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Old 11-10-2005, 01:47 PM   #1
Scooby Newbie
Member#: 77013
Join Date: Dec 2004
Chapter/Region: South East
Location: Savannah, GA
2002 WRX
BMW Steel Gray

Default "ideal" lap time calculator - attention physics students

This is what engineering dorks to to kill time at the office and make it look like we're working really hard:


Check my work if you want. Modify for a different track. Open source excel sheet for your motorhead geeking pleasure. Comment on 'realisticness' if you've ever driven Roebling. Simulation is supposed to predict a stock-ish '02 WRX at Roebling Road, GA, on Hoosier Grand-Am cup tires where I'm going to driving school this weekend.

Formula for acceleration g's based on 0-30, 30-60, 60-100 figures shown, and adjusted to match 104mph at the end of a 1/4mile.

Notice I doubled the 0-70 braking distance spec to give myself a little safety factor, and compensate for the fact that I put in 0 reaction time or effects of transient handling.
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Old 11-11-2005, 02:22 PM   #2
Scooby Specialist
Member#: 43612
Join Date: Sep 2003
Location: Columbia, SC

So by that simulation in an 02 WRX, "stockish" but slick tires you came up with a 1:22.8 for a lap..

Some of your numbers are really close, but I don't see the lap time happening.

I would have to see a track map with what you have listed as a corner to be sure, but I can try to break it down as I see it.

turn 1a. 66mph.. too slow. Even on street tires, this is an 75-80mph corner I probably drop down to 70 in the Impreza RS, but haven't pushed it because.. just not worth it and I have been showing students what to do and being steady.

Turn 1b. 84mph Maybe with the slicks but its hard to say.. 84mph is my slow speed in my 1900lb (with driver) CRX on 235/50/13 Hoosiers. (skidpad g 1.2 on asphalt) I see your speed in this corner being 75-80 at most.

Turn 2, what we call "turn 3" by the track map is a long fast sweeper, I take it in a Stock Evo at 85-90mph, flat (on the street tires) With a slower car in a straight line, but still not having to lift for sure, i think your 84-92mph (straight 2b) is probably pretty close to right.

As I look down through, Everything looks pretty close on MPH, the little bits you are off are well within margins, but the Lap time seems about 5 seconds too fast. A stock evo can/does run 1:26.5 there with similar speeds but with a 136mph front straight mph, and an exit speed off of turn 8/9 (your "turn 6") at 104mph. (running the whole corner flat) I have seen an 05 STi, stock, run a 1:23.9 there. (the LSD helps a BUNCH) So a 1:22, even a high one, seems a bit fast to me. Without the transitional speeds and such, maybe thats where its missing. Hoppe is hoping to run 1:23s in the STi in T2 trim on DOT race rubber..

More comparisons:
Rankins 2000 Impreza RS, Toyo Proxy RA1, Tein HA, Sway bars, full exhaust, intake, 1:30.04
BONE Stock 99 Impreza RS, with T rated tires, 1:33.82

Now if you could plug it in and make a fake track map/data trace... then we could really look at it.

Jon K
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Old 11-14-2005, 09:38 AM   #3
Scooby Newbie
Member#: 77013
Join Date: Dec 2004
Chapter/Region: South East
Location: Savannah, GA
2002 WRX
BMW Steel Gray


Back from the track, and I have to say Racerjon had it pretty much dead on right.

Turn 1 was a lot faster if taking the right line, though, it took me several laps to stop overbreaking and turning in too early. Just something about seeing the edge of the track coming at you at 120 that makes my braking foot twitchy!

It felt good to finally get it right though, carrying a LOT of speed through 3 (I called it 2 in my spreadsheet.).

I'll download my GPS data and get some exactish numbers tonight, post them here along with pics and footage from my wife's 911 'bumpercam'. There's a nice piece of footage, I'm quite proud of with some grey Subaru 4-cylinder 4-door grocery getter flying past on the straight, and out of sight by turn 3 ;-)
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