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# Where can I find "predictive lap timing"?

Hi!
I've heard my non-RaceChrono friends discussing things along the lines of "... predictive showed I was going on a 1:23 lap, but then I got blocked by traffic". I realized many people would like such a feature from RC too.

I was going to start a "feature request" thread here on the forum, but then I noticed that racechrono.com already mentions "Predictive lap timing and time delta graph".
How do I use it?
The only "lap timer channels" I see available are {best/comparison/previous}x{number,time} and "Current lap number".
Was "predictive lap timer" removed in the past, or is it just hard to find?

• I guess it's my choice of words that is confusing. I often call the "Time delta" feature "Predictive timing". That's what it is really, the time is just relative to the comparison lap, and not absolute.

Absolute predictive timing on my TO-DO list.
• Gotcha, I see!
Yeah, I'd presume that for most people "predictive timing" means "predicts the lap time if I keep driving the current lap as good as I can".
A naive implementation would use the "opt lap + time delta against opt lap" equation, but I do remember that time delta against opt lap is also currently not available.

Perhaps this approximation would be simple to implement, and will provide decent results?
"sum(completed sectors) + (time delta against best + current sector of best lap - Opt current sector) + sum(all further Opt sectors)"
• edited October 2021
IMO, comparison to optimal lap is completely different topic.

Predicted (absolute) lap time = comparison time + time delta

You'd then have to select your comparison lap according to your preference. Optimal lap is just theoretic best you can reach with your current driving. It's usually not exactly realistic unless you can improve somewhere, but it's close. The best (or maybe best continuous, rolling lap) would be the realistic choice.

Also comparison to the optimal lap is on my TO-DO list
• I agree with the emphasis on "preference".

Comparison to best is a reasonable option, but becomes less and less useful the more you messed up on your best lap (or there was traffic).
If in turn 123 you had traffic or a mistake and you lost 0.5 seconds, each time you try to beat your best you'll need to remember that as much as +0.5 *until* turn 123 can still give you a new best, as long as you don't mess up 123, and you do the remainder of the lap exactly the same. Then you end up either with a "how well do I remember what I did on my best lap" problem while driving to extract anything reliable from the time/speed delta.

Same thing applies to "predicted lap time". If best lap is used as comparison, and this time there's no traffic / no chance of mistake, the predictive lap time will be slower. It will basically assume that you're going to repeat every single mistake from your best lap on the unfinished part of the track.

Comparison against optimal will of course be too optimistic in most cases, and your time delta will almost always be red. This is how it works in iRacing, and I generally like it.
When it comes to predicted lap time, using opt as a reference will almost always give you a prediction faster than you end up doing. I think that would still be useful though, at least as an option.

Which makes me wonder if we could use some kind of a percentile (such as median) instead of opt. "Lap time predicted based on your 90th percentile best sectors"?
• I just tried fiddling with the UI setup in iRacing and realize what we can do here in a way that's very simple and perhaps even more useful than simply comparing against "Opt" lap.

A "Time delta against best sector" widget. Basically when I'm driving sector 2, in this widget I want to see the time delta against my best sector 2 in the current session, starting from the previous checkpoint. I guess this can also be a data channel.

Also if I set a new PB sector, I want that widget to switch to purple background for a few seconds so that I immediately get positive reinforcement for a good job I've just done :)

Also perhaps this purple color thingy can be used for the regular "time delta" and "current lap time" channels.

While on the topic of opt laps again, it would be useful to have a checkbox to allow imported/reference laps to be included in best/opt sectors.