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  #1  
Old 07-23-2017, 03:28 AM
Splash Splash is offline
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stack to reach ratio

when establishing frame set selection and optimal fitment, does the stack to reach ratio play any part?

If so, is there a set of stack to reach ratios suited to a range of human body dimensions?

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  #2  
Old 11-02-2017, 03:10 AM
Kontact Kontact is offline
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Stack and reach aren't actually going to tell you anything when you compare them. If you add 1cm of head tube height to an otherwise identical frame, that will shorten the reach while increasing stack, yet the geometry of the bike hasn't really changed: With a 1cm spacer you can put the stem in the exact same place.


Stack and reach are kinda dumb.
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Old 11-02-2017, 08:21 AM
Mzilliox Mzilliox is offline
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they aren;t really very dumb once you know your prefered stack and reach. i have longer legs compared to my torso length, so long and low bikes dont seem to fit me as well as more square bikes. to me stack and reach say a lot more than calling something medium, or 55cm. it starts to help you dial in measurement based on your actual body type.
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Old 11-02-2017, 08:43 AM
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I find stack-to-reach ratio (STR) to be a useful metric. Once you go below 1.4, you are in the long-and-low range. Above 1.6, it is quite upright.

Also, while it is true that you could make a bike with a low STR (aggressive geometry) fit someone who doesn't need it, it looks all wrong in my opinion (lots of spacers, stem pointing upwards, etc.).
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Old 11-02-2017, 09:59 AM
ColonelJLloyd ColonelJLloyd is offline
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Quote:
Originally Posted by mzilliox View Post
they aren;t really very dumb once you know your prefered stack and reach. I have longer legs compared to my torso length, so long and low bikes dont seem to fit me as well as more square bikes. To me stack and reach say a lot more than calling something medium, or 55cm. It starts to help you dial in measurement based on your actual body type.
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Old 11-02-2017, 11:30 AM
benb benb is offline
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Originally Posted by fa63 View Post
I find stack-to-reach ratio (STR) to be a useful metric. Once you go below 1.4, you are in the long-and-low range. Above 1.6, it is quite upright.

Also, while it is true that you could make a bike with a low STR (aggressive geometry) fit someone who doesn't need it, it looks all wrong in my opinion (lots of spacers, stem pointing upwards, etc.).
It's not necessarily that you hit long and low or very upright as you stray out.

It totally depends on the rider who gets on the bike.

I guess I'm not above 1.6, my road bike is 1.55 or so. I would have thought my bike would definitely fall into the "upright" category for the average rider, and typically when you see the bike I have that is what it is getting used for, bars at least as high as the saddle. But I could set my current frame up with > 10cm of drop at my saddle height. Just a lot of leg length going on. 1.6 or 1.65 might actually be even better for me in terms of setting up the bike and not having spacers showing.

Likewise I have met a few shorter people who have to get a bike that is incredibly long and low just to be able to have any drop at all, they have short legs. Custom bikes longer/lower than stock bikes just to avoid the saddle being at the same height as the bars when the stem is slammed & flat.
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Old 11-02-2017, 11:42 AM
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You are right; the numbers I mentioned are just rough guidelines. That said, that is another nice thing about STR; if you are of the long legs/short torso kind, then a frame with a high STR might be better as you mentioned. Or vice versa for a short legs / long torso rider.
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Old 11-02-2017, 01:18 PM
Kontact Kontact is offline
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The ratios you guys are talking about a so large that I don't see their value.

If someone prefers a 1.6 STR and finds a bike with the identical geometry and a 1cm shorter headtube, the STR is then 1.567, and is addressed with a single 1cm spacer to make them identical.

But if you are talking such huge gradations between them like a full .2 difference, there is no need to do the math - the bike is obviously going to be super high or low in the front end compared to what you're used to. It will be obvious just looking at it, or by looking at stack or reach directly.


That's why I question the value of making a ratio if you're not actually interested in a very narrow number range.

It is also just a potential confusion because you could have a 50cm and a 60cm bike that have identical STRs. How is that helping you? Aren't you going to have too look at stack and reach directly anyway? Could you buy shoes if they were sold on the ratio of size and width, rather than size and width?

