Cal Club Autocross Forums

I'm new to autocross - been to a few BMW CCA events and have started coming to local SCCA events. I've noticed a handful of vehicles with rear spoilers having extremely sharp angles-of-attack; some 45 degrees and up. I spoke with someone about it at a CASOC practice about two months ago and they were telling me how at the speeds we get to in autocross (<60mph), it's all good. Taking the same car set-up at 100mph would probably give way too much downforce or turbulance in the rear.

I'm sorry for being a aerodynamics noob, but could others give me their opinion on this? It's kind of glam, but is something like the TVR Sagaris rear spoiler completely useless at all speeds or is it possible through wind-tunnel testing they found something that such a sharp angle could help with?

http://www.cartype.com/images/page/tvr- ... eartop.jpg" onclick="window.open(this.href);return false;

BTW, I think I realize that I could spend a couple of year developing driving skill in a way that would completely outperform slight aero-mods. That's a given and I will proceed. I'm addicted to practicing and learning F/R balance in turns - I'm just asking if such angles-of-attack, especially in the case of a spoiler only a couple of inches high, can have any justification at all.

Thanks for any input,
Roy

That's some car!

There is of course a big difference between wings and air dams ... I'll let the experts chime in on that.

Just curious as a fellow Newbie, what class are you looking to run?
I plan to run stock, so I really have no options here.

long story short, the rules dictate that they run at high angles because they're lot allowed to hang off over the back of the car.

Marshall Grice wrote:long story short, the rules dictate that they run at high angles because they're lot allowed to hang off over the back of the car.

In most classes. Can't extend beyond the bodywork. There are odd exceptions, like splitters in some classes [STS] but not others [SP]. Although that might have changed recently; haven't given the ST rules so much as a glance recently.

Screw downforce, I want straightening force yo! haha

The question is ... why isn't the Berrymobile sporting a wing?

Mako Koiwai wrote:The question is ... why isn't the Berrymobile sporting a wing?

I think we all know that aerodynamic devices have no effect at solo speeds. ;)

Mako Koiwai wrote:The question is ... why isn't the Berrymobile sporting a wing?

Tom doesn't pay Marshall enough consultation fees.

Mako Koiwai wrote:The question is ... why isn't the Berrymobile sporting a wing?

Aftermarket wings aren't legal in SP? Factory wing is just drag-inducing anchor?

Mako Koiwai wrote:That's some car!

There is of course a big difference between wings and air dams ... I'll let the experts chime in on that.

Those are exactly the kind of wings I was seeing ... and wondering if the difference could be felt under 60mph. On the flip side, wouldn't they stall out and create turbulence on a car going 120mph on a road course. Guess the answer to the latter is different set-up for different conditions, but I'd never seen such high angles on wings as in autocross.


Roy

Blanco .. wrote:Just curious as a fellow Newbie, what class are you looking to run?
I plan to run stock, so I really have no options here.

I run SM. Mainly because my car had non-stock turbo modifications before I learned about and got interested in SCCA. At this point, I kind of feel I could pick up control faster in an unmodified car - but, at the same time, I want to learn the car I drive and straight-line performance on on-ramps and the like is just too much fun. The 335i w/o an LSD and all its weight is not a truly competitive car in this class - but I'm just trying to learn to drive it better and autocross has been really fun and the people really supportive. If/when I start feeling good enough to compete, I'd have to put the car back to stock or sink several grand into it.

Roy

Bob Beamesderfer wrote:

Marshall Grice wrote:long story short, the rules dictate that they run at high angles because they're lot allowed to hang off over the back of the car.

In most classes. Can't extend beyond the bodywork. There are odd exceptions, like splitters in some classes [STS] but not others [SP]. Although that might have changed recently; haven't given the ST rules so much as a glance recently.

That's what I'd heard. I'm not sure what applies to SM - just getting started, but my trunk ends a few inches before my bumper and I've heard throwing something in between at a high angle could be legal in most classes.


Roy

Marshall Grice wrote:

Mako Koiwai wrote:The question is ... why isn't the Berrymobile sporting a wing?

I think we all know that aerodynamic devices have no effect at solo speeds. ;)

That was my true understanding of it. That basically, under 80mph, you aren't getting much. I certainly have no study or experience in it, but I've heard it from people running IMSA teams back in the 80's. Then again, CFD packages and wind tunnel usage has gone up since then, but these people were talking from some experience...

Also, I wouldn't want to implement something that totally drove aerodynamics wacky at say 120mph. Maybe you have to choose your poison.


Roy

Roy Butler wrote:

Marshall Grice wrote:

Mako Koiwai wrote:The question is ... why isn't the Berrymobile sporting a wing?

I think we all know that aerodynamic devices have no effect at solo speeds. ;)

That was my true understanding of it. That basically, under 80mph, you aren't getting much. I certainly have no study or experience in it, but I've heard it from people running IMSA teams back in the 80's. Then again, CFD packages and wind tunnel usage has gone up since then, but these people were talking from some experience...

Also, I wouldn't want to implement something that totally drove aerodynamics wacky at say 120mph. Maybe you have to choose your poison.


Roy

Well, stick your hand out the window at 45 and turn your palm forward. No effect? The rear wing on the Boxster/Cayman S is programmed to rise at about 75 mph, but stays up until you drop below 60, I think. It's not very big and the angle is nearly flat, but it does what the engineers wanted it too. So, yes, CFD and wind tunnel work have advanced aerodynamics a lot.

