Data analysis between STi and 97 M3: Autobahn South

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Hornswoggler
Club Racing
Posts: 28
Joined: Wed Jul 19, 2006 6:45 pm

Data analysis between STi and 97 M3: Autobahn South

Postby Hornswoggler » Tue Jun 05, 2007 3:53 pm

My buddy Andy and I recently attended an HPDE driving event at Autobahn Country Club, South Course, hosted by AMS. This event occurred on 5-20-07 and the weather was beautiful. We both ran in the advanced group and captured data with my traqmate, with Andy capturing data for three sessions and I ran the traqmate for the last session.

Small track map:
Image

The captured data is available for download HERE You will need the traqview software, as downloaded from the Traqmate web site. Feel free to join along in this analysis!

Introductions:

Andy’s car is a 2004 Subaru STI.
Stock power
Toyo RA-1 255/40-17 comp-r tires
Racecomp Tarmac 2 coil-overs
Hawk DTC-70 brake pads

My car is a 1997 BMW M3 with all sorts of brake and suspension mods. More info HERE

Best lap time summary:
Andy: 1:42.800
Collin: 1:41.300

Write-up Goals:

My goal with this write-up is a couple of things:

1. Compare performance aspects between the two cars (i.e. braking, cornering, accelerating, etc.)

2. Identify any differences in driver technique, and improvement opportunities.

3. Comparing AWD vs RWD?


Analysis:


1. Comparing performance:

Acceleration - Both cars have similar acceleration curves. From 70-90 mph, it is identical. At 90 MPH, I shift into 4th gear, and around 95, Andy shifts as well (into 5th?). 95-107 mph is again, very similar. See chart: (Red = Andy/STI, Green = Collin/M3)

Image

Just to give an idea of how consistently similar our acceleration was, here are the top 10 times from the main straight segment. Notice how they are only separated by 0.150 seconds top to bottom! This is accelerating from 60 to 106 mph.

One thing I noticed is Andy's tire diameter (255/40-17) is larger than stock STI size of 225/40-17, which would have a slight impact on acceleration. With a smaller tire size, I would expect a small advantage to the STI in acceleration.

Image

Braking - Braking is hard to be conclusive as drivers don't tend to "stand" on the brake pedal like they do the accelerator. My data shows much later and harder braking, which could be hardware (including tires), could be driver, or could be a mix of both. Looking at the braking zone at the end of the main straight, we are hauling the car down from 105-110 mph down to 47-53 mph. This is quite a bit of speed to scrub off.

Looking at peak deceleration numbers:
Andy: 1.17 g's of deceleration
Collin: 1.42 g's of deceleration

and best average decel:
Andy: 0.84 g's of deceleration
Collin 0.90 g's of deceleration

Having better brakes and/or using them later is a great confidence builder and all, but how much time does this really gain? Looking at the segment analysis, I am seeing anywhere from .2 to .4 seconds time advantage to Collin (me) in the M3. 0.4 seconds is worth a lot to a club racer. In Andy's defense, I believe his front rotors were installed backwards. I'm sure we'll have a braking rematch once fixed. :)

See below picture for braking zone analysis. Circled in green is time spend in the braking segment (as defined by the brackets on the track map), Circled in blue is the braking zone entrance speed (indicating my continued acceleration while Andy started braking sooner), and red is max braking g forces.

Image

Cornering

The South course has quite a few corners of sustained lateral grip. Turns 1-2 is a partial throttle carousel (slow in-slow out), turn 4 is a very fast left-hand turn (fast in, fast out), and turns 13-14 is a full-throttle carousel (slow in, fast out).

First we will look at turns 1-2. This might very well be an area that either AWD or the wider tires are showing an advantage. Andy gets on the gas a lot sooner here, which might be a result of less trail braking, better grip/traction, or just pushing harder through this turn. here are some metrics:

Best segment time:
Andy: 8.30 seconds
Collin: 8.55 seconds

Peak lateral load:
Andy: 1.50 g's
Collin: 1.36 g's

Average Lateral load:
Andy: 1.09 g's
Collin: .99 g's

Average speed:
Andy: 55.22 mph
Collin: 53.50 mph

Segment Exit speed:
Andy: 68.13 mph
Collin: 67.17 mph

I lost about .25 seconds in this segment to Andy in his STi. Andy was also able to maintain this time advantage through turn 3, although I usually had a better exit speed from turn 3.

