What makes a bike a "59?" Or a "58?" Or a "57?" Etc…

[Kirk007]

Originally Posted by Clean39T

Does your Spectrum have a STA slacker than the Kirk? I figured they were both 72.5 w roughly the same chainstay lengths..

It is a bit steeper and head tube angle is steeper and top tube a bit over cm longer. But honestly as you know, I looked at the geometry really hard and figured I could get the contact points down ok and I have but something just doesn't feel quite right. Unless I go to a wayback seatpost, even a 25mm seatpost leaves me about a cm shy of my normal setback, although it feels fine and passes Dave's setback determination test. so I don't think that's it. My guess is my weight is too far back and if I go to a zero setback post that's going to put me way off my normal setback. Anyway, still working the {first world} problem.

[Clean39T]

One other thing to note is that a steeper STA does allow for reasonably short chainstays though when trying to fit fatter tires in a performance frame and getting things right down to the mm of clearance. You simply can't put a 700x35 tire in a frame with a 71.5-STA and 415mm stays - so even if you can use a 71.5-STA with a zero SB post and get roughly the same position as a 73.5-STA with a 25mm SB post, there may be other reasons not to do it that way.

[mhespenheide]

Originally Posted by robt57

The reason I disagree is where the TT winds up in the window. For me the slack STA means zero offset post, and shorter EFF TT rolling.

I don't think I follow you. A slack seat tube angle with zero-offset post and at the back of the saddle rails can have the exact same reach as a steep seat tube angle with setback post at the front of the rails. I've drawn an extreme example here.

I'm right there with you that it changes the weight balance (and therefore handling). I don't get what you mean by "shorter EFF TT rolling."

(Not picking a fight; just trying to understand.)

[NHAero]

Why is the "weight balance" (assume you mean where the center of mass is?) changed? The saddle is in the same place. (Easily) confused...

Originally Posted by mhespenheide

I don't think I follow you. A slack seat tube angle with zero-offset post and at the back of the saddle rails can have the exact same reach as a steep seat tube angle with setback post at the front of the rails. I've drawn an extreme example here.

I'm right there with you that it changes the weight balance (and therefore handling). I don't get what you mean by "shorter EFF TT rolling."

(Not picking a fight; just trying to understand.)

[prototoast]

Originally Posted by NHAero

Why is the "weight balance" (assume you mean where the center of mass is?) changed? The saddle is in the same place. (Easily) confused...

I think he's confounding a few things. "Reach" isn't affected by STA, but for a given reach, the saddle can end up in a lot of different places, changing the weight balance. Also, across different STA, you can end up with the saddle in the same place through different post/saddle setbacks. This should not affect weight distribution, everything else equal.

[Mark McM]

Originally Posted by prototoast

I think he's confounding a few things. "Reach" isn't affected by STA, but for a given reach, the saddle can end up in a lot of different places, changing the weight balance. Also, across different STA, you can end up with the saddle in the same place through different post/saddle setbacks. This should not affect weight distribution, everything else equal.

When the same word can mean two different things, it is bound to cause confusion. Some people use the word "reach" to mean the distance from saddle to handlebars (i.e., how far the cyclist has to reach their torso and arms to put their hands on the bars). But in the context of frame Reach & Stack, "Reach" refers to the horizontal distance from the center of the BB to the center of the top of the head tube.

In the first definition, the STA can affect the reach, but in the second definition STA does not affect the Reach. The first definition may better reflect the end result of the bicycle fit adjustments, but the second definition is the simplest for describing the actual frame size.

[charliedid]

Originally Posted by Mark McM

When the same word can mean two different things, it is bound to cause confusion. Some people use the word "reach" to mean the distance from saddle to handlebars (i.e., how far the cyclist has to reach their torso and arms to put their hands on the bars). But in the context of frame Reach & Stack, "Reach" refers to the horizontal distance from the center of the BB to the center of the top of the head tube.

In the first definition, the STA can affect the reach, but in the second definition STA does not affect the Reach. The first definition may better reflect the end result of the bicycle fit adjustments, but the second definition is the simplest for describing the actual frame size.

I was jut going to write this ^

[robt57]

Originally Posted by mhespenheide

I don't think I follow you.

Same TT and Reach for example will have a shorter ETT on the slacker STA. I guess that was what I was attempting to get out of my brain.

[flying]

I have read the replies & all I can say is if what your riding feels good & works for you & you ride many miles injury free then it is all good.

But for all the comparisons to seat tube angles relating to TT etc I will just say "for myself" again setback has absolutely nothing to do with reach
(in my experience)

Setback as I see it is strictly the distance I am sitting behind (in my case) the BB. This allows my legs injury free pedaling in all situations & RPM's
Of course we all probably also move a bit on the saddle for different situations but.......

That aside I am not going to get my setback requirement on a steep STA period. I ride a 73 STA with a 25mm setback post & am pretty slammed back at that. For the curious my setback is 8.57cm
That is tip of saddle nose BEHIND BB center on a saddle that is 275mm long

So STA is important to me personally & IMHO is the most important fit factor as it cannot as I said previously be fixed with a longer or shorter TT or stem

Again these are all in my opinion & is what has worked for me

EDIT: I see now too that Dave's post also pretty much said the same as what I think

[dustyrider]

I know what makes a bike a 57, 58, and 59cm. They’re all rideable by me!

[Waldo62]

The whole sloppy top tube movement screwed up frame measurement for the rest of us. 57, 58, 59 -- forget the numbers, now they're all "Large."

[charliedid]

Originally Posted by Waldo62

The whole sloppy top tube movement screwed up frame measurement for the rest of us. 57, 58, 59 -- forget the numbers, now they're all "Large."

Yeah well they are not "all large" and it really isn't that hard to understand sizing unless you are just looking to be mad about something.

[weisan]

Originally Posted by flying

I have read the replies & all I can say is if what your riding feels good & works for you & you ride many miles injury free then it is all good.

flying pal, we are on the same page.