Hello there and welcome to the BMW Car Club of America.

If you are a BMW CCA member, please log in and introduce yourself in our Member Introductions section.

autocross help

Discussion in 'Autocross' started by wanesso, Jul 22, 2008.

    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    Have never done autocross or even seen it, signing up for Oktoberfest as the first--but by the intensity of these threads I think I'll be in over my head-------but not going to modify my car so,
    1)what is the most comfortable helmet to buy? the choices are baffling to the novice....any experienced suggestions are appreciated
    2) am I going to cream my stock tires (Michelin pilot sport) in one event or injure any other part of the car?
    • Member

    az3579

    Post Count: 3,270
    Likes Received:3
    I don't know if I can answer the tire question for you seeing as I've never driven an M-car (and hate myself for it) I don't know how they treat the tires under pressure. BUT, I can tell you that I'm a cheap sonuva** and bought the cheapest $100 helmet I could find and am pleased to report that I didn't notice any uncomfortable moments in my helmet during my entire day at the track, other than the given "I DON'T WANNA WEAR GLASSES!" moments when I had to keep takin' them off to put the helmet on...


    But for reference, the helmet is a Zamp FS-2 and it cost about $100 on eBay. Last I checked, the price was $89 a few months ago. It's Snell SA-2005M approved. I can find it for you if you want...
    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    good helmet advice, thank you--there are some pricey models out there-- if this one is comfortable I'll try it (if you can easily find the link, much obliged)--will start driving to work w/ helmet and scare of few commuters.....
    Regarding tire pressure--is the higher pressure mandatory or a suggestion....
    • Member

    az3579

    Post Count: 3,270
    Likes Received:3
    The optimal tire pressure varies. People play around with their pressures and the serious track day mongers actually write down what pressures they're running every run so they can compare it with the other day's pressures. I'm a beginner, so I couldn't care less about my pressures, so I just fill the tire up with air to the usual 35psi and forget about it the rest of the day. It never really becomes an issue, so I don't think about it again. (I will probably get yelled at by the more experienced track monsters :))


    I looked up the seller from whom I bought my helmet and he is no longer listing the helmets. In fact, he's not listing anything anymore; perhaps he went out of business. I do see quite a few helmets that look similar, but they're different models or a different brand, and I don't know how those compare as this is the only helmet I've ever worn. If you give me your size, I can look up to see what I can find... again.
    • Member

    Brian A

    Post Count: 657
    Likes Received:7
    My thoughts

    Regarding helmets:

    - buy your first helmet in-person from a shop. Good fit is important and you can't try it on when you buy on-line.

    - If you need to keep it cheap, look for deals on Snell 2000 helmets. Snell 2000 is still allowed for 2 more seasons after this one. At the start of this season, I bought a really nice Snell M2000 full face for $40 at a motorcycle shop.

    - For autocross, you basically need a helmet to comply with insurance requirements for the club; yeah, you could knock your teeth out on the steering wheel, bash your head on the B pillar or get hit by something airborne, but extremely unlikely. Autocross is very safe.

    Regarding tire pressure:

    - I run my 195/65R14 tires at 40 psi for autocross. Any less, and I get too much tire roll-over on turns which chews up the sidewall like crazy.

    - Some people mark their sidewall with chalk before each run to see how much sidewall they are burning up and adjust pressure accordingly.

    - Autocross does reduce tire life, but not that much, its worth it and thats what tires are for.

    Regarding first time:

    - No preparation needed; you'll have a blast.

    - Its not that stressful for the car. You just get it to second gear and go; its all braking and steering (and sliding and spinning).

    - Ride as a passenger as much as possible in groups that run before you. Take an instructor along for each of your runs (they are often available) to get tips.
    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    autocross questions--more

    Would that I could try a helmet--the only place near here that I know of is a motorcycle store, they said I could not use their helmets for autocross....perhaps that's incorrect--- If they have the appropriate Snell rating why not?.
    So, one never gets out of second gear-- Do you turn "on" the M-dynamic mode and "off" the dynamic stability control? I'll put tires to 40psi and not worry about that further.
    I know it's frustrating dealing with a novice, I do appreciate the time and patience, I'm sure once I've seen it I'll get it, the motto in medicine is "see one, do one, teach one..."

    Thanks all for the advice.
    (does anyone know of any videos filming this type of autocross)
    • Member

    Bimmerdan

    Post Count: 422
    Likes Received:4
    I've been autocrossing for 19 years now (some years seriously, some years not) and the one thing you can rest assured about is that nobody minds helping a novice!! You have to remember, every single one of us had a "first time"! We all know what it feels like to show up thinking "I'm going to make a fool of myself and people are going to get tired of my questions..." Nothing could be further from the truth.

