Let's talk SM mods if there are still people around
I might do the aero on my car over winter.
Any advice from those who have done it?
Brand you recommend for rear wing?
How much time can you gain on the 60s course on average?
tx,

Ciro Designs SM Spec rear wing 6" above roof line 0" behind rear bumper no wider than the door handles specific sized end plates
Splitter; 100% flat, 3% angle allowed, Maximum size 6" forward 0" wider than front of car (measured at the middle of the front fenders), cannot go passed the front axles.
Canards are a hot topic still

I believe it's worth about 1.5 seconds on a 60 second course.

My biggest gain was my 1st runs are viable, prior to having aero my first runs were always more slidy than I prefer. Now after aero the grip is there.

Ciro is good, and is what I have. Zebulon is also good even though I disagree with some of his rules pushing practices.

Aero lets you set the car up to be neutral or even a bit loose in lower speed then bank on the higher speed being calmer due to aero kicking in (usually around 40ish mph). The biggest draw back to aero is if there's a stiff breeze blowing in one direction across course. Into the wind and the car will hunker down, but with the wind and you lose a lot of the aero effect.

Still, definitely worth it in SM.

This exactly. Add as much aero as you can per the rules, front canards are worth it as they allow you to increase the rear wing angle a few degrees. Setup the alignment to make the car loose at low speeds and tighten up at higher speeds. I once gained 0.5 seconds on a 60 second course (through a fast slalom) by increasing the rear wing angle by 2 degrees.

I think the potential gain of max aero vs. none is around 1.5 seconds on a Nationals style 60 second course.

There isn't anything in the rulebook that specifically says splitter = "flat."

Here is the rule:

L. Front splitters are allowed and shall be installed parallel to the ground
(within ±3° fore to aft) and may extend a maximum of 6.0” (152.4 mm)
from the front bodywork as viewed from above. Splitters may not extend rearward past the centerline of the front wheels. No portion of the
splitter may extend beyond the widest part of the front bodywork as
viewed from above. Aerodynamically functional vertical members, such
as splitter fences or endplates, are not allowed.

I think a lot of this debate goes sideways pretty quickly when some folks haven't studied motorsports engineering literature thoroughly enough to realize that there are different parts of what we generally refer to as a "splitter," olde Americans referred to as a "front spoiler, while the rest of the world more accurately refers to as a "front wing" as a complete element. The actual splitter as part of a full element is only the the area that protrudes forward of the bumper cover and ends at the rear of the bumper cover. A diffuser continues on from rearward end of the splitter towards typically the front axle centerline. The third major component would be the air dam which is pretty self explanatory.

Here is a link to an excellent read written by a respected Motorsport Aero Engineer that walks through what I just described in far better detail, also notice the diffuser component shown here is not flat:

http://www.ricemobile.net/downloads/...%20airdams.pdf


Going back to the SCCA rulebook, its pretty easy to see that sentence two of the SM allowance is in fact describing the diffuser component of the complete "splitter" element and for a sense of accuracy should be corrected to say as much. In practice and technical application this component would never actually be flat because it would fail at being an aero element designed to accelerate airflow thus generating high/low pressure differentials. There are also remnants from the older classes (example being SP, which SM allegedly builds on) using both front spoiler and splitter interchangeably. Allowing an aero device and then requiring it to be flat would be like allowing tires, but only Canadian square ones.

Re writing the rule to read like so I think would more accurately represent what's being described:


L. Front splitters are allowed and shall be installed parallel to the ground
(within ±3° fore to aft) and may extend a maximum of 6.0" (152.4 mm)
from the front bodywork as viewed from above. Diffusers may not extend rearward past the centerline of the front wheels. No portion of the
splitter may extend beyond the widest part of the front bodywork as
viewed from above.

Naming convention aside, I used to be on the rules committee for SM and can tell you the whole panel that's bolting to the car should be "flat". I put it in quotes so we don't get some pedantic person asking what level of flat we're looking for. The point is to have a flat panel underneath that can go to the centerline of the front axle and protrude 6" from the front bumper. No 3d shapes, no ramps, just a simple flat panel.

You're right that it doesn't specifically say flat, but it does say "no vertical elements" which generally means it's gonna likely be pretty flat

That is all fine and dandy but when people are going to be building cars, they are going to go by what is actually written in the rulebook, not track down a former SMAC member to find out what their intent of a rule was back in 2011. Especially if said intent misunderstands how an aerodynamic aide would operate.

Just as a reminder but the allowance read as follows from 2011 to 2015. Also no where suggesting an "intent" of these elements to be flat. Intent that is not defined or written in a rulebook will not be upheld by a protest committee.

M. Front splitters are allowed and shall be installed parallel to the ground (within 3 degrees fore and aft) and may extend a maximum of 6.0" from the front bodywork/fascia as viewed from above. Splitters may not extend rearward past the centerline of the front wheels. No portion of the splitter may extend beyond the widest part of the front bodywork as viewed from above.

No where in any of these rulebooks is a splitter defined as flat, described as flat nor is intent directly stated, therefore it is not a rule.

Besides the fact that I was on the smac from 14-19....

The counter point to your view is the line "Front splitters are allowed and shall be installed parallel to the ground" to me (and most others in SM) that means the entirety of the splitter panel needs to be parallel to the ground. Anything that looks like a 3d shape or other than generally flat is no longer parallel is it? We had some people try to say the outline of the panel was installed parallel, but as soon as you took a measurement off their splitter ramps it was no longer in compliance with the rules. You can't pick and choose which part you want parallel.

