Frs vs s2000

[fatoni]

Originally Posted by Dave-ROR

Really any actual downforce at speed is better than most cars. A lot of car companies use "reduce lift" in marketing materials because that's what their wings/etc do - reduce lift. They do not generate actual downforce though. Most cars generate lift at speed. The BRZ and FRS do IIRC.

why this isnt common knowledge is beyond me. when i look at the profile of a car, its profile is shaped remarkably similar to the wing of an airplane

[chrisl]

Originally Posted by Dave-ROR

Really any actual downforce at speed is better than most cars. A lot of car companies use "reduce lift" in marketing materials because that's what their wings/etc do - reduce lift. They do not generate actual downforce though. Most cars generate lift at speed. The BRZ and FRS do IIRC.

I don't see the two as mutually exclusive, honestly. A wing can "produce downforce", and if it is put onto a car that naturally (without the wing) has more lift than the amount of downforce the wing produces, of course it's going to still have lift (with the caveat thrown in there that you have to account for the aerodynamic interactions between the flow around the car and the wing). The wing is still making downforce though.

I will say, looking into the numbers a bit more because of this thread, a surprising number of very fast cars make lift - off the top of my head from the stuff I was reading earlier (if I'm remembering right), both the GT-R and the Ferrari 458 make a significant amount of front lift at speed, though both do make rear downforce. On the other hand, surprisingly, the Porsche 991 Carrera S is almost perfectly neutral at speed - no downforce, no lift. It just goes to show that it is very difficult to guess the aerodynamics of a car just by eyeballing it.

[fatoni]

Originally Posted by chrisl

I don't see the two as mutually exclusive, honestly. A wing can "produce downforce", and if it is put onto a car that naturally (without the wing) has more lift than the amount of downforce the wing produces, of course it's going to still have lift (with the caveat thrown in there that you have to account for the aerodynamic interactions between the flow around the car and the wing). The wing is still making downforce though.

I will say, looking into the numbers a bit more because of this thread, a surprising number of very fast cars make lift - off the top of my head from the stuff I was reading earlier (if I'm remembering right), both the GT-R and the Ferrari 458 make a significant amount of front lift at speed, though both do make rear downforce. On the other hand, surprisingly, the Porsche 991 Carrera S is almost perfectly neutral at speed - no downforce, no lift. It just goes to show that it is very difficult to guess the aerodynamics of a car just by eyeballing it.

the eye opener for me was when i realized the scion xb has a lower cd than the veyron.

[Dave-ROR]

Originally Posted by chrisl

I don't see the two as mutually exclusive, honestly. A wing can "produce downforce", and if it is put onto a car that naturally (without the wing) has more lift than the amount of downforce the wing produces, of course it's going to still have lift (with the caveat thrown in there that you have to account for the aerodynamic interactions between the flow around the car and the wing). The wing is still making downforce though.

I will say, looking into the numbers a bit more because of this thread, a surprising number of very fast cars make lift - off the top of my head from the stuff I was reading earlier (if I'm remembering right), both the GT-R and the Ferrari 458 make a significant amount of front lift at speed, though both do make rear downforce. On the other hand, surprisingly, the Porsche 991 Carrera S is almost perfectly neutral at speed - no downforce, no lift. It just goes to show that it is very difficult to guess the aerodynamics of a car just by eyeballing it.

For a car with a part that reduces lift, the part makes downforce, the car doesn't. This discussion has been about the S2K making downforce up front and massive lift in the rear so we are talking about the vehicle, not specific parts. My reply to you was regarding your comment that the S2K is not making any significant downforce up front when making ANY downforce IS significant in the OEM automotive world. It's fairly simple to put parts on that create downforce, it's not as simple to create a aerodynamic package for a road going vehicle that results in the vehicle as a whole generating downforce. Evidence of that can be seen with Mike's last post which shows that adding aggressive looking "aero" parts don't always work. Few of these parts are actually engineered for function over form and it's just a lucky guess to hit upon the right design without any wind tunnel/CFD testing/design.. and often those parts that work aren't what most people want on their daily driver.

