Do smaller wheels provide important Aero advantage?
 

Hello, I know that bigger 700c wheels provide higher gain per spin, effectively increasing gear ratio.
But given the same frame, 26" wheels will sit lower than 700c wheels, thus providing lower air resistance (Or does only the difference in wheel size matter here? Not the overall height?).
Is this difference in air resistance insignificant or can it actually be more important then wheel size at some speeds?

Smaller wheels are obviously more aero, but not always feasible ... more importantly ... they aren't allowed by the UCI.
In triathlon people use smaller wheels to gain aero advantage.

As a general rule of thumb, smaller wheels are stronger and more aerodynamic, but are more responsive, have more rolling resistance and are less comfortable. The drivetrain will also be slightly lower to the ground.

Gear ratios don't affect speed, it only means you need slightly different gearing.

The tri community went through a spasm of pushing 650 a few years ago, partly due to the aero advantages, but they've pretty much gone back to 700c.

In terms of performance, it's pretty much a wash.

Actually if you use two 650 wheels it would be allowed by the UCI, the rule there is that both wheels have to be the same size (ie, you can't run a small front wheel wheel and larger rear one).

Most triathletes now run 700 wheels because they roll better, smaller riders (usually under 5'3" will use 650 because it allows them to get into a more aero position as the handlebars don't have to sit up as high.

There are also pedal/ground clearance issues with smaller wheels.

Not if the frame is designed for that wheel size. My bike with 20" wheels has the same pedal to ground clearance as my 700c bikes.

In addition to smaller wheels having less wind resistance, a smaller front wheel also allows the rider to draft more closely behind another rider in a paceline. But, as already mentioned, there are drawbacks in rolling resistance and ride comfort on rough roads. In comparing rides with my 20" wheeled bike to those with 700c wheels I find both the advantages and disadvantages to be rather minor.

I used to do lots or tri's and then stopped until recently. The thing that surprised me geting back into the sport is no one, except very short people, use 650 wheels now.

industry standards... plus the difference in real world physics is negligible.

The availability of good tires and tubes + integrated headsets makes 700c tires the better choice these days.

IMO the only advantage is that you have less rotational mass and the wheel is easier to get it rolling, besides that probably the aero gain part is minimal compared with a 700c wheel.

We got TT track funny bikes back in the day with 650 wheels in the back, 58 chainwheel to compensate for the wheel, the bikes were pretty easy to get them rolling but once in the race personally I did not notice big differences in relation to a regular aero track bike, same stuff.

650 is a good creation of short people so they are able to get some seatpost showing and a descent fit, besides that the % of improvement unless we are talking into super high performance atletes, probably the regular john doe wont even notice the difference.