rec.autos.simulators

  For those who like to know what's out there, I watched Ian Lake do about 5 laps in a row
under 1.27.50 (best of 1.27.17) in a VROC social race about a week ago. Needless to say,
he cleaned us all up (yes, even Wolfgang) in last weekends 2 races of GPLWS at Monza.

  Question - how low a brake bias can you live with? Or how late a braking point.

 http://www.racesimcentral.net/~HOSHUMUNGUS

    and

 http://www.racesimcentral.net/~godsoe/bolt/home.htm

If you're going to figure it out you should compare in reality.

In the comparison you give you have to remember that the second car
(slower) will never reach the same speed as the car which accelerated
earlier, so the difference is not only the final speed minus the
ending speed, it is the cumulative difference all the way down the
straight.

Let's suppose I exit Parabolica 2mph slower than you, call it 109 km/h
(68mph). I reach 309km/h at the end (193mph). You exit at 70mph and
reach 195mph. Given that the straight is (approx) 1.8km long, you will
cover that ground almost exactly 0.5s faster than me. It is quite easy
to lose half a second in such a way, especially around Monza and Spa.

Then look at braking. If we think that you need 70mph on the apex then
someone who brakes in a straight line must be at 70mph at the turn-in
point for that corner. If someone else can trail brake into that
corner then they can be at 70mph at the apex AND they can be doing,
say, 75mph on turn in as well as going from turn in point to apex at
an average of 73mph. This gains approximately 0.2-0.3s PER CORNER.

If you add that up even over a relatively short track like Monza you
can see that braking into the Lesmos and Parabolica alone could
account for almost 1s, without even considering acceleration out of
the turn.

These numbers assume a "perfect" corner which of course would never
happen, but even in real-life scenarios those tenths, which may not be
important as long as you're spinning off every other lap, are the only
way to keep an Ian Lake or a Wolfie from disappearing into the
distance. They are what separates Schumacher and Senna from Irvine and
Berger - they can't be underlined highly enough IMO. I doubt we're
good enough to take advantage of them (I know I'm not) but for those
that are the difference over a lap (or series of laps) is very
significant.

I remember racing for a while in a team with Michael Wollenschein, one
of THE hotshoes on F1GP. We exchanged PRF files at Suzuka, with me
trying to find where he was faster, and it was the start of a pattern
I have often seen when comparing your lap with someone really fast -
there is no one "magic" move or corner where all the time is lost. It
is 1/10 here, 1/20 there, and before you know it there's a second a
lap or more of a difference. He made a tiny amount out of me on every
corner entry or exit, and clawing back the time was a matter of
thinking, setup, practice and application.

Cheers!
John

I disagree - braking and turn-in will gain you time through that small
portion of track, but anything you gain on exit will be amplified by
being carried with you for many seconds along the following straight.

You would think so, but it's surprising how many people take the
second Lesmo exactly the same as the first. There is no "perfect line"
for a particular type of corner, it depends utterly on what goes
before and comes after, and the line is compromised or adjusted
accordingly.

Again I disagree, you cannot take a corner in isolation. It is a
matter of little consequence how fast you are through one corner,
never mind how fast you are through 1/3 or 2/3 of a particular corner.
What matters is how fast you are over the full lap or even a full race
- you've heard of "slow-in, fast-out"? Often it is better to take it
easy into a corner to ensure a near-perfect exit. You may lose a tenth
on the way in, but you'll pick it up and more on the way out and along
the straight to the next turn. Compromise is in everything concerning
racing.

Cheers!
John

--
   _____
 /_______\              .\\ a t t h e a d
I  XT /~~~~                    
I  500\_____       1977' Yamaha XT.Rex 500 Enduro
 \____/\__I_I      http://www.racesimcentral.net/

My example was given for a (very) long straight, were the cars
(nearly) reach top speed, eg. at Spa. This has the advantage of
completely eliminating the real acceleration (which depends on power
curves, grip, gearing, wind drag etc.), about which we do not know
much.
But a top speed of at least 200mph and a maximum acceleration of 1g up
to let's say 120 mph are realistic assumptions.

