ProCoach

No apologies necessary! This is a great discussion and best wishes for breaking the magic minute mark!

Unfortunately, I will have more than thirty cars to negotiate in my quest. With lap
times from :51's to 1:02's...

Manifold

I think it's important to make the distinction between being at the limit versus minimizing lap time.

To do the latter, you need to combine being at the limit with following an optimal line with generally optimally inputs along that line. Otherwise, it's possible to be at the limit, but still be somewhat slow because the line and the general inputs on that line were too far from optimal (I say 'general inputs' because we have to superimpose car control corrections on those general inputs).

Complicating things further, the optimal line does depend somewhat on the power/grip ratio of the car, balance of the car, etc. - there isn't one optimal line for all cars.

But of course the challenge presented by these complications is part of the fun! It if was easy, we'd be bored once we figured it out what to do and could execute it consistently (which is where precision and car control come in).

ProCoach

Hmmm. I disagree. Driving at and straddling the limit of the car a majority, if not all the time, mandates the line...

While control input amplitudes and rates of change might be slightly altered based on weight distribution and other factors that affect how quickly the car rotates, external examination of the selected trajectory would not change, as the car would "be carried" through the committed-to trajectory.

Listen to Colin Braun and Kenton Koch address this very important concept on Ross Bentley's podcasts.

Ross and I are in agreement on this, as well.

1990nein

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Akunob

^^ great discussion going on here. The adage that there is a low HP car line vs. a high HP car line would seem to support the statement that "there isn't one optimal line for all cars". However do changes in the characteristics of a given car alter its optimal line? For example, would the optmimal racing line for two 991 GT3s (one fully stock and the other with pro suspension on R7s) be the same? I posit that the optimal line should be identical for both GT3s, but the car with the pro setup on R7s can attack the corners more aggressively and carry more corner entry, mid-corner and likely exit speeds due to its setup and higher levels of grip (hence quicker lap times, normalizing for the identical driver skill in both cars).

If I understood Manifolds comment, it suggests that the optimal racing line would be different for each car because of their differences (grip, balance etc). Thoughts...

Manifold

Cars with lower power/grip ratio will tend to have an earlier apex, since the lack of power means best use of grip past apex will come from cornering rather than power, so the earlier apex will give a smaller average radius past apex with unwinding of the steering delayed until corner exit.

As a more basic example, consider a car which carries a constant speed through a corner, at a constant radius, at the limit, preceded by threshold braking to reach that speed at corner entry. We all know that's not the optimal way to corner, yet it's still on the limit. (This example involves some simplification due to taking out the spirals associated with winding in and unwinding the steering, but that doesn't change the basic point.)

The difference in line may not be large for cars which are somewhat similar, but there's still a difference. And I agree with those who argue that most drivers are losing time more due to how far they are from the limit rather than how suboptimal their line is.

Adam covers these topics well in his books, and I believe the data bears it all out:



It all comes down to physics. This stuff is complicated (and much easier said than done!), but it doesn't have to be mysterious.

ace37

For the 'one line' discussion, the ideal line changes when the vehicles are significantly different. To make it really obvious, consider these very different track cars:

1. Momentum car in spec class
2. GT3 car
3. Superbike
4. High downforce prototype (like a DSR=P1/2 car)

Just thinking on it one can see the ideal lines will not be the same for all of these vehicles.

In a much milder case, a similarly classed 911 and Corvette will get to full throttle at different times leaving a corner and this will slightly alter the ideal line for each car.

Gary R.

Peter - what run group are you in, pic of your car would help too (unless you will be wearing your sport coat and tie, which makes you easy to spot!)..

ProCoach

Watch the variety of IMSA GT/LM and GTD machinery this weekend at VIR. Different layouts, tires, polar moments, BOP... Same turn-ins, apex areas and most importantly, track outs...

ProCoach

Group 9, Gary, late morning and late afternoon. Friday, Saturday and Labor Day Monday.

We have everything from Formula Atlantics to Formula Fords to Sports 2000 cars. 30 cars from :51's to 1:03's!

Here's my whip!

hf1

What a beautiful car!

ProCoach

Hard to believe it's nearly forty years old! Fully aluminum moncoque, sheet metal folded, glued and riveted together like an airplane fuselage, slicks, big brakes. No juice, though.

Big slip angles and BIG FUN!

Veloce Raptor

Yep!!!!!

dgrobs

She is beautiful. Wow!!

Gary R.

Great, see you there!