Stack and Reach questions

Hello.

It is my understanding that stack and reach are the most important measurements when considering bike fit. With this in mind, I have the following question regarding potential bikes, and which one might best relate to the fit of my current bike (Lynskey).

The chart below shows Stack and Reach measurements for my current bike, as well as those for three other bikes. Two of those bikes, SystemSix and Foil are listed in size 51/52 and 54. The third, Cervelo, is only listed in size 54.

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So when I look at the chart, would I be correct in thinking that the bike who would best match in fit is the Cervelo S Series?
Also, is there one of those two measurements which correlates better in order to obtain a similar fit? It seems that the SystemSix and Foil become quite longer in reach as the stack approximates that of the Helix…so in those cases, which would be of higher importance in getting as close as possible.

Thank you for any feedback with this.

Hi, just went through buying a bike and fit is unbelievably complicated. Check out this site:


It allows comparisons of bike geometries, while this site offers personalized profiles:

I wish I had found bikeinsights before buying my bike, it would have yielded me many more choices. Best of luck with your search :slight_smile:

You’re correct that the Cervelo is the closest in geometry to your current bike, assuming those numbers are accurate. However, you also need to bear in mind what stem length you have on your current bike, since reach is measured to the top of the head tube, but your position on the bike is determined by where the bars are. I believe that all 3 of the bikes you’re looking at have a one-piece bar and stem which may limit your options in terms of adjusting reach to the bars. Maybe the cheaper models have separate bar and stems, or maybe the bars come in a few different sizes and toy can spec the size you want when you order the bike, I don’t know. E.g. If you are running a 100mm stem and want to keep your current position on the Cervelo, you need it to also have a one-piece bar that has a 100mm stem. And the problem is if you get it wrong then swapping out the bars to get more or less reach is going to be much more expensive than swapping out a traditional stem.

Stack is a bit easier to change insofar as you can have spacers under the bars to raise them up. Though a lot of people prefer the look of a bike that is “slammed” I.e. No to minimal spacers.

Other question is whether you actually want to keep the same position? All the bikes you’re looking at are aero and designed to be ridden with aggressive positions I.e. Lower and steeper. That’s why the reach is longer for the same stack on the Scott and Cannondale. Not just because they’re designed to be ridden low, but because if you move the seat forward to get steeper you also need to move the bars further forward.

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I will check these out, thank you.

Thank you.

So in essence, the frame stack and reach is one thing; however, the actual or true stack and reach would account for any spacers currently under the stem as well as the stem length. And those two “actual” measurements are the one’s I want to try and match with what I could obtain with bikes being looked at.

Yes. Frame stack and reach vs complete bike stack and reach. And the handlebars play a role too. Drop bars essentially have 3 stacks and reaches: tops, hoods and drops. Rise, sweep, flare, reach, drop, and width of the bars affect things. The stem length and angle play a role too. That’s why I don’t like integrated bars and stem. Too many variables are constrained.

Also, you don’t necessarily want the same complete bike stack and reach for bikes for different purposes (crits vs cyclocross vs gravel endurance). Generally the longer and rougher the ride, the more upright people will sit, which calls for shorter reach and stack (your upper body pivots at the hips).

And two bikes with different frame stack and reach for the same purpose might be able to get to the same full bike stack and reach, but the handling will be different due to the different stem length.

Bike fit is not a simple topic at all.

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So, an anecdotal story for you.

For years, my main bike was a cyclocross bike: a size 51 Cannondale CAADX. It has a 371 mm reach and 536 mm stack. I run it with a 15mm spacer and 110mm stem. Been riding the same fit for years. It works well for me.

When I decided I wanted to dedicated road bike, I looked at geometries and did all of my comparisons on stack and reach. I bought at size 52 CAAD 12, which has a 535mm stack and 381 mm reach. Figured I’d run it with a 15mm spacer and 100mm stem. Perfect fit, right?

Not even close. I could never get comfortable on the CAAD12. When I took actual comparison measurements between the two bikes, it turns out that, due to head tube/seat tube angles, the bar stack and reach measurements were far off what I thought they were going to be. I don’t remember how off it was, but I know that the numbers made it perfectly clear why I was always sore from riding that bike.

The seat tube was also very long, so I had almost no seatpost showing. I have short legs, so I figure that’s more of a “me” issue that most other people won’t deal with. But it’s something I’m far more conscious about now.

Anyway, I finally had to get rid of the CAAD12 after messing with the fit for 8 months and still never getting where I wanted to be. I sold it and bought a 2018 SuperSix Evo in a 50 (same geometry as the CAAD12, but in a size smaller), which has a 526 mm stack and 375 reach. With a 25mm spacer and 110 mm stem, it fits like a glove–just a tiny bit lower and longer than the CAADX, which feels great.

So, all this is to say one thing: bike fit is about more than stack and reach. Top tube and seat tube length still very much matter in my opinion, as do head tube and seat tube angles. If you buy a new bike based purely off of stack and reach looking to replicate your current fit, there’s a chance you may hit the same issues I did. I learned a lot from that situation though, so now I know.

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Thank you for that insight.

