Strut tube rules

[CU Zcar]

Since the allowance for threaded body struts is relatively new, I wonder if many cars have them yet. I bought a "project" 1972 240Z that already had threaded body struts installed but I'm unsure about the legality. From what I've read here doing searches, strut tube modification is allowed, but this is a bit extreme. The original strut tube is cut off near the bottom leaving only an inch or so, and a new, very short tube with internal threads is welded to the spindle. The threaded strut screws into the tube.



That's an image from the company making the assemblies - Arizona Z Car. Note the weld at the tubing base. The strut would unscrew completely from the short tube.

So would someone have grounds for protesting this?

As a side note, I tried contacting them to ask who makes the shocks and they wouldn't tell me, only that they were a "proprietary design" and that all sorts of racers use them with great success. Yeah, right. After a couple seasons I will probably look into whether these can be tailor-valved or even rebuilt, or try to find replacements from a reputable brand. I've got some stock strut assemblies in a parts car also if I had to use regular inserts.

[x-ring]

9.1.3.5.b.2: MacPherson strut equipped cars may substitute struts, and /or may use alternate inserts.

That leaves the door wide open.

Those brakes, OTOH...

[JeffYoung]

Ty, I always wondered about that. So we are defining "strut" as not just the insert but the entire strut tube? I think the rule allows that, but just wanted to be clear.

So it would be legal to use larger diameter strut tubes to accomodate different types of inserts?

[x-ring]

Well, putting my scrutineer hat on for a moment, if a steward came to me asking for technical input about what a strut is on a Z car, I would look first at the GCR, then at the FSM.

In the GCR glossary, we find the following:

McPherson Strut - (See strut type suspension) A front suspension type utilizing a strut with integral tubular shock absorber and coil spring, with the steering swivel axis that of the strut/shock. Upper location is by strut only.[/b]

And:

Strut Type Suspension - Strut suspension consists of three pivoting attachment points including a single upper attachment point, the spindle being mounted on a telescoping post with no vertical movement at the top attachment point.[/b]

OK, the first seems to indicate the they are refering to the entire assembly, else why would they refer to an 'integral tubular shock absorber and coil spring', presumably as part of the assembly?

Now, from the Nissan FSM I find:

The strut assembly, consisting of a strut-outer casing with spindle...[/b]

The drawing of the assembly, including the 'integral tubular shock absorber', shows the assembly with the spindle and is labled 'sectional view of strut assembly' (figure FA-28).

If the CRB intended that you could only change inserts why would they write the rule, 9.1.3.5.b.2, that allows substitute struts and/or alternate inserts?

Thanks, I'll use a 'substitute strut' just like the OEM strut, except shorter, with threads on the outside, and I'll use alternate inserts from Koni.

If it says you can...

[CU Zcar]

Good, that's more or less how I was reading the rules, and more to the point that is what is already on the car

Sadly, it didn't come with the spiffy brake assembly... I have a 280Z that isn't headed for ITS any time soon that could really use them.

Thanks for the replies.

[JeffYoung]

Ty, I'm with ya..makes sense to me.

[Greg Amy]

...and the ITB Audi Coupe guys take FULL advantage of that rule, completely redesigning the strut and its integral knuckle to where there's Z-E-R-O geometry problems, inherent to lowering McP strut cars...nice...

[JoshS]

...and the ITB Audi Coupe guys take FULL advantage of that rule, completely redesigning the strut and its integral knuckle to where there's Z-E-R-O geometry problems, inherent to lowering McP strut cars...nice...
[/b]

Is that legal? Seems like that would involve relocation of a suspension component. I don't think it would be legal for the positioning between the knuckle and the lower control arm to change, because of this rule:

9.1.3.D.5.d.8: "No other relocation or reinforcement of any suspension component or mounting point is permitted."

These integrated struts/knuckles definitely create a grey area with respect to the rules allowances in my mind. How common is that design?

[CU Zcar]

Whoa, really? Do you mean in a manner similar to using bumpsteer spacers between the spindle bottom and the steering arm/balljoint? I figured changes like that would be out because you were altering geometry.

How common is that design?[/b]

Lots of Japanese cars from the 70s and 80s use them, at least. Datsun and Nissan Z-cars through the Z31, AE86 and earlier Corolla, 79-85 Mazda RX7 to name just a few.

[RSTPerformance]

Not much time to post, but I just wanted to say that we (RST Performance Racing) do not change the positioning between the knuckle and the lower control arm on our cars. Most other "tunners" have changed this on their versions to allow for a more "correct" A-Arm angle and possibly to gain more negative camber. It also helps with keeping the correct distance for the CV joints to move properly (Simmilar issue that a lot of VW fix by using shortened axles). We have certainly thought about this as it is all "one piece" and indeed a "grey area" however none of our versions have ever taken advantage of it.

Raymond Blethen
RST Performance Racing

[Greg Amy]

I've specifically reviewed the rulesets again after seeing those struts on specific Audis (not the RST gang, someone else). My first response was, "Hell, that's not legal!!" (same as I thought when I saw Tom Blaney's front spoiler that incorporated an undertray and splitter). Then I read the rules again, thinking about what they did, and my response was "hot damn, that's clever! And legal" (same as I thought after reading the rulebook in regards to Tom's spoiler....)

See, that's the beauty of that design: they're not relocating any pickup point or suspension mounting point, they're relocating the ball joint in relation on the completely-legal-to-do-whatever-the-hell-you-want-to-do strut in relation to the contact patch of the tire, which happens to improve geometry as the car is lowered. Not only is it legal, it's damned clever.

It's just one of those things that folks who have knuckles integral to the strut, such as the Z-car photo above, can do that the rest of us cannot. Simply IMAGINE trying to police the location of the ball joint mount in that photo above; how'r ya gonna do it? How are you gonna stop someone from mounting the ball joint relative to the contact patch of the tire differently than stock (thus adjusting the roll center, COMPLETELY negating deleterious geometric effects of lowering the car)?

Can't. Won't. Power to ya.

Whoa, really? Do you mean in a manner similar to using bumpsteer spacers between the spindle bottom and the steering arm/balljoint?[/b]

Yeah? Guess what: the Audi *also* incorporates the steering arm *on the strut too*!!! So, guess what: ZERO bump steer.

Most excellent design. Just seeing those struts (and hearing those cars at full-tilt boogies) was enough for me to consider building one. I truly believe that car has scads more potential in it...