurement at handle bars is transferred to bike B, couldn't that affect bike B's pedal stroke angle?

I guess what I am trying to figure out is if you use these three points, bike A may fit really well, but bike B may not and could require major adjustments to stem length, crank length, etc. If that's what you already said in your post, then thanks for the insight. Either way, I am going to give it a shot- no longer does my "ride it and figure it out method" really work effectively, at least initially
The venerable Mr. Kirk has addressed this already, but I'll add my 2 cents. Basically, what Dave showed is a method to get the contacts the same regardless of what the individual components are: top tube length A + stem length B for a given seat tube angle for example. This is because they are all inter-related and you can't just say add 52 cm top tube plus 12 cm stem and assume it will give the same reach on a different bike with 53 cm top tube and 11 cm stem. This is in part because even the same length top tube can be longer or shorter based on the seat tube angle when it comes to having your butt and hands in the same place because of how seat set back works. Well that sounds confusing and can be if you don't see what's going on. With Dave's method, you take all these things out of the equation and just establish relative values that are easily repeatable. Does that make sense?
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  #34  
Old 07-03-2016, 12:35 PM
west_jay west_jay is offline
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Saddle setback

I'm a bit disappointed that my first post makes me seem the dumb-ass, but I'm giving this fit method a try, and I'm at a loss with what to do with the setback number (62mm.)

Duh, and thx!!

PS: Any thoughts on relative position of stem clamp/spacers to, say, front axle or to floor?

Last edited by west_jay; 07-03-2016 at 01:04 PM.
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  #35  
Old 07-04-2016, 05:02 PM
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David Kirk David Kirk is offline
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Quote:
Originally Posted by west_jay View Post
I'm a bit disappointed that my first post makes me seem the dumb-ass, but I'm giving this fit method a try, and I'm at a loss with what to do with the setback number (62mm.)

Duh, and thx!!

PS: Any thoughts on relative position of stem clamp/spacers to, say, front axle or to floor?
Hey.......I'm sorry but I don't understand your questions. I'm happy to answer and help but I'll need a bit more I think.

dave
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  #36  
Old 07-04-2016, 06:44 PM
OtayBW OtayBW is offline
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Quote:
Originally Posted by west_jay View Post
I'm a bit disappointed that my first post makes me seem the dumb-ass, but I'm giving this fit method a try, and I'm at a loss with what to do with the setback number (62mm.)

Duh, and thx!!

PS: Any thoughts on relative position of stem clamp/spacers to, say, front axle or to floor?
My take: sounds like you're mistaking this procedure for a fitting method. What is described here is intended only to transfer existing fit/contact point measurements from one bike to another. E.g., if you know you have a 6.2 cm setback (determined by some other method), you can dial that measurement - and other parameters described herein - in to other bikes.

Or, maybe I'm not understanding what you're asking....
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  #37  
Old 07-06-2016, 08:08 PM
west_jay west_jay is offline
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Quote:
Originally Posted by west_jay View Post
I'm a bit disappointed that my first post makes me seem the dumb-ass, but I'm giving this fit method a try, and I'm at a loss with what to do with the setback number (62mm.)

Duh, and thx!!

PS: Any thoughts on relative position of stem clamp/spacers to, say, front axle or to floor?
OK, so I'm looking at #2 (of four numbers) to measure contact points to transfer Bike A numbers to Bike B ("Now you have four numbers (saddle height, setback, cockpit length and bar drop) that will allow you to set up bike B to fit just like bike A...".) When I do the maths, my number is 62mm. How does that help me?
Maybe I just need to duplicate the BB-to-wall/saddle-nose-to-wall difference(?)
Maybe I was drinking (?)

The PS was just a thought/question about the significance of stem height over the heat-tube.
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  #38  
Old 07-07-2016, 11:12 AM
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David Kirk David Kirk is offline
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Quote:
Originally Posted by west_jay View Post
OK, so I'm looking at #2 (of four numbers) to measure contact points to transfer Bike A numbers to Bike B ("Now you have four numbers (saddle height, setback, cockpit length and bar drop) that will allow you to set up bike B to fit just like bike A...".) When I do the maths, my number is 62mm. How does that help me?
Maybe I just need to duplicate the BB-to-wall/saddle-nose-to-wall difference(?)
Maybe I was drinking (?)

The PS was just a thought/question about the significance of stem height over the heat-tube.
Hey there -

If you measure the saddle setback at 62 that doesn't do anything but allow you to take a different bike and replicate the number if you wish. There's no magic to the number itself.

As for the stem height over the head tube - there is no magic here either. The original post was meant to merely share an easy and repeatable way to measure your contact points on one bike so you can replicate them on another bike if needed. It of course does not reference where the head tube is or how high the stem is as they are not what is in question.....the stem length/angle, spacer count, and all that put the bars in a given place. I'm not trying to deal with that I just want to know where that given place is so that one can see where their feet, butt, and hands are in space on any given bike.

dave
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  #39  
Old 07-08-2016, 08:18 PM
west_jay west_jay is offline
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OK, thanks Dave.
Not trying to over-think this, but I just thought there was some shortcut to saddle fore/aft involved that I wasn't seeing.
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  #40  
Old 08-01-2016, 09:26 AM
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alyosha_s alyosha_s is offline
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nice article, thank you for posting
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  #41  
Old 09-28-2016, 09:36 AM
fthefox fthefox is offline
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Thank you Dave. I will from now on ditch the plumb line. 👍🏾

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  #42  
Old 10-05-2016, 04:10 AM
Vera J. Hogue Vera J. Hogue is offline
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Great resources.
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  #43  
Old 02-26-2018, 06:54 AM
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weisan weisan is online now
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Just refresh my memory again with this very fine and simple write up by Dave pal on how to measure and transfer contact points from bike A to bike B. I have my own home-grown method but this is far better.

https://forums.thepaceline.net/showpost.php?p=1836643
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  #44  
Old 02-27-2018, 02:12 PM
davidb davidb is offline
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Something that might help, Veloangle.

All the above have lots of good ideas about fit point. I do fits and builds frequently. My methods of transferring fits have been improved greatly, accuracy and speed. By using this Veloangle tool. It does cost more than a tape measure however it is very repeatable and accurate. Take a look see what you think.

veloangle.com
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  #45  
Old 02-28-2018, 09:30 AM
MikeD MikeD is offline
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The Dave Kirk posting should be a sticky.
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