I always struggle with understanding what to do when the track conditions change from dry to wet and vise verse. What is a sensible approach and what changes should I make?
Firstly, thanks for the question and it’s definitely complex so I will try to deconstruct the question and answer it in a few parts.
Assuming the race director has made it optional to switch to rain tires, identify how much time you have until the grid is released. If you have 30 plus minutes, then it shouldn’t be too stressful, however, if you have fifteen minutes, well that’s where prioritizing comes into play.
- With a short time window, it’s important to mount the rain tires on the chassis first. If you are going to change hubs as well, it's best to have your rain tires mounted on the hubs, thus eliminating a few steps.
information Once the rain tires are on the chassis make sure that your rear track width is legal. In most series the rear bumper may not protrude past the outer plane of the rear tire, a great race can easily be negated by a millimeter mistake during the haste.
- Let’s assume you have maybe ten minutes left, so turn to some easy quick changes that will be sufficient and positive and possibly allow yourself time for a sprocket change at the very end.
- Normally for us a static change is installing caster in the chassis for the wet condition. It’s fairly easy to remove the bottom eccentric on an OTK chassis and install the J3 ‘5’ Eccentric on the bottom in the inverse position (marking pointing rearward). This change will increase your caster inclination by 2.4 degrees, thus improving the steering dynamics!
- Now depending on the time it’s easy to turn the front torsion bar in a vertical position, assuming you are using the stock torsion bar in an OTK chassis, you also opt for a stiffer front bar and depending on your chassis brand/model your local shop may provide options in this area. Generally this change will again be a positive one and aid in the steering input effectiveness.
- Widening the front track is also critical. Normally, we go maximum width with the standard front hub first. It depends on the track condition and driver preference. It might make make sense to install a longer front hub as well, which will increase the possible overall front track width as well as increasing the stiffness of the stub axle, thus enabling the tire to be for effective and increase the contact patch.
- Assuming you made a few front end changes and you have time left (3-4 minutes) or you have a second hand helping you during this process. A good philosophy normally is to increase the rear sprocket during wet conditions, which will undoubtedly be dictated by the circuit’s configuration. I would highly recommend having a complete front clutch drum/driver combination with one less sprocket (from your dry selection) already built up. This will make an approximate change of 6-7 sprocket sizes fairly quick. Also, you can change the rear sprocket in a more incremental change (Assuming maybe you want to only increase sprocket size from a 76 to 79). Using a different length chain is critical here, you do not have to worry about engine/exhaust placement and making your engine package fit. J3 Competition sells all #219 Chain sizes from 102 – 114 length, this is the most efficient and effective mean for such changes.
- Don’t over complicate it. If you only feel comfortable changing the tires and a small chassis change, then do that.
- Make sure your rain tires are mounted and ready to go before the event starts. Don’t be the person running around the paddock looking for rain wheels and someone to assist you in mounting your rain tires five minutes before a session starts. This nearly always ends in a disaster.
- Experience driving in the wet will definitely make more of a positive impact than that last twitch of caster.
— Justin Stefani, Race Department Director at J3 Competition
J3 Eccentric Pills
Utilizing a J3 eccentric in wet conditions will drastically improve your steering input and improve your performance.More about this product
J3 Eccentric Wrench
A unique 4-1 wrench that allows users to easily adjust their eccentrics washers in addition to being a rear bumper wrench, spark plug wrench, and 17mm wrench.More about this product