Inertia in cycling

Impact absorption has nothing to do with the mass of the helmet. The helmet is designed to break instead of your head. The helemet should also be firmly attached to your head and so won't undergo any relative motion. So its mass doesn't matter.

If Giro can achieve the same level of safety with less material then good luck to them.

In Australia there are standards which must be met and a helmet cannot legally be sold without having been standards approved. So any helmet you buy in Australia meets a minimum saftey standard. I know we couldn't buy Catlike helmets here for a while due to the fact that they were not submitted for testing.

I assume other countries have similar systems.

As to your other question, you are refering to Newtons First law of motion: a moving (or stationary) object will continue moving with constant velocity unless acted upon by an external force.

There is no property that keeps objects in motion (except a lack of forces) and mass has nothing to do with it.

However, in the real world, you hardly ever see a situation where no external forces are acting. A cyclist is acted upon by his own pedalling, air resistance and rolling resistance. This is where newtons second law comes into effect: A body acted upon by an external force will undergo an acceleration proportional to that force. The constant of porportionality is the mass of the body.

A heavier guy will need more pedalling force to accelerate than a lighter guy, but he will therefore also require more breaking force to slow down. If you and your heavier friend decide to coast down from equal speed, your friend will travel further than you becasue he is heavier (and therefore carries more momentum) and the drag forces experienced by each of you are approximately equal.

The extra momentum of a heavier rider may be an advantage in that they would slow down less through the deadspot in the pedalling cycle. Reciprocating engines all have flywheels for the same reason, it stores some energy from the power stroke to carry the machine through the dead strokes smoothly.

Of course it could also be that your friend is just smoother or stronger than you 🙂

ryan_tran03 said:

Hey guys, just wondering... what's your take on inertia in cycling?

Personally, I think it's a good thing as long as people aren't abusing it to gain an unfair advantage. I support random testing. 😉

ryan_tran03 said:

Wouldn't a reduction in weight/mass cause less inertia and would actually be better if there were an impact to occur? So basically I'm asking, would a lighter helmet actually be safer than a bulkier one? 😕

No. In all honesty, the construction and fit of the helmet has way more to do with it's protection than anything else.

But in a way more general sense, greater mass is generally safer because in an impact momentum is conserved. This means that the more massive object has a smaller change in its velocity during an impact than the less massive one. Smaller change in velocity means smaller deceleration forces on the more massive object, which typically means less injury for the people or sensitive parts inside.

Think about a bus colliding with the safest passenger car on the market -- which one would you want to be on?

frenchyge said:

... the more massive object has a smaller change in its velocity during an impact than the less massive one.

True, as long as the impact imparts the SAME FORCE to each object.
But then you're completely neglecting the fact that a helmet is always attached to a much larger mass (the head/body) anyway. Any change in helmet mass is pitiful compared to the mass of a human head (let alone the whole body). As far as impact forces are concerned helmet mass does not matter.

frenchyge said:

Smaller change in velocity means smaller deceleration forces on the more massive object.

Not true at all. The rate of change in velocity must be multiplied by the mass to get the force.
You can apply the SAME FORCE to two objects and the heavier one will have less change in velocity. The key thing is that they still feel the SAME force.

To cite your example: In the collision between a bus and a car the force felt by the bus and the car is the same. The lighter car feels a greater acceleration (and therefore the occupants are tossed around a lot more) but both vehicles feel the same force.

The occupants of the car usually come off worse because (1) they get tossed around more, and (2) because the panels in a car dont have so far to crumple before they start to impinge on the occupants. In a bus there is lots of crumple space.

Quoted post said:

Of course it could also be that your friend is just smoother or stronger than you 🙂

haha... possibly. 😄

Lot's of intelligent answers here so I can definitely assume no one here has experienced any knockin' to the noggin haha.

But would the extra momentum of the helmet be less beneficial though? With more momentum, one could expect an increase in the joules at impact. The amount of force or Newtons on impact is proportionate to the amount of mass and velocity the object is traveling by.

But then again, in the end it really doesn't make a difference as Tafi said. Same amount of force...

What would you guys prefer though? Now I had an old wally world helmet that I just replaced with the Giro, and they are both two completely opposite ends of the spectrum. Would you guys wear the heavier helmet? Or it really doesn't make a difference, and it's all about sex appeal lol...:p

Also, if my qoute thing at the top didn't work right, it's because I'm still kinda trying to get used to this forum thing...

tafi said:

But then you're completely neglecting the fact that a helmet is always attached to a much larger mass

Yeah, I was really neglecting anything to do with helmets by that part of the post and speaking strictly about impact masses in a very general sense. Since the OP was on the wrong side of the underlying principles (ie, "wouldn't lighter be better?"😉 I thought illustrating that would help them get straightened out on the more specific cases as well.

tafi said:

Not true at all. The rate of change in velocity must be multiplied by the mass to get the force.
You can apply the SAME FORCE to two objects and the heavier one will have less change in velocity. The key thing is that they still feel the SAME force.

