There are different classes of costs, if I may use that terminology. There're the costs just to get to the track and run a car, and then there are the costs to be competitive and win. Of course, a lot, if not most, of the people in this discussion are experienced and successful and so we're talking a lot about cheating and $10,000 pro-built engines. For much or most of the field, though, those issues are irrelevant. If we're talking about attracting more racers and growing the fields, it's that first class of costs you need to be thinking about.
In my opinion there should be far more rules and the class should be much more spec. We should be actively looking for where people are spending their money, and more importantly, their time, and be actively squashing those things. That's how you'd make the class more attractive to newcomers and "increase retention."
A few examples and other brainstorming:
At least in San Francisco region we have different sound restrictions at different tracks so people are swapping exhausts/mufflers/pipes depending on the track. Spec the entire exhaust, including a 90 db muffler, and let's be done with it.
There's this nonsense with hub repacking. Let's find a hub that lasts 60,000 miles, add it to the spec, and be done with it. If you wanna still repack your hubs a few times a year, go ahead, but for guys that just want the car to run reliably that's more time and money in their pocket.
Let's find a brake pad that lasts a long time, probably a street pad, spec it, and spend less time and money swapping pads and rotors.
I know that policing tire shaving is difficult or impossible, but that would be nice.
Tire allocations, kinda like they do in F1. You start with four and then you get one tire allocated for each event you participate in. When you get a new tire, it gets registered to your name, taken from your allocation, and an ID or a stamp/seal/whatever is stenciled onto the sidewalls. Can't show up to pre-grid with non-registered tires. Maybe do occasional checks that people are running tires registered to them or maybe just let people swap tires around. This means a set of tires would have to last four events. I don't know how quickly the top guys are going through tires, maybe that number should be more or less. At least some people in the field will be stretching out their tires to last longer. Maybe Toyo won't like this, but maybe we could convince Toyo to market it as them being more environmentally responsible.
Not sure what to do about rain tires, but there has to be some way to do away with them.
For that matter, let's spec a street tire that'll last 10,000 miles. Other classes have done it. Then your allocation by the above plan will be more like 0.2 tires per event.
I'm not sure why a non-stock suspension was specced in the first place if the idea was to keep costs down, but I see there's no un-doing that. Makes no sense to me, though.
For me, and for several people I know, the biggest obstacle to racing is/was towing. One solution is to drive to the track, another is arrive-and-drive rentals. If you really want to increase field sizes, especially in places like SFR where land is expensive, you should be looking at ways to promote those. I have some ideas around that but I think they might be unpopular so I'll keep them to myself for now.
Tougher rules and enforcements around careless, dumb, or overly-aggressive drivers who are damaging and endangering other people's expensive equipment.
This is all just brainstorming (although I do think some of these ideas are fantastic

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