The Guide to Road Racing, Part 15: The Elusive Rain Line

By Corey Rueth

December 04, 2015

Images: IMSA
As a young racer I found myself listening to more seasoned drivers discussing rain lines at the track with great curiosity, like they belonged to a secret club. I read and asked questions but found a myriad of answers that never worked that well for me. Ultimately, I determined that my own aggressive research was my best hope for a rain strategy that produced consistent results. I have a short attention span and sports that can't kill me do little to keep my interest. I guess that's why I found racing so appealing - specifically road racing.
Racing different tracks with different car set-ups will allow you to collect data at every turn and on every lap. This, in turn, revealed the lessons for rain. Nothing facilitates humility and learning better than a slippery surface, 400 horsepower and thirty of your closest friends chasing you. In my quest to unlock the secrets of the rain line I made a fascinating discovery: there is no rain line! That's right, no rain line! How could this be?
I would like to share my logic in this article and keep the focus primarily on the art of car placement while only briefly addressing the other obvious aspects of rain racing that must support a skilled driver. In order to go fast in the rain I recommend that you focus on the following elements:
• Defog - If you cannot see, you cannot go fast, at least not safely
• Car setup - There are many advantages and considerations for rain set up
• Escape Strategies - Examination of safe and not so safe places to test adhesion
• Control inputs - Smooth application of pedals, steering inputs and gear selections have never been more critical
• Line Selection - Only after the above criteria has been met, may you then focus on selection of the racing line through methodical, on-track research
In order to go fast you must be able to see. Who knew? Many racers use powerful blower motors to blow on the windshield as well as defog chemicals. New windshield wipers and Rain X are also critical. I also like to force ram air onto the inside of the windshield and carry a long handled squeegee as a last resort in case the other items are not effective for defog.
Car setup is often debated, but I have found that I prefer a softer set up than I use in the dry. There are many ways to achieve this, but since the weather could shift at any point in the weekend or the race, I prefer to use tire pressures and sway bar settings in order not to stray too far away from a known good dry setup. Many will cite mathematical formulas, and insist that higher tire pressures result in higher speed hydroplaning, but I have found lower pressures yield faster laps for me because hydroplaning is rarely my problem.
With most R compound dot tires, I target low 30s as a ballpark hot pressure. It is also important to realize that you will not gain as much hot air pressure during a rain race. Be aggressive during the warm up with brakes and speed in order to get maximum tire temps for the start of the race. Rain tires are great if you have them, but they’re not absolutely critical until there is standing water – I typically choose the dry tire until there is standing water and an indication that the rain will continue throughout the entire race.
Escape strategies, in my opinion, separate the good drivers from the greats. Finding safe places to run off the track in high reward areas can provide literally seconds of improved lap times. This strategy will allow you to safely push the limits during qualifying or practice, and reap huge benefits when its race time. I try to find areas of paved run offs or smooth grassy areas to push the envelope during practice. Avoid tire walls, ditches and concrete barriers for these testing sessions.
Control inputs could be another article all its own, especially in the rain. Smooth application of brakes, throttle and steering inputs are now your highest priority. Braking in a straight line is helpful and the old tip of pretending there is an egg under your pedal works great. Squeeze the brake and throttle and never jab or stab at it. Steering inputs should be slow and methodical but quick to counter-steer slides. Steering inputs should also be coupled with a release in brake pressure.
Gear selection and throttle is also often debated. I have heard many racers recommend a higher gear combined with higher throttle settings to race in the rain. I disagree with this concept whole heartedly. I prefer to be in the correct gear in most cases and use a lower throttle setting to allow me to truly feel the grip levels and have access to all of my horsepower and torque where the grip will allow it. This requires much smoother inputs and pedal applications, but it will reward you with amazing hole-shots and lower lap times in some conditions. I do use higher gears in times of high workloads or traffic to avoid an accidental slide however.
The Rimshot
Now that we have adequately touched on the prerequisites to going fast with limited traction, we can finally discuss the elusive "rain line”. The rain line is often discussed as a specific and unchanging line at each track, which is a load of malarkey. My pursuit of the rain line usually begins as a “rimshot”. The rimshot refers to the outward most, longest radius - the absolute longest way around a corner. You literally drive around the very outside edge of every turn. I know it seems odd to go the long way, but it’s ok to go the long way if you can travel at twice the speed with twice the grip. The rim shot has a strategic flaw however. It is a racecraft disadvantage and when I'm near a competitor I am forced to use a modified rimshot.
This modified rimshot is basically to start on the inside of the turn, cross the normal racing line and drive to the outside edge of the track (or until you reach an area of improved grip) and then turn to follow the rimshot until you cross the normal racing line again at the exit. This modified rimshot is a shorter distance, usually slightly faster, and will give you a strategic racecraft advantage – but it is more difficult due to a slightly tighter radius on turn-in. Personally, I prefer a full outside rimshot initially, if I'm not being pressured by a competitor, simply because I feel like it's an easier and lower risk line to drive before you get into the groove.
If you just use these two lines you will likely be faster than 80% of the field without any further effort. These are generally the rain lines discussed by the secret rain line club. I drove this way for years with plenty of success, but occasionally someone would pass me like I was sitting still. I do not like getting passed, so my ego forced me to continue my research.

