# What is that row of shark-fin shaped spiky things mounted on a car roof just at the top of the rear window? **URL:** \ **Category:** Factual Questions\ **Created:** [September 20, 2022, 4:00pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922 "2022-09-20T16:00:50Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 20, 2022, 4:00pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/1 "2022-09-20T16:00:50Z")
These are clearly aftermarket items. This is not one thing like the antenna, there is a whole row of them. I see them typically on compact imports that have other types of customizations (most of which seem pointless to me). [![](https://dl.dropboxusercontent.com/s/j183haq5mjdfjvm/car%20spiky%20things.jpg?dl=0) ](https://dl.dropboxusercontent.com/s/j183haq5mjdfjvm/car%20spiky%20things.jpg?dl=0) ---
**Author:** ![Sunny\_Daze](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunny_daze/32/438_2.png) [@Sunny\_Daze](https://boards.straightdope.com/u/Sunny_Daze)\ **Post date:** [September 20, 2022, 4:03pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/2 "2022-09-20T16:03:52Z")
It looks like bluetooth antenna. I don’t know why they need so many. ---
**Author:** ![E-DUB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/e-dub/32/403_2.png) [@E-DUB](https://boards.straightdope.com/u/E-DUB)\ **Post date:** [September 20, 2022, 4:06pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/3 "2022-09-20T16:06:21Z")
I was curious about them myself, only to discover that “shark-fin antenna” is what they’re actually called. ---
**Author:** ![Capn\_Carl](https://avatars.discourse-cdn.com/v4/letter/c/838e76/32.png) [@Capn\_Carl](https://boards.straightdope.com/u/Capn_Carl)\ **Post date:** [September 20, 2022, 4:16pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/4 "2022-09-20T16:16:42Z")
The center fin _might_ be an antenna. The rest are just ornamentation, being about as functional as that wing. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 20, 2022, 4:18pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/5 "2022-09-20T16:18:43Z")
Seriously? People think that actually improves the appearance of their car? I was thinking it was some aerodynamic shit to improve laminar flow which also would be as functional as the wing, but at least it would have a story. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 20, 2022, 4:19pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/6 "2022-09-20T16:19:35Z")
I believe the center one is the radio antenna. I don’t know why you would need a Bluetooth antenna on the exterior of a car. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [September 20, 2022, 4:19pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/7 "2022-09-20T16:19:54Z")
They are another version of “go faster” stripes. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [September 20, 2022, 4:20pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/8 "2022-09-20T16:20:15Z")
They keep the pigeons from perching and pooping on the rear window. ---
**Author:** ![Euphonious\_Polemic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/euphonious_polemic/32/3002_2.png) [@Euphonious\_Polemic](https://boards.straightdope.com/u/Euphonious_Polemic)\ **Post date:** [September 20, 2022, 4:26pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/9 "2022-09-20T16:26:56Z")
pidgin? ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [September 20, 2022, 4:29pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/10 "2022-09-20T16:29:11Z")
Thanks! Fixed it. ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [September 20, 2022, 4:31pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/11 "2022-09-20T16:31:33Z")
> [@Capn\_Carl](#): > > The center fin _might_ be an antenna. The rest are just ornamentation, being about as functional as that wing. Agreed, especially because the smaller ones aren’t evenly spaced, either. Aftermarket ornamentation, and poorly installed, at that. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 20, 2022, 4:32pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/12 "2022-09-20T16:32:34Z")
> [@CookingWithGas](#): > > I was thinking it was some aerodynamic shit to improve laminar flow which also would be as functional as the wing, but at least it would have a story. Before I saw the picture (i.e., when I read the thread title but before I opened it) I thought the OP was looking at [vortex generators](https://en.wikipedia.org/wiki/Vortex_generator); though how useful they’d be on a car, I don’t know. After seeing the picture, I think they’re just decorations as Capn\_Carl said. (Which reminds me… I need to get a [fake car phone antenna](https://www.amazon.com/Pilot-Automotive-Black-Antenna-AB123E/dp/B00AWYBD5A/) for my car. 😛 ) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 20, 2022, 5:08pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/13 "2022-09-20T17:08:54Z")
