Philly SCCA's Summer Series Rust-Off; Dialing in the DC5

Hey all!  Welcome back to Lexi.Laron!

If this is your first time here, then just "welcome," period!

The other day I took part in an autocross event known as the Summer Series Rust-Off.

Every year, the Philadelphia Region of the Sports Car Club of America hosts its "Rust-Off" so that members can dial their cars in that they've been working on over the winter.  This allows us to prepare for the upcoming points season so that our cars are working to our limits, and not the other way around.

With a long day ahead of us, my friends Anthony and Alex rolled up in their silver and blue miatas, respectively.  Alex just finished building his Miata that he calls #TougeTurbo for track use.

Alex is running some insanely wide Rota Grids with Hankook Ventus RS3 Version 2's for the street and some flow-formed Jongbloed Racing Wheels wrapped in Maxxis RC-1's for auto-x and track use.  Protection for Alex is provided by a full Spec Miata bolt-in cage, six-point RaceQuip Harness, and Sparco Sprint V for extra bolstering.  He is running Tein Sport Coilovers, NA8 brakes and blank rotors, and energy suspension bushings in every possible location.

Those are just some of his upgrades and he is currently in the process of saving up for a turbo kit.  Go check him out on Instagram at @MX5Militia.

(From left to right) Alex's car, my car, and Anthony's car

 The lighting was less than optimal for my phone camera.

Again, poor lighting.

With Alex off to a cruise, it was just Anthony, me, and some friends from the 282 Touge Crew.

We walked the course and started prepping the cars for a day filled with many, many, many runs.  I ended up getting 19 runs in total which is way more than an average Northeast Autocross.  Keep in mind, I started racing in the Midwest where the population density is much lower.

After walking the course and going through tech, I began to dial the car in.  With no sway bar at my last event I was spinning out like crazy.  On exit ramps and other long sweeping corners, my car had more grip than ever with a crappy alignment, however without the sway bar, fast direction changes proved difficult.  Autocross and track are very different-- keep that in mind.  You can see how bad I did at my last event in Hershey in the video below:

Hershey PA Autocross with Susquehanna SCCA

For this event, my stock sway bar was back on with new end links and new tie-rod ends.  I also bled my brake system properly and checked my Hawk HP Plus pad life.  For my next track day I will be replenishing my HP Plus's with new HP Plus's!

With all of that in mind, I'll share with you some of the tuning steps that I went through during my first heat.  My GoPro died for the second heat, so I can't do much for you guys there, except tell you that it went really well!  

The settings for all tire pressures are in cold PSI if stated as an actual number (e.g. tire pressure was 30 PSI).  If the tire pressures are stated in differences (e.g. 1 less PSI in front tires) then I changed the tire pressures while the tires were hot.

The settings for my first run were as follows:

• Full soft damping rate in front with full stiff in rear
• Tire pressures:
• Rear tires-- 29 PSI
• Front Tires-- 30 PSI

The tire pressures gave me no sidewall scrub in the previous event that I ran in Hershey, PA.

After the first run, I noticed that the car was rather unpredictable in direction changes.  I was getting a lot of snap oversteer when transitioning from the first slalom to the next.  As a result, I decided to stiffen up my damping rate in the front by five clicks.  Keep in mind the Tein Street Flex has 24 "clicks" of adjustability.

Run 2 went much better.  The oversteer I received in transitions was much more predictable.  The settings for this run were as follows:

• Five clicks from full soft in front for damping rates
• Tire pressures same

For Run 3 I went with the same settings as for Run 2, but I noticed that on the long sweeper in the back I was getting substantial understeer.  As a result I decided to lower my front tire pressures by one PSI for Run 4.

Run 4:

• 1 PSI less in front tires
• Same damping settings

If you're an experienced auto crosser, you know that sidewall scrub is bad.  This occurs when the tire rolls onto its outer edge during cornering.  This is bad because you lose contact patch.

Notice how the front passenger side tire is almost on its edge as this Audi corners

To determine if you are scrubbing, there is a technique that most autocrossers use known as "chalking the tires."  What you have to do is take a piece of chalk and color the side of the tire with the arrow shown below:

If you are just on the arrow, you know you are using the tire to its full potential and your tire pressures are set correctly.  However, if you are riding on this arrow, you are losing grip due to sidewall scrub in most cases.  Of course, there are other variables, but this is an all-else-equal approach to sidewall scrub, contact patch, and maintaining grip.

During Run 4, I noticed that I was not using all of my rear tires thanks to this tire chalking technique.  So, I let out one PSI in the rear tires for my fifth run.

Run 5:

• Same damping rates
• 1 less PSI in rear tires

Run 6, 7, and 8 all utilized the same settings as Run 5.  During these runs I was trying to push my car as hard as possible.  I got a feel for the cars limits and by Run 9 I was able to more gently modulate my throttle during the slaloms, transitions, and sweepers.  

Look at it in the video to verify my improvement.

The last run of the first heat was Run 10.  During Run 9 I noticed that I was still getting a lot of understeer on the "turnaround" in the middle of the course.  I know now that I need more front camber because I am currently running with no alignment.  

Also I am losing grip when my front end is compressing.  This implies that I am losing contact patch in the front of my car upon compression thanks to the wonders of macpherson strut suspension geometry.  

Take a look for yourself and READ the caption!

Taken from Sport Compact Car

So, even though letting out more air in the front would result in more sidewall scrub (I was already on top of the arrow) I decided to let out more air pressure up front for my final run.  It helped me to corner at the turnaround, but again, I was losing contact patch due to sidewall scrub.

Run 10:

• One less PSI in front
• Same suspension settings

Here's a video of all of the runs from my first heat:

During the second heat I marked my fastest time of 29.288 seconds on the course with no cones.  I beat a couple of really good cars (mainly AWD and RWD) with good drivers and good tires (most had Direzza ZII Star Specs).

Fastest Run:

• Suspension five clicks from soft in front, full stiff in rear
• Front tire pressure: 34 PSI
• Rear tire pressure: 28 PSI

Keep in mind that these tires are better than the Bridgestone Potenza S-04 Pole Positions that I am running.  Once I get my camber dialed in to be negative in the front, slightly negative in the rear, and my toe to be at zero degrees all around, I believe I will be poised to be much faster in future runs!

Thanks for reading guys!