I will dig a little deeper into data collection systems in future posts. After I thought about it, it just seemed like a disservice to jump into higher level stuff without first covering the basics. There is a huge amount of insight than can be gained through a little discipline and basic tools. It is best to exploit these to the fullest before moving up the ladder to more advanced systems.
Post #2 – The most basic data you should work with
As a continuation of my first post on discipline and making a habit of recording data, I would like to go a little more in depth on what data is important. By far the most important component of a competition car is the tire. It just so happens that it is also the most complicated thing on a car. A tire is composed of fused polymers and chemical additives that once cured exhibit certain characteristics that directly affect the grip and performance of a car. And to make things even more difficult, tire manufacturers cannot predict what the final performance characteristics will be. It is not uncommon for a new race tire compound to be slower than the compound before, deteriorate quicker, require a different set up, etc. And tire manufacturers do occasionally change compounds. If you are at the sharp end of the stick, you will sometimes see manufacturers release new compounds just before the SCCA Runoffs each year. Sometimes everyone switches over, sometimes not. You don’t have to look any farther than today’s modern F1 racing to see how a team’s tire strategy can make or break a weekend. Just a few degrees of ambient temperature change or track moisture can make a tire compound undriveable, and they must race with at least 2 compound changes during a 2 hour race. And by now it should be obvious if you change tire brands you will definitely have something different to deal with when hitting the track.
So let me make a couple clear statements which will drive our future priorities on data collection.
1. At amateur levels of competition, the DRIVER has the most influence on competitive lap/sector times. Sometimes up to 70-80%. There is no better way to knock whole seconds out of your lap/sector times than becoming a better driver.
2. Following driver ability, most races are won and lost based on the ability to extract the most out of a tire, as opposed to horsepower.
So, getting back to basic data, our top priorities are making sure the tires are happy and somehow measuring the driver. Luckily the first step does not require a large expenditure or knowledge. You are probably already measuring the driver. If involved in competition, you are already comparing yourself to others. As mentioned in my first post, keep a record of where you are at. Here are some examples:
1. Lap times at a circuit and why they were slower or faster than previous run or visit to track. Weather, perceived surface grip, struggles on track are good details here.
2. Your ranking against your peers. Getting better or worse?
3. Get some segment times, have someone with stopwatch measure your time within two key points and other cars at the event.
4. Target another driver who often attends your events
5. Try something different on track and see if the lap times changed for better.
Pretty basic stuff but can reveal some trends. Recording this kind of info does 2 things. Forces you into setting goals, and hopefully understanding why sometimes you are faster or slower than other times.
Next up it tires. As mentioned, a difficult subject even at the most basic level. So let me make another all-encompassing statement here:
Every tire has a happy spot related to temperature, pressure, and camber where it makes the most grip.
Again, not a lot of special tools or fancy systems required at the basic level. And depending on how restrictive your class is, this may be as far as you will ever need to go
The first thing I will talk about is pressure. As mentioned, there is an optimum pressure you want to hit. What is that pressure? Without getting into too many details, you will need to find this out for yourself and that can only come with testing. A tire works best when hot, so that is where you when you want to measure the pressure. Tire manufacturers often provide a window but this can be misleading without knowledge of the weight characteristics of your vehicle. And manufacturer provided info will lean on the side of safety, so usually a little higher pressure than required. So to start out take recommendations wherever you can. Online forums, friends, competitors, and the manufacturer info. Then test for yourself. Don’t make small changes at first, for a radial try what you think is a good number then at least 5 psi above and 5 psi below. If you can’t feel anything, try 8psi delta. Record how it feels and which was fastest. Most likely you will find your happy middle number will need to creep up or down. Then over time you can fine tune with lower increments until you are satisfied. And if running a spec class, it is possible that tire pressure is the only thing you have to change handling characteristics.
