My car people: questions before my autocross tomorrow

Greetings, People of the Church of Car!

I’m hoping my AX is a go tomorrow. Forecasts calls for heavy rain; this summer three of my events have been cancelled due to rain and extreme temps.

First: The interwebs can’t agree on proper tire pressure for AX-type driving. Any suggestions for my BMW 330ci (04) Pirellis? Over/under inflate? It’s stanced, 18x8.5/18.90, should PSIs be different for front and rear?

Second: last Saturday I drove the car up a very, very steep hill at snail pace (a real road, not off-road LOL). The oil lamp flickered on and off during the climb, it’s happened a few times since. The oil is topped off, no OBD codes, nothing else seems to be wrong.

I’m thinking that the extreme road grade confuzzled my oil sensor and it hasn’t reset (or it blew). In your opinion is it okay to drive tomorrow?

I would say if the interwebs can’t agree on the proper tire pressure changes for that particular situation, maybe that indicates there’s too little potential benefit from it to bother. If you could get a significant advantage from an idea that’s been circulating for this long, the way to go about it would likely be very well known. Given that, I say minimize your variables.

That oil light is troubling. I wonder if the oil sloshed all into the back of the pan due to the hill? Has it lit up on level ground? If not, you’re probably okay.

Got nothin’ on tire pressure. I just put mine around 40 and go!

Have fun. Wish I was there.

Oil pressure or level? Level is easy to measure so it could be a bad sensor or loose connection. Pressure would have to be confirmed with a gauge. Or a cloud of smoke and a bunch of rattling noises in a tight turn. Don’t ask me how I know this.

I used to run my street tires quite high for autocrossing, 40 sounds good to me also. Race tires were done more scientifically by measuring temperatures across the tread before they got a chance to cool down. We tried for the same temp across the tire. Cheap non contacting pyrometers make this easy today, we used to use needle probes.


You can have plenty of oil, and still have poor pressure if a gasket is leaking. If the dipstick is showing that your level is good, you are fine. But if it is the pressure, you need to get a mechanic to check it out. However, if you already have a leaking gasket, it needs to be replaced, there’s nothing else to do for it.

You can damage the engine by driving with low oil pressure, but just watch your gauges. If the pressure light flickers for a couple of minutes, or comes on and stays on, stop. If your temperature gauge goes into the red, stop (oil does some of the cooling of your engine, and if the car is not properly lubed, parts get hot fast). Have the car towed. Also, if you smell burning oil or see smoke from under the hood, stop. If none of those things happens, then you are probably OK. But I have not personally looked at the car, so don’t come suing me if your engine seizes!

Thanks, all: just got a text that the club organizer is concerned about storms tomorrow and will make a decision in the morning (worried face).

Did the following today:
-Split the diff and did 39psi for tires.

-No oil light flickering today, I replaced associated fuses and drove a few hours. I haven’t lost any oil over past seven days, nothing points toward low pressure or temp issues. I’m thinking the sensor got triggered when I went up the extreme hill and a fuse went. These E46’s have a rep for oil eating so I check levels often.

When AX season is over I do need to have my fuel injectors checked (replaced mass airflow parts a few months ago, still have a very occasional weird jerk at 80mph). Has anyone mailed injectors to one of the cleaning specialist places?

That’s a fairly common problem. One of the places where I work, there’s one who comes in now and then.

I’m really sleepy, so I hope this coherent-ish. When I autocrossed, I decided to keep the tire pressure the same as what I normally had it at. Since I was using my daily driver, my thinking was it would be most beneficial to any skill improvements I might make by autocrossing, to have the car in the same condition it would be in the rest of the time.

As for injector cleaning, I seem to recall it was cheaper to buy a set of new, aftermarket injectors than to have the old ones cleaned. That was for a Chevy though, not a BMW.

I guess it’s a feature, not a bug :smiley:

I’m a bit too obsessed with this very occasional hitch, I just can’t figger it out and it’s making me crazy!

Reporting back! A great day, no rain though apparently other parts of Nj are floating away.

Car ran perfectly, no oil lights. The course was fun and I did well for me – it was a “45-second” course and I did between 52-45 over 12 runs, not bad for my second AX experience. I’m starting to find the sweet spot with speed and not killing cones. I had one bad run, I knocked the shifter into neutral in a slalom.

Cool cars on course today (in addition to all the Bimmers, of course!): a Lotus, brand new Tesla, huge M-Benz AMG sedan that ran kickass times, and a woman doing amazing things in an ancient Subaru Forester.

Back when I used to do a,lot of track days, the organization I ran with asked inexperienced folks on street tires to drop 5psi (I think, it’s been a while) from the recommended pressure on the sticker in the door jamb. I got a pass on doing that as I had an email from one of the engineers at Lotus stating that their reccomended pressure was the reccomended performance pressure.

The ‘regulars’ were using pyrometers to measure heat across the tread to find their pressure, adjusting to manage fore and aft balance as desired. I wasn’t that well equipped, so I recorded the differential between hot and cold pressures, looking for a rise of about 10 percent.

I never did autocross as I had two tracks in close proximity and few autocross events on the calendar for my region. Friends that I had that were big into that scene had their own analytics, but I never knew if a 45 second run heated the tires enough for the methods I learned at the track applied.

IMHO and VERY amateur opinion, 45 second runs don’t produce enough heat to be significant at open events. At one non-BMW AX I went to a group of guys I label in my head as the “Illest-Hoonigan-Brembo-Drift Dudes” covered their tires between heats. Maybe it made them faster, but they were very sloppy and often out of control on the course. I hung out with some of the older guy drivers and they were ripping on how douchey the Drift Dudes were and making fun of their cars and tire cozies.

What did you decide on your tire inflation level? I would definitely not overinflate, as the tire pressure will only increase as the tires heat up on the course. And for autocross, I like having a little grab on those tires.

I went with 38, a fellow 330 driver with my same Pirelli Pzeroes suggested it.

As a very rank novice to AX, Im still going with other’s PSI suggestions. I don’t yet have a sense of tire performance subtleties and Sunday was the first time I pushed the car beyond my comfort zone and ended up doing an unintentional drift through a tight turn. This was due to braking/steering error, but it built my confidence in the car’s stability and my ability to recover from a bad move. It felt pretty dang cool, though!

One thing that I recall that might be helpful: watch the sidewalls of your tires, most specifically right where the edge of the tread ends and the sidewall begins. The tires I used to run had tiny arrows at that junction. If you see scuffing past that spot (into the sidewall), that’s an easy sign of underinflation. At least at the relative novice level.

Glad to read you had fun, Jennshark!

I realize I’m late to the thread, but I was going to mention the 10% rule. It’s the guideline we used with motorcycle racing tires.