Spoiler
 

Does the Toyota Yaris stock spoiler help or hinder aerodynamics?

Can you post a photo? I Googled the Yaris and if its the small subtle moulded spoiler with only a small deflection angle then I don't think it would increase drag very much, it is good for the air to leave the back of the car in a clean break at as close to horizontal as possible as it prevents it from wrapping round and causing lift (which is drag on a car) and allows it to flow smoothly for a bit longer after the car before becoming turbulent. If it can easily be removed then you could try some A-B-A testing. I think you would notice a small decrease in drag and rear stability but it wouldn't be drastic I don't think.

Do you mean this OE rear spoiler?
https://www.toyota.com/images/vehicle...spoiler_lg.jpg

And viewed from the rear:
https://www.factorywings.com/catalog/1835AYARIS2FS.jpg

I also found this aftermarket one:
https://www.customautotrim.com/spoilers/?a=img&id=2791

Presumably the same spoiler as above, from this angle it appears to be an anti-lift design:
https://www.customautotrim.com/bodyki...yaris-wing.jpg

And this is a nice, unobtrusive design for the Yaris sedan:
https://www.customautotrim.com/spoilers/?a=img&id=2992

And I also found several custom-fit wing designs for the Yaris sedan, but I didn't bother to post them since we all know they're drag monsters.
But as far as the hatchback goes, I'll chalk it up as yet another OE 'positive downforce' design on a two-box...seems to be a trend, hmmmmmmm.;)

lol those useles spoilers are all for looks. i dont see the point of paying $500-$1000 for a chunk of plastic on my roof/trunk.

A spoiler/wing is useless for actually creating downforce I think unless there are side walls on it, or else the air just slips off the sides. I was just wondering in terms of drag. And yes, I had that OEM hatchback spoiler in mind. Thanks :)

Not all the air, only at the very edges, the air will travel on a sort of path of least resistance so it is much easier for the air in the centre on the car to get deflected up slightly then all the way around to the side, it looks like a pretty subtle angle too so I wouldn't worry about it too much. I don't think I've ever seen a spoiler with a sidewall unless it was also supporting a suspended wing. One way to think of it is slightly more down force means you can take corners at slightly higher speeds which means less braking and acceleration (fuel). But again we are not talking in very noticeable changes I don't think.

Actually, those Yaris spoilers are less than $200 painted...not a bad deal imo.

if you like the looks of that thing, sure, i'm not sure what aftermarket spoilers go...and it will fit the car perfectly.

but if you want to get something for 200$ that will save gass... you could look at grillblocks, smooth bubcaps, underbody fairings, or delete the radio antenna and replace it with an interior one... or just use the 200$ on gas...or see if there are any other items on the option list that could save gas...

the only spoilers that are somewhat effective are the ones that prevent the airflow from going where you don't want it... mostely this has to do with bad car body design to begin with, like the beetle article on autospeed demonstrates for example.

the stock yaris has a 0.29 drag coefficient however... there's few cars that do better these days...

yea if ya liek it its your car and money so do what you want but if it were me id rather just save the $200, wait a year or 2 then take one off a car at a junkyard for $10:D its what ive done with my 95 truck, adding options that werent on it to begin with(i added cruise control for $10, fancy multi cigarette lighter kickpannel for $5, bucket seats with center console for less than $100)

ok rear spoilers on a FWD car are useless and all for looks:p

I agree with you to a point but I find your statement kinda broad...there's no Uncle Ben's instant r.i.c.e.:thumbdown: factor here because we're not talking about a 3ft high, double-decker DTM pedestal wing.
I've mentioned this in these forums before, but I'll pose this question to you...how do you explain the use of OE rear spoilers used exclusively on high FE, FWD vehicles?(eg:Honda Civic Hybrid, VW Jetta TDI, ect.)