Racing in the Rain

Introduction

A question came up during the summer of '96 on the karting mailing list about setup changes for racing in the rain. Mid-Ohio is my home track which is run by the Dart Kart Speedway Club and we race in the rain there. Many people don't, or won't, race in the rain for one reason or another. I enjoy racing in the rain lots more than anyone I've met there. That probably has more to do with the fact that my best finishes have been in the rain. It's not like I won, but I've taken some hardware home which was good. I've been racing at Mid-Ohio for over ten years now and when we had the October race there, you could plan on running at least one day in the rain. Eventually you're gonna figure things out if you actually practice in the rain. I prepaid my practice fee so I didn't see any reason not to hit the track. There was maybe four of us out there, but we learned the most that day. One kind of obvious thing is that how hard it's raining totally changes everything, alot. Another thing is that no matter which way the front tires are pointed on a sprinter, the spray goes in your lap. And yes, the water will be cold. A scary thing is that three or more sprinters together will throw enough water in the air from rooster tails to obliterate any vision.

The rest of this document will attempt to present what I've learned about setting up for the rain. Each section will deal with a different component of the kart.

Why the rain can be a good thing

Rain is like a muddy football field, a great equalizer. It can be very difficult to drive at the limit when the limit keeps changing dependent on how hard it's raining on any given section of the track. Understanding what different degrees of rain do to your braking and turning points can only be learned by practice. Obviously, if it's raining harder then your braking will be earlier and probably turnin since you'll be sliding more.

Tires

Obviously this is the first place to start. Rain tires are a must but I'm sure you already knew that. But it must be a wet track in order to run them. If the tires on the karts in the previous race aren't shiny from being wet, then it's a dry track and you should run slicks. It seems like most of the time it's a crap shoot whether it's going to be a wet track or not. You'll have to guess on your own 'cause I ain't no weather man.

Suppose it looks like it's going to be a drying track or you don't have rains to put on. Running slicks really soft will sometimes work. The idea is to allow the tire to run on the edges with the middle not in contact with the pavement providing a path for the water. The lower pressure will also produce more heat in the tire due to increased sidewall flexing.

Now if it's a wet track and you have rains to run, it's my experience is to run them very soft, like 12-14 psi. (My normal pressures are around 20 to 22 psi.) My thinking was that they needed to be able to deflect easily in order to make some heat. This was proven out in practice also. The tires will be dry between the grooves while running on a wet track if they are working right, unless it's really pouring. Pretty cool when your tires are steaming after a run.

One odd feature of running in the rain is that unless it starts to dry, you probably won't see any, and I do mean any, wear on the tires. You can put on brand new tires with the little tire nubbies on them at the start and see the nubbies at the end of the race. If your rain tires stay in the wet they'll last forever, at least as far as tires are concerned.

Just like normal, check each tire's circumference and balance each tire. Nothing changes there. Generally rain tires are a half to a full inch less in width compared to your normal tire. The contact patch needs to be smaller in order to generate sufficient pressure to pump the water out of the tire tread. The different tire size may also include a difference in tire circumference, so be sure to check. You'll have to take that into account when selecting a gear to run.

Gear Ratio

Assuming you have time to make a decision between a rain setup or a dry setup or one of those setups that are neither since the weather won't make up its mind, selecting the right gear ratio is very important.

Your corner exit speeds are going to be very slow, hence your top end speed is going to be reduced, alot. I usually either added five (5) teeth to the rear gear, or, took one (1) tooth off the driver. This should provide a good match with the new kart behavior. If you don't change the gear as I describe and you go slower then you'll spend a very large amount of time on the clutch. That's not good since that will make a lot of heat in the motor which we don't want either. You can also expect a shortened clutch life if it sees too much slip time. When changing the gear, you also have to account for any difference in tire circumference between the slicks and the rains. I've written an application that makes picking the right gear easier by doing all the number crunching for you. It's freeware and it's available at my software page in the gear selector family of programs.

Making the Clutch Survive

Running an engine clutch at many enduro tracks in sprint situp can be a real test of setup. Do it right and it will survive slipping 30% of the time for over 30 minutes. Do it wrong and you come back in on the hook after getting soaked for thirty minutes watching the rest of the field race by. We don't want to go there. Racing in the rain will increase the amount of time spent 'on the clutch'. If the weather conditions stablilize, i.e. steady rain, then you should be able to run consistently lap after lap which is usually easier on the clutch. But if the weather conditions are changing, then you're probably going to be more hestiant about driving corners deep which means you'll be going slower and spending more time of the clutch accelerating when you can. An axle clutch can tolerate this pretty easily, but engine clutches can be sensitive.

