Zipp 900 Disc with 23mm tyre OR Zipp 808 FC with 25mm?

Hi Y’all,

I’m currently training for Ironman Cairns (fairly flat) in 28 weeks. My race wheel options are Zipp 900 disc with 23mm, or the matching Zipp 808 Firecrest with a 25mm (either option would be with Vittoria Corsa tyres).

As the Zipp 900 is quite narrow, I don’t think the 25mm will work/fit that well, so got me thinking - will the drop in rolling resistance of the 25mm tire on a 808 outweight the aero benefits of a disc??

For reference, I will be running the Zipp 808 with 25mm at the front.

Edit - wheels are tubulars.

Any thoughts or advice appreciated.


The disc is going to be faster than the 808 by a pretty significant margin. I would be surprised if the difference between a 23 and 25 outweighed the aero advantage, but I’m just speculating.