Chassis changes for topless wing and spoiler addition.

[rick james]

Have a series coming to town where you can remove the top, run a 12" wing from behind drivers compartment to spoiler, 12"spoiler, and a 4" wing the length of nose ear on left hand side. What kind of chassis adjustments would need to be made to accommodate for these changes?

[Len72P]

take the roof off makes the car tighter, would imagine putting a wing of any sort behind driver would add downforce for lots of tight. Sounds wild.

[rick james]

Looking foward to trying it. Was thinking of lowering j bar on frame or adding more stagger. Does a person need to stiffen left rear spring to accommodate the additional left rear load from wing?

[TheJet-09]

I wouldn't make any chassis adjustments. I just don't think with those few additions (and the removal of the roof) that it should warrant a different set-up. But I obviously could be wrong.

I know in doing some Run Watcha' Brung stuff in the past, some guys would add gear but that was with a sprint car wing on top. And I'm not trying to put a damper on your fun, trust me, but I wouldn't want to see someone increase their workload in anticipation of something, only to have to undo what they did.

[MasterSbilt_Racer]

I ran a race with no roof and 12" spoiler on a swingarm car in the 90s. My car pushed like a dump truck.

[TheJet-09]

The thing I don't get (and I am not arguing, I'm laughing as I type this, but serious) is sitting in the shop, you can manipulate most pieces on a racecar's body pretty good by hand (sail panels, spoiler, rear deck). But you look at pictures of cars at speed and they appear "unfazed" by the air going by. Why is that?

Would anyone be willing to stand on their rear deck? I wouldn't, it'd cave right in. So I guess my questions is: How much "air" is needed for there to be any difference in handling?

I could see if we're running at Talladega (the big one, not the dirt track), but on the average short track? I guess if nothing else I'd want to see more, like size of track, speeds, etc., before I would go adjusting on my car just because I took the roof off. But all things are relevant, so I get it in the grand scheme...

[Matt49]

If you stand on the deck you will cave it in because you are concentrating all of the weight of your body on a small surface area (your feet) and the PSI will be large in those points and fold it up like a cheap tent. Air pressure over the body of the car will distribute itself and the PSI at any given point will be far less but the TOTAL pressure on the body will be quite high.
And it isn't all about high pressure over the top. It's also about low pressure underneath. Which is why sealing the nose to the track becomes so important...along with allowing what air IS under the car to evacuate as quickly as possible...but that is a different story.
Think about it this way. Cut out a piece of plywood the size of the hood fill area behind your nose (roughly 3 feet by 5 feet?). Measure the angle that is at on your car and talk a buddy into standing in the bed of a moving pick up truck and trying to hold that up (at that angle) from both ends while moving down the road at...say...40 MPH. When you get out of the hospital, tell me what you think about downforce :-)
Heck, we've all held our hand out of the window of a moving car and swirled it around and think of what a small surface area that is.
Air matters and it matters even on small tracks.

[MasterSbilt_Racer]

I have removed roof and increased spoiler to 12" and also removed spoiler completely at the same little 1/4 mile bullring. In both cases, the change was quite noticeable.

[TheJet-09]

Okay, I definitely like the example/s and agree.

And in argument of myself, I know you're both aware of how Mastersbilt front bumpers use a sort of a "hinged" bar to support the filler panel (the old one's I guess). I'll admit I have to support that bar to prevent it from falling back no matter how hard I tighten the bolts (they're only 1/4" anyway), and even then, it'll put a bend in the filler panel from the air coming over it.

In the end, I guess I'm so simple minded that I can't really see the effects because you can't "touch" them so to speak, unlike feeling a different spring rate by hand, or seeing the difference in a bar angle or something.

[billetbirdcage]

Have a series coming to town where you can remove the top, run a 12" wing from behind drivers compartment to spoiler, 12"spoiler, and a 4" wing the length of nose ear on left hand side. What kind of chassis adjustments would need to be made to accommodate for these changes?

Generally speaking, you're going to get an overall tightening effect on the car. The biggest problem is you can generally run the car very hard into the corner and drive way more sideways and use the side boards to catch the car from going into a 4 wheel drift, so having a car that can drive in with high speed and be able to turn in under throttle is usually a must. You will likely drive more sideways and use the throttle to drive the car around the corner. Increase your stagger and/or roll steer some and see where your at as it will vary depending on speed of track and track shape a lot.

Least have ready some tires for double your normal stagger as a quick adjustment if needed and then have some general idea's on loosening the car.

Good luck

[rick james]

If adding rear steer to car which way would be preferred. Raising left lower 4 link on chassis, lengthening right hand bars, or some other way?

Thanks for the help

[AmickRacing]

I ran with no roof several years ago, I just went down with my baseline setup and adjusted from there. This was on a 1/2 mile track, fairly fast. I can't say I noticed a huge difference, but it was a bit tighter.

I wouldn't make major changes to the car, maybe just go to a "free" baseline setup.