But “hot” pressure can depend on a few factors. Air expands as it heats up, so where you set your cold pressure will be less than the pressure you read as you come off course. With the exception of tire warmers, most everyone will need to predict a cold pressure to start with and measure the pressure as soon as you come off course. So here are the things to consider:
1. Tire air moisture content. The wetter the air, the more expansion. If you use the same air source over and over, this should be consistent. If you would like to limit the amount of expansion, use a compressed air dryer or bottled gas. Air is mostly nitrogen, so switching to pure nitrogen is no better than just using dry air. You can build your own compressed air dryer on the cheap using silica gel desiccant. We have also used scuba air.
2. Ambient temperature has to be adjusted for. Setting your cold pressures on a 40 degree day will be lower than on a 80 degree day. If you normally allow for 5psi of pressure rise, you may need to allow for a 10psi rise. Be careful here, the fastest way to heat a tire is pushing high slip angles, but if it is really cold you may need to bring up the temp slowly before attacking a corner.
3. Use a reliable pressure gauge that is calibrated. 0.1-0.2 psi resolution. Don’t be afraid to check it against other gauges over time. Never use a friends gauge to set your pressures unless you can verify it reads the same. Repeating the same pressures you like every time is important.
4. Your goal should be predicting the hot pressure +/- 1 psi or better.
5. And as a side note, swaying back and forth to warm the tires before a race has limited impact. You can also use the brakes to create slip angles and put heat in the tires with the added benefit of getting some residual heat through the rotors and wheels. Often this is more beneficial.
Next to consider is overall tire temperature. A tire pyrometer works best but a cheap IR gun also works in a pinch. Believe it or not, this is the simplest thing but many have problems here. Most pure race tires operate in a range from 170 to 210 degrees F. I don’t know what the current crop of 100 and 200 TR tires operate at. So if you are running an R compound or slick, and you measure 130, you are not in the range of most grip. There can be many reasons for this, the least of which is not driving hard enough. Too stiff a spring rate and excess shock valving can also show up here. Along with a damp cold track. If you can’t get enough heat in your tires most other testing is useless. Remember to take good notes. Tires that are too hot can also cause handing problems and deteriorate quickly.
Next up is temperature across the tread. This is where you can really pick up some grip if driving a stock based car. Street vehicles have only a small amount of positive camber allowed within their nominal alignment settings. When a car corners aggressively, the body lean overcomes this angle and most of the weight transfer ends up on the outside edge of the tire. The tire contact patch area becomes very small. Continue and you can cord the outside edge very quickly when track driving. I am not going to go dive very deep here, most race rules allow for some kind of camber adjustment to compensate for this. Even restrictive spec class rules allow you to loosen every thing up and maximize the bolt hole runouts. Better than nothing. Anyway the idea is to have the tire tread as flat as it can be during maximum cornering. This usually requires some positive caster, especially on strut based suspensions. One of the best ways to measure this is by taking tire temperatures when exiting the track. You are looking for even temperatures across the tread measured on outside, middle, and inside. It is generally accepted 10-20 degree more on the outside measurement compared to the other 2 is about right to maximize the contact patch. Some considerations for temp measurement:
1. Take temperatures as soon as you can when safely exiting the track from a hot lap all the way up to the last turn. The tires will cool down very quickly on a cool down lap or a long straight before the pits. Best is to test on a skid pad.
2. Take temps the same way every time and measure pressures following. A recording tire pyrometer works wonders here.
3. Record everything. Adjust camber accordingly. Don’t forget to set toe also following a front camber adjustment.
4. LOOK AT THE TIRES! I mean really look close at how they are wearing. Make notes, take pictures. Look for evidence of over driving, bad camber, flat spots, wear rings, excess or inadequate pressure.
Other data to think about includes various temps and gauge readouts. Ever look at an oil pressure gauge and wonder if it 5psi lower than it should be? It’s a good idea to make a note of what your various gauges read nominally. Maybe even put a little piece of tape on the glass as an indicator. Just knowing there is oil pressure is not enough. Better to know immediately if there is a couple psi drop or a few degrees increase in temp. IR guns are good for this also. Cylinder head temps, transmission temps, differential temps are all good things to record and refer back to if needed.
Enough for now.