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Thread: Bad Fuel Calculations

  1. #1
    Junior Member
    Join Date
    Oct 2018

    Bad Fuel Calculations


    I'm currently using v4.9.8.24, I was in a league race and had some incorrect and conflicting fuel calculations from the commands "How's my fuel? and "Pitstop fuel to the end", it was a 2hr race at Spa in the GT1s, it was meant to be multi-class but only GT1s showed up.

    I came into the pits for the first time about 30 minutes in, the admin threw a caution when I was in the pitlane, I'm wondering if this is what caused the issue with Crew Chief.

    After a few laps under caution, going green and then a few more green laps I gave the command "Pitstop fuel to the end", Crew Chief gave me 10 Litres which I knew was incorrect as I had calculated pre-race I would need around 90 Litres. With the caution laps this would have been reduced but not by so much. This was at 15:12:24.392 in the log.

    I then asked "How's my fuel?" Crew Chief responded that I needed 65 Litres to get to the end which sounded more correct. By the time it got close to my stop Crew Chief was advising nearly 70L so this is what I went with however this ended up being too much fuel, we ended up with another caution so I couldn't work out how much it was over at the end.

    I did give the command "Pitstop fuel to the end" a few more times after the first time and the amount was rising but still incorrect.

    I've attached the log, if you need any more info let me know. Like I said I suspect the manual caution flag being thrown might be the cause.
    Attached Files Attached Files
    Last edited by Sarsi; 09-09-2019 at 11:38 AM.

  2. #2
    Crew Chief Mega Corp CEO mr_belowski's Avatar
    Join Date
    Feb 2017
    thanks for the log. In the run up to your stop (where the app thought 9 litres would be enough) I see a set of laps with low fuel use (around 0.5 litres per minute) and a similar sized set of laps with 'normal' use (about 2 litres per minute). By default, on road courses the app will use a historic average since the last fuel stop, when calculating your average fuel use. In this case I *think* that the yellow flag laps have skewed this average so much that the app is basing the estimate on 1 litre per minute, which is half of what it should be. Because you already had about 60 litres in the tank when you stopped, at this consumption rate you would have only needed 10 litres. But for this to be correct, the rest of the session would have to be subject to a similar number of yellow flag laps.

    So the app is working as intended here (this isn't a bug) but it's clearly stupid and basing the calculation on incorrect assumptions.

    To complicate things further, the app uses the recent consumption (from the previous 5 laps or so) to drive the estimates it gives when asking "how much fuel for...", but it uses a much bigger dataset to get average consumption for actual refuelling. And, to add to the chaos, on ovals the app actually uses the (valid) lap with the maximum fuel consumption to drive the refuelling estimates, so it isn't affected by unusually slow laps. This max-per-lap consumption can be used on road courses too by enabling the "Base fuel calculations on max fuel consumption" property.

    I think the app needs some work here - the max-per-lap consumption should probably be used if the session has been subject to 1 or more caution periods


    issue raised for this - i'll sort it for the next release

  3. #3
    Junior Member
    Join Date
    Oct 2018
    Ok thanks for the reply, it sounds like you're onto it but just to clarify the setup started with 60L, I came in when it was almost empty and added 90L, this is when the caution was thrown and we had 3 or 4 laps under caution with the low fuel usage (also in the log as laps around 4 mins instead of 2). It was after this that I queried the fuel as I originally worked out I'd need almost 90L in the second stop but knew this would be reduced after the caution laps.

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