SCCA SM class rule clarification

[IsItElectric?]

i think the SM rules do not allow you to move the subframe at all. infact, even the IE style camber/toe adjusters are illegal. which is very annoying, because in the spirit of the rule, they should be legal since they arent designed to provide geometry adjustment, only alignment.

edit: and infact, a completely tubular/adjustable trailing arm is legal even though it is countless times better than the illegal adjusters.

Are you sure?

If that's true, then why wouldn't camber plates be illegal? They use the same principle. They attach to the car at the same place (from the rule), but move to change suspension geometry.

I think the spirit of the rules say you must use the original physical location on the car to attach suspension components....you can't make your own subframe for instance.

I believe that lowering / raising / offsetting suspension geometry by using offset bushings AT THE SAME ATTACHMENT POINT ON THE CAR is fine....however please correct me if I'm wrong (and point to the correct page in the rulebook).....

[guibo09]

I think you have it right, I was thinking its not a suspension component so it is free to be changed. But since it doesn't specifically say you can, that means you can't.

So really the only way to get the camber adjustment is to use the eccentric TA bushings. Those are legal because its a method in the service manual to align the car.

I need to get under my car and see what level my TA's are sitting at, from what I understand, you basically don't want them going past parallel to the ground during compression. But my car will have to be raised up somewhat when the bigger tires go back on either way.

Although I think it would be a tortured interpretation of the rules:

H. Subframe bushings may be replaced with bushings of any material
as long as they fit the original location. Offset bushings may
not be used.

Does not say they have to be the same "height" only that they have to fit the original location, any material and not offset. I don't think shortened = offset.

i dont think that logic of the control arm being past parellel applies. that logic is more for the front control arms on macphersons to some extent, although not completely right either.

a semi trailing arm gains its camber from the trailing angle and not from the sweep angle. and is actually fairly linear over most of the possible travel.

as for your interpretation of offset, i think you're really pushing your luck. i can easily say that a shorter bushing offsets the subframe vertically.

anyway, in the spirit of the rules, it's pretty clear that any relocation of the subframe is illegal.

[z31maniac]

I think you have it right, I was thinking its not a suspension component so it is free to be changed. But since it doesn't specifically say you can, that means you can't.

So really the only way to get the camber adjustment is to use the eccentric TA bushings. Those are legal because its a method in the service manual to align the car.

I need to get under my car and see what level my TA's are sitting at, from what I understand, you basically don't want them going past parallel to the ground during compression. But my car will have to be raised up somewhat when the bigger tires go back on either way.

Although I think it would be a tortured interpretation of the rules:

H. Subframe bushings may be replaced with bushings of any material
as long as they fit the original location. Offset bushings may
not be used.

Does not say they have to be the same "height" only that they have to fit the original location, any material and not offset. I don't think shortened = offset.

[guibo09]

^I think by that rule portion up there, moving the subframe is completely legal. But if eccentric bolts are illegal, how could you get some camber adjustment back?

how are you reading it?

the way i read it is that the subframe is not a suspension component. it is therefore not free to be changed. the trailing arm to subframe connection is considered a suspension attachment point, and under sm rules, it may not be moved. the eccentric bolts move the attachment point, and are therefore illegal.

am i missing something?

[z31maniac]

^I think by that rule portion up there, moving the subframe is completely legal. But if eccentric bolts are illegal, how could you get some camber adjustment back?

my ix is already like this. stock ix bushings are about 1/2" taller pushing the subframe down for the 4x4 ride height, so with standard E30 AKG bushings my subframe is moved up. I spaced the diff down with some thick washers, it doesn't interfere with the diff at all, although I had it in there with no washers for 6 years without a problem.

Ahhhh good to know. I know I'll need to take a look after I get the swap done, but do you have any idea how much you could raise the subframe without it interfering with driveshaft? The rear subframe has a "hole" that the driveshaft passes thorugh correct? I can't picture it in my head at the moment.

IE, if you were to move the subframe up you start to lower the clearance between the driveshaft and the bottom of the hole in the subframe.

[guibo09]

i think the SM rules do not allow you to move the subframe at all. infact, even the IE style camber/toe adjusters are illegal. which is very annoying, because in the spirit of the rule, they should be legal since they arent designed to provide geometry adjustment, only alignment.

edit: and infact, a completely tubular/adjustable trailing arm is legal even though it is countless times better than the illegal adjusters.

[nando]

As a follow up to that, just to make sure I'm reading it correctly, we could move the rear subframe up (through shorter mounts for instance) and be legal.

The advantage being, effectively raising the pickup points for the TAs while lowering ride height and attempting to keep a more favorable rear geometry.

But since the diff mounts to the subframe, would we have to then space it back down? And would that interfere with the subframe. Hmmmmmmmm

my ix is already like this. stock ix bushings are about 1/2" taller pushing the subframe down for the 4x4 ride height, so with standard E30 AKG bushings my subframe is moved up. I spaced the diff down with some thick washers, it doesn't interfere with the diff at all, although I had it in there with no washers for 6 years without a problem.

[z31maniac]

That's what this guy did, effectively gives you adjustable wheelbase and toe. Then I suppose use an eccentric bolt in the mounting spot for camber adjustment.

[Joe318is]

i think it was group n. cant find pics. the are trailing arms with spherical rod ends to mount them to the subframe

[z31maniac]

or make group n rear ends.

adjustable control arms are legal too

Group N rear ends? Like the old E30 M3 stuff where they modified the angle? Got any links for that.

The control arms is interesting, I have been chatting with a guy from the GRM forum who has a really slick set of control arms he built. I'll post the pic he sent me when I get home.

[Joe318is]

or make group n rear ends.

adjustable control arms are legal too

[z31maniac]

As a follow up to that, just to make sure I'm reading it correctly, we could move the rear subframe up (through shorter mounts for instance) and be legal.

The advantage being, effectively raising the pickup points for the TAs while lowering ride height and attempting to keep a more favorable rear geometry.

But since the diff mounts to the subframe, would we have to then space it back down? And would that interfere with the subframe. Hmmmmmmmm

[Joe318is]

xp would be my guess.

[z31maniac]

On a somewhat related note, what class does moving pickup points place you in?

XP? Or a straight modified class?

[IsItElectric?]

Great, thanks. Someone in my region replied to my local post as well, and said the same.....so I'm good to cut & weld.

Thanks,