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No Rain Please!

By Dave Karl

Can you have more fun driving in the rain than sitting in the pits? For some the answer is yes but it is just not worth the potential consequences if they lose control. My early DE career was full of unlimited enthusiasm. This, in addition to simply not knowing any better, meant that I went out even when the rain had some white fluffy edges. So far I've survived the learning curve, and I did have fun, but ultimately I decided that I was not very interested in attempting to master this medium. For me the main reason is that in the rain conditions are always changing. You do not have the opportunity to sample a consistent surface, lap after lap, throughout the day. This makes it difficult to quantitatively judge the results of the various inputs you make as you try to fine-tune your skills and line. The dry track reference is much more of a constant and it allows me to more precisely see the effect of any changes that I make, whether they be intentional or not. I can also drive closer to the car's limits without the fear of the next laps varying track conditions putting me over the edge.

Other than describing the theory of driving the rain line to students I have not spent much time discussing car set ups or articulating what I am trying to do when the windshield wipers are slapping as fast as my tires are turning. This March at the VIR Zone 2 event it was 30 degrees and raining very hard. I took some time to organize my thoughts on the subject in the hopes that the process would better prepare me for my students and my own wet weather driving. The techniques described here, while applicable to most 911s, are only suitable for those drivers in the intermediate and advanced run groups. Maybe now that I've gone to the trouble of writing a rain article I've assured us a completely dry DE season, if not it still may be of interest to some of you too.


The most basic thing to remember is that in the rain, although you are piloting the same car, the conditions will mean that you can often exceed the limits of grip even when accelerating in a relatively straight line. For those of us with street cars this is a big change, in a sense it is like adding 150 hp to your ride. Sliding the car in corners, without having induced it with power over steer, can also be accomplished at most any speed. The good news is that with the appropriate amount of caution this is a great learning opportunity. Rain can allow you to safely experiment with the unique handling characteristics of your car at a more relaxed pace. It gives your eyes and brain greater time to anticipate and react. You'll likely find that most instructors value the experience to some degree.

A set of rain tires is all that most drivers need to do to prepare their car. The suspension that I have is a street/track compromise. Typically my pace on a wet track is not affected as much as many of the others in my run group that have more dedicated track cars. The reason is that the softer more compliant set up that most of us has, while not ideal for dry conditions, is pretty well suited to the wet. If this describes your car it probably doesn't have a lot of negative camber either, and again in the wet that is to your advantage. At modest speeds it allows you to put a fat contact patch on the road and not exceed the tires grip. However, if you have a really great dry set up, or are looking at a lot of rain, you may consider going to the trouble of equally softening both of your sway bars. Some high-end suspensions even have adjustable shocks that offer the ability to easily change dampening settings in the pits. All of this techno-setup stuff is great but keeping it simple and just learning how to drive what you have is likely to offer more enjoyment, and greater benefit to your driving skills. All setups are a compromise.

After two or three years of track time most enthusiasts will want to invest in two wheel sets so that they have both dry and wet specific tires. If done correctly this allows you to effectively change set-ups just by changing your wheels. My car's suspension and alignment are biased to dry conditions. Most often I run Michelin Pilot Sport Cups on 18 inch BBS wheels in these sizes: 235/40-18 & 285/30-18. In the wet I use my stock 17 inch 993 rims with Bridgestone S03 in sizes: 205/50-17 & 255/40-17. Although it is not the ideal way to do this, I am effectively changing my car's suspension with the changes I make to the tires width and sidewall. The taller sidewalls of the tires are much more compliant and this simple tactic acts to soften the overall spring rate of the suspension. The tread pattern and narrow overall width of the tires slice through water and reduce the possibility of hydroplaning. The narrow width also means that I still achieve a full contact patch under the reduced cornering forces that generate less roll. These two tires have nearly identical overall diameters so the gearing of the car doesn't change.


In the rain even advanced drivers tend to revert back to the safe, but slow, practice of doing all of their braking in a straight line. Momentum is hampered in most of the slower turns when you drive this way. Keep the same approach and any attempts at increasing corner entry speed eventually result in under steer. Constantly needing to throttle steer through the corner leaves the driver with the impression that trying to go any faster at turn in is fruitless and only causes the car to push. In the rain traction is always the limiting factor, but additional grip can be given to the front tires if the braking is carried just past turn in. With the car pitched forward you can now combine a fair amount of turning with braking. The car is able to enter the corner at a better yaw and ultimately carry more speed. In fact for slower corners in the rain you may need to keep some load transferred forward for an even greater portion of the corner than you would in the dry. Since most drivers' tendency is to revert back to straight line braking carrying the brakes even deeper than you would in the dry is not an easy thing to do. As I bleed off the binders I sometimes use a heel/toe type technique in transferring my foot from the brake back to the throttle. I am not talking about shifting but rather momentarily using some gas and brake simultaneously as I roll my foot solely onto the gas pedal. If the brakes are carried deeper, the transition from brake to gas needs to be smoother.