On the note of the body flapping and wiggling around, it's true that some of the cars have plenty of wiggle room to flop around. But, I'd be willing to bet the good bodies don't wiggle and move much at all (unless it's in an intended way, like the right door kind of cupping in).

I know my bodies aren't the best by any means, but I did watch a kid walk up the nose, across the hood and sat on the front of my roof. The tin didn't move much at all, granted he wasn't heavy... and his parents were mortified lol.
End of the season, I told em he couldn't possibly do more damage to the car than I have lol

[Matt49]

Okay, I definitely like the example/s and agree.

And in argument of myself, I know you're both aware of how Mastersbilt front bumpers use a sort of a "hinged" bar to support the filler panel (the old one's I guess). I'll admit I have to support that bar to prevent it from falling back no matter how hard I tighten the bolts (they're only 1/4" anyway), and even then, it'll put a bend in the filler panel from the air coming over it.

In the end, I guess I'm so simple minded that I can't really see the effects because you can't "touch" them so to speak, unlike feeling a different spring rate by hand, or seeing the difference in a bar angle or something.

You're exactly right. Aero is hard to wrap one's mind around simply because it can't always be visualized. There is a reason why it is referred to as "dark art". I'm no expert but one thing that has helped me with understanding it all is to think in terms of air pressure instead of force. Even though air pressure is a type of force, it helps me to narrow it down to this since it isn't the mechanical type of force we are used to like springs, weight transfer, thrust angles, etc.
Then you get into things like understanding how boundary layers work and it all starts making a little more sense. Air is really a fluid just like water or oil but with a much lower viscosity. And, yes, some air "sticks" to the body of the car. Fun stuff.

[TheJet-09]

^^^ And as I've heard it said, "Air is free, so grab all of it you can."

I just always picture those races where a guys car is torn to shreds, but he still wins (thinking aero doesn't mean that much). But I also don't think you see that much anymore.

Good stuff all the way around!

[billetbirdcage]

If adding rear steer to car which way would be preferred. Raising left lower 4 link on chassis, lengthening right hand bars, or some other way?

Thanks for the help

Sorry if I made it sound like it will be a night and day difference. Removing the roof to me in the past (before the modern day wedges) wasn't much of a change, just enough to maybe notice it on a slow to medium speed track. If I understand what you wrote, you're allow a 12" spoiler over the std 8" and the 4" panel on the LF along the bat-wing and a 12" tall spoiler side board on the LR that can extend up to the drivers seat. I'd say it will make a fair difference but not enough to completely change the set up, just likely need to free up the car some. Again some of this will depend on track and if your in an open motor car or some limited engine deal.

If your on a limited engine deal and are already snug when the track has traction, then it will be more noticeable then if your running with an good open engine where you can get the needed 20% or so of wheel spin to keep the car turning. The big spoiler and side board will put an "S" on you chest as far as entry and it's easy to under drive the car into the corner and get a push.

Adjustments: either one of those idea's are a viable option but without knowing particulars, I'm guessing in the dark. Just keep in mind you may be in the throttle a lot more or longer getting into the corner instead of a coast scenario that can effect your adjustments.

[dirtrace09]

You can use Bernoulli's principle to your advantage for downforce with a roof (and you don't have to dish it). Take it off and you have eliminated a large portion of that downforce.

[Matt49]

My belief (and it could be wrong) is that the roof creates more turbulence than we might think which keeps clean air from getting to the rear deck and spoiler. Meaning that the net affect of the roof is actually less down force. The fact that a lot of the newer roofs have vortex generators on the back of them would be an indication that someone besides me believes that too.
My belief is also that a spoiler on a late model is not as much of a spoiler in the traditional sense and really is more of a wickerbill (Gurney flap for you old timers) for the larger air foil which is the nose and deck of the car. And the fact that I see people running their "spoiler" at 90 degrees to the deck tells me I'm not alone in that line of thinking.
Fun stuff to think about.

[billetbirdcage]

My belief (and it could be wrong) is that the roof creates more turbulence than we might think which keeps clean air from getting to the rear deck and spoiler. Meaning that the net affect of the roof is actually less down force. The fact that a lot of the newer roofs have vortex generators on the back of them would be an indication that someone besides me believes that too.
My belief is also that a spoiler on a late model is not as much of a spoiler in the traditional sense and really is more of a wickerbill (Gurney flap for you old timers) for the larger air foil which is the nose and deck of the car. And the fact that I see people running their "spoiler" at 90 degrees to the deck tells me I'm not alone in that line of thinking.
Fun stuff to think about.

Wind tunnel data seems to back that up, but like everything it varies and overall height of the cage/roof is gonna come into play, I'd assume you could get the roof high enough that it might not effect the deck as much and still use as a wing but probably be way over the legal limit at that point. That's a guess on my part.

[rick james]

It is a limited late deal. Billet you are correct on the wings and spoiler. Car has a tendency to push when track is tacky when entering too hard. I suspect this is caused by right front over traveling, because driver can back entry up a little and problem goes away. Do you think this problem will be worse? Or will the extra pressure on left rear from wing offset the extra force put on right front? Car is money at feature time.