Wednesday, May 16, 2007

lines

ok.. so we talked a little tech.. let's talk a little driving. it is 90% of the equation right?

i'll dive into some data from sunday's event at NYR (our favorite scca chapter!). we have to thank the course designers timmy, jeff, and bo for a kickass course. and of course mark for his dedication to our sport.

ok, let's roll up our sleeves.

here is an overlay from our last runs of the day. gj asked for a codrive, and i happily obliged. there is a lot to learn from a national champ! fortunately (for me!), gj was having an off day whereas i was still on a driving high from etown the day before. and even more fortunately, the gps picked up a big difference in line approach that we can take a closer look at. gj is represented in blue, i am red. the course starts from the upper right hand corner.



as you can see from the snapshot, at this given point, we are pretty much even. the red and blue crosshairs indicate our position on the course. from this point on, this is where we start getting into the fun stuff... sweepers! it's interesting to see that gj always took the textbook wide line, whereas i stayed tight. yet we were both getting the car very sideways! it was way too irresistable, still quick, and put shit-eating grins on our faces! a loose car and power-on oversteer is a beautiful thing.


here we are at the exit of sweeper and about to enter a short technical section. as we all should know, the wide line allows greater exit speed out of corner. and the data proves it. if you follow the blue mph plot just before this point, you can see the mph 'hump'. so here, gj is ahead of me distance-wise in the corner due to carrying more speed earlier. HOWEVER, we have entered a short technical section that the gps does not show. AHA! this comes to bite mr. blue. there is no benefit to carrying more speed out of a corner, and sacrificing more distance to do it, if it doesn't reward you at the exit.

in this case, the exit of the first big sweeper feeds into a tight technical section. blue is ahead, yet has to slow the car down more than red (note the red mph data plot just past this point), and is at the very limit entering a technical section, fighting to get the car stable, and probably losing time doing it. in my case, i now regain some mph, car settled, negotiating the tight stuff with the car better balanced, and accelerate out towards the next sweeper. it is also important to note that i had covered less distance throughout the sweeper we just left, so he doesn't get even further ahead.


bingo.. there is my reward. i'm ahead by the time we hit the apex of sweeper #2, brake hard, get the car turned, and back on the gas. i have covered significantly less distance, and start pulling away.

and of course, i follow the tighter line for sweeper #3. in the end, my run was nearly a full second quicker, and he never catches up.

so what can we learn from this?
  • if there wasn't a tight technical section after sweeper #1, gj's racing line would have been the better approach.
  • covering less distance with a tight line usually beats a textbook racing line for autox.
  • sometimes you have to slow down to go faster
    • slow stuff slow, fast stuff fast.
  • you have to assess what comes before and after each corner to determine how you will drive it.
  • the sti is able to accelerate out of a corner VERY well. the immediate torque response is sick. therefore, this example may be slightly different for an evo or 'momentum' car.. so drive accordingly!
i hope i have explained this clearly. if not, post a comment and i will try to clarify.

also let me point out that i feel that i am NOT a better driver than gj. i just got lucky this day. keep in mind he is driving a car that he has very little seat-time in, yet still is able to keep me on my toes. (plus we were putting on a little drift show and i think he won that contest.) i have learned a lot from him, and owe him huge thanks for showing me how to REALLY drive. so let me emphasize this point:
  • take every chance you get to have a better driver codrive or instruct you! and don't be afraid to ask someone because they most likely won't know to offer!

class dismissed!

-dan

6 comments:

Greg said...

Dear Professor Dan:

Your analysis of the lines and data above was awesome! Thanks for sharing. You discussed the track map and lines but I would also like to understand the other two graphs: MPH and LatG. First, are those graphed vs. time or distance? I think distance might be more meaningful in this case but it may complicate things with wider lines involving more distance.

I notice that your and GJ's LatG traces are very similar, althugh GJ seems to reach a higher LatG than you in most of the corners (except for one near the end where your cornering forces were much higher than his--he probably slid too much).

The speed traces do not match nearly as well and it's interesting to see where your speed is higher than his and vice versa.

Perhaps in a future "lesson" you can compare the LatG and MPH traces as well and relate them to what you've previously said about the track map and overall time.

Thanks again!

dan said...

thanks greg.. it's good to know that it's worth my time to do these writeups. i wasn't planning on posting for the rest of the week but another friend said.. "more blog! more blog!"

the plots above are in fact graphed over time. i'll take a look at it over distance at some point and see how it looks. to be honest, i didn't bother since i was able to see exactly what was happening with the current view. but now i'm curious.

gj's latG traces are higher because he has a better 'feel' for the limit. something i've been working hard on. valuable info that i wouldn't have realized had i not had data aq and overlayed our runs from warminster.

at some point i'll dive into mph and latG overlays.. longG too! lots to see there about braking!

there is so much to write about, not enough time.. and i have to do more events to gather more data and video! jay is supposed to do a writeup real soon.

thanks for the feedback!

dan

Char said...

This was an interesting read Dan. I read "Secrets of Solo Racing" a while ago which also mentioned using faster exit speeds when entering a straight where you can take advantage of the extra speed. But it took me a few events to figure out which straights were long enough, and also that I was losing time going too wide hoping to have a faster exit speed.

dan said...

thanks char. hope it gets everything thinking. the data doesn't lie. for your evo.. you should try to treat it like driving a fwd car- keep the momentum up, and take advantage of that precise handling. the only way to really tell what line is better, is to use data aq. you can try different lines on different runs if you don't have a codriver.

dan said...

oh and jay, kev, and adil are the real evo authorities! they'll give you a better idea of what works where for that car.

Char said...

Oh yeah, I usually try and pick Adil's and Kev's brain when they walk the course ;-)