Nov 24, 2007

Motorcycle Helmets: What does the outer shell do?

If you have read the above, you already know. The basic job of the outer hard shell is five fold. First, it needs to absorb and spread any sharp impacts over a larger area to reduce the peak impact strength. As in, the same force, spread over a larger area will hurt less (or, to paraphrase, have less destructive energy). Second, it needs to offer excellent abrasion resistance so that the EPS liner inside does not come into contact with the road and wear away. Third, it needs to offer very little resistance to sliding along the road. If the helmet happens to resist sliding along, it can put unnatural forces on the neck area adding to the injuries. Fourth, it needs to protect the EPS liner from minor knocks that helmets tend to suffer in daily use. You know the ones I mean, the accidental brush with the elevator door, the careless put down when the lid nearly rolled all the way over etc. Fifth, finally, the helmet, being the highest point of a motorcycle-rider combination also needs to attract attention (getting noticed is a crucial component of safety in traffic) and look good (you'd rather look good, than shabby, right?).

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Motorcycle Helmets: What does the inner shell do?

Again, if read the above, you already know. The inner shell is soft and it has one sole, life-saving function. It absorbs the forces of the impact by self-destructing using these very forces. The inner shell, also allows helmet makers to 'tunnel' in and make pathways for air to enter and exit helmets and promote ventilation. Lately, the inner shell also has the task of hosting various certification and manufacturing labels.

Taking care of the inner shell is very simple and absolutely crucial. Keep the helmet away from small knocks, don't drop it and don't be careless with it. Do not use/store sharp objects inside the lid. Do not place the helmet on your rear view mirror like you usually do. Do not use any chemicals/sprays inside the lid. Do you use deo to 'sanitise' the comfort lining? Well, don't do it. Finally, be mentally prepared to replace the helmet every three to five years. They are consumables (that's EPS lining, again) and like a perfectly good seeming oil filter, there comes a time when you need a new one no matter what the old one looks like.

Image from motorcyclistonline.com

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Motorcycle Helmets: What is comfort padding? Why is it important? How to take care of it?

You already know enough about the comfort padding from above. It is important because no one wants to be uncomfortable. If your helmet gets in the way of your motorcycling, you'd stop using it. The comfort lining needs very little care, actually. It needs to be washed now and then. And that's about it.

If your helmet does not come with removable interiors, I've usually found that soaking the helmet in a bucket works fine. To keep the lining soft, avoid using a heater or blower to dry the helmet faster. Just ignore it for a couple of days and let it dry naturally.

If your helmet does have removable insides, well, just whip out the instructions, do the business and wash them. Remember, helmets like neutral pH stuff, so baby shampoo or detergents meant for delicate fabrics are the ones to go for. Most materials will come clean just with soap, you don't need to scrub anything hard.

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Motorcycle Helmets: What is a retention mechanism? What does it do? How to take care of it?

In most cases, helmets use two kinds of retention mechanisms. The one more common in Indian helmets is the quick release buckle (QRB). Which is essentially the same mechanism that secures your three-point seatbelt in the car. A little sewing machine oil now and then is about all it needs. And if you did oil your QRB, you're obsessive-complusive. Even I don't do that. QRBs are easier to use than the other type of mechanism, but the tightness cannot be adjusted on the fly. You usually have to take the lid off and fidget a fair bit to tighten or loosen the straps.

The other, and probably the better mechanism is the Double D-Ring (DDR), which is the de facto standard in all 'serious' helmets. The reason why DDRs are considered better is because it isn't possible to loosely fasten a DDR. It has to be snug. Why is snug important? I'll tell you in a minute. DDRs are a little more fiddly to use than QRBs. But again, my experience says it's matter of getting used to and within a couple of days you will not notice any difference in ease of use. The DDR is usually equipped with a small catch that secures the loose end and stops it from flapping around.

Most helmet standards require that the helmet retention mechanism, specifically, the nylon straps that host the QRB or DDRs, are not attached directly to the shell itself. Usually, a metal ring (usually a triangle) is attached to the shell and the nylon strap is stitched to this ring. I don't fully comprehend why this should be, but there it is. Further, in most cases, the nylon strap is lined with a softer material to prevent chafing skin.

Open face helmets, or jet helmets may sometimes have a chip cups incorporated in their retention straps, usually with a QRB.

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Motorcycle Helmets: What is the visor made of? What is it for? How to take care of it?

