I know it’s been asked a million times, but over 40K, averaging 25mph how much time would be lost with an aero helmet instead of a regular road one??? Roughly???
Obviously, it will vary from person to person… but like 30s?
Francois told me it was about the equivalent of aero wheels.???
Depends on the helmet and how it interacts with your position. But the savings can be as much as a disc wheel vs. a 32-spoke in the rear, which is often ballparked at around 90 seconds over 40k.
Rappstar,
Probably on the order of 1-2 minutes for a 40 km distance but that is subject to proper use of the aero helmet. One must stay on aero bars and keep the tail of the helmet on one’s back (low to the back of the rider). Tilting one’s head down, either to relax the neck’s muscles or to look at the front wheel or front derailleur and raising the tail of the helmet off the back of the rider negates all aero benefit of the helmet and begins to create even more drag than a standard bike helmet.
According to some pros and coaches, an aero helmet used properly offers the greatest time benefit of all possible aero “improvements.” Of course having an optimized aero position/tuck with aero bars is presupposed.
“an aero helmet used properly offers the greatest time benefit of all possible aero “improvements.””
That is a very interesting statement. I am certainly not in a position to debate it with any authority. It also seems to fit intuitively because the helmet goes toward reducing drag of the rider, who forms the lion’s share of the overall drag equation. But I’d surely like to see several of the experts producing data in consensus on this one.
Its difficult to say. I started using one part way through this year.
From my early season Duathlons I was cycling faster than last year using a normal helmet (35k duathlon bike leg = 3mins quicker). The addition of an aerohelmet hasn’t really seen my performance improve - i have improved my 10 and 25 TT times but not by the amount my early season form suggested or by he time gains I expected the aero lid would give and certainly not by the combine effect. I have had illness problems with an inflamed throat and chest which being stupid I have mainly raced through, ( turned out to be largely due to a secondry infection). So maybe my form has dropped from earlier in the year due to this and my current improvement is down to the lid - its difficult to know. Though I have just got a Powermeter which I guess will help highlight what improvements are down to
I believe that the helmet benefit depends on the rider. I recall John Cobb saying when he wind tunnel tested some riders he found they actually did better when they put their head down and the tail came up. I believe that some riders with hunched rather than flat backs the raised tail helped to deflect air ove the back, hence the shape of the Giro helmet that Lance used because of his pronounced hump.
There were some riders who did better with no helmet and I remember hearing about one whose best drag was with a cycling cap worn reversed! (not an option these days)
It would be good to hear from the true wind tunnel experts, I know John occasionally posts on this site.
KR
flying wombat,
Perhaps we should look at David Zabriske and what he does to ride so fast. He has been described by more than one authority as perhaps the best natural time trialer with a near perfect position and technique. Its definitely hard to argue with his results!
As recently as the May 2006 issue of Cycle Sport Magazine, page 134, column titled, “Aero Freebies” subtitled, “Wind tunnel boss reveals all.”
"A day in the San Diego wind tunnel costs several thousand dollars. A one-hour workshopis $850 per rider. …aerotest manager David Sanford gave Cycle Sport readers some exclusive aero tips for free.
First on the list: “If you are riding time trials get a good aero helmet and make sure you wear it with the tail down on your back,” is his first piece of advice.
“For time saving per dollar that’s the best thing you can do. Triathletes used to refuse to wear aero helmets, but when we showed them how much time they could save 90 percent immediately got one.”
It goes on to reinforce what I wrote earlier about one’s aero position, staying in this position all the time even when climbing and descending, and not tilting the head down because that lifts the tail of the helmet off the back (bad! Increases drag significantly!)
Now one can argue that this guy (David Sanford) is a “nobody” with limited cycling credentials? and question his findings but I will suggest he probably knows a lot more about the subject than all of us combined. In otherwords, he is an authority with every bit as much knowledge about position, equipment and drag as John Cobb, maybe more because this is his full time occupation.
The real question here is are you in the 90 percent or the 10 percent group?
“If you are riding time trials get a good aero helmet and make sure you wear it with the tail down on your back,”
So I am confused… What about Rudy project helmets? Their tails are higher if you compare to LG and other aero helmets?
aliengin,
Very simple. Based on the advice of David Sanford, the Rudy Project helmet would not offer as great an aero benefit as the LG Rocket would as a result of a higher tail that would not sit as close to the back or would require a more extreme head angle to get the RP helmet tail down onto the back.
Don’t forget that what one is trying to do is minimize drag. Initially, this is done by reducing one’s frontal area. If a rider has to lift his head back (or up) to get his helmet tail to set down on his back, then he increases his frontal area (drag) when his head is cranked/craned back.
Becomes a form or function question. Why does a Zipp wheel (LG Rocket) offer more aero benefit than a Mavic Open Pro wheel with 32 spokes (Rudy Project helmet)? Because they are better engineered to satisfy the desired goal.
I can see the benefits for short distances, but what about overheating ?
My pneumo is very airy, but I’m sure I’d just bake in an aero helmet on a long course race on a hot day. That would prob slow me more than any potential time benefits.
.
mastman,
Thanks.
That’s a great illustration of what David Sanford is talking about or recommending to gain maximum aero benefit from an aero helmet design.
