Is it me or today’s 54’s frames are yesterday’s ( 2010’s ) 56?

I may be wrong but I’ve got the impression that most bike brands have shrunk in size, at least on paper, for the past 10/13 years.
At 6 with 33 inseam, my to go size has been 56 for a long time, at least with Specialized up until 2017, that’s when I’ve last owned a Specialized. But today’s frames, unless you pick some very old school stuff from Time or something, all put me on a 54/M frame. That’s what I’m currently riding with Canyon now actually and it’s the most comfortable bike I’ve ever owned. And then of course there’s the old saying “ you may be ok on a 56 frame too” but that’s just not the case. I’m 50 and very flexible, actually in the best shape of my life, but there is now way I would not risk on a 56 when my (bike fit) numbers says I have to get a 54.

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  1. Other than the stated frame size, what values are you actually looking at to judge / compare the size / fit?

  2. What model(s) of bikes (Specialized and/or others) are you discussing? If you can give us precise models and years of bikes you compared, we can get more specific than the random selection below. I did a bit of research to review 54-56 sizes in 3 gens of Specialized Tarmacs’s now and in the past to see if they’ve changed.

The basic sizing in the modern era boils down to changes in Reach and Stack. Those set the baseline for stem & handlebar position. Adjustment to stem length, angle and spacers can usually place a rider in the same physical placement between sizes, unless they are at the limit of something like spacers or stem length.

If you are slammed with no spacers and run a negative stem angle on the 54, then the higher stack on the 56 would likely be too high. But if you are running some spacers on the 54, a bump to 56 might work for height at least.

Then stem length comes into play if you are running something like a 90mm or 100mm stem on the 54, a 56 with longer reach may not work well with a typical length stem (+/-100mm). There’s a lot to it here where the exact setups need to be reviewed closely.

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i bought my current specialized Allez in 2018 and I chose a 54 because the stack and reach were what I wanted and was comparable to some other 56cm models. Prior to that I had a 1995 raleigh with very traditional straight top tube geo and was 56 but had short headtube and short stack height and a fit I had gotten had me with a +17 120cm stem, so I the 54cm Allez seemed to fit the bill for getting me the right combo. If I recall the 56cm may have resulted in a fit that was too relaxed. So yeah, I think there are some blurred lines and looking at stack and reach is important

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Here are just a couple of data points for quick review, at 5 year intervals (and whatever SL? steps those entail):

2012 Specialized Tarmac

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2017 Specialized Tarmac

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2022 Specialized Tarmac

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  • Same for both sizes in 2012 & 2017
  • 54 & both drop 9mm in 2022
  • Delta between 54/56 of the same year is 21mm in these examples. Add in the 9mm if you jump that last 5 year between sizes and you could be talking about 30mm lower 2022 54 vs 2017 56, but that is the biggest possible.
  • The 21mm height difference is easily accounted for with spacers in at least some use case. Depends entirely on what a rider needs and whether the would still be too high without spacers on the 56.


  • Identical for all sizes & years other than 3mm longer on 56 in 2022
  • There is only an 8mm delta in all cases other than the one longer 56mm. In any case, this is easily accounted for by swapping the stem 10mm, which would likely still keep things well balanced for good handling unless a person has used a non-standard length stem on a size at one end.

Seat Tube Length:

  • This shortens over time, which goes along with the trend of moving away from mostly horizontal top tubes per the origin of road bikes, towards sloped top tubes in modern times. This can help with frame rigidity, but also exposes more seat post which tends to improve comfort via longer leverage to flex the post.

But from those values, the only real change between 3 models over a decade was lowering the front ends about the size of one large stem spacer. It doesn’t seem to parallel your swap from 56 to 54 with these values at least. These changes are counter to the direction you moved, since the Stack dropped over time, but may be totally different depending on the actual bikes you rode or evaluated.


Also, it seems that newer frames with integrated cabling have a larger mandatory top spacer. The stack spec usually measures to the frame even when a large spacer is mandatory (which is kind of deceiving).

On a 2017, you could probably even swap out the factory top headset spacer for a minimal stack headset top spacer.

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Yeah, that all gets a bit more finite when we look at changes from external to internal headsets as that relates to the stock (minimum height) added from the headset cap. There can be some bigger deltas in reality once those are factored in for sure. Sadly, that is not something shared for these bikes, so it’s a guessing game at best.