In this example, you assume constant acceleration, or in other words,
that a GPL F1 car can accel from 193 to 195 mph in the same time as it
can go from 68 to 70 mph, which is, BTW,  in 0.09s or within only 2.8
meters, at 1g =9.81 m/s2.
This quick time is very unrealistic for 193 to 195 mph. Just watching
a replay might give a guess. Calculating with a car mass of 600kg,
300kW or 400hp, and a max speed of 200 mph using a simple motion
equation gives only an acceleration of 0.58 m/s2, or 1.5 s to
accomplish it.
(As GPL cars can reach 200 mph on tracks, their real top speed might
be higher: with 220mph, the acceleration at 193mph would be 3 times
better).
At 194mph, the 2 mph advantage would have melted to a speed difference
of 0.58m/s2*0.09s=0.05 m/s, which is roughly 1/9 mph.
So much about your (correct) assumption that "the second car
(slower) will never reach the same speed as the car which accelerated
earlier". But the speed difference is certainly not 2 mph all the
time.

In your example, the unrealistic constant speed difference carried
over the whole straight would add up to 0.5 sec, which is simply
wrong: Calculated with more realistic (but non-relativistic) physics,
it's 0.09s minus the 0.03s needed to travel the 2.8m at 195mph, so it
yields 0.06s or the lenght of a car at the end of the straight, barely
enough to overtake.

BTW: The fast car in my initial example, accelerating with 1g from
100mph, would pass the 50m after 1 sec at 122 mph, while the
non-accelerating car would need approx . 1.1 sec to cruise this
distance at constant 100mph. So, 0.1s gained within the first 50m.
This 22 mph difference in exit speed then adds up to 0.5 sec after a
long straight.

Compared to your example given above, this is much closer to reality.

(The slow guy hits the brakes 357.3 m before turn in to slow down from
200mph to 70mph at -1g, which takes 5.92 sec.
The fast guy passes the 357.3 m brake point at 200 mph, and hits the
brakes 0.08 s later at 350.2 m before turn in to slow down from 200mph
to 75mph at  the same -1g, which takes 5.7 sec, and 5.78s overall.
So  0.14 s are gained here. To gain another 0.06s (0.16s) with a
different average speed of 73 to 70 mph lasts 1.4 s (3.7s) within
45.7m (120m) distance from turn-in to apex.)

Okay, good braking in Monza gains 1 second, I agree.
Plus another second from apex to "turn-out", if we apply the
trail-braking example symmetrically for acceleration.
Small different exit speeds on to the two long straights between
Parabolica and Lesmos don't add very much, as I hope to have made
clear (as long as the same car and setup etc. is used, no wheelspin).

So, were are the other 2 or 6 seconds that are between a 1.27 and my
1.31 to 1.35 laps in the Eagle?
Speed in Curva Grande and Ascari? (Too tired to figure that out now).
Bad gearing setup giving bad acceleration? Not with setups from
hotlaps, as long as I 'm in the right gear.

But 8 seconds behind, as 1.35 used to be my best for a long time
(without spinning), so I must have been braking like on ice, and waaay
too soon?

--
   _____
 /_______\              .\\ a t t h e a d
I  XT /~~~~                    
I  500\_____       1977' Yamaha XT.Rex 500 Enduro
 \____/\__I_I      http://matthead.home.pages.de/

I'm afraid that this flame-war-stopper.xls is incorrect, as it does
not include wind drag, but assumes constant acceleration at all
speeds: with a=1g=9.81m/s2,  I got 495km/h at the end of the straight.

Hardly realistic, even for veryhotlappers.

--
   _____
 /_______\              .\\ a t t h e a d
I  XT /~~~~                    
I  500\_____       1977' Yamaha XT.Rex 500 Enduro
 \____/\__I_I      http://matthead.home.pages.de/

Exactly. In fact, if a car reaches its terminal velocity, as constrained by
aerodynamic drag, acceleration has, by definition, dropped to zero.

The power required to maintain a given velocity varies with the cube of the
velocity and the force required to maintain a given velocity in the face of
aerodynamic drag varies with square of the velocity, i.e. Twice the speed
requires four times the force and eight times the power.

I know, Bernoulli told me so. <G>

Regards,
  Casper

 http://members.tripod.com/~HOSHUMUNGUS

    and

 http://www.frontiernet.net/~godsoe/bolt/home.htm

I agree, but it has the disadvantage of completely negating the point
that we are discussing - why can "Driver X" in the Lotus gain time
over you? The reason is because he _does_ accelerate better out of the
corner, through smoother throttle application closer to the edge of
the friction circle.

In your calculations you assume the "fast driver" and "slow driver"
accelerate at exactly the same rate, and the only difference between
them is the point at which they begin accelerating. Your calculations
still underestimate the effect of that, but the main point is that the
acceleration is, in all probability, very different, especially in GPL
where sensitivity to that is both crucial and difficult.

Plus the same again for the other half of the corner from apex to
exit, so that's two seconds at east given the quality of drivers you
describe and with no wobbles or errors.

