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Which Dimension Do I Need?

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Which Dimension Do I Need?

Old 02-11-23, 09:39 AM
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Which Dimension Do I Need?

This may be an odd, or abstract, or just ignorant question, but bear with me please.

I've had several well-respected framebuilders tell me that the most critical dimensions for getting a new bike to match the fit of one you already have and like are
- saddle height (top of saddle to center of bottom bracket, measured along the seat tube)
- saddle setback (measured with a plumb bob from the front of the saddle nose, and then measured horizontally from the plumb line to the center of the bottom bracket)
- saddle-to-bar drop (measured by subtracting the bar tops-to-floor measurement from the saddle top-to-floor measurement)
- saddle nose to center of stem face (i.e., the seam between the two halves that bolt together)
- saddle nose to tips (tops?) of the lever hoods (measured on an angle)

Irrespective of whether you agree that ^^^that is all that's required...my question is about what else is required if you're talking about bikes with different model saddles?
Because ^^^those metrics presume you're using the exact same saddle on all bikes.

Now, I suck at math, so it's not entirely obvious to me what other measurement(s) might be required to level the playing field when using dissimilar saddles. I think an important measurment would be
- saddle nose to the center of the seatpost clamp? because that way your saddle nose to center of stem face, and saddle nose to tips of the lever hoods measurements can be compared to saddle setback, and then you just

...uh

...um

Yeah, so I'm not sure what the next step(s) for making the two dissimilar saddles "match" would be.

It also occured to me that total saddle length might be important? But I'm not sure I can figure out why.


Anyhow, any ideas what I'm looking for? Thanks,

Last edited by Bob Ross; 02-11-23 at 05:46 PM. Reason: typo
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Old 02-11-23, 02:04 PM
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Those sound good to me. Though the measurements off the saddle will depend on whether or not you intend to use the same model saddle.

Sometimes aspects of the ride and handling of the bike get confused into fit sensations of people. So those things could be wildly different even with you sitting in the same position.

My question is... are you so happy with the particular fit of one of your bikes that you don't want to try something slightly different?
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Old 02-11-23, 04:31 PM
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None of these measurements are super-critical as they can easily be adjusted, especially saddle height and setback. I find this a good guide for taking basic measurements. Note they reference the saddle centre (which is a bit more independent of saddle model).

https://www.myvelofit.com/fit-academ...ry-rider-needs
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Old 02-11-23, 05:54 PM
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Originally Posted by Iride01
My question is... are you so happy with the particular fit of one of your bikes that you don't want to try something slightly different?
Holy good god, yes. Two of my bikes were custom-built for me, based on my physical dimensions + whatever knowledge (or mojo) these experienced builders bring to the table. The other two bikes I currently own -- as well as every other bike I have ever owned, rented, borrowed, or test-rode -- were obviously not made-to-measure. And the difference is astonishing. When I throw a leg over my custom bikes and start pedaling, there is an instantaneous sensation of "Ahhh...everything is exactly where it's supposed to be!" And 3 or 4 hours later, my body still feels that way. None of the non-custom bikes give me that sensation; none of them are as comfortable.

So, presuming the relationship between contact points and the wheels can work from a functional/performance standpoint, I want to duplicate those contact points on any future bike I may ever buy...as well as on the other two bikes I currently own. I have no interest in "try[ing] something slightly different" because I already know what it feels like to ride a bike that doesn't fit perfectly...and I know what it feels like to ride one that does. Life's too short to presume that there may be an even perfect-er set up; I just wanna get everything set up the way I like so that I can stop thinking about fit and just get on with riding.
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Old 02-11-23, 05:58 PM
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A general rule of thumb is to use the nose as a reference. And if you are comparing a normal vs. short nose saddles, 3cm is a good conversion. If you are just swapping saddles, make sure you check saddle height, put in set back, re-check saddle height. If it is two different bikes, your only reliable reference is the BB. A weighted string hanging off the end of a small ruler works well.

If you want something more exact, reach under your thigh and find where you 'sit bone' pushes on your current saddle and set back measure to that point. Get the new saddle in place and ride it a bit. When you've settled out on the new seat, find that same sit bone point and move the saddle to that same measure.
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Old 02-12-23, 12:59 PM
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Originally Posted by Bob Ross
Holy good god, yes. Two of my bikes were custom-built for me, based on my physical dimensions + whatever knowledge (or mojo) these experienced builders bring to the table. The other two bikes I currently own -- as well as every other bike I have ever owned, rented, borrowed, or test-rode -- were obviously not made-to-measure. And the difference is astonishing. When I throw a leg over my custom bikes and start pedaling, there is an instantaneous sensation of "Ahhh...everything is exactly where it's supposed to be!" And 3 or 4 hours later, my body still feels that way. None of the non-custom bikes give me that sensation; none of them are as comfortable.
I don't find one and only one position to be more or less comfortable. I've for a long time been comfortable on bikes with a relaxed fit and am currently comfortable on a bike with more of a aggressive fit.

Your view on this is interesting as it seems similar to another conversation on another forum where the person said they rarely try other beers because they think they found the best tasting beer and don't want to chance trying a beer that they'll consider a bad beer.

