Throughout our time doing this, we've tried to respond as well as possible, as quickly as possible, to customer inquiries. For me, as with a lot of what we do, it's significantly borne out of frustrations I had as a consumer. Now we are challenged more often by requests to make subjective judgements about our products and their use. The three we get a lot of these days are 1) help me choose between 52s and 34s 2) help me choose between stock hubs and White Industries hubs and 3) what tire width do you recommend with Rails?
Jay does take a nice picture, doesn't he?
First, rim depth. When we launched the 34 project, it was in large part a response to customer demand - "when are you guys going to do a shallower Rail?" As riders, Mike and I were both more than satisfied with 52s, I'd enjoyed racing them and had some great results that I honestly thought (and still do) had a ton to do with the confidence that the Rail footprint gives. Their objectively verified speed in the wind tunnel certainly seems to bear out on the road; the simply feel fast. And, despite their depth, I've always found them to be super manageable no matter what the wind is doing. That last bit comes with the caveat that I spent the better part of three decades obsessed by learning and being able to predict how wind acts. Although I can definitively tell you that 52s behave better in wind than our old 38s, I'm probably better suited to dealing with wind than the average bear. I'm also not light - 164 at last check.
People get obsessed with weight. 34 rims generally come in 60g lighter per rim than 52s (440 vs 500). This puts a stock-hubbed build of 34s right around the vaunted 1400g mark. I don't pay that much attention to weight, other than trying quite hard to not be fat when I go to stage races in Vermont, but 34s do seem to have some advantage in a moment of inertia kind of way. I've never found 52s to be sluggish in getting up to speed, but 34s really don't mind getting out of bed. There's the whole "any energy that you put into accelerating a wheel is returned to you in conservation of energy" argument, a balloon which for practical purposes I will pop with one pin: brakes. Any time you have to externally slow your wheels, which may be a tap of the brakes or sitting up or sliding out of the slipstream momentarily, you chuck that one right out the window. I'm not saying that conservation of energy isn't valid, but I am saying that it seems you pretty often don't get four quarters back for the dollar you spent accelerating.
52s, on the other hand, feel fast. They're a broadsword to the 34's dagger. There's a route I ride a lot now, which is fairly straight with lots of small rollers, going north to south along my favorite body of water in the world (the Sakonnet River). Upwind on the way south, bleeding for it, and blasting home with a tailwind, mostly you feel like you're trying to keep up with the bike (which made me appreciate how freaking hard Tour of Qatar must actually be). 52s work so well on that it's just crazy.
I don't think I can sum it up better than by stating that 52s feel very fast, 34s feel very quick. If you are concerned about handling them in breeze, 34s are invisible to crosswinds, and if you are reticent about being that guy (or girl) who's always rocking the deep wheels, go 34.
You brought moment of inertia. Assuming that each rim—34 and 52—had their masses concentrated along the same thin ring at the same distance from the axle's, uhm, axis the fractional difference in MOI would be the fractional difference in the two wheel's masses (ratio of rear wheels is 805/855 or 94%, so the MOI of the 34 rear wheel would be 94% of that of the 52 rear wheel). Obviously, the masses of the 34 and 52 aren't concentrated along the same thin ring at the same radius. In fact, the 52 could have its mass concentrated along a thin ring at a shorter distance from the axle's axis. I only mention this because it's possible the 52 wheels could have lower MOIs than the 32's. Granted the difference in MOI's likely isn't great, and given the small effect that wheel MOI has on bike acceleration, the difference in bike acceleration (sprinting, climbing) between the two wheel sets is likely very small. It would be interesting to measure the MOI of the two different wheel sets, front and rear.
The Sakonnet River? Where in Rhode Island are you from?
Newport/ Middletown/ Portsmouth is great. That explains your sailing background. I was curious because my wife is from East Greenwhich I have have become a Rhode Islander-in-law over the past 20 years.
Robin – My general thoughts are that aero generally trumps weight, but effect of weight has never been accurately modeled. Steve – That's awesome, thanks.