I'm not sure why this is complicated, and I'm not trying to be a dick either. I will guarantee a splitter with anything other than generally flat underside will get protested though and the person with it will lose.

Furthermore regarding the "Aerodynamically functional vertical members, such
as splitter fences or endplates, are not allowed" would prohibit an air dam before any sort of profiling of a splitter. The air dam allowance is inherited from SP rules and is not an SM allowance. So if you wanted to use an air dam, you could not do so in addition to a 6" splitter protrusion as allowed in SM.

This interpretation is in fact described in 16.1

. Competitors may pick and choose between all Street, Street Touring®,
Street Prepared, and Street Modified category allowances when preparing a Street Modified category car. Apparent conflicts between inherited
rule sets from Section 16.1.A shall not prohibit any specific inherited allowance. Allowances inherited from Section 16.1.A may not incorporate
Street Modified-specific allowances. Foreign spec parts may not be used
to substitute for parts which are required to remain standard.

The sentence prior negates the argument you're making. It allows you to use an air dam on the splitter as it's defined as allowed, but since the splitter panel itself is outlined in further detail in 16 it can exist in the specified dimensions. It's an inherited allowance.

I'd also wager a guess here that someone would have protested at Nats if that were an actual violation of the rules. Especially considering each car in the top 10 had an air dam.

The sentence you pointed out is discussing conflicts of allowances between the rule sets of S, ST, SP. An example is once upon a time there were more body allowances in ST than there were in SP, along with currently what ST defines as standard or a model vs SP the term line is used. Another example is conflicting allowances where an AOS could be legal in S but not in ST. The inheritance of an air dam with an SM splitter would not be granted from that sentence and then again specifically not allowed in the sentence I marked red. I'd wager most just glossed over those sections and assumed that an air dam is a component of a splitter.

Sure you could say your air dam is a part of your bumper, but now were back to end fences being part of canards or whole front bumpers actually being a wing.

But besides not being allowed along with an SM splitter protrusion, the air dam itself is specifically banned from the SM splitter allowance as it is an aerodynamic vertical member.

Protest me then

Isn't an air dam just an extension of a bumper cover

Soooooo.... I just spent an hour scrolling through old threads looking for pictures of SubyDude's splitter design.

1) Its really interesting looking back to 2015 and earlier and seeing what has changed in SM and what hasn't.

2) I can't find the pics of SubyDude's splitter design (That I remember reading about at one point).

Would you guys be willing to post pictures of how you framed up your splitter and what materials you used?

Which parts of the design are you looking for?

Mine is on 05 STI, using mounts off the side of the frame rails, then a bracket behind the front bumper directly under the beam. Also, two bolts go through eyelets in the rear for rear support (eyelets screw into the jack plate bolt holes).

Plywood is it's it made of.

Next setup will use professional awesome quick releases in 4 spots with their splitter rods up front (outside the bumper) and in the corners by the tire (under the bumper).

But, I'm not the best example. My M.O. is to over complicate and over spend. haha.

I chuckled.

The best material is alumalite or similar as it's easily replaceable and with a few tricks will last 3-4 seasons unless you're just constantly smashing cones at 60+ mph.

I have two mounts on the front that go to the core support, one main one in the rear, two turnbuckles off reinforced pieces of the front bumper, and two on the bumper by the front wheel opening that I reinforced. It slides on and more or less seats into place and the 4 external bumper pieces help hold it in place.

A friend and I made carbon fiber panels with some expired pre-preg, but the weight savings was minimal. I think I saved 1 lbs total, although the splitter was slightly bigger. Alumalite was roughly 15 lbs in total.

Can you expand on "Alumalite" is there a specific product you like? Ie total thickness, wall thickness, etc. My codriver (Girlfriend) has a propensity to centerpunch cones at 60 and obviously I can't complain because BJs.

It's actually just called Alumalite and is usually sold by sign or graphics companies for applying vinyl or other stuff. A 4'x8' sheet is usually around $200 and I use the 6mm thickness one. That allows you to put a .25" piece of aluminum U channel on the front to absorb and distribute impacts. You can see it in the pic below all along the edge. I used small cuts in it to help bend on some of the bigger curves and just drilled through with rivets to hold it on.

Does the splitter supports actually hit the bumper beam or just go into some really big fender washers?

I just reread your previous post. I think I get it. Any chance you could post a picture of the splitter off the car? I'm assuming (rembering?) that you have a sort of frame on the splitter.

It's a lot easier to just text it. If you want to PM me your number I can send a few shots.

I saw on Facebook that SubyDude has joined the rear radiator club. Once the radiator goes into the trunk, there are suddenly some really interesting things that could be done with an air to water intercooler and front end aero.

I'm thinking big hole in the hood, ducting that turns the whole nose into a wing similar to Audi's Le Mans work around to the ban on front wings.

I opened up the hood up front and blocked off everything minus the intercooler and oil cooler, but high level aero is not super easy with how close the engine still sits to the front of the car. I'm sure it could be done, but the design would be headache inducing, and honestly, having the big vent in the hood is just nice for keeping general temps down while sitting in grid.

I've actually had the rear rad since 2020/2021 winter but haven't posted about it. it's working generally well though.