Reducing Drag for Road Racing

aerodynamics
roadracing

(Bryan Hall) #1

I’m looking at participating in a road race next month with the sprint shifter kart. Drag is obviously the main adversary to speed on long straights, so as an engineer I’ve been thinking about all the ways (that the rules don’t specifically exclude) to reduce aerodynamic drag. The studies several posts here link to are helpful in highlighting the highest points of pressure - the biggest being the driver. Of course they somewhat seem to ignore the opposite low pressure side of the disturbed air behind the driver, which is probably equally if not more important. So what could be done about that I thought. Some ideas so far are:

Add a simple air dam to the bottom of the front bumper to limit the airflow under the kart.

Extend the floor to the rear of the kart to make what air does get under-neigh flow smoothly as possible (and also protect the seat from rubbing).

Attach flaps much like a semi-trailer has behind the seat up to the maximum height allowed. That would help smooth the airflow coming from the driver and reduce drag (and is probably the most likely thing that officials would not allow).

Create a simple soft “teardrop” foam piece to attach to the rear of the neck brace to smooth the flow from the helmet and area above the seat rearward (much like you see on bicycle racing helmets). Hey, it’s added cushioning in case of a crash - so it’s really a safety device! :wink:

Add small half-balls to the front of the brake and gas pedals to smooth the airflow around the feet.

Thoughts? Yes - this is the kind of stuff I think about all day and at night - an engineers curse I guess.


(Eric Gunderson) #2

So, fun fact: My friend is an aerodynamicist for a top-level NASCAR team. I’ve learned a lot from him, and he races karts in his spare time. Through testing we found in an LO206 kart at IMI Motorsports Complex (a relatively high speed track more like a road course than a sprint kart track). Of course, pretty much all we tried wasn’t strictly legal, we were more curious to experiment.

  • simply taping a piece of 1 foot by 3 foot cardboard to the front nassau panel = 3 tenth gain per lap (widened front cross area as air is channeled hopefully somewhat around the driver)

  • Utilizing a wedge shape cone on the rear of his helmet like Moto GP drivers do produced (so far) inconclusive results. He’s rather tall so we suspect any gain by this on the back of his helmet is there, but likely doesn’t cancel out his cross area chest to front area of the helmet.

We’ve joked about finding a way to maximize aero on the kart to see just how fast we could get a 206 to go simply with cardboard and tape:

If I were to do it, I’d start by utilizing this bodywork or something similar (G man type). I’d also try to cover the areas exposed on the outside of the rims (think Mooney wheel covers like you see at Bonneville). An undertray would be lovely, but would need to be sealed at the front otherwise it might actually build more pressure than prevent it. The OTK front nose seems to be, by industry standards, the most aerodynamically sound factory obtainable piece for the front of the kart. That, and an old-school wide front nose like these could be another neat idea. The flap idea I like, I wonder whether an external or internal flap shape would be best…you’ve just given me a new idea to try! Oh! And seal off the holes in the rear bumper if you are using a traditional KG type or something like that.


(Charles Skowron) #3

I don’t know which club and organization is attached to the long track race you’re planning run. But most karting ruling bodies have rules restricting aero modifications on Road Racing classes that run CIK bodywork, which the majority of Sit-up Sprint Shifter classes seem to fall under.

For example, just taking a glance at the tech regulations for AKRA-sanctioned road racing (because they’re one of the few karting bodies that have their tech rules posted online), I would guess Ideas #1, #2, and #3 would be rendered illegal right off the bat.

I know every org. has had rules regarding the length of floor pans for quite a long time. So you might want to check your club regarding aero.


(Bryan Hall) #4

The organization is KART ( Karters of America Racing Triad). With at most 1-2 other competitors in my 80cc class, it’s probably not that big of a deal as it’s all for fun anyhow. Anyhow, under the Aerodynamic Regulations for sprint chassis here is what applies:

Air dam - 4. No “skirts” or vertical aerodynamic sealing devices are allowed to extend below the main frame rails. This does not include the front nose.

So here, I don’t see a problem with adding a rubber wiper below the nose as it’s specifically allowed.

