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TT Newb: Bumper Points Question


loftygoals

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I've been road racing in 944 Spec for a while, but this year I've built a mean little track car out of my 2002 BMW M Coupe. It has served it purpose in 2010, and now it's time to start planning the fun in it for 2011. I'm not ready to go W2W in this car, so I knew the place to have the most fun is NASA TT.

 

Thus, I'm beginning the daunting task of figuring out where my car falls and what changes I need to make it fit where I would like it.

 

So this year, I have gone through front bumpers like crazy. It seems they only last 1 event. Last event (an HPDE) I was going down a straight at 130mph with out another car around me when it sounds like my car was shot with a gun. After the session I discover a baseball size hole in the bumper cover. The event prior to that (a BMW CCA Club Race School) an M3 lost part of it's bumper which of course hit my bumper killing it. And the stories continue.

 

Thus, I have been looking for cheaper bumpers. I have discovered that the bumper cover for the Non-M version of my car is half the price. It also is easier to mount a splitter on, so I have been purchasing them.

 

Here's a picture of the standard OE Z3 M Coupe front end:

M_Coupe_Bumper.jpg

 

Here's a picture of the standard OE Z3 (non-M) Coupe front end:

Z3_Coupe_Bumper.jpg

 

So, my question is do I need to take 3 points for using the Non-M Bumper and 3 points for my splitter? My guess is "yes", but I wanted to make sure I couldn't use those points anywhere else.

 

-bj

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Oh, and here's a shot of my car lapping at Hallett:

my_car.jpg

 

 

If my front bumper aero setup is indeed 6 points, I could do something like this for just 3, right?

ex_splitter.jpg

 

The setup on the orange and blue car uses the stock M Coupe bumper but extended the vertical. Basically the bumpers with the splitters attached are functionally the same, except the second car extends the vertical a little lower.

 

-bj

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I see the orange/blue one as:

 

1) Add, replace, or modify front fascia or air dam +3

2) Add, replace or modify a single front splitter/spoiler/wing/foil +3

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I see the orange/blue one as:

2) Add, replace or modify a single front splitter/spoiler/wing/foil +3

 

I see this for sure.

 

1) Add, replace, or modify front fascia or air dam +3

 

Duh, I just reread the note on 2), "note: No material or part may extend the vertical reach of the OEM front fascia without taking fascia modification points above." I had read this the exactly opposite of what it says. I guess I've spent too much time the past few days staring at these rules.

 

So, I then believe both the setup on the orange & blue car and the setup on my car both costs 6 points--bummer--no points for me.

 

Man it is easy to rack up aero points on the front end: Bumper +3, Splitter +3, Canards +2 = +8 points for a little front downforce. That makes +4 for a rear wing seem like a bargain.

 

-bj

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You can do an air dam all the way down to the ground with the replaced fascia for free... it's included in the +3. I know it's different than a splitter, but it might be worth testing and may help you save 3 points...?

 

Patrick

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ANY "normal" splitter would net you 6 points regardless. There really is no point in having a splitter not stick out in front of the front bumper.

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ANY "normal" splitter would net you 6 points regardless. There really is no point in having a splitter not stick out in front of the front bumper.

Eric,

A "normal" splitter (only), will only net you 3 points. We have plenty of cars with no fascia mods or air dam mods, with a simple flat splitter (with flat bottom in front of the axles) that take only +3 points.

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ANY "normal" splitter would net you 6 points regardless. There really is no point in having a splitter not stick out in front of the front bumper.

Eric,

A "normal" splitter (only), will only net you 3 points. We have plenty of cars with no fascia mods or air dam mods, with a simple flat splitter (with flat bottom in front of the axles) that take only +3 points.

 

Greg, dont the majority of splitters extend past the front of the car? That is by definition what a splitter is. A simple flat piece under the bumper is more like an underpanel, rather than a splitter.

