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I'm trying to determine where I fit on the Cannondale Slate geometry because it doesn't seem they use top-tube actual or seat tube, but rather they're using the Stack? I see a great sale on a 56cm bike but that is classified as a Medium and I'm generally a large. I'm 5'11" with around a 33in inseam. Long arms. I believe my other road bike is a 56cm and I'm going to assume it was measured correctly for me. This is sort of an "all road" bike that will be taken on mild single-track, if that changes my measurement decision. What I don't understand is, it appears they're using stack as the bike measurement?

Is a 56cm too small for me? It appears the top tube and seat tube are tiny and has me really confused. I'll also mention I'd prefer not to ride with an overly aggressive seating position.

** edit - These are 650b wheels.

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    The problem is that frame designs have changed so much that traditional measures (seat tube length, standover height, etc) are no longer meaningful. Almost always now the top tube is fairly strongly slanted toward the rear (along with other changes), making the seat tube much shorter and making "standover height" somewhat meaningless. Yes, it makes the purist among us cringe, but it's the way the industry has been moving for 20 years now.
    – Daniel R Hicks
    Commented Aug 1, 2018 at 22:22
  • That explanation makes sense, thanks.
    – xhermit
    Commented Aug 1, 2018 at 23:13
  • I don't see Cannondale using a length measurement to size their their bikes, just small, medium, large etc. Is the vendor you see the deal at saying bike is 56cm? They may just be making an equivalency, i.e. most 'medium' frames are 56cm so they are giving that as the size.
    – Argenti Apparatus
    Commented Aug 1, 2018 at 23:52
  • The seller is telling me it's a large, but that does not align with the geometry listed on Cannondale's site. Since it's an online purchase, what's the best way for the seller to prove the size? I suppose taking a picture of the stack/reach next to measuring tape is one way.
    – xhermit
    Commented Aug 2, 2018 at 1:04
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    Honestly the only practical way forward is to try the bike before buying it.
    – Criggie ♦
    Commented Aug 2, 2018 at 7:02

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Stack and reach are a 'system' of alternative bike frame measurements always used together. They are supposed to be meaningful absolute values, unlike seat tube length (or 'effective' seat tune length, where top tubes are not horizontal).

They are based on two datum points: the bottom bracket axle axis and the top of the head tube. Stack is the vertical distance between those two, reach is the horizontal distance.

If you have a meter long ruler (or a tape measure and something long and straight) and a level you can measure the stack and reach of your existing bike and make a comparison to the Slate geometry.

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  • Just did a rough measurement of my current bike and I'm right with Medium. 21.75" stack, 15" reach
    – xhermit
    Commented Aug 1, 2018 at 23:12

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