> [@Johnny\_L.A](#): > > Before I saw the picture (i.e., when I read the thread title but before I opened it) I thought the OP was looking at [vortex generators](https://en.wikipedia.org/wiki/Vortex_generator); though how useful they’d be on a car, I don’t know. > **[Do Vortex Generators Actually Help Road Cars?](https://www.motorbiscuit.com/do-vortex-generators-actually-help-road-cars/)** > > Car spoilers have a purpose besides being flashy accessories. Although they’re technically not wings, both they and spoilers use the air rushing around **TL,DR:** the claim is that they can delay/reduce boundary layer separation behind your car, similar to what vortex generators do on aircraft wings. This can improve fuel economy, and for high-performance sports cars, it can improve flow over the rear wing/spoiler, resulting in greater aerodynamic downforce - although both of these benefits are likely to be modest at road-legal speeds. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [September 20, 2022, 5:29pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/14 "2022-09-20T17:29:04Z")
Only [$9.37.](https://www.aliexpress.com/item/2251832627032950.html?gatewayAdapt=4itemAdapt) ---
**Author:** ![jjakucyk](https://avatars.discourse-cdn.com/v4/letter/j/3d9bf3/32.png) [@jjakucyk](https://boards.straightdope.com/u/jjakucyk)\ **Post date:** [September 20, 2022, 5:36pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/15 "2022-09-20T17:36:20Z")
Those shark-fin center antennas are for the satellite radio (Sirius, XM, etc.). The standard AM/FM radio antennas have mostly been moved to the rear window nowadays. They look like the strips on the defogger but they’re not actually connected with those. ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [September 20, 2022, 5:42pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/16 "2022-09-20T17:42:39Z")
Or speed holes [![](https://img.youtube.com/vi/whnms4CLJys/hqdefault.jpg "Speed Holes") ](https://www.youtube.com/watch?v=whnms4CLJys) ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [September 20, 2022, 6:29pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/17 "2022-09-20T18:29:12Z")
I’ve seen similar on semi tractor trucks, dozens of vortex generators up the rear of the cab. They’re apparently effective in that application. Explaination and photo at the bottom of the article (below the comically boxy truck): [https://spinoff.nasa.gov/Spinoff2008/t\_3.html](https://spinoff.nasa.gov/Spinoff2008/t_3.html) ---
**Author:** ![steronz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steronz/32/11765_2.png) [@steronz](https://boards.straightdope.com/u/steronz)\ **Post date:** [September 20, 2022, 6:43pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/18 "2022-09-20T18:43:41Z")
As pointed out in **Machine\_Elf** ’s link above, vortex generators as a _trend_ started out with the 2003 Mitsubishi Evo VIII MR. The Evo was a [homologation car](https://en.wikipedia.org/wiki/Homologation_(motorsport)), meaning Mitsubishi had to build a road car with all of the body work they wanted on their rally car. Furthermore, the rules restrict how high and far back a rear wing can be mounted. You want your wing to be mounted in “clean” air, which means high up away from the turbulence of the body itself, and far back in order to get more mechanical advantage. Both of those are restricted by the rules, so the rear wing had to be mounted too close to the rear window and too low to be as effective as Mitsubishi would have liked. In this configuration, the vortex generators help to delaminate airflow over the roof and make the air hitting the wing a little cleaner. I have no doubt that this had a measurable effect on that specific car. There’s no accounting for taste, and stick on vortex generators are both cheap and easy to install. Such is the case with the car pictured in the OP. I will say, while that wing probably isn’t functional, it at least _looks_ sorta like the Evo VIII wing. ---
**Author:** ![peccavi](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peccavi/32/388_2.png) [@peccavi](https://boards.straightdope.com/u/peccavi)\ **Post date:** [September 20, 2022, 10:14pm UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/19 "2022-09-20T22:14:02Z")
> [@CookingWithGas](#): > > Seriously? People think that actually improves the appearance of their car? This guy probably does… [![](https://menhairstylist.com/wp-content/uploads/2018/05/liberty-spikes-mohawk-haircut.jpg) ](https://menhairstylist.com/wp-content/uploads/2018/05/liberty-spikes-mohawk-haircut.jpg) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 21, 2022, 1:42am UTC](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922/20 "2022-09-21T01:42:59Z")
> [@CookingWithGas](#): > > Seriously? People think that actually improves the appearance of their car? People will add anything that looks like the features found on actual high-performance cars. Vortex generators, wings, spoilers, low profile tires, loud exhausts, racing seats, the list goes on and on. Of course, it helps if you position them more evenly than the owner of the car in the picture you posted in your OP. [Next page](https://boards.straightdope.com/t/what-is-that-row-of-shark-fin-shaped-spiky-things-mounted-on-a-car-roof-just-at-the-top-of-the-rear-window/971922.md?page=2)