extended ball joints

Front spindle is attached at 2 points...upper and lower ball joints. Draw an imaginary line between them. Now, without changing any other element, move the bottom mount point outboard 2 mm...that line has now moved as has anything on it(hub). Same drill, this time move the top mount inboard 2 mm...result is the same for argument sake in regards to the angle in relation to plumb. But the hub moves the opposite direction in the 2 cases...minimal but it changes(in or out...or wider/narrower).

I do wood for a living so gladly be corrected if my understanding is flawed

Track width? Lets get out the longacre toe plates...take some averages...and come up with a max number rule for front and rear! So simple! I recognize tires are a factor so add that to the equation...

my understanding is that the GCR spec for track width and method of measuring leaves a lot to be desired, which ultimately means that track width enforcement is not really a thing. 

Correct. Not really a thing. The last time, and only time, I saw track measured was when I asked for a competitors car to be measured last year. Took tech quite some time to figure out how to do it.

my understanding is that the GCR spec for track width and method of measuring leaves a lot to be desired, which ultimately means that track width enforcement is not really a thing. 

Really not difficult to do if Tech has something similar to a toe gauge with pointers on the end. One fixed end and one sliding end with measurement marks on the beam which holds the pointer ends.

SCCA

5. Wheels

c. The front track shall not exceed 1450 mm. The rear track shall not exceed 1475 mm as measured
per Appendix G, Measuring Track.
 

e. Tire tread (that portion of the tire that contacts the ground under static conditions) shall not

protrude beyond the fender opening when viewed from the top perpendicular to the ground. To
determine compliance, the vehicle should be rolled through a powdered substance, as raced with
driver, in order to indicate the tire tread contact patch under static conditions

G Measuring Track:

Track is the distance between the centerlines of the wheels as raced, without driver, measured at a horizontal
plane through the wheel hub centerline. Alternatively, it may be measured from the inside of one wheel at the
hub centerline height to the outside of the other wheel, then conversely from the outside of the first wheel
at hub centerline to the inside of the second wheel. The 2 dimensions obtained are to be added together and
divided by 2 to obtain the average. Measurements are to be taken at both front and rear of the wheels and
averaged to compensate for toe-in/out. Under certain circumstances it may be preferable to measure from the
outside of one wheel to the outside of another and from this dimension deduct the thickness of one wheel.
This should be repeated 180° opposite to the first measurement and the two dimensions averaged.

The SMAC and tech have worked together to very accurately measure track width. It is a very tech-able measurement. 

The angle is whatever you set your camber to. Use ebjs and set your camber to -3.5 and the angle is -3.5, use spacers and set your camber to -3.5 and the angle is -3.5 , use offset bushings and set your camber to -3.5 and the angle is -3.5.

Track has been checked on my car twice in last 18 months or so.


Ron
What about wheel offset and spacers? You can get to max either way and the angle is then the same.. correct?

Agree! Can always count on you Jim

Because of the difficulty in measuring track width for the average person...many of us have relied on information given by others. 95% sure it was you Jim who posted(within the last 10 years) that 25mm offset wheels(very available size) puts you right at but safely within max track width...I think on average a 3mm cushion? I have taken this as gospel and never questioned it!

My original point(frankly dont care which way anyone does it nor arguing one or the other better)was all things being equal, track width is changed when you install the offset bushings or the LBJ...in opposite directions! Minimally! 

Agree! Can always count on you Jim

 

Because of the difficulty in measuring track width for the average person...many of us have relied on information given by others. 95% sure it was you Jim who posted(within the last 10 years) that 25mm offset wheels(very available size) puts you right at but safely within max track width...I think on average a 3mm cushion? I have taken this as gospel and never questioned it!

 

My original point(frankly dont care which way anyone does it nor arguing one or the other better)was all things being equal, track width is changed when you install the offset bushings or the LBJ...in opposite directions! Minimally! 

I think you are correct. I think the general consensus was that the 25 mm put you real close to the max, then the 949 wheels came out and I think they are 23mm and was still within.. then EBJ and believe the SMAC ( current)  readdressed this and found there was a little more room. I have not gone back an remeasured as i run 949 or 25 mm wheels, no spacer and upper control arm bushings.  I would definitely remeasure if i was running 949 wheels and extended ball joints. I believe the current SMAC has, maybe they can elaborate. I cant answer that as I have no rechecked this is 8-10 years

A minor geometrical point, that has negligable effect....nevertheless, for precision:

More camber = wider track width, (almost) always. 

Using offset bushing pulls the TOP of the tire in, yes.  But, the tire (wheel, hub, spindle assembly) pivots around the lower spindle mount in the LCA.  So, the bottom of the tire actually moves outboard (like a see-saw).  Now, if you install the bushing such that the UCA is maximally inboard, then you will likely have to change the LCA cam bolts to REMOVE some camber.  This will pull the LCA spindle mount inboard also, which will result in a more narrow track width...in some cases.  So, -3.5* with offset bushings (maximally inboard) will have a more narrow track.  But, -5.0* lilkely has a wider track, regardless.

