Are bigger bicycle wheels more efficient?

Factual Questions
21

The penny-farthing (the thing with a five-foot front wheel) was a design due to the fact the pedals were locked to the front wheel like a tricycle. To get anything beyond tricycle speed, the front wheel had to be quite big.

Think of how a shopping cart with tiny wheels will jam and come to a halt with the least little obstacle under the wheel - a small pebble, etc. To go over an obstacle, the key is the angle of the obstacle. To climb a curb or similar obstacle, for example, the axle must pivot up and over around the point where the wheel touches the top corner of the curb.

If the curb is as high as the axle of the wheel, the forward momentum must turn into vertical momentum to be gin the pivot - which usually aint gonna happen.
If the curb is half the radius of the wheel, the vehicle must translate forward momentum into a 45-degree lift.
and so on…
The smaller the angle from vertical that the wheel hits the obstacle, the less forward momentum is turned into lifting momentum.
I just have trouble imagining that in real world cycling, 26 vs 29 makes that much of a difference over obstacles.

(This is why pulling is easier than pushing. In pulling a two-wheel cart, the pivot is at the handle, a point well in front of the obstacle. In pushing, like in bicycles, the pivot point is behind the obstacle.)

22

My bike was stolen a few months ago and I replaced it with a 29er. Anecdotally, it has reduced the time taken for my commute by about 10%, but then the 26" bike was a full suspension model and the 29" is a hardtail, so that is probably partly responsible.

I do also find it rolls over obstacles much better off road. It gives a much smoother ride than a 26" hardtail, more different than you would think for the relatively small change in wheel size.

The trade off is slightly more weight and slower acceleration, but once you are up to speed you have more momentum.

23

I love my 29’er but it certainly is a bit more to manage when negotiating technical trails. I’m much more into cross-country riding where you get some speed and the bike’s ability to roll over stuff I might have had to maneuver around is well worth it. If I enjoyed the more technical stuff I’d definitely stick with a 26’er.

24

One place a 29’er is better than a 26" is in ground clearance. If you are travelling over rough terrain, that extra inch or so of clearance under the bottom bracket might help.