# Aerodynamic Drag of Lasers vs CX-Rays

One of the things we've learned is that offering choices invites questions. One we get all the time is the difference between Sapim Lasers and CX-Rays, which we offer in all our wheels. Or rather, the question really is whether CX-Rays are worth the extra money.

The answer we've always provided is that the spokes are the same weight but CX-Rays are purported to have some aerodynamic advantage. If you're looking for "every last watt of speed," they're the way to go. But we have never seen anything that quantifies the difference between the two in a wheelset. So we decided test Lasers against CX-Rays in the tunnel to give a more informed and specific response than "every last watt of speed."

It turns out, however, that we've been exactly right all along.

We sent two RFSC 38 (38mm) wheels to the wind tunnel, one built with 20 radial laced Sapim Lasers and the other with 20 radial laced Sapim CX-Rays. Here is how the wheels tested against a range of Angles of Attack (AOA):

At all AOAs, the wheel with the CX-Rays was a smidge faster, generating about 11 fewer grams of drag on average at 30mph. If you recall the calculations from yesterday's blog, you'll see that 11 grams of drag at 30mph is - yep - 1 aero watt. You really do save "every last watt of speed" with CX-Rays, and not a watt more.

You remember also from yesterday that aerodynamic impact is diminished at lower speeds. Here is the difference in aero watts between the Laser and CX-Ray wheels at 30mph, 25mph and 20mph. In these calculations, the average drag is calibarated by the frequency of different AOAs at different speeds, which is why at 30mph the difference between the two wheels is 1.8 watts instead of 1.

Most brands assume that if you're spending between \$1K and \$3K for a carbon wheelset, you're after that every last watt of speed and they make CX-Rays or other bladed spokes standard. The logic starts to break down with shallower alloys though, where the upgrade to CX-Ray spokes may net you a watt, but still leave you a handful or two behind your training buddy on deep carbon, or oblivious if you're training on your own. For alloys in particular, we think it makes a lot of sense to offer the choice so people are not paying for performance they don't need.

Well, you tested only 20 spokes.
I assume therefore that 36-spokes gain is about close to 2 aerowatts.
Thats something reasonable. Is it worth the money, probably not, but a lot of stuff isnt worth it in that terms, like ultrasoniccleaning and hotwaxing the chain or removing seals of bearings and so on, bigger jockey-pulleys, all just expensive minor…. so.

What about the new Sapim Super XR Ray, they are 10% thinner and still as stable.

So it might turn out 2,5 aerowatts for 2x 36spoked wheels. Its 4,4 euro per sppke, hella expensive, do i need it and is it worth it? Nope, but am I gonna do it?? FOR SURE, call me enthusiast! I do expensive things for the fun of it, just to have it, like others collect stamps. Whats next, market? Shut up and take my money…. :D

Maik

Nice post!
But why the difference at 25mph was smaller than the expectation? I mean, based on the 0.5Watt at 20mph and 1.7watt at 30mph, it should be around 1watt at 20mph, not 0.4 in the test.

roger

Yes, Jimmy, of course it’s done that way. This protocol is basically the same as any other quality wheel test you’ve ever seen,

dave

Hi are the tests done with a spinning wheel at an rpm correlating with the wind speed? If not then its not a realistic scenario.

Jimmy Hor

Parts is parts, and watts is watts, and an approx. two watt saving at 30 MPH probably won't net you a PR. But taken in context, I noted that the diff. in watts absorbed, from the RFSC 38 (w/ CX-Rays) to the 404 FC, is a rather unexciting ~ 5.5 watts. That's the lot,from a 38mm to a 58mm deep rim? So, chasing an extra watt or two saving from an aero-profile spoke doesn't sound that loony. Heck, we must ALL be happily loony…5.5 watts, indeed. Big thanks, from all us in the loony bin, for testing and publishing this data. When do my 38s ship?

Rico