Maybe I’ve spent too much time reading stuff on this forum and the internet at large but during the shopping process for various bike parts I have in my head “yes, but is it aero?” This was part of my last 2 helmet purchased, my POC ventral which I get along well but is reportedly the least fast and my more recent Giro eclipse. The Giro is the reason for the displeasing. I bought it prior to the release of the article on cyclingnews.com and was pleased to see it hit 4th place but that thing breaths like a plastic grocery bag on my head and the sweat strip dumps right onto my glasses in a way I have rarely experienced and makes it rather hard to see. I can wear it during shoulder season days but because of it I’m thinking I want to go the other direction and get a fully ventilated helmet. I know some folk on here have had good luck with the Specialized Evade and the Scott cadence has been recommended as being both aero and well ventilated but at this point since the eclipse was also supposed to breathe well I’m dubious of the breathability claims of a fast, closed off full aero lid. But at the same time that nagging thought of “but is it aero?” comes in to which the answer will be a no not really. So as the topic states, I was wondering what fully vented helmet, like the POC ventral air or the Giro Aries, might be the “fastest” as a relative term? I’ve seen folk win in the pro peloton with vented helmets versus their aero counterparts so clearly it doesn’t hold them back and comfort is a concern when it comes to going fast because overheating is certainly slower than good temp regulation. So I was wondering if anyone has insights as to which brand’s ventilated helmet has the least compromises to speed i.e. most least aero i.e. fastest slow helmet?
I don’t know how it compares with others but have heard that the Trek Velocis is almost as aero as their Ballista. Might be worth consideration.
I have a 2nd gen Ballista. I like it better than all of my previous helmets with holes in them. I’ve worn it training in New Mexico on 100F days and it was good. The air flows under the brim and over your scalp.
I have the latest gen of the Ballista and haven’t found it to be too bad in terms of ventilation. Not sure what Gen the current model is. I assume the latest Velocis would be cooler though.
I have a Prevail ii and it breathes great and tests towards the bottom of the cycling news test but above the ventral. That said all of them are within a pretty small margin in that test
Interesting discussion about that article and the validity of the test.https://youtu.be/hUbV6zdEQys?si=Lvg2A7z1e42BB4Z9
I’m of the opinion that a helmet complements a riders position and what works well for me may not for you.
The helmets can all test against one another in controlled situations, though those situations are rarely ever what we face when out on the bike.
The Nero show linked above had a chat on them recently and the notion that 7 watts was the difference between top end and low end made me realize that it just doesn’t matter. Wear what feels the best.
I have an Evade 3 and a Prevail 2 and find them both to be decent in the heat. The huge air chamber on the Evade really works to move air through the helmet, however I find this depends on speed. It’s a helmet made to go fast so as your speed drops it’s ability to cool drops as well. The Prevail works just about the same at any speed. I wear the prevail when I know I’m riding with friends who may want to take it a little easier or for MTB and other stop and go type rides. The Evade is definitely a faster helmet in the wind though.
I want to give the new Prevail 3 a shot just to compare the Aero advancements over the 2 but that’s just because I like trying things out.
One caveat I will give is that huge air channel on the Evade is a real bee catcher. Zipping along at speed and it just sucks them right into the front in the summer. So, depending on where you ride, that could be something to consider. I got stung once this summer, but had a few close calls as well. Also, it hurts like hell when you hit one going for a KOM.
Pogacar would still win with a wool jersey, POC Ventral, mountainbike shoes etc etc.
The issue isn’t what the pros use when they win 
For me as an amateur, I think it’s important to use all advantages that I can that are “cheap”: Tight clothing, aero helmet, low rolling resistance tyres etc.
Of course it doesnt matter since I don’t race, but why go slow than you need to 
I have the Evade 3 and POC Ventral Air. I use the Ventral on hot days, commuting, climbing. Evade 3 for all other days.
Evade 3 can really get hot if it’s 20+ C outside, and you’re climbing etc.
My experience with vented Vs aero helmets is that it comes down to AVG speed of the ride. I switch between a Scott Centric a Scott Cadence (the newest model). The Cadence feels at least as ventilated as the Centric at speeds above 25km/h or so, it just needs enough airflow so that the internal channels work. Even at the peak of summer, if I’m doing a flat-ish or flat road ride (anything bellow 350-400m of gain per 30km) I pick the Cadence. If I’m chasing cols in summer and my AVG speed drops significantly, then Centric.
As for the usual talk of certain pros winning even on a Dutch bike, sure, some have enough performance gaps to overcome suboptimal setups. But those setups would still be suboptimal. Pogacar on a not super hilly or hot course with shallow wheels, crappy tires and a “vented” helmet is slower than Pogacar with an optimal setup. Maybe for him the difference doesn’t matter, but for other pros (and most of us) it does
I own two POC helmets and at least for my head shape the fit is second-to-none. And even in the humid Japanese summer heat, my head was cool. Fit >> aero gains, me thinks.
I have both the Evade 3 and Prevail 3 . One for hot days over 80F and one for cooler days. There is a difference in air flow. Not offset by the protection you get from the sun burning your head. I ride at 15 to 18 mph average.
Lazer Genesis highly recommended. Light, fast, well ventilated.
It’s not like good fit and aero are mutually exclusive.
I tried the Specialized Prevail/Evade 3, the Giro Aries/Eclipse and the Scott Centric/Cadence and the fit was highly consistent within the brands.