I'm a little short of data on this one, but here goes. The cheapest visors are usually acrylic. Among Indian brands, most use acrylic visors. These shatter pretty easily, are light and almost too easy to scratch. They are, however, inexpensive. The better, more expensive shields, almost without exception are polycarbonate. In feel, they feel like hard plastic and when you flick your index finger (carrom striker style) against it, you should hear a clear, almost musical ting. An acrylic one will respond with a dull tick sound.

The perfect helmet impact safety-wise would have the hard shell going all-round. But to look through the shell, we need a hole. Again, a hole isn't perfect because you can be blinded by flying debris or worse, bleed when a stone chip finds skin to collide with. The faceshield or visor's primary task is to be optically perfect and protect against this kind of flying debris. And lest you be worried, most helmet standards specify the hole's dimensions so that visbility, focal and peripheral is not hampered. Among the list of growing secondary tasks is to stay fog free (your breath can fog up the visor), UV protection (really), contract adjustment (dark visors, or the new age amber coloured hi-def ones) and yes look good (reflective finishes look great!).

Taking care is quite simple. Remove the shield from the helmet, wash it out with running water (to sweep away dust) and then hand wash with a mild soap (baby shampoo, as usual is where it's at). I tend to first pat dry with a regular towel before a more comprehensive wipe down with a lint-free cloth. In my experience, used dhotis/vests work wonders. I also remember a Swagat Baniyan ad that claimed that it was lint-free but I never got around to trying that. Then remount the shield.

Mounting the shield, actually is a topic in itself. But we'll come to that.

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Motorcycle Helmets: Why do all the big names harp on and on about vents and airflow?

At the end of the day, no matter how much technology goes into your helmet. You are still placing your head in an enclosed, tightly-fitted spherical box. So the least the helmet makers can do is make you comfortable, right? Vents are the accepted way to control airflow through the helmet. Initially, there were only intake vents, but with wind tunnel testing (really) the latest and greatest lids emphasize exit vents as much as intake vents. The massive diffusers you see nowadays on some of the lids exist for that purpose, and to smooth the aero profile of the helmet. Most top-line lids today, in fact, offer as much control to the rider over air intake as over air exit.

Most often, the helmet will have one chin vent at the bottom center of the visor, and one or two vents above, ranging from just above the visor center to the crown of the helmet itself. On the back, similarly, there can be sets of exit vents on top, at the bottom and sometimes, there is even one on the bottom of the helmet, a little inset from the bottom rubber ring on the lining. Does it work? Leaving an airconditioned room having worn the lid inside for five minutes or so, you can actually feel cold air on your shoulders when you start riding.

Airflow refers to the aerodynamic profile of the helmet. The first time you cross 150 kph on a motorcycle (don't scoff, you'll be doing that sooner than you think), you will how good or otherwise your helmet is. The AGV Pacific, for instance, my personal pick for the best Indian lid, squashes flat against your nose at anything over 130 kph. Designers can design the helmet to smooth airflow. There's a reason for this. As the air leaves the helmet, the smooth flow breaks up behind the helmet, and that's the deep bass fluttering you hear inside. Diffusers can help cure this.

Similarly, helmets with plastic plates over the visor mounting (Arai, Suomy, Vega etc) tend to be noisier because the air catches on the edges and adds whistling sounds. Further, top of the helmet vents also tends to add noise. The plates also make the process of changing visors – I ride with a dark on in the day and a clear one at night – fiddly and cumbersome.

Wear a helmet and stand in a closed, silent room. You will hear nothing – the helmet makes no sound of its own. All the noise you hear is just wind. Given that wind noise can reach almost a 100 dB, well past the safe hearing limit, I think it's important to pick quiet helmets.

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Motorcycle Helmets: What happens when your head hits the ground with the helmet on?

Again, you should already know most of this. When you impact the ground, the solid ground applies a pretty serious brake on your downward (and usually forward) acceleration. The helmet will absorb an astonishing part of this force, destroying itself in the process, if the need arises. The danger to you, serious trauma apart, is the acceleration of your brain inside your cranium. Snell tests helmets so that only 290gs or less (no kidding) is recorded inside the helmet by the test headform. That's the peak and 150gs cannot be exceeded for more than 4 or 5 ms at a time. The ECE 22-05 is, evidently, even tighter, not allowing more than 275gs. That much, you can handle. I am given to understand that 150gs, roughly equals a headache.

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Motorcycle Helmets: What happens when your head hits the ground without a helmet?

If your brain accelerates at past 300Gs, you're going to be seriously injured. That's assuming that the cranium has the strength to stay together from the impact... I think you can work the rest out.

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Motorcycle Helmets: Do helmets cause hairloss?

No.

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