Most if not all of the slow corners require at least one downshift and that offers an additional option. If you are very experienced with trail braking, and can heel/toe downshift very smoothly, you might also try to delay the last downshift until just before corner entry. However, this time blip the throttle just a bit less than you normally would so that the RPMs are just shy of a perfect match for the given gear change. As the clutch is released the rear of the car is then "braked" slightly by the engine. Like a brake bias adjuster might this in effect proportions more braking to the rear tires, but just at the given corner. When done well this type of "brake" allows the front tires to do more of the turning work while the rear tires slow the car and keeps the weight transferred to the front tires for additional steering grip. Rotation takes place allowing a straighter line and stronger acceleration to track out, an ideal situation in the rain. Smooth inputs are essential and are quite difficult since the cockpit is quite busy. A lot is going on in a very compressed period of time. Most often we like to do all of our downshifts in a straight line and with good reason. It is much easier to initiate a spin when braking and/or downshifting in a corner, be careful!

In wet fast corners exceeding the front tire's grip is not as much of an issue. Entering the corner under braking is usually not advised since transferring load is really not needed to get the car to turn. In fact, you may find that slightly increasing the length of your braking zone on wet fast sweepers allows you to time a smooth release of the brakes right before the turn in, and at the exact speed you need.


Experimenting with different gear choices can also help you gain some time. If you are debating on which gear to use when cornering in the wet the taller gear is likely the better choice if you are still following the dry line. The bigger gear allows you to mash the gas pedal a bit earlier without the worry of being in your engine's peak power band and it getting the better of you. Driving the wet line this may not be the case. Even with the need to make the ensuing added up shift on the following straight the lower gear is typically more beneficial. I have experimented with race rains and in addition to offering a super sticky soft rubber compound the tires that I used were a bit smaller in diameter than my Michelin dry's. That effectively changed my gearing so that my car was at a higher rpm at any given speed. So far I have found this is usually advantageous, it's like changing the ring and pinion so that the car's gearing is better suited for the wet. Driving the rain line typically means that you do more of the turning in the early portion of the corner and follow a straighter path past the apex to track out. At the slower mid corner speeds the shorter gearing allows me to keep the car in the engine's peak power band and have better acceleration.

There are some universal basics that should always be mentioned in any discussion on rain. Start with your tires close to their ideal hot pressures and bleed off some air if need be after a few laps. Stay off of the painted surfaces, even apex turtles, since they are all slippery. Don't ask a lot of the car when it's on concrete it's also slicker than the asphalt when wet. Although the fastest way around the track is often not the dry line most of the same principals still apply, especially the need to be smooth and to fully track out. If you are applying more gas you need to be unwinding the wheel. Common areas where cars go off the track in the dry are worn and may be small ponds of mud in the wet. Rivers can and do appear in the middle of a session. Learn where they come from and check their origin as you pass them to determine if they are likely to be a problem for you by the time you return on your next lap. If you can't avoid the puddles, hit them in a straight line. If the track is open but there is so much standing water that hydroplaning is unavoidable pit out. Just because control has not called the session doesn't mean that the conditions are safe for you, you've got to judge that yourself. Unless the rain is so heavy that the traffic has no effect on the conditions the ideal rain line is usually a bit of a moving target. Some mid session experimentation and adaptation usually reaps rewards. If conditions improve, and a partially dry line begins to appear, keep the loaded portion of the car at least a foot within the dry zone in case you slide a bit more than you anticipated. If you are slow and smooth with your inputs you are less likely to overreact when something needs a correction and cause a spin. With a loss of control the adage "both feet in" still applies, but I would advocate that a good fight be made first. As long as you are sliding on the pavement you still have some chance of slowing down. Once the friction of the paved surface disappears so does the braking and g forces that your body had been experiencing. That's why you may hear people falsely claim that they "accelerated" when they hit the wet grass.

Even though I consider my rain skills to be pretty good I always have some nervous energy when I get ready to enter a wet track. A bit of fear is a healthy thing as it sharpens your senses. If it were completely safe it would be pretty boring wouldn't it? How much of this applies to your 911, and whether all of this is wet weather specific for you, depends on how you like to drive and your car's set up. For the past 5 years Kristin and I have had pretty much the same suspension, this year we stiffened things up and will be back in the learning curve of how to drive what we now have. Wish us luck and if you see me heading out in the wet, and enjoyed reading this, please feel free to Rain-X the windshield for me. For some in-car video check the You Tube footage my friend Mike Kenny posted of me filling the car with water at Tremblant's German Challenge 2006.