Before diving into finding the other 20%, I think it is imperative to realize that the inherent array of variables with machine and Mother Nature prevents any one “line” from working; we must discard this idea. The rain line is nothing more than an ever changing pursuit of grip and there are often multiple fast lines for every turn.
I almost always start my discovery process on the out lap and test for slip and grip in unusual places. I then begin the race with these grip spots added to a basic rim shot, being very aware of the normal racing line because it is slippery like ice. You must also be aware that when you are driving the outside edge of a track, there is very little room for error, or your race will be spent waiting for a tow truck. The normal line, in the dry, is the smoothest and most polished part of the track, therefore making it the worst place to be on a wet race track.
My mission is to avoid the normal racing line at all costs. Obviously, you cannot run a rimshot without crossing the slick line in two spots, entry and exit. Entry is usually a non-event as you are going straight and there is no reason to get loose. On the other hand, getting by the slick line on corner exit can be an art form. You must know where the slippery line starts and ends and be certain that you have straightened the wheel to be sure that the car is under no "g" loading while you cross the slick line. I accomplish this by slowing enough to get the car turned earlier and straightened out before reaching the slick spot.
Now, also consider that this slippery exit line usually extends from the outside of the turn down the straight away. So the goal is to sidestep the corner exit at least one car width to the inside. This allows me to find a less polished surface to allow max grip to accelerate down the straight as safely and as quickly as possible.
Here it begins to feel like point and shoot racing - I'm trying to get through the corner as quickly as possible so I can drag race down the straight on my newfound grip. As I get into the rhythm and fine tune these lines, my objective immediately shifts to a more in-depth discovery mode. While looking for grip and modifying the rimshot, I always test and look for opportunities to run a tighter radius by driving the modified rimshot. Opportunities to tighten your radius often arise during the race, especially if the track begins to dry.
Cheater Grip
Now I can begin to search in unlikely places for my "cheater grip". This is also a great time to utilize a predictive lap timer to test different lines. Cheater grip can be found a lot of different ways. The first thing I look for is patches of new pavement. Obviously concrete is usually good and asphalt is usually bad. Asphalt is much more prone to being polished and slippery. Look for these concrete patches or edges, and believe me when I say it's well worth your energy to drive out of your way in order to pursue this grip.
Find this new pavement and test it to see if it’s grippy. Use concrete for braking assistance too – even one tire on concrete is amazingly helpful. I love to use the narrow concrete perimeter edge for braking and corner entry. I generally find more grip in the marbles and rough surfaces identifiable as dull and not shiny. Always be vigilant looking for an oil rainbow laying on the track. Other points of interest are the areas off track at the edge covered in left over gravel. These areas of gravel beyond the tracks edge often have more grip than the wet racetrack. I never pursue this area intentionally, but it could save your asset in times of accidental agricultural research.
In other words, if you accidentally leave the track, add steering input to see if you lost or gained grip. It's odd, but I often gain grip in this off-track gravel. The normal understeer process of leaving the wheel steady until grip returns should be adhered to for most rain racing, except for testing like I mentioned above. Never turn the wheel too far beyond where you lost traction or you will never regain traction. Otherwise, as the surface grip returns, you will have too much steering input for the given radius and speed. Once grip returns you may then add additional steering input to try and save the day before you end up in the mud or wall.
Situational Awareness
From this point on, we cannot rest - this is where the magic happens. What if it stops raining or begins a torrential down pour? For better or worse, the track can change during a rain race in seconds. If it stops raining, be aware that the track may dry quickly and the normal line will start to become the fastest line again in some high ground areas, and gradually transition back to the normal line. I have lost many a race because I was too busy surviving in the rain to realize that a section of track was drying and getting faster. Sometimes you don’t realize it’s faster until somebody blows your doors off.
Be vigilant and continue to test and look for areas of opportunity and learn from your competitors. The same goes for deteriorating conditions. We must look for rivers, standing water, mud on track and accidents, to continue going fast as your competitors go into survival mode. Turning consistently faster laps in any weather requires the ability to test and change your strategy based on constant feedback from the machine and racing surface.
Racing is an unusual discipline that can be practiced every single day without going to the track. I don’t drive normal all week long in an automatic Honda Accord wagon and then turn on race-car-driver-mode to get my aggression out from the long commute. My peers often joke that I had to tone down my street driving to be allowed to go road racing. My point is that we drive cars every day, so let’s make every second count. I am not advocating that you terrorize the streets, like I did in my younger days. I am merely suggesting that you drive a manual transmission car daily, heal-toe at every stop and take your hot rod to the parking lots and dirt roads and slide around in the rain at every opportunity. Ice storm? Yes Please!
Go to the local racetrack when it rains in your daily driver and try to set a new personal best; use these tips and be constantly seeking that secret grip where nobody else is looking. That is the only way to be the fastest guy on the track in unusual conditions. Adapt, overcome, be strategic and hyper aware to find new levels of grip that may slip by the less aggressive researcher. Discuss your findings after the race with trusted team members and mentors and share your best practices.
The rain line is more of a rain strategy- a never ending quest that will change from the beginning of the race to the end. Remember, if it were easy everyone would do it. So grab your helmet and join me at Harris Hill Road next time it rains. I'll likely be there in search to find the elusive rain line of that day...

+ The Guide to Road Racing - Table of Contents