Of course this is not the answer to your question since I have not owned a pair of Sidi shoes since '88 but in my experience, the Specialized Pro Carbon Road shoe fits nearly identical to Diadora Veloce's. I am told by a friend that rides Sidi's and tried my shoes on that his Sidi's (very used) were slighty wider but that might have been due to about 3-years worth of riding.

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Tim-

Here are my sizes in the various bike shoes I have owned: Sidi Tri 46, Specialized Road & Tri 45, Northwave 45, Pearl Izumi 45, Carnac 45. I hope this helps. I love the PI Tri shoes, but just got a pair of the Specialized Tri's because I damaged the PIs in a minor crash (they are a cloth outer material). I probably have 200 miles on the Specialized Road shoes & they feel better each time.

-Tim

I just replace my Sidi Mega's with the Specialized Pro Carbon road shoe. Both are size 45. The mega's were a little too wide form me especiallty after 4 years and many rides in the rain. The specialized fit great and I really find them comfortable and a lot less expensive. $175 at LBS.

I agree with Tim W, buy your buy your Sidis at least a half, more likely a full size large than Specialized. Sidi 46=Specialized 45