[VaporPressure]

I installed an AJ Hartman double element wing and was curious about testing downforce, and if balance would be changed much. I logged a bunch of data with the PDR and looked at suspension travel at various speeds using Pi Toolbox. This was compared to previous data with the OEM wing. I tried to log all data points at nearly unchanging G forces (i.e. not braking, accelerating, turning). In the graph, you can see that rear compression increased dramatically (Red vs Green). It's interesting to see the front get a little light at high speed even with the OEM set up. The Hartman wing worsens that a little bit, though not as dramatic an effect as in the rear.

I was also curious about spring rates. I've seen it published on these forums that front springs are 450 lb/in, and rears are 1100lb/in. With motion ratios of 0.98 (front) and 0.56 (rear), that gives wheel rates of 432 lb/in (front) and 345 lb/in (rear). Which seems strange because I've read almost all manufacturers engineer a rear wheel rate to be higher than the fronts. So I'm already wondering if something is a little off about these numbers.

I tried oscillating the rear of the car while logging suspension data and got a very regular rate of 0.4s (2.5 Hz ride frequency). Assuming an unsprung corner weight of 722 lb (taken from some posts where ZLEs were on scales and assuming 15% unsprung weight), that would come out to a rear spring rate of 1474 lb/in. The wheel rate would then be 462 lb/in, slightly higher than the assumed front wheel rate.

If my calculations of the rear wheel rate are to be trusted (maybe they're not), the Hartman wing generates about 484 lb @100, and 571 lb @130. Basically a 50% increase over OEM @100, 38% increase @130.

I did not notice dramatically poor handling or any floatiness at high speed. Rear felt more planted mid corner, and possibly a little more mid-corner understeer.

Anyway, I can't seem to find any official source on spring rates and motion ratios for the ZLE, so maybe this data is interesting to someone. At some point this year I'll add a splitter and see if the data changes.

[NG329]

This is fantastic data. Please add a splitter and report back. I'm very interested.

Aero is the only thing holding me back (besides weight) from beating GT3 RS at NJMP Thunderbolt and running low 1:20-1:23 range laps. I'd rather go the aero route to carry more corner entry and mid corner speeds while preserving my car's interior, as opposed to stripping things out of the car to get faster pop off the corners.

Any pics of the wing?

[joelster]

I love the fact that you're doing legit research to get data that is useable. When I did my own aero testing, I used a gutted trunk, and mounted a load cell. There was some deflection for sure with the trunk lid bending, but my speeds were much lower as I race autocross. Too many times I see guys just slap a wing on and set it at whatever angle, because the guy next to them has it set at a certain angle. AJ Hartman does a ton of wind tunnel testing, while a LOT of manufacturers of wings simply do computer modeling. 500+lbs of downforce is insane!

[Christian1LE]

Great post, I love data like this and I've been debating getting aero or not. Nice to see the plot measurements.

I will probably remain stock aero and just go all in on a salvaged corvette at some point since I don't drive my car on the street anymore. Good to see that the OEM wing also doesnt introduce a lot of understeer.

[Patriot Motorsports USA]

Great Post and data!!

Note that "Spring Rate" measured at the spring is relative to the force of the arm moving it. So you might see higher rates where the arm is longer (more leverage) vs a lower rate where the arm is shorter.

Having the data you recorded is awesome... so let me ask a few questions about your front aero setup.

• Have you installed the ePowerSteering duct kit
• Have you removed the Noise abatement panels in the fenders
• Have you removed the "rain ducts" on the hood shield
• Are there any other Aero elements added to the front?

When I removed the hood scoop shield and dropped the scoop as Pratt & Miller did on the GT4.R cars, the difference was impressive AF!!! Johnny at NineLives Racing is making the scoop brackets for me in a one piece bolt-on that is set to make a 2" drop from stock. I would love to see you make this mod before going with a splitter to see the benefits with your data as this is exactly what P&M did to offset their wing.

Skip to about 4 minutes in my video below.

Patriot Motorsports Hood Scoop Mod

[VaporPressure]

I attached some pics of the set up. It's set at 0 degrees for the main element, 35 for the 2nd (Hartman suggested default). I didn't try adjusting it during my one track weekend with it but this would be a relatively lower drag, lower downforce setting, I believe.

Hartman suggests chassis mounting the dual element wings because of the downforce. I ended up trying to keep the ability to easily convert back to stock. So I bought a salvage trunk and tried to do a lot of work reinforcing it. Then created a brace that would hopefully transmit the downforce down to the chassis. The only cutting on the car was 2 small rivnut holes at the bottom of the brace. It was a lot of work and maybe should've just chassis mounted it somehow. The rear edge of the trunk itself still got compressed a bit further from the downforce because it's 3 separate layers there that are easily compressed. But no damage to the bumper.

