Mounting seat

Mount it where you get the range of motion you need for your shortest to tallest driver.  Mine is where the stock seat rails went.  You can mount it at an angle so that the seat rises as you move it forward.

You will need a sliding seat brace.  Here is an example: https://pyrotectstore.com/product/sport … ack-brace/

Mine is similar made out of square tubing welded to the cage where the straps attach.  Make sure the piece that contacts the seat has enough surface area that it wont pierce the seat.

THAT. get the seat in and set the cage for the tallest driver. Your helmet cannot be closer than 2 inches from any bar. We run a Gen III f-body, we are all around 6'1"-2" Our seat is basically on the floor. It backs right up to the cross bar.

We found our Sliders have way more throw than we need so it was easy.  Tallest is 6-1 shortest 5-9 I think

We mounted our cage with maybe 1 click to go back on the seat in case we ever have a 6-2 driver.

Once the seat touches the cage there is no point in it being able to slide back further (I think ours could slide maybe 1" beyond cage but we have plenty of forwards slide so haven't messed with it)  I think we just bought the commercially sold bracket and slider for our car from the seat manufacturer (corbeu) bolted it up and where like oh hey this is plenty of room.

In a car with a lower roof we likely would have needed to figure out how to make it lower.

I have heard of people mounting the seat Sliders on like a slope so seat effectively raises when slid foward.  Might be nice if you have a huge range of driver heights, we didn't need to worry about this with only a 4in spread.  We can all see just fine.  Some teMs appear to use foam "booster cusions" to help short drivers.

Another thing is when finding seat positions might wanna put on full gear or at least shoes and helmet/hans then belt in fully.   Our tallest driver ended up racing 2 clicks foward from where he originally Said he would sit.  Not a big deal for us as our shortest driver still only has the seat like 4" from the harness bar.  It would suck for your short driver to end up too far from the bar and get called out trying to get on track.  It's nice to have a margin of error and not plan on running all the way up to the 6in max (or if you do, maybe get the brace)

Just make sure your tallest driver's melon is 2" away from the cage and you should be fine.

I have to also imagine that things go differently depending on how hard your car is to cage and how tight the seating is.

Like if you are caging a small 2 seater for example a hard top miata and keeping the cage inside the bounds of the hard top (many people push the roof higher on these to get helmet clearance) or someone said the c4 corvette is very hard to cage due to the height of some rail.  Either way on these cars you may be very limited on where you can put the cage especially if trying to fit tall drivers and a slider.  I imagine that takes a lot of planning.

If you have an easy car (4 door 4 seater with headroom for example) all we had to do with the seat was bolt in a commercially available sear slider and rails to the factory mount no fab needed.  Then just marked tallest and shortest driver locations on a slider with a sharpie.  Since we welded our own cage in we didn't have to communicate with a cage builder.

If I had to tell a cage builder where my seat goes in an mg midget or how to fit a 6'7" driver it would have been a different experience

^This is an excellent explanation. And i totally understand: "we got it in the best we could." - that makes perfect sense to me. At least _something_ in the seat space to visualize clearance for measuring out the cage. Thanks for that.

what is it?

^ This.

But as I've said before, the text of the rule is unclear in its interpretation.

3.5.1 [snip]
"On all sides, all drivers’ helmeted heads must be at least two inches inside the area enclosed by the cage."
[snip]

First: the cage defines a VOLUME, not an AREA.
Second: the volume enclosed by the cage - and here's where I agree with Mr. Yuck, the "(whatever it is)" enclosed by the cage ACTUALLY DOES MEAN INSIDE the cage.

Though, as interpreted for so long, it's the exterior dimensions the rule contemplates, not the interior.

I have suggested changing the words to something like:

" 2" below the volume defined by the exterior dimensions of the cage (meaning the outside surface of the cage) " .

(I had posted a more succinct sentence, but can't remember it right now - though it's in my posting history).

That's a little more clear than just referencing "the broomstick rule"; where a stick is laid on the top of the cage, and the helmet can't come within 2" of the stick.

(There's got to be a better way to check, especially when the cage is installed close to the inside surface of the car; but that's not my area of responsibility - or expertise ).

I wouldn't want my head 1/4" away from the cage.

Good point!

But: remember you'll be in the seat, and how thick any 'ears' the seat may have, so even the helmet shouldn't be that close. And I can't imagine a cage builder putting another halo cross tube directly over the seat track - I have to think it would be in the middle, front-to-back, to give extra support and height, but not that close to the seat.

Anyway, I looked at the rules of:
The-Series-Which-Shall-Not-Be-Named,

... and their rules state that when belted, "the top of the driver’s helmet does not extend above the centerline of the main hoop. (my clarification: any driver);

and that's even closer to any crush / deform space in the case of a rollover, flip, or tilt.

But it may be easier to inspect.