It is true if you open up the context of your reading a smidge. I was referring to damage sustained due to *deceleration forces* (g's) on sensitive internal parts, like a brain inside a skull or person inside a vehicle. When the outside shell slows down less, the squishy bits suspended inside experience smaller forces.

Keep in mind that responses on a cycling forum are written with the OP in mind, so sometimes technicalities are glossed over for the sake of greater understanding by the poster.

tafi said:

The lighter car feels a greater acceleration (and therefore the occupants are tossed around a lot more) but both vehicles feel the same force.

See, you got it. The vehicles may experience the same force on the outside, but the occupants do not feel the same force, as I was talking about before.

ryan_tran03 said:

What would you guys prefer though?

I'd prefer the lighter one because it's more comfortable, less fatigue on the neck, and presumably still passes the same safety standards due to improvements in fit or design. Ultimately it's still about riding the bike, or we'd all be wearing American football helmets, right? 😄

I just got a Specialized S-works this year, and it is sweet! Feels like I'm barely wearing anything at all (although still passes the US safety standards) which makes it a lot more enjoyable. Too many variables in a cycling collision to worry about a few grams of helmet mass, but reducing neck fatigue while riding or racing for hours on end is a different story, however. Enjoy your new Atmos. 🙂

Well hey, thanks guys. This thread gave me that reassuring feeling of being safe just incase I get the asphault. Lot's of informative stuff, but you guys definitely did answer my question haha. So I guess this thread is coming to a close...

Is there a specific way to close this? Or do I just let it rot? :eek:

Before you let it rot, I'd just like to add that I have in my garage the carcasses of not one but two Giro Atmoses that have "given their lives" to save my skull. In the criterium crash (not my fault) that left me with a grade iii-v shoulder separation, I have a distinct memory of the three major slow-motion moments of contact between my head and the pavement. Good helmet. JMO.

OldGoat said:

Before you let it rot, I'd just like to add that I have in my garage the carcasses of not one but two Giro Atmoses that have "given their lives" to save my skull. In the criterium crash (not my fault) that left me with a grade iii-v shoulder separation, I have a distinct memory of the three major slow-motion moments of contact between my head and the pavement. Good helmet. JMO.

I'm very sorry to hear that! I think it's safe to say that you're living proof of a quality helmet haha 😄. Thanks for letting me know, I'm now 100% confident that in the event of catastrophic dooming, I'll have a fighting chance against the pavement.

Would you happen to know how much force it takes to render a helmet under an unusable condition by the way? Would simply dropping a helmet ruin it? All I know is that it's supposed to be designed to split...

Can't comment re force required; all I know that if it's crashed, it's trash. Not all cracks are easily visible, so you have to grasp it firmly and press this way and that and look closely to see if any hairline crasks are present. Brain surgery is a lot more expensive than a new helmet.

Anything to rationalize buying a $200 helmet instead of a $40 one.

This falls under the category of hair-splitting.

I like my expensive helmet because I look less dorky in it.

As a former bike shop employee, it always makes me twich when parents asks me if I have a cheaper helmet than $40 when their kid have $100+ sneakers on their feet.

All bike helmets seems to pass the same crash test, but it's how well they fit your head that allow them to protect your head in a crash. Get fitted properly.

oldbobcat said:

Anything to rationalize buying a $200 helmet instead of a $40 one.

This falls under the category of hair-splitting.

I like my expensive helmet because I look less dorky in it.

The $200 ones does look better (relatively speaking); however, I only paid about $80 each for mine via eBay. Last one came from Canada. Both were new, not used. (Don't think I'd want to buy a used helmet; no telling where it's been and what it's been in contact with.)

oldbobcat said:

Anything to rationalize buying a $200 helmet instead of a $40 one.

I raced a $40 helmet in my first season, and I like my S-works muuuuch better (although I didn't pay $200 for it thanks to our nice team sponsorship).

Lighter, airy, more comfortable -- I think a quality helmet provides a noticeable improvement in ride pleasure for the money. 😎

....but yeah, if you're planning to go banging your head into solid objects then any ole skull bucket will do. :p