Bulb shaped fat tyres over aero rims

So I went a bit nuts making my 2019 Tcr as comfy as I could, going from 25mm tyres to 28mm and finishing with 30mm.

The bike is now hella smoother to ride than it was on 25’s but the wheels just weren’t made with the fat tyres in mind and now my nice 42mm SLR rims have these big ol’ tyres stretched on to them, I’m almost positive any aero effect has been all but lost :sweat_smile:

The tyres are light bulbed over the rims. Was wondering if anyone can actually confirm what kind of wattage or aero benefit I’ve flung down the drain?

Specialized put out this video a little bit ago comparing their 24mm wheel to a 50mm wheel with 26, 32, and 42c tires.

In a straight head winds
with 26’s the deep wheels saved 20s over 40K
with 32’s they saved 16s
and the 42’s saved 12

Those savings were much bigger with crosswinds but still less of a difference with bigger tires.

I’m not sure what that translates to in watts though


The question is ‘do you need those extra 10 watts’? Or whatever the actual loss is…

If you are at the pointy end of races then you need those skinny tires. If not then ride what feels the best.

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Yeah I don’t really need anything tbh.

Would be nice to know the answer tho.