Turn 4 is a very fast and very fun left-hander. Entry speeds are between 70-80 mph, with exit speeds reaching upwards of 90 mph. If you are full throttle through this turn, then your entry speed was too low! :P Lets look at the segment times:

Best segment time: (tied!)
Andy: 4.950 seconds
Collin: 4.950 seconds

Best Peak lateral load:
Andy: 1.33 g's
Collin: 1.39 g's

Best Average Lateral load:
Andy: .97 g's
Collin: 1.06 g's

Best Average speed:
Andy: 79.34 mph
Collin: 80.22 mph

Best Segment Exit speed:
Andy: 89.06 mph
Collin: 85.38 mph

And picture of segment four with times:
Image

While the times may be close, I believe Andy had a traction advantage at corner exit, which would carry him down the next straight a little faster. This corner takes some major commitment, the exit is blind, and requires some good faith in your tires before corner entry. Get this one wrong and you could be in the grass. Seeing Andy's turn 1-2 numbers, I would guess his car to have some more capacity in this corner that has yet to be explored. In other words, I think his hardware could beat me here next time out. :)

Turns 13-14 are not as tight as 1-2, so they can be taken at full throttle. Looking at the segment analysis, Collin usually gains about .1 seconds here in his M3.

Comparing best segments, lateral grip was very similar, with the M3 braking quite a bit harder before the turn. Exit speeds are very similar. Collin was able to apply just a little bit more acceleration through this turn. I think the tires on both cars have a little bit more grip in them. While it takes a little nerve at this corner, I try to force myself to be full throttle. I am assuming Andy applies a partial throttle here.

Image


2. Differences in Technique and improvement opportunities:

A lot has been mentioned already in comparing the performance between these two drivers/cars. Sorting them out, here are some of my observations:

- Braking. Andy is braking a lot earlier and not as hard. This could be hardware, could also be technique. I attribute a .8 second advantage due to better brakes and/or technique.

- Low speed carousel. Definate advantage to Andy in the STI for this one, by about .25 seconds in turn 1-2.

- Consistency. While this can be very tough at an HPDE event due to traffic and waiting for passing zones, Andy's three recorded sessions show a lot more deviation than Collin's one recorded session. Andy shows some strength in segments, but putting all of those "best segments" into a "qualifying" lap could be something to work on. Both car and driver have shown a lot of capability, just need to tie it all together in the same lap.


3. RWD vs AWD:

Trying to isolate any AWD vs RWD differences is a lot tougher than I thought, atleast with the sensors and data that I have gathered (or may be a limit of my interpretation abilities or knowing what to look for). Except for what I can identify as braking or gearing, our driving lines are very close and driver technique/style could account for any differences. Acceleration was amazingly similar. Anybody have a dyno chart of a stock STi? My car puts down 246 rwhp and 229 torque (vehicle weight about 3,200 lbs). I hear stock STI's usually dyno just as high, if not a hair higher but may weight about 150 lbs more.

The most obvious advantage for AWD has been the ability to apply more power and more grip through the low-speed stuff (turns 1-2), and maybe a slight edge to better acceleration out of the corners, although that could easily be a difference in torque.


Summary:

Good times out there and well driven! I can honestly say I gave it everything I had that day, and with the right prep, I think Andy could come back with a faster lap next time.

