I have heard that the heavier a rim, the more force it will take to spin it at the same speed. I thoroughly believe this is the case with acceleration, however once you are at a steady speed, does the weight keep creating drag? I previously thought this to be true, but why then are Mavic Cosmic Carbones so popular? Wouldn't the weight in the rims eventually overcome any benefits given by the aerodynamics and silky hubs? I am asking this question because I myself am thinking of buying a pair of new wheels for everyday use, tris, and road racing. I have heard the Cosmics are very durable, more so than comparible carbon wheels. Otherwise I would buy a carbon clincher.
Originally posted by isdsms I have heard that the heavier a rim, the more force it will take to spin it at the same speed. I thoroughly believe this is the case with acceleration, however once you are at a steady speed, does the weight keep creating drag? I previously thought this to be true, but why then are Mavic Cosmic Carbones so popular? Wouldn't the weight in the rims eventually overcome any benefits given by the aerodynamics and silky hubs? I am asking this question because I myself am thinking of buying a pair of new wheels for everyday use, tris, and road racing. I have heard the Cosmics are very durable, more so than comparible carbon wheels. Otherwise I would buy a carbon clincher.
Thanks in advance, isdsms
If anything, the heavier rim will keep spinning longer than the lighter rim because of its higher angular momentum, the flywheel effect. As you say, a heavier rim takes more energy to accelerate. But the difference is miniscule, and you don't do much accelerating on the bike. Absolute weight and aerodynamics seem to be the important things to consider. This stuff is analyzed using Real Science (TM) at:
Originally posted by jgatts ...... and you don't do much accelerating on the bike.
I would question this ????
Unless you are timetrialling or doing some other kind of "smooth" ride you often spend a significant amount of time accelerating & decellerating as attacks happen etc
Originally posted by gw709 I would question this ????
Unless you are timetrialling or doing some other kind of "smooth" ride you often spend a significant amount of time accelerating & decellerating as attacks happen etc
my 2 c worth gaw
I guess you're right, but the effects of rotational inertia differences between rims are still minimal overall.
There are lots (and I do mean *lots* of opinions about this available out on the net. However one of the articles which I think does a pretty good job of looking at the issue is this one http://www.softride.com/bike/triAero.asp
At the end of the day though, it seems to be pretty much the sort of argument where you can take your pick of the opinions!
Originally posted by Ratface There are lots (and I do mean *lots* of opinions about this available out on the net. However one of the articles which I think does a pretty good job of looking at the issue is this one http://www.softride.com/bike/triAero.asp
At the end of the day though, it seems to be pretty much the sort of argument where you can take your pick of the opinions!
Good article. Note that the author got his information from analyticcycling.com. There are indeed lots of opinions out there, but just make sure that the one you believe has some basis in reality, not marketing.
Originally posted by Ratface However one of the articles which I think does a pretty good job of looking at the issue is this one http://www.softride.com/bike/triAero.asp
The article was pretty good, but the author's analogy of running up stairs with a wheel and then again with a wheel spinning seems to indicate a lack of understanding because it makes no sense.
I did some rough calculations on acceleration a while back when I was trying to select wheels for the new bike. Results were that the torque required to spin up the wheels is about 1.4% of the total required for linear acceleration, based on OP rims and a 190 lb bike/rider. If you could drop 25% of the wheelset weight, say 400 gms, you'd save about 0.35% of total effort required in angular acceleration, plus another 0.45% in linear just due to the weight reduction....about 0.8% overall.
The rough estimate does confirm the old adage that rotating weight is worth about twice that of static weight when it comes to acceleration.
I may have missed something; will certainly stand to be corrected. You can confirm the low effort needed by spinning your rear wheel up by hand on the pedal while it's off the ground. It takes some force on the pedal, but not much relative to how hard you stomp when going for max acceleration.
