elcruxio

I've been trying to find a definiton and found a pretty good one from the cervelo site
"frame stack is the vertical length from the BB to the top of the headtube"

Now the trouble I'm having is trying to figure out how stack is measured, or rather in which angle.
My assumption is that stack is measured with the fork installed and with theorethical wheels attached. Thusly the actual fork length would affect the stack measurement and so a longer fork would increase the stack number.
But what confuses me is that some stack measurement illustrations either have the frame skewed in a weird angle or, actually do not incorporate a fork.
So how is stack actually measured and what variables should be taken to consideration?

I'm asking because my road bike is actually a converted cyclocross. This makes comparing different frames a bit difficult since I can't (yet) be sure how fork length in accordance with stack and head tube length affect my comparisons.

emveezee

Stack is always measured with whatever fork the manufacturer or frame builder intends to be used on the bike. Sometimes they'll provide and axle-crown length. Most road forks are within a few mm these days. But yes, a cross fork may require you to do some trigonometry or just actually use a yardstick and a plumb line.

topflightpro

When calculating stack, the measurement is made assuming that the front and rear drop outs are level. In this regard, yes, the fork length is factored in. The images you see may be skewed or angled, but the measurement is pretty standard.

The dropouts are level. A horizontal line, which is parallel to a line drawn between the center of the dropouts, is drawn through the center of the top of the headtube, and the distance from that line to the center of the bottom bracket is your stack.

elcruxio

ok thanks for the quick answers

rpenmanparker 

What topflightpro said!

According to what you wrote, "frame stack is the vertical length from the BB to the top of the headtube," here is how it would be measured. With the line from the front to rear dropouts perfectly horizontal, stack as you describe it would be the vertical distance from the center of the BB shell to the center of the top edge of the head tube (just underneath the top of the headset, not including it. The rear half of the top edge of the head tube would be below the measurement point, the front half above it, because of the head angle. For all geometry measurements the frame always needs to be angled so the dropouts are horizontal (or INW so the identical wheels/tires both touch the ground). Sometimes you measure along an angled line (head tube angle, seat tube angle, seat tube length). Sometimes you ignore the lines of the tubes and measure vertically or horizontally. It is all according to the definition of the parameter and the diagram usually shown.

Campag4life

And OP more generally if you are trying to wrap your mind around how tall the front of a given bike is, bikes as you know for many years were and still are defined by head tube length relative to their overall height. Generally, and there are exceptions...a typicall cross bike with have an axle to crown fork height of 410mm or so...and typical road bike 375mm +/-. So for general comparison purposes and again there are exceptions...a head tube on a cross bike....with typically be about 35mm shorter for the equivalent height road bike frame. This is a general guideline and as noted there are exceptions.
If you check axle to crown spec's for your bike this will help...you can measure it easily with a tape measure...and then measure head tube length.
Yes...hta also factors in marginally...as does fork rake. Stack is the best predictor but the clearance for larger volume tires are why cross bikes and 29ers and mtbs have more distance from axle to crown and typically shorter head tubes for the same height front end.

RollCNY

Thanks for pointing this out Campag. I have been eyeballing Pacer vs Cross Check, but couldn't figure out the shorter head tube on the Cross Check. With less BB drop and a shorter head tube, I was picturing larger saddle to bar drop, but now the numbers all make more sense. Another excellent post!

Campag4life

Thnaks Roll. To indulge our bike geekness even further...take a manufacturer like Specialized and compare their stack/reach geo charts between their road and cross bikes...say the Crux or Tri-Cross verus Tarmac and Roubaix. You will see stack equivalency between the two with the Cross bike having a much shorter head tube. Because some if not most cross bikes have a shorter top tube, if you want an equivalent fit for a cross bike, I would consider sizing up for say the Crux model. Sizing up on a cross bike with slightly shorter top tubes...many times creates a similar fit to a comfort geometry like a Roubaix.

RollCNY

Here is a puzzler for you:
I am a fan of the Ridley frames, and CC has the good prices on the gamut of them. They tout the aero benefits of the Noah, the race characteristics of the Damocles and light weight Helium, and the endurance characteristics of the Excalibur. But if you compare geometry of all 4 models, they are identical in every size. Now I know carbon layup and design can modify attributes, but I expected some geo differences. I even suspected an error in CC's web info, but Ridley's parent page has the same info.

Thoughts? And OP, no thread hijack intended. Feel free to give me a stern rebuke

Campag4life

You would that that the three parameters you reference would be somewhat competing. Endurance geo isn't particularly aero...nor maybe race stiffness....but I believe an endurance geo bike can be designed with these properties which is likely the case.
My Roubaix has race stiffness for example and endurance geo of course...and maybe 'loosely' construed as designed with an eye toward aerodynamics...but a slammed aero frame is gonna beat it in a wind tunnel of course. What you have likely is a bit of marketing going on.

RollCNY

I am thinking marketing, because I see no differences in the Ridleys, and here are my specifics

Start with 58cm Roubaix vs. Tarmac. Both have effTT of 582 and STA of 73 deg, but the Roubaix has taller head tube (225 vs 205) and a slacker HTA (72.5 vs 73.5). So I can see specific geometry differences that say Roubaix is targeted toward a slightly less agressive, more relaxed steering (I lack fork rake but assume them to be consistent), hence this is Spec's "endurance" geo.

With Ridley, Damocles vs Excalibur (which is the one I am ogling), the numbers are identical for all sizes, specifically the large being effTT of 585, HT of 205, STA 72.5, HTA 73.5. They are almost an exact match to the Tarmac in that size, and are identical to each other. They even list identical stack and reach.

I know that spacers and stem can more than make a race bike into an endurance, I just found it very odd that all of the Ridley models share that exact same geometry, but advertise themselves as different.

Largely just mental exercise anyway, as the most likely next candidate for me is a Surly Pacer.

Campag4life

I agree it is a bit odd. While many endurance frames out there don't have the head tube length of a Roubaix size to size, endurance geo's for all the big OE's like Giant, Cannondale, Trek, Cervelo etc all have a distinctly different geometry than bikes considered more applicable to racing.