USAC Rule Update 1/24
 

Where and why are we sticking a fifth shock on?

https://www.usacracing.com/news/usac...ational-season

Re: USAC Rule Update 1/24
 

Silver Crown only:

207: STEERING & SUSPENSION | USAC SILVER CROWN NATIONAL CHAMPIONSHIP

H. Cars are limited to five (5) shocks. No electronic shocks allowed. If a second shock is used on any corner of the car, the second shock cannot be a through-rod shock or have a cannister attached.

I. No electronic weight, shock, sway bar or any suspension item adjuster. Only five total cockpit chassis adjustments are allowed at any one time. Brake bias will not count toward the five adjustments.

Sounds like we need a chassis specialist to weigh in here, but I am guessing it has to deal with the right side loading on tracks like Winchester & Salem?

The floor and microphone is open to anyone who wants it. :)

Nope scroll down, it's in the Sprint Car and Midget rules as well.

That was my first thought too, that it was a pavement thing.

Rules? We don’t need no stinking rules!
Unless you’re going to enforce them.
As you all know I love USAC, but they are not without their warts. I didn’t dissect it, but it appears you can bolt weight anywhere now, including in front of the axle provided it’s labeled to your car. That’s an easy way to bury a past controversy. If I’m wrong, please correct me. Thanks

Re: USAC Rule Update 1/24
 

F. Additional bolt-on weight must be mounted and fastened to the frame and/or chassis in a secure manner. Weight must be
identified with a car number and any bolt on weight lost on the racetrack is subject to a fine.
G. Weight must be mounted in an area between the bottom frame rails, front and rear axles, and no higher than mid-rails at
the cockpit. All weight must be mounted within the confines of the frame. No weight may be added during a yellow or red
flag.

Re: USAC Rule Update 1/24
 

Yeah. You're right. Hmmmm...

KKM started using a 2nd shock late last year on the RR and now it’s monkey see monkey do. Here was a chance to nip it in the bud and prevent the additional cost of the 5th shock. And don’t get me started on the irony of lightening the cars over the years, only to now want to bolt weight on.

Re: USAC Rule Update 1/24
 

If you can save weight someplace on the car and shift it to a place more advantageous teams are going to do it.

I noticed a few of the Kkm cars had the 5 shock setup but not all of them. They were running a much smaller dimensionally rr torsion arm on the cars with the setup compared to cars that had standard shock layout. My brothers tq team has to bolt quite a bit weight to his car to make weight.

Re: USAC Rule Update 1/24
 

Good eye. :6:

I’m well aware, especially reducing rotating weight and putting static weight where you want it. It’s just my frustration with sanctioning bodies doing nothing to control costs.

Seen multiple cars at Chili Bowl with an extra shock on RR like few of the KKM cars.

What I think I understood the 5th shock would do was improve their ability to slam into the ledge that builds up at the Chili Bowl. I assume it works in conjunction with the Jacob’s Ladder and lets them bite into the ledge more effectively. The people commenting on it say micro guys (Dicely, in particular) have run them on micros for some time.

If you’re not slamming a tall cushion, I don’t think they help.

I could understand that helping on a big cushion. The shock is at a pretty severe angle, mounted center top of birdcage and just aft of the ladder mount. I thought it was interesting that axsom made the comment when asked about the setup that he told Keith they’d never won chili bowl with a 5th shock so I wanna stick with 4.

Re: USAC Rule Update 1/24
 

".....I assume it works in conjunction with the Jacob’s Ladder....."
.

A picture is worth a thousand words.

Re: USAC Rule Update 1/24
 

The Karl Kinser effect.

Re: USAC Rule Update 1/24
 

Same as when Penske added that vertical fin behind the drivers head. Later on Cendric it was added to get some additional sponsor
signage!!

Yeah, if anyone can find a picture of a KKM car with a fifth shock I'd like to see it.

I didn’t take any while I was in Tulsa, I had noticed it on screen during the Sunday practices while I was on my way down there. Standard 7” ars shock, no canister, the regular rr shock was canister equipped. I’ve always been kinda surprised with all the boutique shock companies out there that kkm has stuck with advanced all these years. But why mess with success

FLO did a brief piece on the shock with pictures during Chili Bowl coverage. I’d have to dig deep into the archives to figure out the day and time stamp for the video. Maybe they clipped it themselves.

Re: USAC Rule Update 1/24
 

Not the best photo, but it might give you a better understanding. I took this photo Saturday.

Bart

Re: USAC Rule Update 1/24
 

Here is a better angle, but I still don't understand if this it the 5th shock.

Bart

Your first picture showed it. It’s tied from the top of the birdcage to a tab on the chassis at about a 45 degree angle. I don’t see it in the second picture. There’s no spring associated with it (coilover). I assume what it’s doing is dampening the lateral load that the ladder controls when you slam into the cushion. The chassis is still going to move sideways until all the slack is out of the ladder, but dampening it slows that down for a split second. And since it’s mounted at that angle, it splits the dampening in half, so it’s an even more slight adjustment than you might think. Tying it to the top of the birdcage instead of the side probably also has an affect. Creates leverage to plant the RR due to the car’s lateral momentum?

Drinan or Dicely could explain it.

Missing in 2nd picture but the mount is there on the bird cage.

Re: USAC Rule Update 1/24
 

Whereas the "main" or "usual" shock is oriented close to the vertical and approximately at 90 deg. to the axle, and is most effective in dampening wheel motion in bump and rebound, the "5th" or auxiliary shock, by virtue of being oriented at about 45 deg. is more effective at dampening chassis roll motion.
If the valving of the main shock were stiff enough to provide the same roll dampening as is provided by the auxiliary shock, it would be too stiff to allow the needed compliance for good tire performance.

Re: USAC Rule Update 1/24
 

What Frank is saying here is correct. With the current car design the chassis suspension (torsion bars, etc.) on the rear is mounted below the vertical center of gravity. Since the suspension is the only means of controlling chassis roll (until the jacobs ladder locks up, that is) it must be stiff enough to limit the rate of said roll, which potentially makes the suspension too stiff to maximize tire contact/weight transfer, etc. This 5th shock appears to allow some control of the roll rate while keeping the suspension as soft as possible. Kind of like installing an adjustable rate anti-roll bar. Probably not a bad idea, but all I need is to have to buy another 4-600 dollar shock.

By the way - coil-over suspension suspends the car at or above the roll center which adds some anti-roll itself.

Tim Simmons

Re: USAC Rule Update 1/24
 

I really appreciate these topics about the technical side of open wheel cars. Frank and Tim made interesting comments about the fifth shock helping to control the roll center of the chassis. I was wondering if the fifth shock would work similar to the QRP CL2 bird cage that had a small coil spring in it's assembly that was connected to part of the W link, I think it was created to help prevent a bind and keep a true arc in the roll center? Many sprint car sanctions banned this birdcage early last year and I was wondering if it's the same idea presented in a different way.

Re: USAC Rule Update 1/24
 

As to the location of the roll center, that is determined solely by the geometry of the locating links, in this case by the geometry of the Jacob's ladder. The auxiliary shock functions to control/dampen roll movement but has no influence on roll center location.

The reason that the spring linked ladder connection fell out of favor, as I understand it, was because of very erratic handling when the spring failed.

Re: USAC Rule Update 1/24
 

Thanks Frank. I find your posts quite informative, much appreciated..