I hear/read everywhere that if you can spend some extra money on the bike, buy better wheels. can someone explain for me why? Is it because they are rotating or are there other comfort factors? thanks
Wheels and tires are the interface between the bike and the road; and are the parts that take the most stress (wear and tear) along with the bottom bracket. (IMO)
lighter wheels will reduce the rotating mass (rotational inertia); you will need less energy to make the wheels accelerate/decelerate.
higher quality bearings in the hub will reduce friction.
better aerodynamics in the rim and spokes (less energy needed to cut through air)
IMO, In the end it all matters to weight.
If you are doing serious cycling (i.e. keeping time, strava segments, ... ) it might be a good upgrade; but if you are a little less serious about it, maybe just an expensive christmas gift to self. :-)
Wheels are an easy upgrade to make as you can put them on your bike immediately with little mechanical hassle.
There are many factors related to a wheel's performance, but the one that makes the greatest difference to energy/power demand, speed and accelerations is aerodynamics. Hence why one of the most popular upgrades is to wheels with better aerodynamic properties. Wheel weight is generally way over rated as a factor in performance, and I'll come back to that later.
Factors other than aerodynamics and weight include:
- ability to stay round and true
- lateral stiffness
- repair-ability and service cost
- suitability for the purpose/race/riding situation
- braking demands
- handling characteristics
- available tyre choices
- bearing and freehub quality
- rules of competition
- suitability for the bike (e.g. will it fit?)
- sex appeal / bling factor
and so on.....
Even adding weight to a wheel rim in order to improve aerodynamics is a good trade off. However don't get sucked into thinking that the performance improvement will turn you into a racing star. The performance improvement is incremental, not revolutionary, and other factors are important when training or rolling around town.
While reducing a wheel rim's mass does give you very slight advantage during accelerations (it has no impact on steady state riding), improving the wheel's aerodynamics is by far more important.
A heavier but more aero wheel will still accelerate faster (or require less power to accelerate at the same rate), and it will attain higher speeds (or require less power to sustain any given speed). This is also true even when climbing, except when the climb gets very steep (how steep depends on your individual power, mass and aero properties).
Here is a blog post with more detailed example of the small impact to performance of adding mass to your wheel's rims, and how that extra mass is worth it if it results in better aerodynamics, even for the hardest acceleration scenario there is on a bike, a standing start:
[My knowledge is not racing-specific, but as they say, any time two bicycles are moving in the same direction, it’s a race.]
Hand-built wheels will tend to be stronger and more reliable than machine-built wheels. That is only very loosely true, but the way it was explained to me by an experienced wheelbuilder in a large local shop was that wheelbuilding machines can turn out wheels just as good as hand-built, but to do so the output speed has to be turned way down. This brings up the finished cost of the wheel to a point where the insanely expensive machine has no cost advantage over the human, so is rarely if ever done.
A more rigid wheel will transmit more energy to the ground because any deformation is inherently a loss of energy, or least a diversion of energy away from your goal of going forward quickly.
Lighter wheels give you a large advantage, as rolling weight matters much more than static weight. How much is a matter of some debate, and I find the 2x value given here to be overly pessimistic, but it’s still definitely more than 1x.
Better spokes matter, too. Spoked wheels are an aerodynamic cluste— well, they’re extremely sub-optimal. So more aerodynamic spokes will help considerably. As will lacing patterns with lower spoke count (which also help with weight), although those sacrifice some durability.
Now as to whether all those improvements will help? I am of the opinion that even for those of us who aren’t competing (but see qualifier statement above), anything that makes us feel like we are riding faster and/or with less effort is helpful in that it increases effective endurance. In other words, if you make a cyclist feel faster and/or more powerful, they will tend to ride more, which will, over time, make them faster and/or more powerful.
You win non-TT bike races by being able to accelerate just that little bit much more than your competition. 99.9% of the time you are riding exactly the same speed as everyone else, what makes the difference between winning and losing is your ability to accelerate just a bit better than your competitors.
Humans are very low power engines. Since F = MA, one of the easiest ways to increase A is to decrease M. Low weight, low drag wheels will help you accelerate faster. Since wheels are rotational mass, you get a bigger bang for your buck in reducing their weight.
Bike racers obsess over the weight of gear to improve their ability to get to speed, reducing weight generally doesn't help your average speed much ( except when climbing a long hill).
Less rotational mass can be felt immediately, even 200 grams. It would be incredibly evident right away in acceleration. The number one thing I hear people say after buying stock bikes is they got a new wheelset and "it feels like a new bike". Now, it's been proven why complete with formulas.