Five OSC subscribers finished top-5 in IMSA GTP splits at Watkins Glen in Week 8. With permission from each of them, we pulled the telemetry from the races and overlaid the laps to see what the setup was doing for them and where the driver gains were coming from.

Here's what the data showed.

Sector 1: T1-T3

This is where the OSC file shines and the data agrees. All five drivers were within 0.04 seconds of each other through T1, and all five were 0.15-0.22 seconds quicker than the average of the next 10 finishers. The setup gives you a stable car under heavy braking into T1 and our drivers were able to brake later than the field by about 8 meters consistently.

The car is doing the work here. We're running a more rearward brake bias than the IMSA-suggested baseline (52% vs 54%) and softer front bar (-2 clicks). The car is willing to take threshold brake all the way to the apex without the front darting.

Sector 2: The Esses

This is where the driver gains compound. Through the esses (T4-T7) the spread between our five drivers widened to 0.18 seconds. The fastest of the five was 0.32 seconds quicker than the field average. The slowest of the five was 0.14 seconds quicker.

What separated the fastest from the slowest of the OSC drivers? It was throttle modulation through T6 (the inner-loop section). The fastest drivers were lifting partial-throttle through the apex of T6 rather than coasting. The car has enough rear grip to handle the partial-throttle attitude through that corner; coasting wastes it.

If you're running this file and you're not partial-throttle through T6, you're leaving 0.1+ seconds a lap on the table. Try it next time. The car will let you do it.

Sector 3: Bus Stop and Front Stretch

The bus stop chicane is where the driving style matters most. The setup is built to be neutral through the bus stop - it doesn't want to push or rotate; it wants to be slotted in and driven through. Our five subscribers had three different lines:

  • Two ran a late-apex-late-throttle line (slower mid-corner, faster on exit).
  • Two ran a mid-apex-balanced line (faster mid-corner, neutral on exit).
  • One ran an aggressive early-apex line (fastest mid-corner, slightly slower on exit).

Net result on lap time across the bus stop: within 0.04 seconds. The car's not picking favorites. Run the line you're comfortable with.

Front stretch onto T1 was where the second driver gain showed up. Two of our drivers were carrying 4-5 mph more onto the front stretch than the rest. That came from a tighter T11 line, not from any setup adjustment. If you're losing time on the front stretch, look at T11 entry - that's the corner that sets it.

Net Lap Time Gain

Across the full lap, the OSC file is giving you somewhere between 0.4 and 0.6 seconds over the average-finishing GTP file in the field, assuming you drive it correctly. The biggest delta is in Sector 1 (the setup) and the biggest available gain is in Sector 2 (the driver).

If you can find the partial-throttle T6 trick, you'll close 0.1 of that gap to the fastest finisher in your split.

File Available

The Watkins GTP file is in the shop. All Access subscribers have it as part of the road-course tier. If you're running it this week at Mid-Ohio or Road America, the same brake-bias philosophy carries over but the rear-spring split is different. Different post.