Floor “belly pan” - It must be fully confined within the outside edge of the main frame rails. Full (the key word) belly pans are allowed in all Road Race classes with the exception of 125cc, 80cc…

So as long as its not a full pan (stops short of the rear bumper) I can’t see a problem with that. Although it does help aero (in theory), it also is there to protect the seat from bottoming out.

Rear flaps - yes, not specifically disallowed, but as I said rather obvious. Not something I plan to use for the race, but more rather for experimentation. It would be interesting that with the flaps if I could match pace ~ 105 MPH with a friends 125’s without one. I bet it would be close.

As to bigger and wider fairings, here is what applies - Driver fairing maximum width is 14 inches. Driver’s feet must be visible when viewed directly from above with pedals in normal driving position. Minimum 2" clearance between fairing and steering wheel.

So here I can’t have those crazy wide fairings or bumpers that were linked to, but I could make it a little wider (up to 14"), especially above the feet where it is more narrow currently, so long as it is a clear acrylic sheet in that area so you can view the feet from above.

Bodywork specifically: CIK Bodywork Type ONLY

No problem there that I can see… It is of that type.

Flush Hubcaps - great idea. I’ll have to look into that.


(James McMahon) #5

Welcome! See also: #aerodynamics


(Ty Schlorer) #6

As a long time Road Racer here’s my advice. The best aerodynamic tool you’ll find is free, doesn’t require extra fairings, tape, or tricks. It’s the draft plain and simple. You’ll find more aero speed there than spending all the time and effort doing the other stuff.


(James McMahon) #7

I agree, to an extent…

When you pull out of the draft 100ft before the finish line… you want your kart to keep as much speed as it can. Better aero helps there.

The second best tool… getting your shoulders down and out of the wind.


(Ty Schlorer) #8

That’s what the preceding laps are for. Test out where to start your run for the finish line.


(James McMahon) #9

Why not both :man_shrugging:
Don’t show your full hand when you’re sizing them up. Crush em at the end.

Then do a Dempsey at the line…


(James McMahon) #10

Some insights from Bob Vehring at 4 Cycle Central on Facebook comments. Bob has done a LOT of road racing over the years.

While I agree with some of the stuff posted, something big is missing. My kids have Road Race since they were 12, their 38 and 40 now. First at least for now, I’m talking about what is commonly seen as WKA Sit Up Sprint rules. We do have some CIK experience but unless someone asks will limit this now. We have been through alot, currently we are allowed full floor pans altho there was a period where they had to confined to main frame rails. We and others then built chassis that the main rails simply went out to the side of the karts. Problem solved. We have been through all sorts of NACA ducts, skirting, wheel well boxes, and way back alot of time was spent directing air around back to clean it up.

I assume that we all understand that just like a old station wagon, a blunt rear sucks in air behind you to fill the hole you just punched in the wind. Spending time to address this did to a degree add a little speed when running alone. However theres one big problem. Anyone ever watching the Animal class at speed know its about drafting 2, 4, 10 karts 1 in apart in a line. If you don’t have a partner, your pretty much left out of the pack

Karts create a suction behind them, this pulls another kart in to the single stream. The more karts you have using their HP to move the train along, the faster you are. The issue when designing a “smooth” areo design behind the kart is, it fills that area up, other karts will now bounce of all that air and no one can get close enough to be a drafting partner

Look at any current Sit up sprinters, its not that we can’t design better rear body work, its that we don’t want to, you must be able to draft

Now on CIK, years back said something to me that yes we win in 4 stroke classes, but we couldn’t do that in 2 cy, We chose CIK can. Rules then simply specified CIK bodywork. We chose a 36 in wide Coyote chassis and mount CIK bodywork Almost all other forgin karts were much wider really by alot. Both Drivers, Regan and Jessica were 1 and 2nd at almost every race.

Now what we learned, Regan id 5’3" Jess is almost a foot shorter. While Regan could make up ground in the infeild tight sections, once they got to the Straights Jess would make it up and pass on by, She could “hide” behind the small bodywork much better then a big person could and there was nothing Regan could do to make that up. A small person in CIK simply will have an areo advantage over a big person. There was then some pretty heavy hitters in that class, but Regan and Jessica ended up 1st and 2nd, it was because of the narrow kart