It just sounds like another distracting junk number that doesn't directly tell you anything for fit.
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  #9  
Old 11-02-2017, 02:05 PM
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I think STR works best when comparing across different manufacturers for a given frame size. For example, you could look at a 56 cm Trek Domane, with a STR of 1.57, then look at a Cannondale SuperSix 56 cm, with a STR of 1.44, and see pretty quickly that one is more aggressive than the other (of course you could also see this by looking at the geometry tables for the two). Also, that doesn't mean that the SuperSix can't be made to work. But you are probably right, to the average Joe it might create more confusion than anything else.
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Old 11-02-2017, 02:24 PM
Kontact Kontact is offline
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I think STR works best when comparing across different manufacturers for a given frame size. For example, you could look at a 56 cm Trek Domane, with a STR of 1.57, then look at a Cannondale SuperSix 56 cm, with a STR of 1.44, and see pretty quickly that one is more aggressive than the other (of course you could also see this by looking at the geometry tables for the two). Also, that doesn't mean that the SuperSix can't be made to work. But you are probably right, to the average Joe it might create more confusion than anything else.
It doesn't mean that one is "super aggressive", it just means that one has either a longer top tube or a shorter head tube.

Where it fails is that you could have a "56" with a short head tube and top tube (50 and 75) that has the same ratio as a "56" with a long top and head tube (60 and 90). And since the advent of compact frame geometry, using the stated frame size as a starting point can create exactly that short of problem.
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Old 11-02-2017, 04:40 PM
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oh nevermind.
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Last edited by false_Aest; 11-02-2017 at 04:43 PM.
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  #12  
Old 11-02-2017, 04:47 PM
Kontact Kontact is offline
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nah, TT + ST length are dumb.

also so are those testicle hangy lights
Any dimension that gives the consumer a false sense of fit is kinda dumb. TT at least observes the relationship between the parallel seat and head tubes that is preserved as you raise seat and handlebars.

Reach is such an oddly arbitrary number in measuring a vertical distance to an 73° line running through the head tube.
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Old 11-02-2017, 06:54 PM
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Originally Posted by Kontact View Post
Any dimension that gives the consumer a false sense of fit is kinda dumb. TT at least observes the relationship between the parallel seat and head tubes that is preserved as you raise seat and handlebars.

Reach is such an oddly arbitrary number in measuring a vertical distance to an 73° line running through the head tube.
Being on the short side of normal I have yet to ride a bike with a 73*/73*. Ben Serotta tried to do that to me once and I ended up having to push my saddle all the way forward on a 0-setback seatpost. It worked but it was FUGLY AS FCUK.

If you're obeying ISO standards as the bike gets smaller you necessarily need to move your HTA toward 72* to compensate for toe overlap. Not an issue for custom builders but it is an issue if a company plans on selling a bike in the EU. So when the stem and seatpost move up/down the relationship isn't preserved.
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  #14  
Old 11-02-2017, 07:16 PM
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I find stack-to-reach ratio (STR) to be a useful metric. Once you go below 1.4, you are in the long-and-low range. Above 1.6, it is quite upright.
So I went ahead and plotted the STR data for a few of the more popular frames out there. In doing that, it reminded me that the 1.4 - 1.6 range I mentioned is really more for the frame size that I happen to ride (57-58 cm) and pay attention to. As the figure shows, the STR increases more or less linearly between sizes.

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Old 11-02-2017, 07:42 PM
Kontact Kontact is offline
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Being on the short side of normal I have yet to ride a bike with a 73*/73*. Ben Serotta tried to do that to me once and I ended up having to push my saddle all the way forward on a 0-setback seatpost. It worked but it was FUGLY AS FCUK.

If you're obeying ISO standards as the bike gets smaller you necessarily need to move your HTA toward 72* to compensate for toe overlap. Not an issue for custom builders but it is an issue if a company plans on selling a bike in the EU. So when the stem and seatpost move up/down the relationship isn't preserved.
It really isn't that much of a problem. If you have a 72° head tube, the difference from a 73° is going to be a milimeter or so in stem position. Nothing worth compensating for.

The seat tube is more of an issue because it is 50cm+ long, so the amount of offset due to 1° of angle difference is closer to a centimeter. (Actual range is 9mm for 1° on a 50cm frame and 10.5mm for a 60cm.)


I don't know why you'd use a zero set back seatpost with a road bike. Road bikes are normally designed for a standard setback seatpost (25mm or so). If you wanted to build a custom frame to use a zero set back, you would relax the seat post angle by 2.5°, so you'd need a 71.5° seat tube angle. So when you use a zero setback with a 74° small bike seat tube angle you are automatically going to have to clamp the seat 3.5cm further forward of optimal. That's not only ugly, it destroys saddles.

I'm surprised Ben was okay with that.
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