With the ELBJ, however, track width doesn't change for the same camber.  Yes, the ELBJ pushes the spindle mount outboard, which will widen the track...but that also results in maximal camber (eg, -5.0*).  BUT because the UCA (more precisly the UCA spindle mount (upper ball joint) hasn't moved, in order to get the same camber (eg. -3.5*) you have to move the LCA CAM adjustments inboard, by the added length of the ELBJ (if the ELBJ is 2mm longer than stock, then the LCA cams must be adjusted to remove the 2mm).  So, you have the exact same spindle geometry as with the stock LBJ with respect to the centerline of the car.  Thus with the ELBJ you are just moving the adjustment cams away from their maxxed out adjustments, but the distance from LCA pickup-axis to lower-spindle-mount remains unchanged. 

All these bets are off, if the subframe is bent.  Usually that means that the LCA/UCA mount points have moved inboard.  If the LCA has moved, then the cam adjustments will just put the spindle back where it was supposed to be (at best), in which case track width again remains unchanged.  If the UCA mount points moved inboard, then track width at the same camber will be slightly narrower (same as the offset bushings case above).

The SMAC and tech have worked together to very accurately measure track width. It is a very tech-able measurement. 

Care to elaborate on how a much of a SM's new tire's tread width touches the ground via the GCR's measurement process?

Drago, do you have any insight into how they measured?

The process delineated in the GCR leaves, by my approximation, 1/6 to 1/5 of the outer tire width not touching the ground with a typically setup SM (-3+ degrees of camber F/R) leaving the chalk/flour method of measuring a wide margin for wheel offsets.

Care to elaborate on how a much of a SM's new tire's tread width touches the ground via the GCR's measurement process?

Drago, do you have any insight into how they measured?

 

The process delineated in the GCR leaves, by my approximation, 1/6 to 1/5 of the outer tire width not touching the ground with a typically setup SM (-3+ degrees of camber F/R) leaving the chalk/flour method of measuring a wide margin for wheel offsets.

They checked me at the track with a jig that slid under the car and to the center of the wheel. Seemed easily repeatable.  I don't know how the SMAC did it

Care to elaborate on how a much of a SM's new tire's tread width touches the ground via the GCR's measurement process?

Drago, do you have any insight into how they measured?

 

The process delineated in the GCR leaves, by my approximation, 1/6 to 1/5 of the outer tire width not touching the ground with a typically setup SM (-3+ degrees of camber F/R) leaving the chalk/flour method of measuring a wide margin for wheel offsets.

The rule is what we live by.   "That portion of the tire that contacts the ground under static conditions."   Check the GCR or post #24 of this thread. Throw some powder on ground with driver/weight in car, roll through and measure.

The rule is what we live by.   "That portion of the tire that contacts the ground under static conditions."   Check the GCR or post #24 of this thread. Throw some powder on ground with driver/weight in car, roll through and measure.

That's great but in 17 years of SM, I have never seen them check it that way

That's great but in 17 years of SM, I have never seen them check it that way

I'll buy into that, but please tell me how how you've viewed them check part "e." of the rule. "e. Tire tread (that portion of the tire that contacts the ground under static conditions) shall not

protrude beyond the fender opening when viewed from the top perpendicular to the ground."

I'll buy into that, but please tell me how how you've viewed them check part "e." of the rule. "e. Tire tread (that portion of the tire that contacts the ground under static conditions) shall not

protrude beyond the fender opening when viewed from the top perpendicular to the ground."

Interesting, from what I have seen, several outlier cars fall foul of part e. of the ruleset, but I have never seen part e. measured in tech. 

I've also never in  tech viewed power tracking compared to fender opening. I have viewed track width checked two times. If the point is to argue rules, here's a SAFETY rule which could bit MANY car drivers/owners. Remember the Spec Miata video which was posted a few years ago where the cockpit lit up from fuel like a bomb went off. Please don't argue what "fills such opening" means.

9. Safety

d. In any automobile where allowed removal of upholstery, seat belts, etc., creates an opening
between the driver/passenger compartment and an exposed gas tank, or part thereof, including
the filler tube, a metal bulkhead which completely fills such opening shall be installed. See GCR
9.3. Fuel Cell Specifications.

Part of the problem with that rule is the taper of the fenders an quarters, narrower towards the ends. So the rule is interpreted by racers as being at the peak of the wheel arch. When “rolling” the fender lip as allowed by the rules it is a simple matter to be a little more aggressive than strictly necessary, bringing the fender out more particularly around the top. This was talked about more back in the day but frankly seemed pointless given a track limit, and doubly so now combined with a symmetrical wheel spacing rule.

Not only this but...ever stack a set of Hoosiers next to a set of RR's? I would think this might also show up in rule "e"? 

Track width rule as written is difficult for the average racer to check.

Portion "e" in theory seems fine...reality would argue it all day...to many factors involved. Add to that the change in track width for the NA car...I've never measured but my guess would be the outer measurement of the quarter panel fenders of a NA vs NB car are not the same? Definitely looked at cars(NA with lots of camber) as they drive away and think...man that car looks wide!

Based on what Ralph said it sounds like the SMAC has visited track width recently...my guess would be because of the 949 wheels and extended LBJ(since/before it became legal). Any discussion of a simpler measuring method and eliminated the non-enforced portion of the rule?

DD...Safety goes down another path. Lets keep this to Ball joint failure(and maybe track width )