 

For the whole year I was running in TTB, I was removing my splitter because it sticks out in front of the bumper. Hard to see, but here is a picture:

 

IMG_2060.JPG

 

Please correct me if I am wrong.

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I think all splitters go forward from the front of the bumper, otherwise it would just be an undertray..no?

 

My point exactly, but the rules say:

 

(note: No material or part may extend the vertical reach of the OEM front fascia without taking fascia modification points above.)

 

Therefore, a "splitter" (by definition), would require the +6. An undertray would be +3. Which was what I was getting at, but Greg then said "normal" splitters run by people all the time dont carry fascia points.

 

ie. Greg is defining undertrays as "normal splitters", correct?

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I believe the "extend the vertical reach" part means that you need to take a top-down look at the OEM fascia - if the splitter doesn't extend past it, then you don't have to take fascia modification points - so the splitter alone is only 3 points.

 

Those pictures posted earlier in this thread show kind of part-airdam/splitter setup, and the splitter is far out from the body. For a different take look at a Miata... the furthest part of the bumper is very high, but at the bottom of the bumper it cuts back in towards the body. Here's a googled pic of a splitter that looks like it would only be +3: http://images.cardomain.com/member_images/11/web/287000-287999/287673_12_full.jpg - see how it's tucked under the front bumper all the way around?

 

Stated another way, if you were to push the front of your car against a wall, what would hit first, the OEM front bumper or the splitter? If it's the bumper, it's probably +3. If it's the splitter, it's definitely +6.

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so as long as the splitter is no lower than the OEM fascia (ala Eric's setup) then just the splitter points apply is what I'm reading. Been wrong before though

 

(as long as its also not too wide and does not have any non-parrallel to the ground parts as the rule states of course)

 

Usually you see some horizontal constraints - but I guess the width and the rear being on or ahead of the front axle centerline are the only ones in this case and it can go as far ahead as you want...?

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As per the rules, the splitter can only extend 5" front the bumper line. Also, the splitter can be where ever you want vertically (i.e. below the front bumper), it just has to be completely flat horizontally (if it's not, then it's also a canard). Of course, you probably want it pushed up right against the bumper for maximum effectiveness, but it doesn't strictly have to be.

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Ok, so here's what I understand.

 

A simple splitter (+3): It can not extend more than 5" beyond the front of the front most portion of the bumper (looking from the top down) and extend no further back than the center line of the front axle.

 

Bumper modification (+3): This includes replacement, and/or modification. An air dam (something that changes the vertical reach) is included in this.

 

My splitter is basic with no air dam, so that's only 3 points. I'm using a replacement bumper from a different model Z3, so I take 3 there. I can't use the stock bumper with a splitter w/o creating an air dam, thus no matter how I slice it, if I want a splitter I have to take 6 points.

 

-bj

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so Ive been taking my splitter off for no reason!? dang it.

 

I interpreted it as if the splitter stuck out past the vertical reach (ie. the very front) of the bumper then you add fascia points. But I can now also see the interpretation that the vertical reach means the actual height of the splitter creating an air dam.....

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I can't use the stock bumper with a splitter w/o creating an air dam, thus no matter how I slice it, if I want a splitter I have to take 6 points.

You can, it would just leave a gap and not be quite so effective. It sounds like you should either use all 6 or save all the points for something else. If you go with all 6, it might be worth seeing if you can drop the front fascia even more to better utilize the fascia points.

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so Ive been taking my splitter off for no reason!? dang it.

 

I interpreted it as if the splitter stuck out past the vertical reach (ie. the very front) of the bumper then you add fascia points. But I can now also see the interpretation that the vertical reach means the actual height of the splitter creating an air dam.....

It doesn't say extend past the vertical reach, it says extend the vertical reach.

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You can, it would just leave a gap and not be quite so effective.

 

You are correct. I could, but the splitter would be open right where the low pressure area is supposed to be, thus negating the effect.