    For your helmet, go to the motorcycle shop. Like Brian said, if you've never bought one before, you really need to try it on to see how it feels. As long as it's Snell rated (and dated 2000 or later), it will be fine for autocross. If you think you may get into the sport a little heavier and start doing some track days (driver's schools), you may want to consider investing in a more substantial helmet but for now, the one you can get at the motorcycle shop will be fine. Later on you'll have a better feel for what size/style feels most comfortable and you can buy on-line for some decent savings.

    For tires, 40 psi is probably a good place to start. Unfortunately, the new M3 doesn't really have enough history behind it for people to know how it's going to react to tire pressures. There should be air available at the autocross though, so you can always adjust up or down as needed. Invest in a good pressure gauge and keep it handy during the event (whenever I'm helping out a novice, I'm always impressed by the ones that bring their own gauge...don't ask me why, I just am).

    The most important thing to remember though is to have fun! O'Fest can be a little different than some autocross events regarding instructors and/or passengers. I'll try and get an answer for you about that.
    • Member

    Bimmerdan

    Post Count: 422
    Likes Received:4
    I just got word that there WILL be instructors available for this year's O'Fest so if you want someone to ride with you for the first couple of runs (or all day), they will be there for you!
    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    That is great! I will ask for an instructor and I appreciate your support and kind words.
    • Member

    az3579

    Post Count: 3,270
    Likes Received:3
    Thank you! I run the same exact tires and that bit of info will probably be very useful for my upcoming track day.

    Isn't the maximum pressure for the tire like 44 psi? Won't it reach that pressure when the tire heats up?

    agranner guest

    Post Count: 20
    Likes Received:0
    This novice's tire pressures

    I've been out at Windy City's autocross only 4 times. It's a lot of fun, the experts are VERY nice and helpful, and my times are already starting to come down (I'm not last in my class anymore).

    I decided to pick a good pressure and not mess with it too much (improve the loose nut behind the wheel). So here's what I did:

    BFg g-Force Sport 205-60-15 new this spring (< 5k miles)

    Started at 40. I quickly realized that the pressure goes up A LOT and I was up around 48!

    Adjusted to 44 HOT (took a guess, drove the first set, adjust to 44 as soon as I park, leave it all day). Then I guessed these were too high so I lowered it to 42 and my times improved so I kept going down. At 38 I had too much roll-over. So at the last event I set them to 39 and got my best position ever.

    -- Aubrey Granner
    '93 325i
    • Member

    az3579

    Post Count: 3,270
    Likes Received:3
    Are the tire pressure differences obvious or do you have to pay attention to minor details to notice the difference?

    agranner guest

    Post Count: 20
    Likes Received:0
    Oh, you can definitely feel the difference.

    Lower pressure = less feedback and "mushy feel"
    Higher pressure = more feedback and a "snappy" steering feel

    From everything I've read, the above has NOTHING to do with maximum grip. The key to grip is to get the tire contact patch pressing down evenly across it's width.

    -- Aubrey Granner
    '93 325i
    • Member

    MGarrison

    Post Count: 2,892
    Likes Received:150
    If you have a stock car, or mostly stock, tire pressures are probably the only thing you can adjust, to attempt to adjust/improve the car's handling, and improve your autocross times. I don't think it's critical to worry about your tire pressures being higher than the max. recommended driving pressures in an autocross situation. I suspect it would take upwards of 20lbs+ or more over the max. recommended pressure to get into a range where a tire might blowout, and it would probably have to take a direct hard hit to do that. Unless you jump a curb in an autocross with a way over-inflated tire (highly unlikely for most course layouts), a few pounds over max. recommended pressure just isn't going to be that critical.

    On a hot day, I think it would be easy to see your tire pressures jump up to 4 pounds by the end of an autocross run. It's a good idea to know your cold pressures, and your hot pressures, it helps for tweaking handling, and keeping track of things so you'll have an idea where to start next time.

    People use chalk, liquid shoe polish, or maybe even a light colored grease pencil, to make it easy to see how far their tires are rolling over onto the sidewall. If you look closely, you can observe from the scuff marks how far the tires are rolling over (without chalk, etc.). I recommend adjusting pressures to a level that keeps the tires from rolling too far over and onto the sidewalls. Try to keep the primary scuff marks in the 'meat' of the tread edge, if you let them roll over too much it's easy to have the sidewall tread feather, and then ultimately wear off, which would amount to some premature sidewall wear (easily avoided with a small bump in pressures).

