I've always been a big believer in wheel inertia's effect on racing. I went against my thoughts and bought a heavier set of aero wheels (the HED Jets), thinking that if the pundits were right, they'd be better for me in the normal flat crits I do regularly. However I found that I had difficulties accelerating the heavier, more aero wheels. Eventually, against my "educated" thoughts, I used my non-aero clinchers. I immediately noticed a reduction in effort required to follow the group (a Tuesday night training series, normally driven by a few regular Cat 1s).
I proposed that weight does, in fact, have some significance in performance, but everyone (and I mean everyone) shot me down.
The problem is I can't prove it using any logic (math etc).
I think I found the answer.
Most aero pundits will point to the site analyticcycling.com, where they have a lot of interesting power/speed calculators. Using different wheels it's easy to see how their calculations show very little difference in distance covered given a certain power. Even using a pretty wide range of wheel weights (basically off their site), I couldn't come up with a significant difference between wheels in their calculators (like speed, given power, or power, given speed). I put in my own numbers for power, put in some wheel weights, and found that, wow, based on the math, I should race my TriSpokes all the time.
The reality is that "spin up", i.e. how fast a wheel spins up, makes a difference in acceleration. I find it exhilarating when I first ride the race wheels in March. My bike just leaps out from under me. I've measured pedal strokes required to get up to speed, sacrificing aero when dealing with multiple super hard accelerations. I'd be up to speed literally 2 or 3 pedal strokes before the others, soft pedaling while they finished ramping up to speed. I had some good results using the light wheels, and others using the aero ones.
(The races I have in mind were at the Tour of Michigan, where I could either run a TriSpoke or a 280g 28H box section wheel, the only two sets of race wheels I brought. Since the field was the same for each of the 8 races, the riders didn't vary much at all. Coincidentally my wheels were very similar to the wheels analyticcycling lists.)
Ultimately I raced most often with light, semi-aero wheels. My favorite wheels for many years were the Zipp 340s, as light as the Campy Record Crono 280g rims but a bit more aero. Later, after a few years of Spinergy Rev-X use (I wanted to support the company), and then some TriSpoke use (those early generation Zipps broke), I settled in on Reynolds DV46 tubulars. They happened to be very similar in profile to the Zipp 340s, were very light, and much more rigid than any other wheel I had in my quiver.
In 2010 I decided to try the wide aero wheels. The driving force was the Stinger 6 wheels. They were lighter than the DV46s and they were supposed to be significantly more aero. Light and aero, a win-win.
The wheels work great.
So I also got the HED Jet 6 front and Jet 9 rear, both aero wheels, both similar in profile to the Stingers. The Jet 6 front would be my training wheel so I would feel fluent on the Stinger 6s, and the Jet 9 I got because I figured aero trumps weight, and I wanted a really aero rear wheel.
(My wheel inventory philosophy is to get one very tall, very light rear wheel, and get two or three front wheels, one each of a shallow, kinda tall, and very tall. In the HED line up my ideal setup would be a Stinger 9 rear and the 4, 6, and 9 front. Now that they have a Stinger 7, I'd maybe go 7 rear, 4 and 7 front.)
When I got the Jets I was really psyched to use them in the Tuesday Night races. Slightly heavier, no dealing with wearing out tubulars, and more aero for the fast speeds I'd see in my only regular Cat 1-2-3 race (since the drivers at the races are basically Cat 1s).
To my dismay I found the Jets hard to accelerate. No matter what the math said on analyticcycling, I couldn't accelerate the wheels well, and I found myself getting tailed off quickly. When I used the lighter Stingers or, one night when I forgot the race wheels at home, the "non-aero" Bastognes (aka Ardennes), I found that I had a much easier time responding to the accelerations.
Something was wrong.
It wasn't me. I acknowledge that I explode regularly when I race, but I also know when it feels like something isn't right with my bike. The bike was fine but the Jet wheels were just a bit too heavy.
It had to be the math.
I examined the analyticcycling site a bit more in depth and I found something I think significant - the way they measure wheel inertia. They hang a wheel from a string (or similar non-stretch object) and measure the pendulum rate. The illustration shows the wheel being suspended from the tire area. This means the whole wheel acts as one unit. It does not allow differentiation between rim and hub. A 5 pound wheel with a 4 pound rim should swing in a similar fashion as a 5 pound wheel with a 1 pound rim. Hanging the wheel from the rim should (I think - remember, I failed physics, at least on paper) negate the weight distribution of the rim.
The wheel inertia table from that site (http://www.analyticcycling.com/WheelsConcept_Disc.html#Wheel Rotational Inertia) shows very little difference between wheel inertia measurements. This leads to the very close calculations of speed/power in the site's various calculators.
I found it hard to reconcile the site's calculators and my own experience.
I went as far as to contact the site but they politely brushed me off. Without any equations as suggestions I think I came off an an uneducated myth-chaser.
And I am, so I have no problem with that. I'm chasing the myth that, yes, weight does count. Aero is good but weight still matters.
Recently, when I clicked on an aero wheel ad (I find them absolutely irresistible), I found another site that had some interesting thoughts on the topic. 3T has some thoughts on aero and wheel weight. In it they calculate inertia a bit differently, by taking the mass and the radius.
(Page 4 of 5 has the inertia calculation)
3T's results show a dramatic difference in inertia just through a few spoke nipples (18 of them at 0.9g each, so 16.2g). Their numbers - if you move the spoke nipples from the rim to the hub, your inertia goes from 1.4 g m^2 to 0.008 g m^2.
If you used larger numbers, like a 100g difference in rim weight, the inertial differences would be even larger.
These numbers would reflect inertial differences between wheels more accurately. For example, if I used those 5 pound wheels as example, they'd come out like this:
5 pound wheel, 4 pound rim or hub, using 3T's dimensions for hub and rim radius (22mm and 294mm respectively).
Inertia = mass x radius^2
4 pound = 1816g
4 pound rim = 1816 x .294^2 = 156.97 g m^2
4 pound hub = 1816 x .022^2 = 0.87 g m^2
There is a tremendous difference in wheel inertia using this calculation. Using analyticcycling's methods I think there wouldn't be a lot of difference, if any. I have to admit that's speculation on my part because I haven't done the pendulum thing (or asked a physics person about results for my 5 pound wheel example), and the site doesn't detail the separate component weights of the wire wheel, i.e. the 32 spoke wheel.
I'll have to do some more research on this but this is the first time I made any kind of progress on this whole thing.
I knew there was a reason I was holding a sleeping Junior at 1 AM.