ZLElvira - I haven't done anything for front aero except I have a splitter on order from Zebulon. It will cover up the trans cooler so I'm gambling a bit but it's an M6 and I have backup plans to help cooling if needed, including having watched a few of your videos on cooling so thank you for those. Not sure what the noise abatement panels are? I would definitely do the hood scoop lowering, particularly if 9lives puts out a kit. When the splitter goes on I am planning to remove the SS brake cooling scoops because I have the brake ducting kit from rm motor werks.

Here's a lap at Putnam Park, the car was quite stable but definitely had more trouble getting up to the top of 4th

[Patriot Motorsports USA]

Ouch... that looks expensive!!

Johnny at NineLives is building a new wing for my car, twin element end mount like the Aussie V8 Touring cars so there is no drag increase with bottom/swan/pedestal mounts also disrupting the airflow. It is going to have billet mounts on the quarter edge at the trunk with LMP-style endplates.

I might even add the Anderson Composites duckbill trunk to reduce weight and add to the splitter front I have now.

[BoilerUP]

I was the red ATS-V there with Motorvault on Saturday...you were scootin'

[NG329]

Originally Posted by VaporPressure

I attached some pics of the set up. It's set at 0 degrees for the main element, 35 for the 2nd (Hartman suggested default). I didn't try adjusting it during my one track weekend with it but this would be a relatively lower drag, lower downforce setting, I believe.

Hartman suggests chassis mounting the dual element wings because of the downforce. I ended up trying to keep the ability to easily convert back to stock. So I bought a salvage trunk and tried to do a lot of work reinforcing it. Then created a brace that would hopefully transmit the downforce down to the chassis. The only cutting on the car was 2 small rivnut holes at the bottom of the brace. It was a lot of work and maybe should've just chassis mounted it somehow. The rear edge of the trunk itself still got compressed a bit further from the downforce because it's 3 separate layers there that are easily compressed. But no damage to the bumper.

ZLElvira - I haven't done anything for front aero except I have a splitter on order from Zebulon. It will cover up the trans cooler so I'm gambling a bit but it's an M6 and I have backup plans to help cooling if needed, including having watched a few of your videos on cooling so thank you for those. Not sure what the noise abatement panels are? I would definitely do the hood scoop lowering, particularly if 9lives puts out a kit. When the splitter goes on I am planning to remove the SS brake cooling scoops because I have the brake ducting kit from rm motor werks.

Here's a lap at Putnam Park, the car was quite stable but definitely had more trouble getting up to the top of 4th

Don't worry about the trans cooler. You can drill holes and vent it. The high pressure | Low pressure relationship will suck air into it. Or you can fiberglass a ram air duct on the bottom of it. Plenty of ways to get creative if ventilation is still a concern.

Definitely the coolest thread I've seen in a while.

As far as going back to stock. It's easy if you buy a spare trunk lid and provide a custom reinforcement. It's just nuts and bolts at that point.

[VaporPressure]

Originally Posted by BoilerUP

I was the red ATS-V there with Motorvault on Saturday...you were scootin'

Nice! Such a great event, guaranteed plenty of open laps every year.

[wakespeak]

I have wear through the paint on my bumper at the trunk lid. Not sure if its the bumper riding up, the spoiler pushing down, or chassis flex (its passenger side only). COTA has a high speed(85-100mph), slightly off camber carousel to the right that might be the cause.

If I am slower into the carousel I have less grip which to me is the aero kicking in above 80mph.

[Slurpee]

Originally Posted by wakespeak

I have wear through the paint on my bumper at the trunk lid. Not sure if its the bumper riding up, the spoiler pushing down, or chassis flex (its passenger side only). COTA has a high speed(85-100mph), slightly off camber carousel to the right that might be the cause.

If I am slower into the carousel I have less grip which to me is the aero kicking in above 80mph.

I also have wear through my paint on my rear bumper right where the trunk meets it. This is with ZLE aero. That was after a good amount of Road America weekends, which can see straights at 160+. It's a pretty consistent strip across the bumper. I put painters tape across the bumper before events now.

[Slurpee]

Originally Posted by ZLElvira

Johnny at NineLives Racing is making the scoop brackets for me in a one piece bolt-on that is set to make a 2" drop from stock.

I saw this on Facebook. Can't wait to buy it once it's available.

[eimarshall]

Sweet data!! I think the quoted 300lbs of downforce is total downforce in the stock ZLE guise. if you are making ~470 in the rear, you are making WAY more than the stock. You are likely right about the front getting lighter though. The leverage of that extra in the rear is probably negating some of the front downforce.