Whether beer or bikes, for me it just seems like not trying something different means you'll never know if something is as good or better.

But I'm totally okay if that is the way you wish to be.
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Old 02-12-23, 01:22 PM
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I ride with a consistent BB to mid-seat distance. (I put a mark halfway back on my seats. That is relation to my hip joint doesn't vary a lot.) Now I swing this location through a little bit of arc depending on whether the bike is an easy going, just ride in town or serious road bike or even more serious road fix gear. (Those road fix gears - getting far forward and aero is the only way to go upwind!) My "cockpit" gets rotated the same amount around that same BB so I am effectively just to rotating my entire self.

Now, for my bikes for casual riding, I may go for more HS washers or a higher quill stem to open up my thigh-torso angle more. (That changes. If I'm riding that bike more seriously, the bars go back down.)
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Old 02-12-23, 03:14 PM
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Originally Posted by Iride01
Whether beer or bikes, for me it just seems like not trying something different means you'll never know if something is as good or better.
Except that with beer, there's no overriding objective or goal to trying different beers other than Pleasure. Whereas with bike fit, the overriding objective or goal is to improve Performance, Comfort, or Both.

I can drink the most exquisite beer on earth and think "Wow, this gives me an extraordinary amount of pleasure!" without also thinking "I cannot imagine any other beer ever giving me as much if not more Pleasure!"

But what would "More Comfort" even feel like if you're already as comfortable as you want/need to be when riding? And "More Performance" is easily measured: I've seen the before & after metrics that led to my preferred setup, and between the measurable differences that small changes around that preferred setup revealed, plus the fact that I'm getting older and all those numbers are on the way down anyway, it just doesn't seem likely that searching around for another bike fit is going to yield improved Performance, Comfort, or Both, just because it's a big world with infinite possibilities.

It's kind of a Pick Your Battles philosophy: I could keep looking for a better fit (or a different fit)...or I could be content with the one that already yields the objectives/goals I seek from adjusting my position on the bike, and instead spend my time & energy pursuing other sources of mystery and investigation. Like, what's the most exquisite beer on earth?
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Old 02-12-23, 04:08 PM
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I know that my saddle height is the same on every bike at 71cm. Pretty much any frame that is in my size range is going to allow me to get that height. Thus the very first measurement I look at is effective top tube and I know that 55 to 56 is a bike I can work with, the reach is adjusted with varying stem lengths. Pretty much every seat post I use is a 25mm setback and the saddle is neutral on that.
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Old 02-12-23, 09:36 PM
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Originally Posted by Iride01
I don't find one and only one position to be more or less comfortable. I've for a long time been comfortable on bikes with a relaxed fit and am currently comfortable on a bike with more of a aggressive fit.

Your view on this is interesting as it seems similar to another conversation on another forum where the person said they rarely try other beers because they think they found the best tasting beer and don't want to chance trying a beer that they'll consider a bad beer.

Whether beer or bikes, for me it just seems like not trying something different means you'll never know if something is as good or better.

But I'm totally okay if that is the way you wish to be.
I had my eyes opened 46 years ago. May of my second year of racing I bought the last year's Fuji Pro in the shop basement. First ride I just moseyed; brand new bike, much longer cranks and it was mid-season. That mosey around my regular morning training loop matched my best time ever. Next time, two minutes came off and the times kept falling the rest of the summer. That August I rode the fasted (by far) race I ever rode with Cat 1 and 2 riders, made the split in the field and finished with the lead group under the old course record. All this despite helping initiating a doomed break earlier in the race.

The point? That bike extracted everything this body had to offer. (I suspect the shop mechanic and the fellow racing salesman suspected that bike would do me well.)

Over the years my fit has evolved but hasn't changed very much. I still get reminded by my body that if I stray too far from the fit of long ago I'm headed for lower performance, less comfort and perhaps chronic issues.
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Old 02-13-23, 09:47 PM
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Originally Posted by Bob Ross

So, presuming the relationship between contact points and the wheels can work from a functional/performance standpoint, I want to duplicate those contact points on any future bike I may ever buy...as well as on the other two bikes I currently own. I have no interest in "try[ing] something slightly different" because I already know what it feels like to ride a bike that doesn't fit perfectly...and I know what it feels like to ride one that does. Life's too short to presume that there may be an even perfect-er set up; I just wanna get everything set up the way I like so that I can stop thinking about fit and just get on with riding.
I drew a triangle. Assuming you're going to use a handlebar that you absolutely can't live without and similar pedals and identical crank lengths, connect the widest part of the saddle (presumably the most reliable indicator of where the butt contacts the saddle, the bottom bracket, and the center the clamp on the handlebar stem. Measure the spans. There's your spec for a new bike setup. If you use a different handlebar, measure to the brake hoods instead. Or subtract the difference in handlebar reach from the stem length.
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Old 02-15-23, 06:26 PM
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Originally Posted by Iride01
I don't find one and only one position to be more or less comfortable. I've for a long time been comfortable on bikes with a relaxed fit and am currently comfortable on a bike with more of a aggressive fit.

