Check it out here.

Put the plant X 101 in the first drop down box and then play with the numbers.

At 0degree wind, the 808 with aero jacket (closest match I could think of) giver you 21 seconds. As you increase the yaw, the difference gets bigger.

According to that website, the Planet X 101 is 3 seconds slower than an OEM alloy rim, and an 808 is only 1 second faster than an OEM aluminum rim. Sure....

Sure, at zero yaw. Unless you are are on a track, I'd suggest changing some more variables. At 15degrees, those PX rims save 8 seconds and the 808 FC have 31.

I have no idea how accurate those numbers are. Its just one site. Try stacking up their estimates to some real world tests and see if they are track or not.

Two things to keep in mind:

1. The planetX 101mm wheel may not be shaped very well

2. The data you see from wind tunnels comparing 808ish wheels to discs does not include the watts required to spin the wheel. 808ish to disc saves another 1-3 watts from that

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
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What do you mean the watts required to spin the wheel? You mean the rolling resistance of the tire and aero drag from the spokes spinning at speed and the friction of the wheel bearing? I thought aero tests are done with the bike in use, thus the wheels spinning?

It is all highly bike frame dependent as well. Some frames shield the rear wheel better than others. So I doubt anyone here can really tell you how much time you will save. Only a windtunnel could will do that. Obviously you should save a little with the disc.

They are spinning, but how much power does it take to spin them? This number is generally not reported because I think it is pretty hard to measure accurately.

I think Jackmott is referring to drag from the spokes. But when installed on a frame, its' hard to quantify as the air is so "dirty" at the back of the bike.

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Zipp has some very good reading available about power to spin spokes. Unfortunately I don't have a link. I will never ever run a non disk wheel if I don't have to.

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24 Hour World TT Champs-American record holder
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That's a good lad.

It's not just the spokes. It's everything in the wheel: spokes, rim, hub bearings, even the tire. Imagine that the bike is just sitting in still air. The wheels don't rotate on their own; it takes some power to rotate them. Imagine that there are radial paddles stuck to the rim. There would be a ton of aero drag. Obviously this is an unrealistic example, but there is still aero drag on a rim just spinning in still air along with all the other pieces of the wheel.

Except installing a cover on the rear wheel does not eliminate spoke drag as the volume inside the cover is not a vacumm, so the spokes still have to cut through the air when spinning. The only thing the cover would eliminate is the wind produced by moving forward.

It probably wouldn't save that much. You're already at 101 mm, which is deeper than most deep wheels. I have heard from some engineers at other wheel companies that a deep rear like that can be within 5-15% of a disc, enough that the company in question does not make a disc. It's too hard to tell from drop down menus etc. The only way to know is to measure in-frame, in a wind tunnel, and the actual "savings" will be a handful of seconds, if any.

In my opinion: put the money elsewhere. Your set-up is pretty fast.

How can a fly buzz inside an enclosed car travelling at 100km/h? Or better yet, a truck with an open rear?

Air inside the disc will (at steady-state riding) move at pretty much the same speed as the wheel. And since it has so little inertia, it will also adapt quite quickly to accelerations.

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