Wheel Tethers – Just how dangerous is a flying F1 tyre anyway?

[Music] during the british grand prix kevin magnussen was heated into the barriers in what seemed like a fairly low energy accident nonetheless his wheel appeared to break loose from the chassis something we see a lot less of these days thanks to mandatory wheel tethers this particular incident was different to the daniel kavia accident which happened a few laps later in which his wheel hub stayed attached to the car but the rubber tyre was ripped loose wheel tethers cannot prevent that from happening wheel tethers are only designed to prevent uh lucille watch out for lucille i don't know so the wheel is attached to the wheel hub which is part of the suspension assembly which is attached to the chassis until the late 90s that was basically it so if the suspension broke in an accident or due to failure the part with the wheel attached could just go flying away from the car at extremely high speeds where it could hit another driver a spectator or one of the many circuit workers positioned close to the track two marshals were killed by flying tyres in 2000 and 2001 each as single wheel tethers failed to keep wheels fully attached sometimes it's kind of difficult to understand just how dangerous flying tyres can be so we need to quickly discuss momentum whether something hitting you does damage or not very much depends on its momentum momentum is an object's mass multiplied by its velocity both are important momentum is how an object transfers its kinetic energy to you when it collides with you a bus hitting you at just 10 kilometers an hour is going to do you more injury than a pillow flying at you at 100 kilometers an hour even though the pillow is going 10 times faster motorway speed even it weighs 10 000 times less and as momentum is mass times velocity the 10 times slower bus is hitting you with a thousand times more momentum and carrying a hundred times more kinetic energy a formula one tyre is about 10 kilograms in mass a bit less at the front and a bit more at the back but 10 is a nice round number to use it flies off a car and hits something at say 100 kilometers an hour which is not an absurd estimate as these cars can get over 300 kilometers an hour and that tire is carrying momentum of about 280 kilogram meters per second with a kinetic energy of about 4 000 joules now don't worry about all the units and stuff for now just remember 280 and about 4 000 is a sense of scale and i'm aware these are just numbers and it's very hard to convey in animation exactly what this momentum feels like how do i convey a sense of weight and impact [Music] this is just a four kilogram weight it's less than half the weight of an f1 tire and while most adult humans can lift it fairly easily it's as heavy as you know four bags of sugar and you wouldn't want it dropping on your bare foot if we drop it from about one meter off the ground we can do a simple calculation to work out that the dumbbell will hit the ground with about 18 kilogram meters per second of momentum and be carrying around 40 joules of kinetic energy [Music] now if you were lying on the ground and the weight fell on you could easily break a bone you know crack a rib or get some serious bruising and this weight falling a short distance has over 15 times less momentum and 96 times less kinetic energy than a formula one tie hitting something at 100k so what i'm saying is we really don't want these tyres flying all over the place which brings us back to wheel tethers wheel tethers were made mandatory in 1998 and are essentially a way of tying the wheel to the chassis so that even if the suspension breaks the wheel stays attached to the car instead of flinging off god knows where one end of the tether is connected to the wheel hub the the part of the car you screw the wheel onto the tether feeds through a suspension arm and is then attached to the survival cell at the car end the tether itself is kind of like a high-tech rope made of xylon fibers xylon is a very lightweight man-made fiber polymer which has a number of extreme characteristics such as its resistant to heat and uses a ballistic protection including in bulletproof vests and actually around the driver's cockpit to prevent penetration it also is extremely resistant to being stretched and most importantly for wheel tethering has an extraordinarily high tensile strength that is how much force can the xylon rope hold before it breaks the wheel tethers are just 110 square millimeters in area and yet can support over 70 kilonewtons of tensile force meaning a single wheel tether can suspend nine formula one cars without breaking and each wheel must have three tethers attached to it now this isn't to increase the overall tethering strength but to allow for redundancies back when we only had the one tether per tire pre-2011 we'd still quite frequently see wheels go flying as the xylon rope could break if cut or twisted by particular circumstances so in 2011 a second mandatory tether was added and in 2018 a third tether was required per tire each tether must be proven to function completely on its own the only reason for extra tethers is to allow for one or even two to fail and still keep the tyre attached to the car as such no more than two tethers can pass through the same suspension part and must be fastened at both ends completely independently of each other millimeters apart at least this way even if one attachment point fails or is damaged the other tethers will not be affected now you'll only really see the xylon if there's a tether failure as the tether is entirely inside other parts of the car and the xylon is kept inside and outer skin to protect it from damaging uv light now there are two important things tethers cannot do with respect to keeping the wheel and car connected the first is keeping the tyre attached to the wheel rim if there's a tyre failure or an accident that causes the tyre to detach from the rim and go flying there's no way to hang onto that tyre fortunately the rubber tyre by itself is much lighter and flexible on its own and less likely to cause damage the second thing the tether cannot do is prevent a wheel from detaching if it's improperly screwed onto the wheel hub mechanics with wheel guns will firmly connect the wheel to the hub and the hub is the tethered part of the car if the wheel nut is loose the wheel can detach from the hub and cannot be stopped it's for this reason that the fia are extremely strict about making sure cars do not leave the pit lane with an insecure wheel now so all of this makes magnuson's separated wheel at silverstone particularly rare and my guess is that the tethers were all broken by twisting and shearing as the right front suspension dug into the tyre barrier and the rest of the car twisted around that pivot point rather than a high energy collision it was more of a ripping tearing action at slower speeds and as such the tyre really didn't go anywhere who knows how many lives or injuries wheel tethers have saved over the years we've seen some truly high energy impacts over and over again and in almost every case all four wheels have remained tethered to the survival cell and kept from doing damage away from the car it's simple unseen innovations like this that keep f1 incredibly safe despite its high energies [Music] [Music] [Applause] [Music] okay it

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