Obviously having a good pressure gauge is key, but in my opinion, so is having a good tire inflation system. Many are the times when one finds oneself gridded up and in finding the sprayer, helmet, gopro battery etc, and swapping tires, cleaning out the car putting on driving shoes, going through tech and trying to remember the course you just walked (or that you drove in the morning), one discovers... "oh crap I didn't air up the tires!" If you have one of the rinky-dink consumer inflators you now have to choose which tires to inflate how much and maybe take your first run under inflated. We don't get many runs to begin with, it really sucks to have a throw-away run.
The problem is that most inflators have been designed to a task and the cost of parts minimized. The task they are designed for is road side and parking lot or driveway tire inflation, usually of a single tire that has gone flat to facilitate limping to a service station, or for topping up your tires. In either case spending 20-40 seconds to add 1lb of pressure is perfectly fine. The under inflated tire will be good to go in 5 min...
At an autocross one wants to NOT spend time on airing, but rather spend time mentally preparing for the run. Typically 4 tires need to be inflated 2-4lbs each. so 8-16 lbs at 30sec/lb becomes 4-8 minutes... which is an eternity when the grid chief is already sending cars at the head of the line. Or in the morning when you want to get to the tech line, or when course is already open and you need to get out and walk it...etc. Time is valuable.
I realized this long ago when I went to my one and only track day and nearly missed the start of my session because I was adding air to my tires with a commodity inflator. The following winter (2008-2009) I cobbled together this unit:
What that is is a Viair 300p compressor and an autozone whatever battery pack bolted and tied to a piece of plywood. It's heavy, the cord tangles on nearly everything, it takes forever to charge, and has a couple of sharp screws sticking out where they can gouge apolstery and leggs, but adding 2-4 lbs of air to the tires on my car is about 15-30 seconds. each.
This has been my solution for 10 years and it's been very durable, very reliable if somewhat heavy and unwieldy. But alas I've found that the battery pack is now not holding very much charge at all. Other drawbacks include an on-going risk that the clamps that connect the compressor and the battery pack are live 12v leads exposed where short circuit could be a problem. This poses an on-going risk during transport if the battery master switch is not attended to, and is just downright risky at rain events. It's been good, but now I've found better.
As the trend toward more and more powerful battery operated tools continues, small cordless air compressors have come out and currently there are 3 on the market, One by Dewalt, one by Rigid, and one by Royobi. They all feature a small tank, lithum batteries and standard 1/4 air hose couplings. The Dewalt unit sells for $300 with one 60v 2ah battery (6ah printed on the battery is only if it's in 20v mode). It's bigger more capable, and too heavy. Overkill for my use case. The Rigid unit is a 1gal tank and correspondingly smaller, but it sells for $250 with NO BATTERY. However, the Royobi unit without battery and with and included air nailer, hose and tire chuck is $129, or $99 by itself. With battery and charger, it's $179. It's also the smallest and as shown above comes with a very convenient storage for the hose.
It fills itself in 1-2 minutes and then stands ready. How fast is it at filling tires? When I got it I checked the inflation on my F150, and realized that the cold weather had me down almost 5lbs. Also the newly installed snow tires on my wife's camry were down a similar amount from sitting in storage. I topped up all 8 tires on about a half a 4ah battery. So one battery appears to easily provide 80lbs of pressure going into a 25-30 psi tire standard size vehicle tire. I set the output pressure to 90psi and the time to put 5lbs into my truck tire was 18 sec.
The pump comes on after about 2.5-3lbs added to the truck tire, so I suspect adding more than 5lbs at a time would get a lot slower. I suspect the pump on it is somewhat less than the Viair pump, but it has the opportunity to do work while you are moving between tires, so it's a very efficient design for topping up tires, which is exactly my use case.
The Dewalt unit is probably the winner for contractors with the larger tank, and better price than Rigid. The winner for autocross however is clearly Royobi on cost, size and accessories.
Note: I am not sponsored by any of these companies, and all of them are about to be completely blindsided by my review :). Prices for Rigid/Dewalt taken from Amazon on 12/16/2019, Price for Royobi from Home Depot (actual purchase: $129 kit with nailer/chuck and 2 4ah batteries on sale almost 2 for 1 price = $208 total before tax). I did not purchase or test the other units, analysis (and my buying decision) was based on features listed on the above mentioned sites. Royobi unit also was in stock at my local store, and available same day vs ~ 1-2 wk shipping for other units.
