Corvette Z06 GT3 Part 1

This is a series focused on setup development for the Corvette.

Before you start, be sure to read the iRacing User Manual for the Corvette

Chevrolet-Corvette-Z06-GT3_manual_V2.pdf

Rule #1. NEVER EVALUATE A SETUP ONLY ON A FEW LAPS OF TESTING. IT TAKES A MINIMUM OF 25 INTENSE PRACTICE LAPS TO DRAW ANY CONCLUSIONS. EVEN THEN THERE IS A HUGE POTENTIAL FOR AN INCORRECT CONCLUSION. 

The first task in developing a setup is to select the gearing most suitable for the track/s.  You need to know that you are allowing the car to reach the best top speed on a long straight in a draft. You also need to know which gearing best suits the corner exits of the track you are running. In many race cars you can change each gear set--1st thru top gear.  iRacing offers two basic gear combinations: FIA and IMSA.

Below is a chart showing the max speed in mph for each gear in the set:

At this point, the question is “Where do I start?” 

Start with a setup that you trust is reasonably close to your goal and modify it. Use iRacing “canned” setups, setups from VRS, Apex, Coach Dave or your League Engineer

Note that the FIA set allows a higher top speed in 5th and 6th AND more torque (lower speed=more torque multiplication) in 1st-3rd gears.

To choose what is best, test the top speed possible at the longest straight of the track/s you will be running at. Let's consider Road Atlanta, SPA, Mosport, and Suzuka. Testing indicates max top speed not in a draft is:  Road Atlanta 162 mph, SPA 158 mph, Mosport 155 mph, Suzuka 159 mph. 

Add 3% to these top speeds to adjust for maximum 2 car draft: Road Atlanta 167 mph, SPA  163 mph, Mosport 160 mph, Suzuka 164.  Although the IMSA gearing would be suitable for the top speed requirments, you also have to consider how the gearing works in corners.

Note the FIA gearing torque is higher than the IMSA:  20% more in 1st, 8% more in 2nd, 5% in 3rd, equal in 4th, 4% less in 5th; and 4% less in 6th. Bottom line: The FIA gearing will allow significantly higher acceleration (and potential wheel spin) in 1st thru 3rd resulting in higher speeds at the beginning of long straights--this speed "carrying thru" the entire long straight. 

On the other hand, the IMSA gearing will allow more acceleration in 5th and 6th gears. 

The "best choice" depends on the track. In a theoretical "drag race" for example at SPA: after exiting the hairpin in 1st gear, the car with the FIA set would reach Eau Rouge sooner with the car having the IMSA set catching up by the end of the Kemmel Straight. A driver with the FIA set defending the entry at Les Combs would have an advantage. The driver with the FIA set would almost always have an advantage in a race. 

In hot lapping the gear sets most probably do not produce different lap times. 

As can be seen by the chart, the rear wing setting results in only a small change in top speed. The difference between 9.5 and 8.5 are not significant. The difference between 9.5 and 7.5 and especially 6.5 is significant and would make a difference in lap times if the driver is able to cope with the reduced grip in the corners. 

Testing grip at the Centripetal Track

The vast majority of downforce on the Corvette comes NOT from the rear wing but rather the sophisticated air tunnels under the car. Rake or the difference in ride height from front to rear and total ride height WOULD have a significant effect on downforce. (The car needs to be as low as possible--just so high as not to drag on curbs.) The rear wing tends to be more of a fine tuning of the understeer/oversteer balance. Running a test at the Centripetal Track with 190 foot, there was less than 0.5 mph difference between each incremental change from 9.5-8.5-7.5-6.5. The most noticeable difference was the car had an understeering tendency at 9.5 and an almost oversteering tendency at 6.5.  A driver unable to cope with the oversteer tendency would do better staying with the 9.5 on all tracks where top speed is less than 160 mph. 

So, once you choose the gearing and the wing, move on to the adjustments that determine: 1) Brake bias for max stopping power and optimum trail braking that fits with driver's preference; 2) Adjustments that affect the understeer/oversteer balance in all corners--giving priority to the corners leading to the longest straights; and 3) Adjustments that affect the "transitions" and weight transfer front to rear, and side to side, during corner entry and exit. See Parts 2, 3 and 4 of this "series" on the Corvette.