Caution with rear spoiler

[outnumbered]

Just wanted to pass along a bit of information that I got from Jon B in regards to the rear spoiler that I installed. Admittedly, I installed the TA spoiler on my GTS purely for aesthetic reasons. I had no real desire to install the other half of the aero package, which were the front splitters. The problem is that SRT designed them to work together, and one without the other can be dangerous.

Apparently, the rear spoiler exerts around 400lbs of force on the rear of the car at 120mph. This in turn creates a certain amount of lift on the front end. The splitters were designed to redirect the airflow at higher speeds; consequently keeping the front end down, and ensuring the tires are making full contact with the road.

Jon explained to me that even though I had lowered the car with the Tomball domes (which was good) driving the car without the splitters could still be very dangerous at high speeds; especially if I was on a road course making a high speed turn. The likelihood of me tracking the car is slim. However runs at the drag strip are likely, as well as an occasional country road punch, which leads me to my recent experience. During one of these back road sprints the other night, I topped second gear and shifted to third. Several seconds after the shift, I felt the nose of the car begin to drift to the left. Immediately, I thought of what Jon said, and rather than go with my instinct of turning the wheel to correct my direction, I let off the throttle, and lightly touched the brakes. The car settled down, and fortunately all was well. To say that I got scared at that moment is an understatement.

I can't be certain that my car was doing what Jon described, but I have been driving for 30 years, and I have never felt anything like that before. The splitters will definitely be on prior to any trips to the drag strip.

[Dajerseyviper]

The funny thing about aerodynamic parts is, they are designed to actually work...why you start messing with the stock aerodynamics of a car like the viper you had better know what you are doing..

[dethred]

I'm not very knowledgeable about these things, but I assume having the opposite scenario (increased front down-force only) would at least be safer in a straight line? I'm sure around a corner it'd be at least as dangerous due to increased likelihood of oversteer? Be safe out there!

[Voice of Reason]

I doubt the car drifting to the left was caused by the rear aero wing. I had only the rear wing installed on my 13 Track Pack and I ran it up to 170 on a road in Mexico and it was stable as can be. On a road course *maybe* I'd feel a difference on a high speed corner, but I don't think I'm brave enough to take corners anywhere near fast enough to really experience the aero difference.

Think of it this way - if rear only spoilers were really that dangerous then there would be daily reports of kids in civics dieing in fiery crashes at 90 mph, approximately the speed you were at during your 2-3 shift.

Wayne Rauh also has the giant wing on one of his Vipers with no front aero. With that big thing he'd be heading for the ditch at the top of first but he somehow manages ok.

[TrackAire]

outnumbered,

I'm glad you didn't have an incident and were able to pull your car back in.

Regarding the aero, I will say this. I am not an expert at aero, an aero engineer or work in fluid dynamics, etc. But, I have put a lot of study into this, spoken to people that work directly for race teams such as NASCAR, specifically on aerodynamics to get their opinions and knowledge.

My opinion is unless SRT shows wind tunnel data or at least some computational data showing 400 lbs of physical down force, I don't believe it. Please notice I said "physical down force" meaning if you could put some sort of scale under your tires while going 120 mph, the rear axle weight would go up by 400 lbs.

The 400 lb number may be more relevant when taking into account the anti lift properties of the rear spoiler. The faster you go, the more the air tries to lift the car off the ground. Aero can counter act this and although it may produce some physical down force (your windshield is probably the biggest physical down force generator on your car), my opinion is that 400 lb number is a total of down force and anti lift combined, with the anti lift number being over 60% of the value.

I think the feeling you felt on the country road that night is a combination of cool temps, lots of hp, the engine hitting 5000 plus rpm's and the rear tires hunting for traction.

Cheers,
Geoge

[triblk6spd]

Shit. There goes my idea of just running the front winglets. :(

[viper04]

Interesting! I know Ralph Gilles did run his white 13 GTS (storm) with only the rear spoiler. Is it safe?? I have no idea. Here is a video with it.
https://www.youtube.com/watch?v=EK0CcPV77BY

[outnumbered]

outnumbered,

I'm glad you didn't have an incident and were able to pull your car back in.

Regarding the aero, I will say this. I am not an expert at aero, an aero engineer or work in fluid dynamics, etc. But, I have put a lot of study into this, spoken to people that work directly for race teams such as NASCAR, specifically on aerodynamics to get their opinions and knowledge.

My opinion is unless SRT shows wind tunnel data or at least some computational data showing 400 lbs of physical down force, I don't believe it. Please notice I said "physical down force" meaning if you could put some sort of scale under your tires while going 120 mph, the rear axle weight would go up by 400 lbs.