There's the rub - no wheelspin. Beyond that even you have to assume
neither driver bogs down due to being too conservative with avoiding
wheelspin and drops too low in the powerband. Now think how that
starting difference and acceleration difference would add up.

Ascari would be a good place to start looking, since not only is it a
long corner in and of itself, but it leads onto a long straight where
again speed can be lost. There is also a fair choice of lines through
there depending upon style and setup.

It could be that - if someone else's foot is more sensitive than yours
you may induce too much wheelspin if their setup is stiffer than you
like or your style induces wheelspin due to their choice of
ramp/clutch settings.

This is also a strong possibility. Like in real life you get "locked
in" to braking points, and often don't try to improve. I remember my
driving style at Silverstone being described as "mental" one night on
VROC because of how late I was braking at the end of Hangar Straight,
but that to me is not a problem as there is a lot of room to gather
things up if it goes wrong. Where I have a problem is Parabolica,
where I know I can brake real, real late, but only if I really nail
the braking action will I keep the car on the track. I find in GPL
that my first half-second on the brakes determines whether I'm pulling
up short of the corner, fighting to stay on the track or cruising in
perfectly. If I lock up I slide so far in that short time that it's a
fight to stay on the track once I release the brakes and get back on
them. If I don't brake hard enough initially, same story. If I get it
perfect then the car stops in a very short space of time. Now your
braking point at any given corner has to be at least "mean braking
distance plus standard deviation", otherwise you're going to be
spending a lot of time picking hedge out of your teeth. That means the
less consistent your braking the longer it will be on average, and
that's the problem I have at Monza. My braking isn't _bad_, but I'm
not confident enough to go as late as I know I can, due to the high
possibility of ending up in the gravel. When I get it right I can run
low 1:28s, but typically I'm in the mid to low 29s in the Eagle for
the reason described above.

Cheers!
John

My examples took this into account, in an extreme way: I estimated and
calculated that the fast driver accelerates from 100mph at the apex
(or any other given point) at +1g, and a slow driver travels 50m or
1.1 second with constant 100mph before accelerating at all.
Can there be a bigger difference between max acceleration and no
acceleration?
This IMO big difference in driving ability leads to a speed difference
of 22mph (and a time gain of 0.1 sec) 50m after the apex (the speed
difference then adds another 0.4s over the straight).
Oh yes, I assumed that a slow driver can accelerate from 100mph on the
straight(er track) as good as a fast one can in the corner, 50m
sooner. How bad has as slow driver to be to get even that wrong?
So, this already is a worst-case calculation as far as perfect
throttle control is concerned: one does it, one not at all.
Oh well, one can extend the 50m to 100m, or the whole track ...

See above. This is physics, considered to be an exact science.
Assume different but realistic accelerations (by looking at replays)
and figure out the difference.

Thats what I had written in the sentence you deleted.

Been there, done that, got the reply. See above.

--
   _____
 /_______\              .\\ a t t h e a d
I  XT /~~~~                    
I  500\_____       1977' Yamaha XT.Rex 500 Enduro
 \____/\__I_I      http://matthead.home.pages.de/

Which I explained.

Not at all - what you described is equal accelaration starting from a
different point. What I was talking about was starting later as well
as less efficient acceleration.

Both do perfect throttle control in the example, one just does it
later. That is not because of throttle control, rather because of poor
line or whatever.

The difference can't be figured out since driver ability is an inexact
science. We already know the car is fundamentally capable of the speed
(albeit perhaps with a different setup) therefore the difference is in
the driver.

You never addressed driver ability as far as I could see, simply
theoretical calculations. We already know from the work, theoretical
calculation and practical experiment of experts in the field what
difference exit speed makes, and from that can be seen how much time
will be lost. So too under braking, when you consider that pretty much
any racecar can lose about 3-4km/h per tenth of a second under braking
a difference of just one or two tenths in when you apply the brakes
can see you be too fast or too slow into the corner, thus wasting time
beyond the theoretical to correct and recover.

Then too there is the point about Ascari/Curva Grande, where carrying
slightly more speed would yield an advantage for longer. If we say
that I am within 98% of your performance I can expect to run 46mph
through Lesmo 1 where you run 50mph - you gain 2mph for a short time
which is soon minimised by being "squeezed" under acceleration. In
Ascari however I can only manage 176mph to your 180mph, a difference
of 4mph which not only will you hold all the way through that much
longer corner, but for much longer down the following straight since
the acceleration is much less efficient.

Add together braking, acceleration, Vmin and Vmean in high speed
corners as well as minute driver erros and it's easy to find many
seconds at most tracks.

Cheers!
John