[Closed] Cav and co's sealed helmets

aero advantage. At that level it all counts.

When somone was going for the hour record recently they worked out they would be measurably quicker without a helmet.

Presumably someone bald? You would think hair would cause turbulence and disrupt the clean air flow.

Hair is more aerodynamic than shaved... supposedly (could be pub science).

When somone was going for the hour record recently they worked out they would be measurably quicker without a helmet.

They've long known that, hence the fuss about riding with helmets in the pro peleton. Even more so when TT head fairings were banned and had to become proper 'helmets'.

aero advantage? in a race that long? If thats right why not wear them all the time in the Tour etc. And why not wear solid helmets?

Depends on heat really although a lot of Sky riders often ride the 'filled in' version of the Kask helmet (even in grand tours). Triathletes seemed to be the first to start wearing the Spesh shell which Cav was using - for him it's not aero during the entire race that matters as he's sheltered anyhow but the last 200 metres is important and he only won by half a wheel so every little bit helps...

I did wonder if they rode the whole race with them - in theory they could have swapped to the sealed vent ones with, say, an hour to go.

That said, I don't think it was all that warm in Copenhagen so the lack of vents would be less of an issue.

maybe just have a little lever ont he side of the helmet than can open/close the vents so they can climb with ventilation (when speed is slow) and descend/go on the flat with the vents shut for aero advantage.

Yep heat is going to be the main reason not to wear them all the time. Nearly all the riders started with arm warmers and what not, so it obviously wasn't that warm.

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wwaswas - Member
maybe just have a little lever ont he side of the helmet than can open/close the vents so they can climb with ventilation (when speed is slow) and descend/go on the flat with the vents shut for aero advantage

As used in ski helmets for ages. I would very much imagine that we will see such features on bike hemets in the not very distant future.

Weight?

TJ, my ski helmet, with slidy vents and nice warm lining/earmuffs (stop s****ing) isn't much heavier than my trail helmets.

It doesn't need to be heavy.

[i]Weight?[/i]

possibly although they all seem to use aero rimmed wheels that have a weight disadvantage that is outweighed (sic) by their aerodynamic benefits so it wouldn;t be too hard to do a weight/benefit analysis of a movable helmet vent system, I guess?

I meant the extra weight on a helmet as adding to its disadvantages. All other things being equal a helmet should be as light as possible. adding complexity must add weight

TJ, you really will do [i]anything [/i]to argue against helmet use won't you?

The weight of slidy vents in a helmet is very small indeed. When combined with a helmet as light as a Prevail, as worn by Cav, there's really no reason why they shouldn't be used more widely.

possibly although they all seem to use aero rimmed wheels that have a weight disadvantage that is outweighed (sic) by their aerodynamic benefits so it wouldn;t be too hard to do a weight/benefit analysis of a movable helmet vent system, I guess?

That's because bikes are under the weight limit anyway, so they may as well introduce other benefits. We didn't see any aero components used until the weight limit came in, and it would be interesting to see if their proliferation would remain if it was dropped.

Helmets are not bound by weight limits, and manufacturers continue to strive to make them lighter, I doubt you could add any 'moveable' vents without adding significant weight and complexity to the helmet. The snap on covers make far more sense, hand them out from a team car for riders to fit in the last 20k.

TJ, you really will do anything to argue [s]against helmet use[/s] won't you?

FTFY

I seem to recall that someone did some calcs on Laurent Fignon's ponytail and reckoned if he had cut it off, over the course of the Tour he would have saved more than the 8 seconds or whatever it was that he lost to Greg Lemond by!

Maybe in theory, but in practise!?!? I'm not convinced.

Njee, snap ons really do make sense for pro/supported riders, I would agree. Sliding vents for "normal" riders make a lot of sense too. As mentioned, the increased weight when the system is applied in ski helmets (Such as a Giro G10, for example) is negligible.

I meant the extra weight on a helmet as adding to its disadvantages. All other things being equal a helmet should be as light as possible. [b]A[/b]dding complexity must add weight[b].[/b]

1st. Punctuation needed correcting

2nd. They're looking for the fastest helmet, whether thats the lightest, the best ventilated, or most aero would depend on the rider, course and race surely? Hence as someone said, the use of aero wheels rather than something even lighter.

That's because bikes are under the weight limit anyway, so they may as well introduce other benefits. We didn't see any aero components used until the weight limit came in, and it would be interesting to see if their proliferation would remain if it was dropped.

A slider to open/close isn't a bad idea though, much more practical to use on races where cars don't have such easy access to the riders as at the World Champs (say at the top of an alpine climb before a descent), also much easier to sell to the public. My helmet already comes with a winter pad set the covers more of the holes but it's internal so no aero benefit. As long as the shell wasn't glued to the polystyrene structure all the way around a slider system between them should be simple to do and only and a few grams.

As long as the shell wasn't glued to the polystyrene structure all the way around a slider system between them should be simple to do and only and a few grams

As mentioned, go and look at ski helmets (notably Giro, Salomon and Smith)

Sliding vents for "normal" riders make a lot of sense too

[i]See, I thought the opposite, based on the 'rotating weight counts double' hypothesis there would be the most advantage to be gained building a heavy/stiff BB and chainstay in the frame and using the lightest wheels possible[/i]

As far as I am aware, the 'rotating weight counts double' thing is a bit of an old cycling wives tale. Essentially weight is weight whether it rotates or not; and any 'it's easier to accelerate' stuff is not really significant and is also cancelled out by the flywheel effect.