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Thank you, agreed, not that simple at all.

I’m assuming that all the bikes you have listed, being aero road bikes have basically the same geometry. If that’s the case, then the stack and reach is the correct way to compare how the frames are going to fit you. It’s worth checking that your current bike has approximately the same angles too. If the angles are very different (as summerson experienced), then while the bars might be in the same place relative to the bottom bracket, the seat might be somewhere else entirely, and not possible to move fore/aft enough on the rails to compensate.
On your original question - if you don’t have integrated bars/stem, you can to a certain extent adjust both stack and reach. Stack is the easiest to adjust (upwards) because you can just add spacers until you run out of steerer tube, but the hardest to adjust downwards because you have to start messing with negative angle stems. I don’t think you need to worry about that if you are looking at an aero race bike though. Reach is just stem length (or bar shape) and there are a wide variety of stem lengths in normal angles - it can get expensive if you need to try a number of different stems though!
The other question is how looks affect whether you would want to apply the adjustment to the bike. Putting 35mm of spacers under the stem of the 51cm SystemSix might get you to the right stack, but if the end result looks strange to your eyes then maybe it’s a compromise too far and you’d be better off choosing a frame that doesn’t need to so many spacers.

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On bikegeo.net is a stack and reach calculator which I found great at comparisons as it also takes stackers, stem length etc into account it overlays one outline of a bike against the others, Takes some jiggery-pokery to get it bang on - if you have unknown values estimate until the stack and reach on the calc are the same as quoted for the frame before the stem risers length etc.
One thing I did was focused on stack and reach and nearly got caught out. The horizontal top tube is what it is and the proportion of that in front of the BB is reach. Some types of bikes have much longer reach measurements than others with the same top tube length - they put you more over the BB if the top tubes are the same though it’s not as simple. As above it’s a very big subject.

I had more concerns about stack so it also allows you to see what flipping the stem does as does this one: http://yojimg.net/bike/web_tools/stem.php

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This is not correct…Stack and Reach measurements were specifically designed to remove variables from bike fit. When measured properly (i.e. from the center of the BB), Stack and Reach are objective measurements that allow you to achieve the same position between bikes, regardless of frame geometry.

If you use the old school measurements of seat tube (i.e. a 56cm frame) and top tube length, then different frame angles definitely affect how different 56cm frames fit. But if you have two bikes with the same stack and reach for the headtube, that point on the headtube is in the exact same place relative to the BB on both bikes.

Stack and reach only tell you the relative position of the top of the head tube in relation to the bb. You also need to consider seat tube angle, since that affects the “effective” top tube length and position of the saddle, relative to the bb.

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Oh well in that case we can completely eliminate my actual real world experience from the equation. It’s not like I spent countless hours trying to figure out why my 12, which had very similar stack and reach to the X, didn’t fit anything like the X. If only someone would’ve told me that stack and reach were the only important metrics!

I’m not saying that stack and reach aren’t good resources, because they are. I’m saying that you should also look at the full geometry instead of just a small portion. Like I said, the seat tube on my 12 was a lot longer than I expected—something that stack and reach didn’t tell me in the slightest. Head tube and seat tube angles, along with top tube and seat tube length, should be scrutinized alongside stack and reach.

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No…Stack & Reach are measured from the center of the BB. That measurement eliminates the confusion of angles, tube lengths, etc.

If you have two bikes with the same Stack and Reach, and you saddle is in the same position relative to the BB on both bikes (which it should be), then you fit is the same. It doesn’t matter how you connect the dots in between if the BB, Saddle and HT points are all in the same position.

You both are right & wrong :stuck_out_tongue:

Both measurements matter. R&S are great for looking at pure position ideology, but it ignores potential limitations in saddle placement than can exist from seat tube angle and seat post positioning. Generally speaking, you can get a saddle anywhere you want relative to the BB, but some bikes and related component choices lead to restrictions in location (seat tube angle and seat post setback in particular).

So as ever, it’s wise to look at the broader picture and not focus on just a pair of values.

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My guess is that you had other elements in play…different saddle position relative to the BB, different HB measurements, etc.

In addition, you were trying to use a CX position and adapt it to a road riding…one position is not necessarily applicable to both.

Correct…but that is a different issue than saying Stack and Reach aren’t the same between two different bikes. As noted, if you saddle is in the same position relative to the BB, then you can achieve the same position between two bikes of identical S&R, no matter what the frame geometry differences may be.

You’re doing a lot of assuming here. The saddle was in the same position relative to the bottom bracket on both bikes. HB was the same width, etc.

And I’ve never ridden CX in my life. My CAADX was my gravel bike and I rode it so much that I ended up just selling the roadie at the time and using the X with two wheelsets. For all intents and purposes, it was my road fit.

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The saddle will not automatically be in the same position as the angle of the seat tube effects where the saddle is relative to the BB and to the headtube/bars. The length of the stem also matters.

So, the BB and HT will be in the same position relative to each other, but the saddle (and bars) may not be. That said, for a given stack and reach it should be possible to achieve the same position by adjusting saddle fore/aft and changing the stem. However, this can effect the balance and handling of the bike.

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