    Tires have indicators on the sidewalls that are typically an excellent marker for max. tire rollover, typically little triangular shaped pointers around the tire's periphery. (see pic) - a little light scuffing beyond the pointy ends of the markers is ok, but if you have them scuffing heavily into the diamonds, it's probably a good idea to adjust pressures up enough in order to preserve your tires (obviously, you run out of tread depth as the tread tapers to the sidewall).

    So, after that, if you have your tire pressures adjusted to where they're rolling over to the edges of the diamonds, then you should assess how balanced your car's handling is with those pressure settings (note that there will probably be different pressures for all 4 tires, the driver's side will likely need 1 or two pounds more than the passenger side, due to the extra weight-loading of the driver on that side). Is the car fairly balanced and neutral, or is there understeer (front end wanting to push out), or oversteer (back end wanting to step out, come around, etc.)?

    Then, within a range of adjustment, you can start tweaking pressures to get the handling balance you want for an autocross. Since autocross courses are tight, I usually find I want the car to oversteer a bit, and oversteer more than I'd want it to for driver's school track handling, or for the street. The oversteer helps the car to rotate a bit, and facilitates making the tight turns of auto-x courses. Of course you don't want too much oversteer - if you find that you're having to let-off and countersteer because the back end's sliding too much, you'll be losing time on the course.

    Typically, adjust tire pressures in 2lb increments, or 3. If you find you're rolling way too far over, or not far enough, then maybe as much as 4 or 5 lbs to get you into the ballpark.

    By the way, any autocrosser with some experience (as mentioned in an earlier reply) should be happy to help w/ settings and any advice, don't be afraid to ask. All this, word-wise, might make it sound intimidating, but it's not, and standing next to a car, all this could be explained verbally in about two minutes.

    Grassroots Motorsports got it's start as Auto-x, the grassroots motorsport magazine, and waaaaaay back when had a little guide for auto-x basics - from that:

    More Oversteer, Less Understeer:
    Front Tire Pressure: Higher
    Rear Tire Pressure: Lower

    More Understeer, Less Oversteer:
    Front Tire Pressure: Lower
    Rear Tire Pressure: Higher

    Up to a point, increasing tire pressure should increase grip at that end of the car; decreasing tire pressure, the opposite. If you have pressures _really_ high, you could decrease grip because the tire's crowned, and unable to roll over, but that would be way above the range most tires will probably be in for autocrossing, which generally would probably run from 35-50 psi for most stock, non-modified cars.

    36psi might be a good starting point for cars with regular tires, low profile or ultra low profile tires, particularly on a high horsepower car, I'd guess 40, or maybe even 44, or the max recommended tire pressure. Might not hurt to factor in the potential pressure gain, so perhaps 2-4 lbs less than max recommended pressure, cold, for late model M-cars, or tires w/ an aspect ratio of 45 or lower.

    Doublecheck the helmet requirements for O'fest, typically Snell SA rated helmets are required.

    Sorry for the length, hope that helps some -
    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    Great info--
    now regarding tire profile and pressure---this car has the 19" wheels, rear tires sl. bigger behind (?), low profile----does this change how I would modify the tire pressure---or how it handles in autocross mode?
    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    I see you did address that last question in the last paragraph-----I'll go 2-4psi under the max. Regarding the 19" wheels--, is there a performance difference with bigger wheels, lower profile tires?
    • Member

    Brian A

    Post Count: 657
    Likes Received:7
    You'll have fun and learn a lot for next time

    At your first autocross, it's unlikely you'll notice the performance differences between subtle changes in tire pressure. Probably it'll become something you become sensitive to (and start tweaking) over time.

    Be careful not to blame slow times on "wrong" tire pressure. Going fast requires a lot of skill. Likewise, a season of autocrosses will teach you what you want (crave!) to modify on your car. It's not worth guessing in advance.

    At your first autocross, you'll be amazed at how fast a car can go through the cones. Likewise, you'll be horrified as to how devilishly difficult it is to do. Going too wide is slow. Going too tight is slow. Drifting is slow. Spinning out is real slow. Plowing is slow. Perfect is fast. The good news is that lots of people are slow; even folks driving massively modified cars. More good news is that no one sticks out as "incompetent" while they are out there; it's just that some turn out to be slow and some fast.