The 400 lb number may be more relevant when taking into account the anti lift properties of the rear spoiler. The faster you go, the more the air tries to lift the car off the ground. Aero can counter act this and although it may produce some physical down force (your windshield is probably the biggest physical down force generator on your car), my opinion is that 400 lb number is a total of down force and anti lift combined, with the anti lift number being over 60% of the value.

I think the feeling you felt on the country road that night is a combination of cool temps, lots of hp, the engine hitting 5000 plus rpm's and the rear tires hunting for traction.

Cheers,
Geoge

Thanks for the insight. Uneven pavement (back country road) could have also been a factor. However, for me at the time, it was just all too coincidental. At the end of the day, it could have been my inexperience with the car, along with all the factors you mentioned. But like I said, it was a unique feel; one that I hope not to duplicate. The fact that the car demands respect was just reiterated.

[SSGNRDZ_28]

Some general comments....

I don't think the spoiler will "remove" downforce at the front, rather add at the rear and therefore shift the aero balance rearward.

Aero balance can be critical, especially for oval racing. At Indy tents of a percentage of balance shift can mean a car in the wall. This said I've witnessed drivers lose half a front wing on a street course and set their fastest lap times. And this is after spending millions on aero efforts.

Unless taking high speed turns I'm not sure you'll be in danger. If you were the rearward balance should cause under steer which in theory is "safer" than oversteer.

All of this said, sticking with the OEM designed layout is probably the safest bet, however how "unsafe" just adding a wing is hard to quantify. Maybe remove the grilles in the hood vents to gain back some of that forward balance.

[XSnake]

Adding just the TA rear wing will cause a little bit of understeer on the front which you'd probably only notice on track on a high speed corner. I wouldn't worry about it on the street.

[SADVIPER]

Intresting, been poundering that rear spoiler lately!

[JonB ~ PartsRack]

As Outnumbered mentioned, my concern is with aero balance at "High Speed Cornering" which when we chatted was mentioned at 120-160 mph+ Fast sweepers can have a reduced front contact patch, especially with an OE alignment. The front end can 'skate' instead of turn.

Trackaire is correct, that 'downforce is not the same as reduced lift' but the net effect is the same. The OP lowered his car, minimizing both aero-lift and drag. In our chat I also mentioned 'crosswind components' which could have been a factor in his queasy moment.

trivia:

Does anyone remember the cosmetic bat-wing spoiler of the 1996 Carroll Shelby Special Edition? If that aftermarket unit was mounted too far rearward it would scoop the air under it! If you forgot to latch your trunk, it would lift the trunklid up at about 50 mph ! Conversely, the Mopar spoiler of that era would push down noticeably. I actually did a rudimentary aero test by putting hotel room pillows in the trunk until it was about 2" up off the latch. At about 70 mph the trunk latched itself ! Gen 1 cars with the Mopar deck spoiler were very prone to 'skating' understeer at 140+ mph due to the crappy aero properties of Gen 1, and no good options other than lowering springs.

[FSTENUF]

88068807

i went with this. A little on the front and a little on the rear. Had the car to 160+ on the street straight line no issue.

[venum4u]

I currently have the rear spoiler installed minus the front splitters. However i am considering going with the canards just as FSTENUF did.

[Dman]

I currently have the rear spoiler installed minus the front splitters. However i am considering going with the canards just as FSTENUF did.

I much prefer the canards as well and may go that route.

[ViperSmith]

how do the canards install?

[JTS VENOM PERFORMANCE]

your front splitters are ordered outnumbered, this way you can hang with helen

[FSTENUF]

Pull the front clip. Line them both up they only fit one way and in one spot. Drill 4 holes and bolt them on. Total time from start to finish less then 2 hours.

[FSTENUF]

the front splitter will drag in and out of my driveway. so this was the best op for me.

[Dman]

the front splitter will drag in and out of my driveway. so this was the best op for me.

Yea, that's a major reason for my interest, clearance for the street, driveway and my lift .. and they look uber cool and the functional thing too.

[SADVIPER]

88068807

i went with this. A little on the front and a little on the rear. Had the car to 160+ on the street straight line no issue.

I'd like the same thing, do you have the part number and installation method?

[Dman]

Hmm, can we get a group buy going on canards???

[JTS VENOM PERFORMANCE]

Hmm, can we get a group buy going on canards???

get with Jon b on that sir

[steve911]

Interesting! I know Ralph Gilles did run his white 13 GTS (storm) with only the rear spoiler. Is it safe?? I have no idea. Here is a video with it.
https://www.youtube.com/watch?v=EK0CcPV77BY

I've spent several days with Ralph trackside in and around his Gen V. I can tell you that car is as planted at 130 as my Full aero modded Gen 3.

I wouldn't have a concern in the world wet or dry...

[JTS VENOM PERFORMANCE]

the canards from xtreme will be here tomorrow, im sure he will be here tomorrow night for an install