Bike Size Question - Tarmac SL8 52 vs 54 - I have a Crux 54

Hello everyone,
I’m currently riding a Specialized Crux in size 54 with two wheelsets. Since changing the wheelsets is extremely annoying, I’m thinking about buying a new bike. I took the Crux to a bike fitter and had it optimally adjusted. The bike fits perfectly. Since then, I’ve ridden 6000 km on it and taken part in many events, including Mallorca312. I never had any problems with the bike fit.

I contacted my bike fitter and he said that a size 52 might be better for the Tarmac. However, I am of the opinion that he is not quite right. With the 52 I would have to use some spacers under the handlebars, which I don’t like visually. I would also have less leeway for any later adjustments. With a 54 I wouldn’t need any spacers. In addition, the frame of the 54 is closer to the Crux, but the cockpit is not. I was recommended the 90x380 cockpit on the Tarmac.

If I calculate reach + stem + handlebar reach, the result is as follows:
Crux: 388 + 80 + 75 = 543mm
SL8 52: 380 + 90 + 75 = 545mm
SL8 54: 384 + 90 + 75 = 549mm

There is also a Roval cockpit with a 75mm stem, but I don’t think that would work.

Here is the comparison:
bike-stats - Alles zum Thema Fahrrad Geometrie Tarmac SL8_2024_54

Fitting data for my 54 Crux:
Stem length: 80mm
Seat height: 711mm
Cant: 45mm
Rear seat: 183mm
Seat length: 630mm
Seat length brake levers: 765mm
Crank length: 165mm
Handlebar width: 380mm
Handlebar reach: 75mm

Now to my question. Which size should I buy? I think both will fit.

I would get the 54!

If you fit perfectly on the Crux, and looking at the geometry, I would not size down :slight_smile:


Sizing down from the Crux to the Tarmac is the LAST thing you want to do. My 54 Crux feels a good bit bigger (unfitted, stock setup) than my 54 Tarmac. Both fit well for my uses (mostly gravel and some dirt on the Crux, with some but not much road).

Anyone who feels right on a 52 Tarmac should be absolutely swimming on a 54 Crux.

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