Asking for your SWAG on the relative difference in aero performance between a Tarmac with 42cm bars vs an Allez with 38.
I am deciding between the two for a long Mercxx TT. At some point, I want to switch the bars on the Tarmac over to a narrower fit, but that won’t happen beforehand.
If everything else is equal (wheels, stack and reach, ability to hold a good position) or close to - would go with Allez with the 38cm bars. Should be significant watt savings having a narrower position
Tarmac Pro or better, go with the Tarmac. Here is my reasoning…I think the frames, aerodynamically, are pretty similar at yaw angles you are likely to experience…no allez comes equipped with aero handlebars but Tarmac Pro or better does…the aerodynamic difference in handlebars due to width will be much less than the aerodynamic difference between and round handlebar and an aero handlebar.
I am sorry, I wasn’t being clear. I already have the two bikes, standard tarmac vs an Allez sprint. I have the choice between the two, and suspect that the position gains from the narrow bars surpass the aero benefits of the frame, but I thought I would see if others feel the same way.
Neither bike has aerodynamically shape bars. Both are using Spesh’s expert bars with the “top perch,” which I find pretty comfy for climbing.
I’d go for the narrow bars. Just make sure you don’t flare out your elbows.
Tour Int Magazin pretty much answered this.
Allez Sprint = 231w on basic wheels and round bars.
Tarmac SL6 = 239w on same components; 224w on Zipp 404s
Tarmac SL7 = 229w in basic/round config.
Tarmac SL7 = 210w in Sworks 60mm wheels/aero bar config.
(All sizes 56)
They also did bars. I can’t find the article, but 2cm narrower = the same savings as round to aero bars.
So, like for like test, generally…
frame = 9w
Rimz= 14w
Narrow bars = 4w
Aero bars = 4w
So, if I am reading this correct, the Allez Sprint is already faster than a Tarmac SL6? If that is the case, the aero decision is easy since the wider bars are on a SL6, both the frame and the bars are more aero on the Allez.
The SL6 is a non-aero bike. 239 is about as non-aero as it gets… I’ve only seen a 240w, which was a TCR (fat round bike) TOUR Magazine Wind Tunnel Results - Google Sheets