I have seen a couple threads with people complaining about the fuel consumption of the cars, or that the endurance races are hard and the AI are broken because the AI can drive 4 or 5 more laps than the player can. I have just completed the Spa 100 endurance race and did a little experiment and tracked some data.
Highlighted info is wrong see post #5 for additional information. Just a quick forward. The way fuel consumption is calculated has not changed since Forza Motorsport 2, I never played the first one so don’t know how fuel consumption was handled. I have not tested it in this game but in Forza Motorsport 3, all of the cars got the exact same fuel mileage. The only thing that determines the amount of fuel you use is how much throttle you apply. RPM’s do not matter, car speed does not matter, and drafting does not matter. A car doing 5mph at full throttle, a car doing 200mph at full throttle, a car doing 1500rpm at full throttle, a car doing 7000rpm at full throttle, and a car drafting at full throttle all use fuel at the same rate. So for example all of those cars would run out of gas in 50 miles. So the ONLY way to save fuel on Forza is to either drive at below full throttle, or coast into/through corners and use no throttle at all. I did several laps shifting half way through the rev range and it used the exact same amount of fuel as when I was just normally racing.
I play on Pro difficulty and long races, the Spa endurance race is 46 laps I managed to come in 1st place, I only had to pit one time in the race, all of the AI pitted twice. The first half of the race I drove the car like I normally would until I realized I was going to run out of fuel too soon to only pit once then I started saving fuel. At the end of lap 23 (half way through race) I only had 2% of fuel left (averaged 4.26% per lap), the second half of the race I drove conservatively and had 10% fuel left at the end of the race (average 3.91% per lap).
The raw numbers:
My normal racing lap: 4.4%-4.5% fuel consumption per lap at Spa
My fuel efficient lap: 3.9% fuel consumption per lap at Spa
Lap time difference between best lap and fuel saving lap: 3.5 seconds slower
Time to get from pit entrance to exit at race speed: 18 seconds
Time to get from pit entrance to exit by pitting: 40 seconds
Time difference between pitting and not pitting: 22 seconds
Taking 4.4% as a normal lap, at Spa I can travel 22.7 laps before running out of fuel, meaning I would have to pit every 22 laps. So using the 46 lap long race as an example I would need to pit twice (once at the end of lap 22 and once at the end of lap 44). By pitting twice I am costing myself 44 seconds over the entire race. Driving every lap as a fuel efficient lap being 3.5 seconds slower per lap, and only using 3.9% fuel per lap I would need to only pit once (at lap the end of lap 25) The 46 laps times 3.5 seconds per lap costs me 161 seconds over the entire race, and the one pit stop costs me 22 seconds. So driving every lap as a fuel efficient lap is 139 seconds slower over the entire race. So you would not want to do that.
If instead you came up with a pit strategy and decided you were only going to pit one time but drive as fast as you could to do that, you would drive the 20 normal laps and 3 fuel efficient laps to pit at the end of lap 23 with only 0.3% fuel left. You would then drive 20 more normal laps and 3 fuel efficient laps and finish the race with only 0.3% fuel left. By doing this the 6 fuel efficient laps would cost you 21 seconds, and the one pit stop would cost you 22 seconds. So this strategy means you are 1 second quicker over the entire race than you would be if you just drove flat out and pitted twice.
If we switch to an 69 lap extra long race. Driving flat out means you have to pit 3 time costing you 66 seconds. With a pit strategy to only pit twice you would want your final pit stop to be at the end of lap 47, so you would plan your first pit stop for the end of lap 23. With this strategy you would drive the first 20 laps flat out, then do 3 fuel efficient laps, then you would pit at the end of lap 23 with 0.3% fuel remaining. Then you would do 19 flat out laps and 4 fuel efficient laps and pit with 0.8% fuel remaining at the end of lap 47, you would then drive 22 more flat out laps and finish with 3.2% fuel left. By doing this the 7 fuel efficient laps cost you 24.5 seconds, and the two pit stops cost you 44 seconds. Meaning by only pitting twice you are costing yourself 2.5 seconds over the course of the whole race.
On the 23 lap short race, driving flat out will only require 1 pit stop at the end of lap 22 with 3.2% fuel left, costing you 22 seconds. Running the race without pitting would require you to run the first 20 laps flat out, and the last 3 laps as fuel efficient laps to finish the race with 0.3% fuel left. Those 3 fuel efficient laps cost you 10.5 seconds. So by not pitting you are saving 11.5 seconds over the entire race.
So based on the way I drive at Spa, pit strategy does not matter for me at all unless it is a short race. As on an extra long race only pitting twice takes 0.036 seconds longer per lap, and on a long race, pitting once only saves 0.022 seconds per lap. On a short race by not pitting I would be saving 0.5 seconds per lap.
Someone better or worse than me at the game may have completely different results, and there is no guarantee that my method of coasting into the corners is the best method to save fuel, or that the amount of fuel I am saving per lap is the best amount to save, and who knows maybe Spa is just a bad track to try to save fuel on? I did have fun though keeping track of my fuel usage during the race to ensure that I did not run out or have to pit twice.