Cage Tubing Diameter

The rules below dictate the tube diameter for various car weights. How do these rules apply - for actual car weight, or classed car weight?

My ITS car might be classed at 2600 lbs but with me in it with fuel it weighs 2750 lbs.

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The following table shows the minimum allowed tubing outer
diameter and wall thickness by vehicle weight:

GCR Vehicle Weight Tubing Size (inches)
(outer diameter x wall thickness)
Up to 1700 lbs 1.375 x .080

1701 - 2699 lbs 1.500 x .095
1.625 x .080

2700 lbs and up 1.750 x .095
1.625 x .120

If the tubing diameter used is at least .250 inch above the
minimum diameter required, based on vehicle weight, the
minimum wall thickness may be .080 inch.

Weight without driver (vehicle weight).

No, note that the table says "GCR Vehicle Weight", which in all cases includes the driver. So regardless of what your car actually weighs, your required cage tube size is based on the minimum weight listed in the GCR. In your case, you can use the 1700-2699 pound category tube size, since you're listed at 2600.

Quick history lesson - for many years the tube size was based on a table of under 1500, 1500-2499, and 2500 up, using vehicle weight without driver. Then SCCA started basing vehicle weights on all-up at the end of the race, including driver, in most cases by adding 180 pounds to the previous (without driver) weight. And to maintain the cage rules unchanged for existing cars, tube sizes were then to be based on listed weight less 180 pounds. SCCA also came up a completely different table for SS and IT cars, based on the presumption of bolt-together cages. This had breaks at 1500, 2200, 3000 and 4000 pounds (also based on GCR weight less 180 lbs). In the latest iteration (starting 1/1/08), all cars including SS/IT now have to meet tube sizes based on GCR weights, which include driver. And the weight breaks are now at 1700 and 2700 instead of 1500 and 2500. So the newest rules are just like they've always been for most cars, except the presumption is now a 200 lb driver instead of 180. And the SS/IT cars how are treated just like all other cars instead of having a more stringent set of requirements - this eliminates the silly situation where IT cars had to have better cages than the (usually) faster Prod and GT cars.

Except they removed the option of using 1.5x0.120 tubing for cars over 2700lbs. Since I have a cage with 1.5x0.120 tubing and a log book from before the change my cars been grand-fathered. But what whould happed if I tried to run STU for example?

OK, cage GCR changes got me again. GCR weight (with the assumed SCCA driver) not actual vehicle weight with or without driver.

Yea, I forgot the part about the 1.5 x .120 option going away (also I ignored the older option of using a thinner/smaller tubing if it was chrome moly). On your STU question, it depends on whether you'd be required to have a different logbook for running the car in another class. I've never seen anything that specifically addresses such a change. And I do have a real life example where I'm using the old ITB logbook for a car that has been converted to FP. But I'm not sure if this might be an oversight by tech, or it is in fact the way the rule is supposed to be interpreted (i.e., no new logbook required). But in my particular case, the cage rules are the same for both classes, so I'm legal either way.