To put our laptimes into perspective, here are the NASA time trial results from the same course a year ago:

Code: Select all

[FONT=Arial][SIZE=2]Jon Krolewicz        [/SIZE][/FONT][FONT=Arial][SIZE=2]EVO[/SIZE][/FONT][FONT=Arial][SIZE=2]               1:35.28[/SIZE][/FONT][FONT=Arial][SIZE=2]     7/23/06      [/SIZE][/FONT][FONT=Arial][SIZE=2]TTA[/SIZE][/FONT][FONT=Arial][SIZE=2]  963[/SIZE][/FONT]
[FONT=Arial][SIZE=2]Derek Whitis         [/SIZE][/FONT][FONT=Arial][SIZE=2]Corvette           [/SIZE][/FONT][FONT=Arial][SIZE=2]1:37.51[/SIZE][/FONT][FONT=Arial][SIZE=2]    7/23/06[/SIZE][/FONT][FONT=Arial][SIZE=2]      TTB[/SIZE][/FONT][FONT=Arial][SIZE=2]  193[/SIZE][/FONT]
[FONT=Arial][SIZE=2]Robert Dudek[/SIZE][/FONT][FONT=Arial][SIZE=2]        Corvette[/SIZE][/FONT][FONT=Arial][SIZE=2]           1:40.07     [/SIZE][/FONT][FONT=Arial][SIZE=2]7/23/06[/SIZE][/FONT][FONT=Arial][SIZE=2]     TTC  [/SIZE][/FONT][FONT=Arial][SIZE=2]175[/SIZE][/FONT]
[FONT=Arial][SIZE=2]John Slinkard[/SIZE][/FONT][FONT=Arial][SIZE=2]         S2000             [/SIZE][/FONT][FONT=Arial][SIZE=2]1:38.70[/SIZE][/FONT][FONT=Arial][SIZE=2]      7/23/06[/SIZE][/FONT][FONT=Arial][SIZE=2]    TTD  [/SIZE][/FONT][FONT=Arial][SIZE=2]13[/SIZE][/FONT]
[FONT=Arial][SIZE=2]Allen Skillicorn[/SIZE][/FONT][FONT=Arial][SIZE=2]       S2000[/SIZE][/FONT][FONT=Arial][SIZE=2]             1:40.69[/SIZE][/FONT][FONT=Arial][SIZE=2]      7/23/06[/SIZE][/FONT][FONT=Arial][SIZE=2]    TTE  [/SIZE][/FONT][FONT=Arial][SIZE=2]120[/SIZE][/FONT]
[FONT=Arial][SIZE=2]Jose Pietri[/SIZE][/FONT][FONT=Arial][SIZE=2]New       Beetle Turbo[/SIZE][/FONT][FONT=Arial][SIZE=2]    1:47.71[/SIZE][/FONT][FONT=Arial][SIZE=2]      7/23/06[/SIZE][/FONT][FONT=Arial][SIZE=2]    TTF[/SIZE][/FONT][FONT=Arial][SIZE=2]  111[/SIZE][/FONT]
[FONT=Arial][SIZE=2]Bill Marquardt[/SIZE][/FONT][FONT=Arial][SIZE=2]        Miata[/SIZE][/FONT][FONT=Arial][SIZE=2]               1:50.43[/SIZE][/FONT][FONT=Arial][SIZE=2]      7/22/06[/SIZE][/FONT][FONT=Arial][SIZE=2]    TTG[/SIZE][/FONT][FONT=Arial][SIZE=2]  510[/SIZE][/FONT]
[FONT=Arial][SIZE=2]Joe Hayes[/SIZE][/FONT][FONT=Arial][SIZE=2]             Neon[/SIZE][/FONT][FONT=Arial][SIZE=2]               2:14.54[/SIZE][/FONT][FONT=Arial][SIZE=2]      7/22/06
[/SIZE][/FONT]


Hope you enjoyed the analysis. Any questions, post up!

Comparing the two Dynos:

Stock STI:
Image

My M3 (the blue plot is post-cam install, red was same car with just Intake/Chip/Exhaust):
Image

Some action photos from the event:

Image
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Some in-car from Andy's POV:
http://www.youtube.com/watch?v=6brnB1YbqfQ

Guest

Postby Guest » Wed Jun 06, 2007 9:16 am

Outstanding post and analysis!
Thanks!
Andre' Surles
Track Systems


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