    Note MGarrison's warning about O'fest helmet standards. You might need a "SA" (automobile) helmet rather than just an "M" (motorcycle) helmet. Find this out before you buy.
    • Member

    Bimmerdan

    Post Count: 422
    Likes Received:4
    OK, I copied this directly from the O'Fest Autocross home page:

    The required minimum helmet rating allowed is a Snell-rated SA2000 or M2000.

    Like I said earlier though, if you plan on doing any high-speed track events or running with clubs other than BMW CCA, you may want to consider upgrading to an "SA" rated helmet but for this event, either will work.
    • Member

    wanesso

    Post Count: 150
    Likes Received:0
    wow--I'm psyched! This sounds so fun.....
    (and ordered a helmet which meets all standards)

    Again--thank you all for the advice.
    • Member

    MGarrison

    Post Count: 2,892
    Likes Received:150
    To address how your car handles with staggered tire widths - wider rear tires means more lateral grip at the back end of the car, which means that your car will likely tend to understeer (push) more before transitioning to oversteer.

    BMW's tire sizing is purposeful, with the intention of making the car a little easier to handle by your average driver should they find themselves beginning to approach the car's handling limits.

    BMW presumably doesn't expect all of its customers to be expert drivers; a driver unexperienced with rear-wheel drive cars and how to properly react and countersteer when they're in an oversteer situation may quickly find themselves spinning-out (as it were), or even suffering a collision due to loss of control, particularly if the car's basic handling tendency is tail-happiness. BMW dials in understeer just to increase the likelihood of disaster avoidance.

    An inexperienced driver's reaction, should they find themselves pushing the car's handling limits enough to make the front end push out and the car's initial tendency is to understeer, is likely to be something like 'oh, I'm going too fast, I need to slow down, so I'll lift off the throttle', which is an appropriate reaction when experiencing an understeer situation. You lift off the throttle, weight is transferred to the front of the vehicle, the forward weight transfer increases the front tires' footprint (contact patch), front end grip is increased, and the car will start to turn back in on a tighter arc, rather than the wider arc it was wanting to follow when the front end was wanting to push out.

    Rear-wheel drive vehicles like BMW's will certainly oversteer, but your staggered front-to-rear widths will make that transition typically occur a bit more gradually than if you had the same width tire on all 4 corners. Not that it's recommended (for either safety, sanity, your license, or the life of your tires), but higher hp. vehicles can use their power to get a power-induced oversteer; much like your classic burnout, but if you stomp the gas in the middle of the turn, particularly in an M3, you'll likely the find the front and rear ends wanting to swap locations with an alarming alacrity.

    In any case, in any rear-wheel drive car, you always want to be mindful of the potential for oversteer, and be ready to react to it.

    Fwiw, I think auto-x's are a good way to build your car control skills, including sensing what's going on with the vechicle and responding appropriately. The speeds are relatively low, and you're likely to get understeer, oversteer, skids, sudden weight transfers, braking, etc. and even if one completely loses control of the car, the most you're likely to hurt are a few orange cones. Auto-x doesn't necessarily build the smoothness desired for a driver's school skillset, but most driver's school events don't have the luxury of a skidpad (some do) to allow you to practice car control, catching skids, etc.

    If you want to consider tire-grip optimization (for max handling), that would be the next step beyond adjusting pressures for rollover. As Aubrey mentions above, he's tweaked pressures to get his car working well for that particular course, day, temps, weather, and been able to both feel a difference and see it reflected in reduced course times. Obviously that can be accomplished tweaking pressures.

    The 'ideal' maximum cornering grip would be to have the tires' contact-patches 'flat' while the car is cornering, and thus the maximum of the tire's tread contacting the ground, when turning. The various things out there to adjust camber and provide increased negative camber are designed to attempt to achieve just that. So okay, you have a stock car with no type of camber or any other adjustment, how to tell if your tire pressures are good beyond just feel and not having them rollover too much?

    Using tire temperatures! Of course the tires get hot when they're getting a workout, and the tread temperatures will vary depending on which area of the tire is being worked the hardest. The ideal would be the outside edges and middle temperatures to be even all the way across, which indicates the tire is being worked evenly. With a car that has completely stock suspension & settings, you'd never see that (I think you would likely see it in only the most highly modified dedicated track and auto-x cars, at that). The outside front edge is always going to have a higher temp. than the inside edge, particularly if everything's stock. That doesn't mean a temp. reading is useless, because it can indicate if you're underinflated, or say, if the middle temp is higher than the outside edge, you'd be over-inflated. For a stock street car, you'd shoot for a relatively even spread as temps increase up to the outside edge.

