Anything you can share on smooth road testing based on tire size? I’ve not tested it (yet) but I’d wager on smooth roads, if you have the correct pressure in for the tire size, you can mix the widths and optimize for aero without a loss due to Crr. The rougher the roads the more it tends to add up. There’s also the weird issue of, at least with Conti, the 28’s are measured using an ERTO of 19 vs 21 for the 30. So the 28’s and 30’s on the same internal width rims end up within .5-1mm of each other.
Most of my racing is on pretty smooth roads, so hopefully I can maximize the aero/Crr equation by running 25/28 combo or a 28/28 or 28/30 for rougher stuff and wet crits.
Many wheels are now saying they’re “optimizing” around 28mm tires, but what I’m seeing is 28mm at the brake track and a 28mm tire that overhangs the edge. The deeper the wheel the less this is an issue, also if the wheel is toroidal it seems to let the air reattach pretty well. There are a lot of “U” or modified “V” shaped (UV?) rims that don’t extend past the brake track. I know you can feel the wheel stall when this get’s too far out side the operating window of the rim/tire system.
Also the riders should love you!
Let me take a closer look, there are 1000 ways to look at this data. I do have tests of same riders, same wheel, different tire widths. I will compare.
I do have data for a tire a little too big for the rim vs optimal. I don’t have data for a tire too small.
Generally, there’s not a big penalty for a tire that’s too small, it’s usually an aero “win”. The back is somewhat agnostic to tire size. The biggest issue with a tire that inside that, quickly fading105 rule, is that you lose some protection of the rim itself. I’ve definitely knicked the edge of the rim due to a tire sitting inside the rim profile.