I will be doing Ironman Arizona in April,and I’m hoping to qualify for Hawaii.
I think I can ride the course in about 5:40,which is an avg. of a little under 20 mph.
If I were to buy a time trial helmet,roughly how much time can I expect to shave off my bike time?
Thanks
This is highly debatable. Based on averages of all the estimates around, I would say 2-5 minutes.
A guy from the Allied Aerospace wind tunnel was interviewed in one of the tri magazines and he indicated that their average test subject showed a potential 5-10 minute improvement in an IM. Based on some wind tunnel figures I’ve seen, I’d say that sounds about right; 10 seems a little on the high side, but there are always outliers. It’s certainly as much time as a disc wheel.
Nobody really knows how much time the helmet will save. 2-5 minutes sounds like a good guess, but everyone has to agree that these helmets will all save you time, so why not use one. Don't obsess about which one, there seems to be lot of that around here, like disc wheels, they are all about the same.
Be careful with the heat with an aero helmet. The minutes you save during the bike could become hours on the run if you overheat.
Can yo keep your head in pretty much one postition for 5:40??? If the answer is yes, you can get about 10 minutes. If the answer is no, yo umight actually lose time by putting the tail of the helmet into the wind like a billboard.
Depends on how much of a fathead you are. 
Bob C.
stageracer hit the nail on the head here. I see so many people with aero helmets and then they let the tail sit up in the wind like a sail and they are loosing time!
At the state TT’s my 1min man had a aero lid and I could see the under side of the tail for the 2-3mins as I closed on him. He said afterward that he did not ride with it much and could not hold the position.
Kurt
If you haven’t seen it, here’s a Slowtwitch article on aero helmets written by John Cobb:
http://www.slowtwitch.com/mainheadings/techctr/helmets.html
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Two interesting points from the John Cobb article. http://www.slowtwitch.com/mainheadings/techctr/helmets.html <During these years I kept noticing that the pointy helmets were always faster when the riders would drop there head down,and have the tail sticking up in the air.> So according to this article,its in fact faster to put your head down,and have the tail sticking in the air.
Two interesting points from the John Cobb article. http://www.slowtwitch.com/mainheadings/techctr/helmets.html <During these years I kept noticing that the pointy helmets were always faster when the riders would drop there head down,and have the tail sticking up in the air.> So according to this article,its in fact faster to put your head down,and have the tail sticking in the air.
All the more recent stuff to come out of wind tunnel shows the exact opposite. The tail of the helmet should be flat against the upper back. JC’s findings in relation to helmets and water bottles seem to be at odds with what current thinking is.
i don’t buy it.
kurt
The benefits a aerodynamic helmet, and the effect of different head positions is very individual. It depends on where the top of the head is in relation to the high point of the back, and the shape of the back.
In general it seems that the higher your head is in relation to the high point of your back, the bigger the potential gain. Head position, or tipping, is probably a little more complicated as it matters not only how high your head is, but also on the shape of your back and the resultant wind flow.
For what it’s worth, for me, different head positions, from having the helmet perfectly horizontal against my back to pointing way up in the air, made absolutely no difference in drag (using 3 different aero helmets…I didn’t test with a regular helmet, something I wish I had done in retrospect!). Even with my head pointing down (and the rear tip therefore sticking up), the high point of the helmet did not go above the high point of my back though.
Here’s the data (static, non-pedaling, CDA values)!
LG Rocket neutral, turtled, head tipped down: 0.2389, 0.2367, 0.2364
LG Chrono neutral, turtled, head tipped down: 0.2346, 0.2334, 0.2372
All values within the noise…
Scott
Check Gordo’s site. he did some comparisons with aero vs standard helmet. He also tested with different positions and even with the aero helmet sitting on his head differently.
Check Gordo’s site. he did some comparisons with aero vs standard helmet. He also tested with different positions and even with the aero helmet sitting on his head differently.
Which is great data for him, but after my experience in the tunnel, I’m not convinced extrapolating anyones specific data (in regards to percentage differences) to anyone else is accurate at all! This is not to say that I think aero helmets don’t work, clearly they do, it’s just the magnitude of benefit they provide, and the magnitude of difference caused by different head positions, is an individual thing.
Scott
Miniscule differences between the two LG helmets. It’s too bad that you also didn’t test with a regular helmet. Then the numbers would be more meaningful.
Does anyone have a link to Gordo’s research?
go to gordoworld.com and access the forum. You’ll have to do an archive search.
It would only be meaningfull to me if the regular helmet showed no difference at all, which I had (and still have!) no reason to suspect to be true. In retrospect it would of been interesting to know from a curiosity standpoint though!
Scott