I would drop the clutch engagement quite a bit. By that I mean about 200 rpm. You'll be spending more time on the clutch than normal, particularly if you didn't change gear enough, and it's easy to waste a clutch. It is also desirable to have a smoother power delivery than normal. By this I mean that the power should ramp up instead of slamming on. A good two stroke will hit the power band like hitting a switch. That kind of transition can be difficult in the wet. A smoother application of power is easier to handle and more desirable. This will avoid spins which are very fast in the wet; there isn't the same kind of warning like in the dry. Engaging the clutch earlier will will allow the torque to ramp up to maximum. How much earlier to engage is something that you'll need to determine by experimentation. This will avoid spins which are very fast in the wet.

Chassis Adjustments

The chassis will not work like you're used to. It does not have enough traction to generate the same chassis dynamics. The chassis will not flex as much as normal. The most likely result, which is undesirable, is that the inside rear tire will not lift upon corner entry. Everyone knows from pushing their karts to the line that they don't like to turn with that live axle grabbing pavement at both ends. It's real happy going straight but doesn't want to turn at all. I've always experienced a big push in the rain. So, given the limited stick available, you need to change chassis settings to help the chassis work. I recommend narrowing the rear as much as possible and widening the front as much as possible. It seems to require both actions, especially if your seat is reclined. You can also either make the seat more upright to raise the center of gravity to transfer more weight or you can just sit up straighter for each turn. I suppose you people who actually add weight to make class could mount the weight higher.

Air Filter

I have heard many stories about what air cleaner to run with lots of different reasons but I think I've figured out what is really desired. I've always been told that a paper filter will absorb water like a sponge and eventually choke the motor off. So following that logic, the standard approach would be to run a foam cleaner since they won't clog with water due to the oil on the foam. The flaw there is that the paper filter is also oil impregnated so it shouldn't absorb water either. I've run an unshielded K&N paper filter with the K&N filter oil on it in a 30 minute rain race without problem. But I'm sure that the motor is still ingesting water which is not good. You can expect accelerated wear on everything. Now our cars, the big ones we used to get to work everyday, can drive in the rain without wearing out so there must be a way. The big difference is that the airflow path is setup to collect the water before feeding it to the motor. A simple method we can do to mimic that is to attach a large plastic jug over the air filter to act as a rain shroud. The idea is that the air is drawn from the rear instead of the front or sides. The air can easily make the 'U' turn to enter the plastic jug, but the rain will not be able to make the turn and will be separated.

Instruments and Water

No matter which way they're pointed, the water picked up by the front tires will go in your lap and it will be very, very, very cold. Drain holes in the seat sometimes help. Any kind of gauge should be wrapped in clear plastic like Saran Wrap. A perfect seal is not required, you just need to eliminate any driving water that could hit it. Sometimes they freak out for a while after getting wet and sometimes they break.

Seeing where you're going

Unless everyone is running bodywork, the open wheels will generate some major rooster tails that will remove most of the visibility. Be very careful. Not much else you can do other than keep in mind that the other driver may not be able to see you. Three karts together will generate a 'wall' of water that you can't see through. Visor fogging can be a major pain too. Go to a motorcycle place and get some anti-fog for helmets. Nothing but the genuine article will work since applications for glass don't seem to work on polycarbonate. If you run tear-offs, remove as many as possible. The tear-offs will draw the water between the layers and make it impossible to see. Be sure to use a clear visor, even a light smoke will become a problem. There are products available for glass that make water bead and flow off. Unfortunately, they don't seem to work well on polycarbonate for the entire race. It seemed like it worked for 2 or 3 laps and then was gone.

Carb Adjustments

Chances are your driving will be very different int he rain and you'll probably spend more time off the throttle than normal. The question then becomes, do we want to change the carb settings to get the temperatures up? Chances are the head temperature will be very low while racing in the rain. Probably incredibly low. Even the exhaust gas temperature will spend most of the time at low readings. DON'T lean out your mixture!! Chances are your carb settings should stay the same. Two things are happening to make the motor look cooler. First is that you're not spending near the time at full throttle meaning that you're not adding waste heat to the motor. Second, the rain water flowing over the motor is able to take away vast quantities of heat in comparison to dry air. The outside of the head will be cooler, but the inside, where it counts, will still be the same when at full throttle. You can't tell the temperature inside your house by putting your hand on the outside wall.

Contact info. Click here to send me email at chuck@chuckbunnell.com
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