PurpleFrog":29uaalch said:
I think most people believe that the wheels store a significant amount of energy as flywheels, but this isn't true. If your and your bike weigh 100kg and the wheels and tyres are 2kg of this, then at most they'll store about 4% of total energy. And 29er wheels only store perhaps 25% more energy that 26s - and 25% of 4% will have no noticeable impact on bike performance.
I'm a physicist and even I have trouble sorting out what is hype and what is real in the 26 vs 27 vs 29 debate. I find it difficult to believe that 29er wheels are harder to get moving to the same speed as 26er ones - or that they store more rotational energy (angular momentum; for sure they store more kinetic energy due to their forward motion with the bike).
The circumference of a wheel is pi x diameter. Unless there is some major design difference between the 26 and 29er wheel and tire, the 29er versions would be a factor of 29/26=1.12 heavier (12%). When rotating at the same frequency of revolutions per second, the 29er wheel would have angular momentum (stored rotational energy) that is 12% greater than an equivalent 26er wheel rotating at the same frequency. However, one must also consider that for the same linear velocity of the bicycle, the 29er wheel, due to its 12% larger circumference, will rotate at a proportionately lower frequency than a 26er wheel. Both wheels should be equally easy to accelerate to the same bicycle velocity.
Edit: I suspect I have forgotten something important in the above... too much overthinking is not good for you.
As part of my work I also enjoy thinking way outside the box. Let me throw this one to the people with more knowledge and experience of bike and riding 29ers: What is it that makes the 29.0 inch wheel the perfect size for obtaining the benefits of larger wheels, and bottom bracket height)? Surely if 29ers give much better speed, why not go to 30" wheels to get even more of the same benefits? I don't doubt that people's experiences with 29ers are very real, but it strikes me that the marketing people have simply plucked the number 29 out of thin air.
And if even short riders can handle riding 29ers, wouldn't/shouldn't super tall riders like me be able to handle 30-31" wheeled MTBs? How cool would that be ...
All these things put aside, I do really want to own a 29er at some point in the near future, but I think I'll skip the 27" ones, unless I find a really nice XC FS 27" I like.
I've read a few guys here have ridden or own steel 29ers. I'd love to know how they compare to a good old skool steel MTB, do they they still have a soul, etc.?