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I am about to invest in a used Specialised Tarmac SL4 but I am unsure whether to go for a size 54 or 56. Been riding a size 58 and found it to be too long for me. Was wondering if I could go for a lighter size 54 and perhaps put a longer stem on if too short? What size should I go for?

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    For expensive bikes I would recommend at least a basic professional bike fit. This bike is a (lower?) middle class so you have to decide but it is important to at least try the posture. The size numbers for various bike models can be deceiving. Commented Aug 13, 2022 at 16:05
  • Odd that you have the choice in frame sizes on a used bike. Can you do test rides on both in turn ?
    – Criggie
    Commented Aug 14, 2022 at 0:49

2 Answers 2

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The size 56 is only 7mm shorter (reach) than the size 58. The size 54 is 15mm shorter than the 58 and – as listed on the Specialized website – comes with a 10mm shorter stem (90mm instead of 100mm) as well.

I’d go with the 54 and if it ends up being too short you can always upgrade to a 100mm or 110mm stem. With a 120mm stem (that’s still an okay length) it would even be longer than the size 58.

The 56 could make sense if you like your handlebars high. The stack of the size 54 is almost 5cm lower than that of the 58. That’s usually too much to compensate with spacers and/or a stem with an upwards angle.

If the size 56 is too long you can change its 100mm stem for a 90mm stem. A 80 or even 70mm stem wouldn’t look extremely stupid either.

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  • 7mm/15mm shorter in what dimension? Standover height? Top tube length? Other? Please specify.
    – Ted Hohl
    Commented Aug 13, 2022 at 16:22
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    Reach of course. Maybe it’s because my native language is German, but “shorter” („kürzer“ in German) somehow implies a horizontal-ness to me. A short car makes me think of a Smart, not of a flat/low Lamborghini race car.
    – Michael
    Commented Aug 13, 2022 at 16:25
  • Rereading the original question, I can interpret that they are referring to reach as well (I think!). Good answer, and thanks for the clarification.
    – Ted Hohl
    Commented Aug 13, 2022 at 16:40
  • Thank you for the great answer. On the 58 bike I am riding, the reach is definitely too long. The seat is too low as well. Looks weird. I will try out the 54 I think and as you say, put a longer stem on it necessary. But the seat won’t get too high on a 54 size with my inseam? I am all for the aggressive seat position but I don’t want the bike to look ridiculous either
    – BatS00p
    Commented Aug 13, 2022 at 22:54
  • With seat too low you only mean relative to the handlebars, right? It’s not like you reached the minimum insertion length of the seatpost, correct? Have you ridden a road bike with known stack and reach values before? I’m 1.8m and ride a Rose X-Lite 4 in size 55 which has 12mm more stack and 1mm more reach than the Tarmac SL4 in size 54. I have several centimeters margin in all directions and the bike fitter told me I could have gone down a size if I wanted to. It kind of really depends on how low you like your handlebars.
    – Michael
    Commented Aug 14, 2022 at 6:21
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If you are a competitive cyclist, you ride races, criteriums, you want the shorter bike. If you don't do races, but you do ride longer distances, you want the longer bike. Without knowing what type of cyclist you are, others can't advise.

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