STU Rear Suspension question

M

mustanghammer

New member
I have quesiton about the following rear suspension rule that is listed in the STU section of the STCS.

9.1.4.A.F.1 (page 473)
Cars that come with a solid rear axle or trailing arm suspension are
permitted an aftermarket or fabricated rear suspension. Cars with
an altered rear suspension must add 50 lbs. Cars with live axle rear​
wheel drive may reduce the minimum weight by 50 lbs

What constitues an aftermarket or fabricated rear suspension? What may be fabricated? Can the OE design of the solid axle rear suspension be altered as a result of this allowance? IE: OE 4 link replaced by a fabricated 3 link.

Final question - is this rule additive to the two rules that follow it - 9.1.4.A.F.2 and 9.1.4.A.F.3.? Meaning that a solid axle car may have a "fabricated rear suspension" AND it must conform to 9.1.4.A.F.2 and 9.1.4.A.F.3.


 
We kinda covered that in my question earlier this year.
http://www.improvedtouring.com/forums/showthread.php?t=29328

The conclusion that came from that is "Altered" would mean a change in pick-up points on the chassis, and would incur a weight penalty.
Anything that is a "bolt-in", either aftermarket or fabricated, using stock pickup points, would not incur a penalty.

Examples of "Altered" would be a Griggs 'World-Challenge' suspension, with lower control arms that are about a foot longer than stock and require you to cut out the torque-boxes.

So yes, you can run a 3-link. (As I do in STO)
Whether or not you still get the 50lb addition, has not been clearly established.
 
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Your weight should remain the same. Alltered get 50 added Live gets 50 removed. =0 change in weight

I thought about a Second gen or Miata rear suspension in mine as well. That would have incurred a 50 pound penalty. The frame rails are the same width +/- a little and all you would need is to drill thriu the frame rails to attach the Miata rear stuff. It basically self contained. Shock mount poses the biggest issue.

Its more work than I make it out to be,but Ive seen the stuff you built so far and its about even.

Could be done in the front as well.

Dan
77 IT7/A to EP
 
Thanks for the replys. As far as a weight penalty is concerned it looks like a wash to me. I subtract 50lbs for having a solid axle and then add 50Lb for altered pickup points.

When this rule was added I wrote to tech services and the definition I received of an aftermarket/fabricated rear suspension was less clear than the rule in the GCR.

At the same time I also asked if this rule meant that I could go from a solid rear axle to IRS and I was told no. This was about two years ago and as I recall there was language in the STCS that supported this answer. So I started down the path I am on with the solid rear axle. Now, reviewing the rule set, I see that this language has been removed. I guess this is the downside of building a car to a rule set that changes with the wind.

I would still like to see some clarifications made to this rule section. If 9.1.4.A.F.1. allows me to fabricate a 3 link then rules 9.1.4.A.F.2. - 3. must not apply. Perhaps they are intended for cars with an IRS?

Thanks again.
 
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mustanghammer said:
I have quesiton about the following rear suspension rule that is listed in the STU section of the STCS.

9.1.4.A.F.1 (page 473)
Cars that come with a solid rear axle or trailing arm suspension are
permitted an aftermarket or fabricated rear suspension. Cars with
an altered rear suspension must add 50 lbs. Cars with live axle rear​

wheel drive may reduce the minimum weight by 50 lbs

What constitues an aftermarket or fabricated rear suspension? What may be fabricated? Can the OE design of the solid axle rear suspension be altered as a result of this allowance? IE: OE 4 link replaced by a fabricated 3 link.

Final question - is this rule additive to the two rules that follow it - 9.1.4.A.F.2 and 9.1.4.A.F.3.? Meaning that a solid axle car may have a "fabricated rear suspension" AND it must conform to 9.1.4.A.F.2 and 9.1.4.A.F.3.
Click to expand...

That's good point. Take a semi-trailing arm rear suspension that comes with normal rubber bushings for example :

heim joints/rod ends are allowed in place of bushings. does that constitute altered?
does adding a reinforcing bar/plate/gusset constitute altered?
seeing as it doesn;t really matter what shpe the actual arm is within the three point(two pickups and hub placement) it kinda doesn;t matter what goes on in the middle.

but keeping the same arm arm geometry, and keeping the same pickup points, but making the arms out of HY100 or Ti3Al2.5V...would be a stornger lighter trailing arm...does that constitue altered?

I would think that moving pickup points clearly is "altered".
 
JS154 said:
That's good point. Take a semi-trailing arm rear suspension that comes with normal rubber bushings for example :

heim joints/rod ends are allowed in place of bushings. does that constitute altered?
does adding a reinforcing bar/plate/gusset constitute altered?
seeing as it doesn;t really matter what shpe the actual arm is within the three point(two pickups and hub placement) it kinda doesn;t matter what goes on in the middle.

but keeping the same arm arm geometry, and keeping the same pickup points, but making the arms out of HY100 or Ti3Al2.5V...would be a stornger lighter trailing arm...does that constitue altered?

I would think that moving pickup points clearly is "altered".
Click to expand...

I just submitted this question as well.

EH
 
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