 

It sounds like you should either use all 6 or save all the points for something else. If you go with all 6, it might be worth seeing if you can drop the front fascia even more to better utilize the fascia points.

 

The current splitter was setup for a series where I was worried about ground clearance. On a road course that is not as much of an issue, so I plan on lowering it some. Also, the entire car ride height needs to be dropped a full inch for road course use.

 

-bj

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Here's my +3 splitter. It's parallel with the ground, doesn't extend more than 5 inches from the furthest point of the OEM bumper and does not have an air dam. I have a little piece of angle aluminum, which is shorter than the OEM plastic piece, to support it against the stock bumper so it doesn't get pushed back.

 

1011517739_fxzzv-L.jpg

 

1011516353_BK3zZ-L.jpg

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Looks good, Rob. That recessed part of the bumper on the bottom gives you a lot of room for the splitter, I bet it works well!

 

If I can add something though, it looks to me like you are probably running your wing too steep. That's an APR GTC-300, right? It has a twisted chord and is designed to be located like you've got it, behind the cab of the car. I imagine you set the wing with the center section at what you thought was a reasonable angle of attack with respect to the ground plane. However, the air is hitting the center section at a different angle. Imagine it following the profile of your roof line in that second picture (it's not quite that steep when it hits the wing, somewhere in between that the ground plane). That makes the effective angle of attack much steeper than it appears at first glance.

 

The GTC-300 uses a highly cambered airfoil and makes plenty of downforce even at 0 or positive angles of attack. An easier way to set the wing is to look at the outer sections near the end plates (after the angle change). These should be seeing the free stream (parallel to the ground) coming around the side of the car.

 

Give it try on your next track day. I'd be willing to bet (since I've experienced it myself) that cranking that wing up will net you a lot more speed at the end of the straights without noticeably reducing your cornering speed!

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Looks good, Rob. That recessed part of the bumper on the bottom gives you a lot of room for the splitter, I bet it works well!

 

If I can add something though, it looks to me like you are probably running your wing too steep. That's an APR GTC-300, right? It has a twisted chord and is designed to be located like you've got it, behind the cab of the car. I imagine you set the wing with the center section at what you thought was a reasonable angle of attack with respect to the ground plane. However, the air is hitting the center section at a different angle. Imagine it following the profile of your roof line in that second picture (it's not quite that steep when it hits the wing, somewhere in between that the ground plane). That makes the effective angle of attack much steeper than it appears at first glance.

 

The GTC-300 uses a highly cambered airfoil and makes plenty of downforce even at 0 or positive angles of attack. An easier way to set the wing is to look at the outer sections near the end plates (after the angle change). These should be seeing the free stream (parallel to the ground) coming around the side of the car.

 

Give it try on your next track day. I'd be willing to bet (since I've experienced it myself) that cranking that wing up will net you a lot more speed at the end of the straights without noticeably reducing your cornering speed!

 

Correct - APR GTC-300.

 

Thanks for the info. I agree 100%. The angle of attack in the second photo is at the second lowest angle of attack setting. I still need to try the lowest setting....amongst many other things next year. My first outing this year was in July and I was breaking in my new motor. The only other event I made it to was Aug and I was trying different sway bar and shock settings while keeping the wing at the same position. Too many input changes is hard to manage.

 

On a separate note, I was bummed there weren't enough TTC cars at the Nationals to keep the class. It seems on the right side of the country there are quite a few so we need to gather the troops to have a good TTC showing at 2011 Nationals.

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so Ive been taking my splitter off for no reason!? dang it.

 

I interpreted it as if the splitter stuck out past the vertical reach (ie. the very front) of the bumper then you add fascia points. But I can now also see the interpretation that the vertical reach means the actual height of the splitter creating an air dam.....

It doesn't say extend past the vertical reach, it says extend the vertical reach.

 

DANGIT! So I was removing my splitter for no good reason!!!!!!! Thanks for the clarification

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