    There's infrared laser-pointing temp. sensors that work easily for that, as well as probe-type tire temp. gauges. However, tires cool off quickly, so surface readings need to be taken quickly after a run to be meaningful. A temp. probe takes a reading further into the tread, so an immediate reading is slightly less critical, but you still can't wait all that long either. If you really get into auto-x, tire temps can be useful as a guide to pressure adjustment and optimizing handling. Hardly necessary though, and I think at O'fest it's unlikely we'll see anyone manically hopping out of their car after abruptly pulling to the side after a run and trying to take tire temperatures. Willing spouses, s.o.'s, or other like minded partners-in-crime (well, sorta) can be handy for getting temps taken and recorded.

    Other tips -
    Walk the course as many times as you can, slowly, and processing visually and mentally what you may expect to be doing at any point on the course. When you walk the course, walk it in the position you expect you'll be in when you're sitting in the car (easier to visualize what you'll have to negotiate). If they draw up a course map, study it. An autocross course can look like a sea of orange cones, it's easy to get lost, so knowing the course is important. Do a little googling (I'm sure there must be something out there) to get familiar with terms, like how a 'gate' is layed out with orange cones, what pointer cones are and how they'll be setup, and so on.

    It will be critical when you're driving the course to keep shifting your eyes well ahead of where you and the car are on the course, to both keep from getting lost, and to allow you to setup and anticipate whatever's coming up next, which is gonna be coming up quick.. real quick! So, practice that as you walk the course. It's easy to just shift your eyes when walking, but very sharp turns may require you to turn your head 90 degrees and look out the side windows, make sure to incorporate that into your course walk, if necessary.

    When you get your helmet, wear it around the house a bit to get used to how it feels on your head.

    Your driving position for an auto-x probably will be closer and more upright than your typical daily street driving. You'll want to be able to have your left foot firmly planted on the dead pedal, and able to fully press in the clutch (assuming you have a manual transmission). You should have the seatback in a postion that allows you to touch the top of the steering wheel with your wrist or the base of your palm, without having your shoulder break off of the seatback. If you have to reach much, you're too far back. Any of that may have to be compromised depending on your personal dimensions. For instance, if your ideal seating position has your head banging the roof when you have your helmet on, you'll have to compromise a bit and angle the seat back a bit. Ideally, you should be able to have your hands at 9 & 3 o'clock positions, with your elbows bent. A straight-out elbow-locked position means you can't move your hands all the way around the steering wheel (which you'll likely need to be able to do).

    If you have the habit of flipping your hand upside down, grabbing the inside of the steering wheel rim, and pulling the steering wheel one-handed through a turn...... you'll want to break that habit and get used to keeping your hands on the outside of the steering wheel, only! Virtually impossible to negotiate a tight auto-x course without having to do some hand-over-hand steering, but you'll want to keep your hands moving around the outside and no more hand-over-hand than's necessary. Flailing at the steering wheel won't help course times.

    Likewise, try to keep shifting to a minimum, the course will probably be mostly 2nd gear after you get going (less of a concern w/ SMG, presumably).

    You can use the seat belt's inertia lock to help lock you into the seat, particularly if you have power seats - get your seating position, fasten the belt, move the seat back several inches, snug the belt a little bit, grab the seatbelt near the top and give it a quick yank to engage the inertia lock (it should stop pulling out when yanked quick), keep the pulling tension on the belt, and move the seat forward again; as you move the seat forward you should be snugged into the belt, and if it's tight against you, the inertia lock will stay engaged, keeping the seatbelt tight.

    Another seatbelt option - get your seating position, latch the seatbelth, snug the belt up fairly tight, hold the buckle in position on the belt, unlatch it, and turn the buckle several times (twisting the belt in the process locks the buckle into a set position and the belt can't slide through the buckle), and re-latch.

    Try not to do a smoky burnout on the launch, if you have the engine revved too high, you're just wasting time after the tires start spinning for them to hook up again and start moving the car. Tires provide maximum grip at about 20% slip, so a extremely noisy launch is just wasting time, as well as your tires. You'll want a bit of squeal, but not too much, and you don't want to bog down either. Takes practice, so don't worry about it too much, just get launched as quickly as you can.

    After your first run, and at the end of the day, you'll be saying 'Wow, that was a lot harder and more challenging than I expected, but.. holy cow was that fun!' ;)

Share This Page