I notice a couple of things from this picture. How far out on the end of the saddle DZ is and that he is not a flat back rider, either. DZ’s helmet and head are tucked in about as tight as one could get. If it were tucked in any more, he wouldnt be able to look forward and see where he was going.
I think that there is no chance a current legal aero helmet could gain very much time savings compared to a disc wheel or “race wheels”. The current helmets are all faced with having larger frontal areas for impact worthiness, larger frontal areas require more power to push down the road. The very tight fitting shell helmets of a couple of years ago could gain 15 - 20 seconds on a 40k for elite time trialist over a standard road helmet but now the difference is about half that. If you take a rider and map out the drag over a 0* - 30* yaw run and do the run in two helmet positions and average all that, the gains will be about 1 minute over a IM course comparing a good aero helmet to a std. road helmet. Why do all that? because no Triathlete can ride 112 miles without moving their head around, if you don’t use real world simulations in a wind tunnel you are only fooling yourself. Back in the early 90’s when Troxel came out with a very extensivly developed “aero helmet”, dimples et all, compared to the current road helmets, the difference over a 112 ride was about 20-30 seconds. The LG helmets and other aero helmets I’ve tested lately are sometimes better and sometimes not depending on the back shape and shoulder shape of the rider. Certainly if you put a rider in a windtunnel and don’t yaw the bike you can achieve a position that will make the helmet seem pretty impressive, it’s easy to get fooled by that. Most of the readers on this forum are triathletes not TDF time trialist, it’s hard to do a 40k and not move your head around. In the summer or in Kona it can get pretty hot, at 18 - 19 mph ventilation is a bigger issue than helmet aero. If you avg. 24 - 25+ mph then helmet aero becomes a little more important but know where as important as wheel choice. Wheels help your speed by reducing the watts required to spin them throught the air, those wattage savings start to really accumulate over longer distances. I looked up some drag numbers I had from a test done this past Feb. and for this rider, , the Avg. 10* drag was 7.87 lb. and at 200 watts that put his IM bike time at 5:35:52 which was right at his actual times he had been doing. A helmet change brought that down to a avg drag of 7.75lb for a time of 5:35:37, he had big square shoulders but a pretty flat back. Hand width and tight clothes are more important.
Awww, John…you’re no fun.
I think that there is no chance a current legal aero helmet could gain very much time savings compared to a disc wheel or “race wheels”. The current helmets are all faced with having larger frontal areas for impact worthiness, larger frontal areas require more power to push down the road. The very tight fitting shell helmets of a couple of years ago could gain 15 - 20 seconds on a 40k for elite time trialist over a standard road helmet but now the difference is about half that. If you take a rider and map out the drag over a 0* - 30* yaw run and do the run in two helmet positions and average all that, the gains will be about 1 minute over a IM course comparing a good aero helmet to a std. road helmet. Why do all that? because no Triathlete can ride 112 miles without moving their head around, if you don’t use real world simulations in a wind tunnel you are only fooling yourself. Back in the early 90’s when Troxel came out with a very extensivly developed “aero helmet”, dimples et all, compared to the current road helmets, the difference over a 112 ride was about 20-30 seconds. The LG helmets and other aero helmets I’ve tested lately are sometimes better and sometimes not depending on the back shape and shoulder shape of the rider. Certainly if you put a rider in a windtunnel and don’t yaw the bike you can achieve a position that will make the helmet seem pretty impressive, it’s easy to get fooled by that. Most of the readers on this forum are triathletes not TDF time trialist, it’s hard to do a 40k and not move your head around. In the summer or in Kona it can get pretty hot, at 18 - 19 mph ventilation is a bigger issue than helmet aero. If you avg. 24 - 25+ mph then helmet aero becomes a little more important but know where as important as wheel choice. Wheels help your speed by reducing the watts required to spin them throught the air, those wattage savings start to really accumulate over longer distances. I looked up some drag numbers I had from a test done this past Feb. and for this rider, , the Avg. 10* drag was 7.87 lb. and at 200 watts that put his IM bike time at 5:35:52 which was right at his actual times he had been doing. A helmet change brought that down to a avg drag of 7.75lb for a time of 5:35:37, he had big square shoulders but a pretty flat back. Hand width and tight clothes are more important.
Hey John,
Nice to know you are still out there, researching and lurking.
Thanks for taking the time to set us straight.
Keep up the great work.
callidus,
Sorry, I just didn’t get it. Insider’s joke? Maybe I’m retarded too?
I’m hesitant to disagree with one of the world’s foremost bicycle aerodynamics titans… But, when I tested at the LSWT in San Diego, my CdA with the LG chrono helmet was .2343. With the LG Rocket helmet, it was .2172.
That equates to 1 min and 29 seconds over 40k at ~ 25 mph. That’s just the difference between a semi-aero helmet and a full aero helmet. The diff for a standard helmet would presumably be even bigger.
Now I will grant you, we only tested at 0 yaw. I do most flat time trials at ~28mph. Do I ever encounter a30deg yaw? If my seat-of-the pants trig is right, that’s a ~30mph crosswind coming at a 90 degree angle. Not bloody likely.
My field tests with aero helmets have replicated the tunnel results. Is it hard to keep your head in the right position? Yes. But it is doable; with the Rocket helmet, you tend to get a distinct whistling sound when the tail is up or sideways.
– jens
Oopps, I did type “Very interesting. Thanks” but it didn’t display it. Oh well.