Helmet Envy or not

[ufkacbln]

I was at an Air Station which had a fast service road. I used to ride the Trike at a sedate 15 mph which was the speed limit.

Then one night in the Mess we got into a conversation about just how fast recumbent trikes could go and I suggested 30 was easily achievable on that stretch, and 40 a bit further along... as there was a slight downhill slope

Hence a bet was made with the proceeds to Charity

Quick chat with the MOD Police, who would provide to evidence with their speed gun.

Two speeding tickets were then issued .. one for 32 mph and one for 45 mph.

So they didn't actually cost me anything, but cost a few sceptics!

 

[ufkacbln]

The second point is open to debate.... however there was no suggestion thatthe helmet would be ineffective, simply less effective, hence the rider would have contributed to their injuries by exceeding that limit.

It reflects the matter of choice.

If someone decides that they wish to exceed the performance then fine, and they can take that risk without penalty.

However equally if someone decides they don't need to wear a helmet then they should also be able to take that risk without penalty

 

[Red Light]

It does not follow that if an item is designed to be effective in given conditions, it will be ineffective outside those conditions.

True but a) the helmets struggle to pass the tests as it is, which is part of the reason the old Snell standards are now the watered down BS/EN standards and b) their performance drops off fairly fast as the impact energy, which is what matters, goes as the square of the speed. So at 15mph you are exceeding the design limit by 40%, at 20mph by 160% and at 30mph by 480%.

 

[Bicycle]

... as the impact energy, which is what matters, goes as the square of the speed. So at 15mph you are exceeding the design limit by 40%, at 20mph by 160% and at 30mph by 480%.

I read this and I'm not sure I follow the sense. My apologies.

'The impact energy goes as the square of the speed' means little to me.

Any chance of clarification?

Does impact energy increase by the square of the difference in speed or is it equal to the square of the speed, or is there some other meaning?

 

[Little yellow Brompton]

Does this help?

Mass (M) Velocity (V) KE =MVV/2





1 10 50 1 11 60.5 1 12 72 1 13 84.5 1 14 98 1 15 112.5 1 16 128 1 17 144.5 1 18 162 1 19 180.5 1 20 200 1 21 220.5 1 22 242 1 23 264.5 1 24 288 1 25 312.5 1 26 338 1 27 364.5 1 28 392 1 29 420.5 1 30 450 1 31 961

Bugger! that looked fine till I posted it! :-(

 

[Norm]

Does impact energy increase by the square of the difference in speed or is it equal to the square of the speed, or is there some other meaning?

My understanding is that it is the square of the absolute speed, which isn't quite qhat you suggested, but it is almost.

So, 3mph would have a factor of 9, whereas 6mph (a doubling of speed) would have a factor of 36 (4 times as much).

From 10mph (10x10=100) to 15mph (14x14=196) doubles the energy, as does 14mph (196) to 20mph (20x20=400).

(Hopefully a little more clearly represented, although much less rich in details, than LyB's post)

 

[Red Light]

I read this and I'm not sure I follow the sense. My apologies.

'The impact energy goes as the square of the speed' means little to me.

Any chance of clarification?

Does impact energy increase by the square of the difference in speed or is it equal to the square of the speed, or is there some other meaning?

The impact energy, which is what determines the severity of the impact, is given by half the mass of the object times its velocity multiplied by itself or "velocity squared". So if the velocity increases two fold, the impact energy goes up four fold; three time the velocity gives nine times the impact energy etc.

HTH

 

[growingvegetables]

Very simple - wear a helmet and cars pass you even closer. Not some sort of epidemiological epistomological analysis of eclectic statistics - just plain simple observed behaviour, here.

Me - I won't wear a helmet; I prefer the extra space. 8cm? Enough space to prevent/avoid an accident.

Others - well, if you prefer to take the increased risk of an accident, but trust to the helmet's protection? Fine by me - your call.

 

[david k]

Very simple - wear a helmet and cars pass you even closer. Not some sort of epidemiological epistomological analysis of eclectic statistics - just plain simple observed behaviour, here.

Me - I won't wear a helmet; I prefer the extra space. 8cm? Enough space to prevent/avoid an accident.

Others - well, if you prefer to take the increased risk of an accident, but trust to the helmet's protection? Fine by me - your call.

If reducing your width by 8cm is enough to prevent you having an accident you must only be leaving an 8cm gap between you and objects, you say this is safer than a helmet. I say 8cm isnt enough, so youd be btter off wearing a helmet and leaving a much larger gap. It would appear that removing your helmet is making you take increased risks

 

[Little yellow Brompton]

If reducing your width by 8cm is enough to prevent you having an accident you must only be leaving an 8cm gap between you and objects, you say this is safer than a helmet. I say 8cm isnt enough, so youd be btter off wearing a helmet and leaving a much larger gap. It would appear that removing your helmet is making you take increased risks

It's not him that is leaving wider gap it's the drivers passing the cyclist ( who wasn't him either) in the study.

With helmet X distance, without helmet X+ 8cm Distance.


I know you don't need facts to make a decision but others do, those others include the drivers around you. This (albeit) small study showed that wearing a helmet increases YOUR risk becuase of other's choices.

 

[david k]

It's not him that is leaving wider gap it's the drivers passing the cyclist ( who wasn't him either) in the study.

With helmet X distance, without helmet X+ 8cm Distance.


I know you don't need facts to make a decision but others do, those others include the drivers around you. This (albeit) small study showed that wearing a helmet increases YOUR risk becuase of other's choices.

if true i do not support changes in own behaviour because of others, if you do were will it end? the people whos habits are poor should be held accountable

 

[Red Light]

if true i do not support changes in own behaviour because of others, if you do were will it end? the people whos habits are poor should be held accountable

That's a big about turn. Since the vast majority of cyclist head injuries are caused in road accidents being hit by a motor vehicle with the driver at fault it would seem you don't support cyclists wearing helmets to protect against them. Drivers should be held accountable instead.

 

[Red Light]

It's not him that is leaving wider gap it's the drivers passing the cyclist ( who wasn't him either) in the study.

With helmet X distance, without helmet X+ 8cm Distance.


I know you don't need facts to make a decision but others do, those others include the drivers around you. This (albeit) small study showed that wearing a helmet increases YOUR risk becuase of other's choices.

More important than the 8cm difference was that 23% more motorists made passes with less than 1m clearance when the cyclist was wearing a helmet. Its not the ones giving you lots of room or reasonable room coming a bit closer that matter. Its the ones that come close that are going to hit or unsettle you and there are more of those when wearing a helmet.

 

[Little yellow Brompton]

if true i do not support changes in own behaviour because of others, if you do were will it end? the people whos habits are poor should be held accountable

You don't support changes in your behaviour because of others? Good we finally agree, there is no need to change your default behaviour and wear a helmet because of others, otherwise where will it end? The people who's habits are poor ( drivers) should be held accountable . What made you change your mind, or haven't you yet realised that you have?

 

[2Loose]

if true i do not support changes in own behaviour because of others, if you do were will it end? the people whos habits are poor should be held accountable

Errr, like wearing a helmet because of others behaviour? That statement would be great tagline for the anti-helmet brigade (if such a thing were to exist)