Your view on this is interesting as it seems similar to another conversation on another forum where the person said they rarely try other beers because they think they found the best tasting beer and don't want to chance trying a beer that they'll consider a bad beer.

Whether beer or bikes, for me it just seems like not trying something different means you'll never know if something is as good or better.

But I'm totally okay if that is the way you wish to be.
False equivalency. If I found a fit that caused all my cycling related pain to go away, I would not deviate from it.
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Old 02-16-23, 09:21 AM
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Originally Posted by Lombard
False equivalency. If I found a fit that caused all my cycling related pain to go away, I would not deviate from it.
I guess I've never had cycling related pains I've considered so horrible. I've been able to make different positions whether I'm upright or aero, comfortable.
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Old 02-16-23, 01:15 PM
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Originally Posted by Iride01
I guess I've never had cycling related pains I've considered so horrible. I've been able to make different positions whether I'm upright or aero, comfortable.
You're either younger or have better genetics.
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Old 02-17-23, 10:04 AM
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Originally Posted by Lombard
You're either younger or have better genetics.
Probably goals are part of it. For me I saw the advantage of getting a more aero position on the bike after I started riding for fitness back in my 50's with bikes that gave me a relaxed position. So now about to be 65 y.o. in March I'm in a much more aero position than I've ever been.

Sure there were some pains and odd feelings. I figured out what was causing the pains and dealt with that before they became huge annoyances. And moving back to a more relaxed position was always on the bottom of the list of things to try. Thankfully I never got that far down the list. The odd stuff you just get use too because it's just the differences between how two differently designed and constructed things are.
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Old 02-19-23, 12:53 PM
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Originally Posted by Bob Ross
This may be an odd, or abstract, or just ignorant question, but bear with me please.

I've had several well-respected framebuilders tell me that the most critical dimensions for getting a new bike to match the fit of one you already have and like are
- saddle height (top of saddle to center of bottom bracket, measured along the seat tube)
- saddle setback (measured with a plumb bob from the front of the saddle nose, and then measured horizontally from the plumb line to the center of the bottom bracket)
- saddle-to-bar drop (measured by subtracting the bar tops-to-floor measurement from the saddle top-to-floor measurement)
- saddle nose to center of stem face (i.e., the seam between the two halves that bolt together)
- saddle nose to tips (tops?) of the lever hoods (measured on an angle)

Irrespective of whether you agree that ^^^that is all that's required...my question is about what else is required if you're talking about bikes with different model saddles?
Because ^^^those metrics presume you're using the exact same saddle on all bikes.

Now, I suck at math, so it's not entirely obvious to me what other measurement(s) might be required to level the playing field when using dissimilar saddles. I think an important measurment would be
- saddle nose to the center of the seatpost clamp? because that way your saddle nose to center of stem face, and saddle nose to tips of the lever hoods measurements can be compared to saddle setback, and then you just

...uh

...um

Yeah, so I'm not sure what the next step(s) for making the two dissimilar saddles "match" would be.

It also occured to me that total saddle length might be important? But I'm not sure I can figure out why.

Anyhow, any ideas what I'm looking for? Thanks,
I agree with your insights. I use a few basic traditional leather Brooks and Ideale, a more modern Selle Anatomica, and occasionally I try a Specialized Toupe or other Spec road saddle. To accommodate the different designs I approximate the widest part of the saddle as the location of my sit bones, and I assume that saddles (yes, all saddles, but remember it's just an assumption) are intended to have the sit-bones mainly perched where the saddle is widest. To quantify setback I measure from the fore/aft position of the widest part forward to a plumb line which falls down through the BB axis.

It might look like all Brooks' and other vintage leather are the same, but not true. The mechanical limit on setback for a given saddle is that it cannot be slammed any further than when the forward end of th straight rail hits the end of the seat post clamp. Some seat makers have their own limits marked on teh rail, either for lawyers or for reliability. The fore/aft distance between the front end of the saddle rail and the widest point on the saddle (where I assume the saddle maker wants my butt bones to be) is not the same for all hi-quality vintage saddles. But interestingly, for some recent B17s, 1979 Professionals, a 2005 Swallow, a pair of pretty old Ideale 80s and a 1984 Ideale those distances are not the same. The racier ones, like the Ideale 80s, the 1979 Brooks Professionals, and the Swallow all place the sitbone platforms at least a cm, sometimes two cm (the Swallow and I think the Ideale 80), behind the corresponding positions found on a B17.

I guess I won't say this is fascinating, but it helps me understand why certain saddles were favorites for racing or for touring BITD.
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Old 02-19-23, 01:07 PM
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Originally Posted by oldbobcat
I drew a triangle. Assuming you're going to use a handlebar that you absolutely can't live without and similar pedals and identical crank lengths, connect the widest part of the saddle (presumably the most reliable indicator of where the butt contacts the saddle, the bottom bracket, and the center the clamp on the handlebar stem. Measure the spans. There's your spec for a new bike setup. If you use a different handlebar, measure to the brake hoods instead. Or subtract the difference in handlebar reach from the stem length.
I like this!
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