[quote=fishboy,Apr 24 2008, 01:02 PM]Test number three this morning. Limar Chrono 05 v Giro Advantage 2 with taped vents. Subjectively, don't think taping has helped improve the situation, but need to run the data.
Better get to the LHS (local hardware shop) and get some duct tape.
Turns out that with the vents taped the Giro Advantage 2 performs exactly the same as the Limar. Kind of surprised me - how can 5 pissy little vents on the front of the helmet result in 0.9-1.0 kmh slower speed at 200 watts??? :blink: Should repeat this test with vents taped and de-taped to make sure.
So the first rule of aero helmets would seem to be: [quote]Buy aero helmets without vents in preference to ones with vents.*[/quote]
And the second is: [quote]If you have vents on an aero helmet, tape them.[/quote]
* Sure, if you think you're going to have a hot head, get one with vents, and ride that bit slower.
Here's the data:
Also interesting to note that this test with done with different clothing to last time - looser (but warmer) jacket which is not skin tight. This jacket is responsible for dropping the speed at 200 watts from:
37.1 and 38.1 kmh for Advantage 2 and Chrono (test 1)
37.1 and 37.9 kmh for Advantage 2 and Chrono (test 2 - same clothes as test 1, skin tight)
36.0 kmh for both helmets (test 3) - looser jacket, non skin tight