[serialk11r]

Originally Posted by fatoni

why this isnt common knowledge is beyond me. when i look at the profile of a car, its profile is shaped remarkably similar to the wing of an airplane

Crap I had a nice response written but my internet connection blew up. A car is not wide enough for this to be a significant effect, not much of the airflow makes it over the roof. In fact the ground effect probably cancels it out (both are small).

It's more like most cars just don't have a lot of money spent on the aerodynamics, or certain design criteria mean they have compromised aerodynamics. Most cars aren't streamlined well, and those turbulent areas will often cause lift. In the case of the S2k, the trunk is too short to allow air coming from the roof to reattach, so the entire trunk and rear window sits inside a very low pressure area.

Another thing is tires, tires add massive amounts of drag and lift to all cars. Supercars usually have very well thought out aerodynamics on the body, but their massive tires will ruin it a bit.

[DylanFRS]

Originally Posted by gramicci101

That's why people swap in Toyota badges. Everyone knows Toyota has a proven racing history.

Yep! That is why I am leaving the Scion badges on, learn to drive the car with the handicap, then put on Toyota badges once I max out my skillz.

[chrisl]

Originally Posted by Dave-ROR

This discussion has been about the S2K making downforce up front and massive lift in the rear so we are talking about the vehicle, not specific parts. My reply to you was regarding your comment that the S2K is not making any significant downforce up front when making ANY downforce IS significant in the OEM automotive world. It's fairly simple to put parts on that create downforce, it's not as simple to create a aerodynamic package for a road going vehicle that results in the vehicle as a whole generating downforce.

I absolutely agree with this - even if the s2k makes no front downforce but is just neutral (no front lift either), that already puts it in a pretty limited group of cars, since the vast majority (even including some very fast, high end cars) make front lift at speed.

For anyone interested in the only data I've been able to find on this across a wide range of cars, if you either know German or are willing to put up with an autotranslated webpage, the supertests at sport auto (http://www.sportauto.de/supertests-978719.html) include aero data such as Cd and front and rear lift/downforce measured in a wind tunnel. It can be really interesting to look into the data. For example, according to their data, the 911 Turbo S makes more downforce (by quite a bit) than the GT3 - I never would have guessed that from looking at them.

[CSG Mike]

Originally Posted by fatoni

the eye opener for me was when i realized the scion xb has a lower cd than the veyron.

Cd or CdA?

[Boxer486]

Originally Posted by DylanFRS

Yep! That is why I am leaving the Scion badges on, learn to drive the car with the handicap, then put on Toyota badges once I max out my skillz.

Lol

[Boxer486]

Originally Posted by CSG Mike

Cd or CdA?

Cd and likely CdA. The Veyron is not very slippery, it's just a big brute. I believe the P1 is something around .31-.35 somewhere in there for obvious reasons. I love that the 86 can get the same Cd as a Prius and blow it out of the water with a diffuser (around 0.23ish).

[ZDan]

It is unusual for a "normal" car to make downforce up front. Even if the body of a car is totally neutral, producing no lift or drag or moments, there is effective lift at the front and effective downforce at the rear because of the offset between the Cp of the body and the ground plane (pure drag on the body makes a moment that is resolved as additional load on the rears and reduced load on the fronts).

The 240Z produced a TON more front lift than rear. Some guys tested a lot of aero mods on the Z in a wind tunnel a few years back, the best single thing that addressed front end lift on the car was when the hood released during a run!

[fatoni]

Originally Posted by CSG Mike

Cd or CdA?

the veyron has a cd of .35x and the xb has a cd of .32 if my memory serves me correctly.

[OrbitalEllipses]

Originally Posted by ZDan

It is unusual for a "normal" car to make downforce up front. Even if the body of a car is totally neutral, producing no lift or drag or moments, there is effective lift at the front and effective downforce at the rear because of the offset between the Cp of the body and the ground plane (pure drag on the body makes a moment that is resolved as additional load on the rears and reduced load on the fronts).

The 240Z produced a TON more front lift than rear. Some guys tested a lot of aero mods on the Z in a wind tunnel a few years back, the best single thing that addressed front end lift on the car was when the hood released during a run!

So that's why they all run without hoods...

[CSG Mike]

Originally Posted by fatoni

the veyron has a cd of .35x and the xb has a cd of .32 if my memory serves me correctly.

You'll find the CdA of the Veyron is smaller

Cd is only half of the equation.