i don't think anybody has data comparing those two helmets on you.

that'd be the only data that matters.

the shorter answer is: "it depends."

What is a road time trial?

Why just those two helmets?

Hasn’t giros own test shown the Vanquish is not the fastest of their helmets?

These are the two helmets I have available to me.

A road time trial is a plain ‘ol time trial but I added the word “road” just to be more specific.

If Giro fits you, for TT get Giro Aerohead https://www.giro.com/us_en/aerohead/, same price but better aerodynamics https://www.giro.com/us_en/vanquish/.

Although Vanquish is outstanding helmet (my daughter owns both), it is mostly for RR, crit, and draft tri.

Tangent police.....

I fully understand that the Aerohead is faster. I don’t have one right now to use. I have the Javelin and Vanquish.

I posted here hoping someone would have empirical data showing which one is faster. Or if someone has a really solid educated guess based on testing they’be been party to.

Thanks for the replies.

The Bell Javelin is one of those helmets that works well on many people and is nearly impossible to improve upon for some. Probably your best bet given no other info.

One is an aero helmet, the other a road helmet...it’s pretty clear which one is faster :)

Do you have a power meter? You could test which one is faster on you using the Chung method. I tried it myself and was amazed to see a ~5 watt difference between skin suits (Castelli PB 3.0 vs. Jackroo Aero Flash), and ~6 watt difference between my Javelin vs. Protone helmet.

In this case, testing is the only way to know for sure!

Give the minor differences between Vanquish and Aerohead, I’m not convinced the Javelin is a clear winner here and it’s a hot box!

https://www.giro.com/us_en/vanquish/

Does anyone know about where to find any "cooling" vs aero data in something like the Vanquish, Aerohead involving a Synthe? On one hand you have the first two, more aero obviously, but hotter than the Synthe. As a "aero road" helmet, the Synthe is lighter and will keep you cooler. In the end, full on aero you've come to know as *faster* on the bike, but overall, the Synthe may be *faster* for your overall race by keeping you cooler and taxing your hydration levels when being on the edge in a race. Being ultra heat sensitive, I've taken to the Synthe since its release to stay cool and not dehydrate as fast.

It'd be nice to see side by side temperature differences each helmet holds in and the savings in time from aerodynamics over a given 40k or more distance. At the end of a long day, you may need that extra 1% of fluids to keep you in the game on the run. Arm chair coaching would likely say drink more, but anyone who has done Ironman races knows that isn't always possible beyond a certain point. If you want to back way off the pace then, that's one thing--but that would negate the whole point for some athletes doing certain races.

The answer really is ‘it depends’. For example we recently did testing and for that rider the Javelin was noticeably quicker. https://twitter.com/.../1029698634701565952

You could always test them yourself if you’ve got a powermeter. :)

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Developing aero, fit and other fun stuff at Red is Faster

I would have to say Javelin. It is a well proven performer and even still used by pro cycling teams. I own a vanquish and only reason I would use it over the Javelin would be if you wanted a cooler helmet.