Same for the little tab on the original Audi TT ... added after the prototypes showed instability

Just seeing that steep angle in pictures of the TVR Sagaris' stock wing I listed made me think "Are they crazy?" or else figured they found something in testing where it helps with their specific body shape that's hard to intuitively understand...

Track reports from magazine reporters on that car say it handles awesome. In fact, I think TVRs leave traction control off the list of options. It's definitely fun to drive in video games.

I guess the only way to know would be to put some kind of body height or spring compression measurement on such a car at varying speeds.


Roy

My understanding of the theory behind wings in Solo is that it allows you to tune the car loose for the slow stuff, and in the higher speed (>45mph) sections, the rear wing plants the rear end. I imagine the AWD on the Evo adds some stability, similar to what you would get with the rear wing. And SP only allows spoilers, which aren't as effective as the big wings.

I was talking with Bob Tunnell in 2005, as he had added the big wing to his M3 in SM, and he said that he really didn't want it to work, as he didn't like the look, but in testing they were significantly faster (1-1.5 seconds on a typical 60 second course) with the rear wing added and the set-up tuned to that versus no wing and a tighter set-up, or the same set up without wing. The tight set-up was more stable in the fast sections, but gave the car major push in the slower turns, while the loose set up worked in the slow stuff, but was a handful in faster parts of the course.

David Avard wrote:My understanding of the theory behind wings in Solo is that it allows you to tune the car loose for the slow stuff, and in the higher speed (>45mph) sections, the rear wing plants the rear end. I imagine the AWD on the Evo adds some stability, similar to what you would get with the rear wing. And SP only allows spoilers, which aren't as effective as the big wings.

I was talking with Bob Tunnell in 2005, as he had added the big wing to his M3 in SM, and he said that he really didn't want it to work, as he didn't like the look, but in testing they were significantly faster (1-1.5 seconds on a typical 60 second course) with the rear wing added and the set-up tuned to that versus no wing and a tighter set-up, or the same set up without wing. The tight set-up was more stable in the fast sections, but gave the car major push in the slower turns, while the loose set up worked in the slow stuff, but was a handful in faster parts of the course.

Thanks for the detailed info - when someone doesn't really want something to work, good results are really meaningful. By "big wing", I take it the width of the car, 10 or so inches deep, <20 degree angle, and near the height of the roofline, right?

David Avard wrote:I was talking with Bob Tunnell in 2005, as he had added the big wing to his M3 in SM, and he said that he really didn't want it to work, as he didn't like the look, but in testing they were significantly faster (1-1.5 seconds on a typical 60 second course) .

I'd never want to call Tunnell wrong as he has the creds...but as a mechanical engineer who's done some L/D and CdA work on bombs, missiles and such, I was pretty much convinced aero was for AMods only...maybe an occasional BMod if they had really good skirts and diffusers. Above 60mph it becomes more worthwhile, but most of us don't spend much time above that speed. I can tell you for sure that a BIG YAC wing on my Lola mostly sucked, although it did provide shade while waiting to run. It's a good technical design, but multi-elements are better, and maybe with more power...

For most cars it's eye candy.

-- Bill

Bill Martin wrote:

David Avard wrote:I was talking with Bob Tunnell in 2005, as he had added the big wing to his M3 in SM, and he said that he really didn't want it to work, as he didn't like the look, but in testing they were significantly faster (1-1.5 seconds on a typical 60 second course) .

I'd never want to call Tunnell wrong as he has the creds...but as a mechanical engineer who's done some L/D and CdA work on bombs, missiles and such, I was pretty much convinced aero was for AMods only...maybe an occasional BMod if they had really good skirts and diffusers. Above 60mph it becomes more worthwhile, but most of us don't spend much time above that speed. I can tell you for sure that a BIG YAC wing on my Lola mostly sucked, although it did provide shade while waiting to run. It's a good technical design, but multi-elements are better, and maybe with more power...

For most cars it's eye candy.

-- Bill

You're thinking we want them for downforce... making drag is way easier.

Aaron Goldsmith wrote: You're thinking we want them for downforce... making drag is way easier.

if you guy's are just trying to add drag, i'll bring some plywood and a nail gun so you can quit woosin around with the fancy wing thing

Chuck Fowler wrote:

Aaron Goldsmith wrote: You're thinking we want them for downforce... making drag is way easier.

if you guy's are just trying to add drag, i'll bring some plywood and a nail gun so you can quit woosin around with the fancy wing thing

Bryan did the calcs on plywood, it would work work just as well but be damn ugly and illegal for our car in our class.

Aaron Goldsmith wrote:

Chuck Fowler wrote:

Aaron Goldsmith wrote: You're thinking we want them for downforce... making drag is way easier.

if you guy's are just trying to add drag, i'll bring some plywood and a nail gun so you can quit woosin around with the fancy wing thing

Bryan did the calcs on plywood, it would work work just as well but be damn ugly and illegal for our car in our class.

http://www.arcspace.com/books/Bent_Ply/ ... _book.html plywood's fantastic, i figure you need about 400lbs for you new aero device

Chuck Fowler wrote:

Aaron Goldsmith wrote:
Bryan did the calcs on plywood, it would work work just as well but be damn ugly and illegal for our car in our class.

http://www.arcspace.com/books/Bent_Ply/ ... _book.html plywood's fantastic, i figure you need about 400lbs for you new aero device

Why do you think we have 2 eames lounge chairs in teh living room? ;)