Helmet Question - No Answer in Search
 

New to biking, after 45 years since last rode. When I bought bike, picked up a size large Bontrager Quantum. My head is 24” even (60.96 cm). The large is for 58mm-63mm, whereas their XL is for 60mm-66mm. Adjusted, the large seems to fit, but feels awkward on my head. I can adjust the boa system (which I had to spread apart vertically) tighter after I place helmet on my head and it stays in place. The thing that concerns me is the adjustment wheel sits on top of my occipital lobe instead of beneath where the instructions say the wheel should rest. Can’t see any way to make the wheel lower on the back of my head after I vertically expanded the boa system without tilting helmet back on head, which isn’t a proper fit.

I can shake my head in all directions and helmet doesn’t move, but does the inability to place the boa adjustment wheel as instructions indicate mean that I might need an extra large helmet instead? The large is approx 2 cm bigger than my head at max end, whereas the XL is approx 1 cm smaller than my head at the low end.

Or am I over thinking all this and since helmet stays in place when boa tightened, the location of boa doesn’t matter?

Over thinking.

You should be able to fit your helmet the way you prefer. If you’re out of adjustment range with that particular helmet, then it simply doesn’t fit. Advertised helmet size is only part of fitting a helmet. Even within the same brand some will fit better than others due to fitment systems and helmet shape.

return it and get a helmet that you can adjust properly and that feels comfortable.

Good luck!

Thanks folks!

You're not overthinking it. Helmet fit is critical. And helmets of the appropriate size don't all fit the same.

My skull is 59 cm and I can wear medium or large depending on the helmet. I have to try 'em to find out.

I have Bell helmets in medium and large and with both the adjustment dial on the rear contacts the point of the external occipital protuberance. Ideally it should fit slightly below there in the hollow space between the base of the skull and neck. That would help resist tipping.

My POC Omne Air Spin in large fits as expected, with the harness dial right in that hollow area between the external occipital protuberance and neck. Snugged up, it feels secure.

However POC helmets are already like head mushrooms, wider than most because they use thicker EPS foam and polycarbonate shells. Like other users I find the overhanging brow just visible at the top of my peripheral vision, which can hinder my forward view from the drops unless I crane my neck up. Good protection and better ventilation than my Bell helmets.

Some road helmets seem minimalist compared with mountain bike helmets. My Bell Formula MIPS runs on the minimalist side, while the POC is noticeably larger in external diameter. The Omne Air Spin is more of a commuter helmet but with excellent ventilation where most commuter and skater helmets have terrible ventilation from a few dinky holes -- they look like bowling balls. I like the POC so well I've been using it on my road bikes on hot summer rides for the ventilation.

POC uses its own "SPIN" system rather than licensing MIPS. Seems to work the same way. I know the MIPS system in my Bell helmet works -- found out the hard way earlier this year. A railroad crossing arm came down unexpectedly quickly as I was passing a railroad crossing slowly. Hit my helmet, which deflected it, with the outer protective shell tipping while the harness remained in place. No harm to helmet or skull. POC just uses a different, less sophisticated looking but less cluttered approach, which probably helps with ventilation.

The POC Ventral and Octal run a bit smaller in outer diameter, so if you don't mind the hefty price they're worth considering.

Thanks Canklecat. I wore mine first time yesterday for a bit past 8 miles. The adjuster felt a bit high (not in the hollow below the occipital, more about half and half). It did dial down well and during my ride there was no side to side, or front to back, or really any movement. Steady winds between 15-20. I used a Halo skull cap as well (folic challenged head) and everything seemed to function as intended. Halo a bit tight, but was brand new and first use as well. I ended up with the Bontrager Quantum as that’s what LBS recommended. Research over last week has enlightened me to the multitude of helmet options so next helmet will likely be a bit lighter and a bit bigger. Thanks again for taking the time!

Skull caps and bandanas will change the helmet fit a bit. I often wear bandanas to soak up sweat and usually need to fiddle with the position of the knot and my ponytail knot to get the helmet seated and adjusted correctly. It's a bit easier with the POC because the harness and dial sit a bit lower on my skull.

On days when it's not too hot or humid I might go without a bandana and the helmets usually fit a bit better.