The only time I'd want my vents sealed up is when it's really cold and in those circumstances, I just use clingfilm. I don't find that the temperature fluctutes enough that I'd ever need to change it mid ride.

But then I'm not trying to win a rainbow jersey...

Skiing is quite different IMO - Cycling doesn't often get so cold as it can get when skiing.

See, I thought the opposite, based on the 'rotating weight counts double' hypothesis there would be the most advantage to be gained building a heavy/stiff BB and chainstay in the frame and using the lightest wheels possible?

I have to admit, I can't think of a single occasion when I've thought "I wish I had sliding vents on my helmet" - when purchasing I'd pick the one without every time. You're going to have to explain to me why they're such a huge advantage.

sometimes it's quite cold

[i]In summary, wheels account for almost 10% of the total power required to race your bike and the [b]dominant factor in wheel performance is aerodynamics[/b]. Wheel mass is a second order effect ([b]nearly 10 times less significant[/b]) and wheel inertia is a third order effect ([b]nearly 100 times less significant[/b]). The best wheels in terms of performance are the ones that are lightweight, aerodynamic, don’t rub brake pads and are strong enough to get you to the finish line. The problem with these high performance wheels, though, is that they sacrifice on the other two key variables important in wheel selection: durability and price. High performance wheels are neither durable nor cheap.[/i]
From: http://biketechreview.com/reviews/wheels/63-wheel-performance

As far as I am aware, the 'rotating weight counts double' thing is a bit of an old cycling wives tale. Essentially weight is weight whether it rotates or not; and any 'it's easier to accelerate' stuff is not really significant and is also cancelled out by the flywheel effect.

Not really - the maths actually says that it's exactly double (though that's at the outer edge of the tyre, it's reduces proportionally towards the axle centre. Of course the points you made about flywheel/accelerate stuff is sort of right but road racing is characterised by changes of pace. Do it often enough and it will make a difference at that sort of level which is why you won't always see them with aero wheels.

CFH - not arguing against helmet use - pointing out a possible area of conflict between its secondary functions - ( comfort and ventilation) and it primary functions - protection.

~The lighter a helmet is the less extra forces it generates in an accident - this is a part of the reason why we don't use motorcycle helmets on a bike. Helmet design is a compromise but any weight that does not add to the protection is unhelpful.

Cold, rain, going down a country lane with a sudden explosion in the amount of flies about are all times I would have closed the vents on my helmet if it were an option. Ofc it's not something that's essential but given helmet manufacturers seem to have pretty much reached the limit of low weight whilst still passing the standards tests the odd new feature makes sense. I'm still surprised bug nets aren't standard on any helmet over about £50, lack of them was enough to make me switch helmets this year

[i]Do it often enough and it will make a difference at that sort of level which is why you won't always see them with aero wheels.[/i]

I think it's more the case that even the aero advantages are actually pretty small in the grand scheme of things, they may make a few watts difference, but there are far more factors at play when winning bike races.

Actually if you watched the whole BBC coverage on Sunday as Chris B did his walk round and review of the course he talked about there being a bitterly cold wind blowing in off the baltic. So I suspect (and probably rightly) that the fairings were actually to reduce the cooling effect of modern top end helmets? Why not wear a buff/skull cap? Probably not cool enough for that and you don't actually want to cook or have something that will soak up sweat for a while and then start it running down your face. The faired helmets probably stop "ice cream" headache syndrome without over heating the head.

I think it's more the case that even the aero advantages are actually pretty small in the grand scheme of things, they may make a few watts difference

To quote the British Cycling mantra (which has apparently been quite successful...)

[url= http://www.teamsky.com/article/0,27290,17547_5792058,00.html ]"The aggregation of marginal gains,"[/url]

Cold, rain, going down a country lane with a sudden explosion in the amount of flies about are all times I would have closed the vents on my helmet if it were an option.

[i]if it's cold I just put on a buff/thermal underhelmet [/i]

and if the slidey helmet protector thing weighed less than either of those you'd get one instead?

Only if you were often having to make the change mid ride...

Agreed, you tend not be caught out by such conditions that would make me want to block my vents. Personally if it's really cold I'd rather have something covering my ears than just something blocking the air flow onto my head.

Not really - the maths actually says that it's exactly double (though that's at the outer edge of the tyre, it's reduces proportionally towards the axle centre.

Actually I realised the numbers are easy - to accelerate a 100g rim from stationary to 30mph costs 18J (KE = 1/2mv^2 - times 2 to account for the linear and rotational KE). So even if you're making a standing start acceleration like that once a minute, the wheel only has to save 0.3W in aero drag to be worth it!

if the slidey helmet protector thing weighed less than either of those you'd get one instead?

That's because bikes are under the weight limit anyway, so they may as well introduce other benefits. We didn't see any aero components used until the weight limit came in, and it would be interesting to see if their proliferation would remain if it was dropped.

I think we have only just seen the start of proper analysis being done for performance gains and trade offs rather than just using common beliefs.

For example with components/frame design it was all about lighter is better. But know is recognised that aero can be more important than a few 100 grams.

so, a clip on slidey vent for the winter months;

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problem solved 😉