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Long-time readers of this blog will know that we’re huge fans of using data (especially video) to improve driving performance. A recent talk given by Andy Hollis at the SCCA Motorsports Expo reminded us that data comes in many shapes and sizes; and that it often involves zip-ties.
Andy started his presentation with the rhetorical question, “What is Data?” He asserted that data is the digital representation of a car’s performance across a set of constraints, either recorded or perceived. Your “butt-dyno” just isn’t calibrated fast enough for the rate of inputs per second of a car at speed. The advantage of data over “feel” is objectivity.
For example, do you sense that your suspension is bottoming out in a given corner? Put a zip-tie around the strut shaft where it meets the tube and see how far it moves. If it moves as far as the photo below, then it is bottoming out.
Want to know how much body-roll you have? Someone is always taking pictures at autocross or track events, so find a good high-resolution image of your car head-on and measure the angle? A good amount is probably in the two to four degree range. More and you get too much weight transfer to be efficient, too little and you’re losing grip. If the angle looks good, what is the loaded tire doing? Do you have enough negative camber? How about air pressure? This photos shows body-roll of about three degrees, but the loaded front tire is deforming suggesting more negative camber is needed.
Data will show some surprising results, such as all other things being equal, a narrower car will be faster through a slalom (think old vs. new Miata). In Andy’s experience, tire compound is more important than width. And testing requires a different mindset than competition. You need to be consistent and remember your objectives when testing so you can isolate and focus on the aspect that you are testing.
For suspension tuning, he starts on the skid pad. Time is the most important factor, not feel. Use zip ties to see if bottoming out. Look at tire temperatures front/rear and side to side. To get good data run in 3rd gear. He uses a 100 foot radius skidpad. For alignment changes, work on the end of the car that lets go first. For a front heavy car, a thicker front bar can help it push less (again counter intuitive.) Rake is important, but consider dynamic toe effect when changing rake after changing ride height. Once you have steady state on round skid pad, then go to oval skid pad and introduce the pitch variable. If too extreme, go back to round skidpad and adjust. Next add braking/acceleration on the oval skid pad. If the rear steps out, it could be a brake bias issue. If you can’t adjust bias, then go back to suspension. Next he moves on to the slalom and takes acceleration of out if to just work on the transitions. This requires a constant speed through the slalom. For autocross, a little toe out in the front can help (not recommended for the track.) For an underpowered car with over-steer a little toe out in the rear can actually help, but can also make for an interesting ride in a straight line over bumps. The B Spec cars in PWC are running as much as a half an inch toe out [which is nuts.] In the end you may have to compromise, but consider where you spend most of your time on course. If you’re running autocross in a small parking lot with many tight turns, you may make changes that are different if most of your time is spent in long sweepers. The same goes for the track.
Today was the SCCA practice event at FEDEX Field. It is a non-championship event where drivers can knock off the rust and organizers can try to get their act together before the season starts. It was unusually cold today. Most of the cars in the super-sticky-tire Street Mod class were running street tires for a change, including the GeorgeCo Stealth BMW powered by Beano.
Yesterday we had a bit of a set-pack in the suspension department. When we went to adjust the rear sway-bar, we found the drop-link was a wee bit bent.
Nobody likes having their drop-link bent out of shape. After (quite) a bit of judicious pounding with a sledge hammer and re-cutting of threads, it was almost good as new. Not really, but good enough for autocross. We won’t run it on the track. Not sure why only one side bent. Don’t remember any wheel-eating DC potholes.
There were some interesting cars there today. Of special note is Jeff’s E-30 with an E-36 M3 engine. More power. Ho, ho, ho, ho. Unfortunately, no grip in the cold, but if it ever hooks up, watch out.
Speaking of all fury, no grip — check out the Home Depot Spoiler on this C6 Z06 Corvette.
The autocross season drew to a close on October 24th with the final event for the NCC at Baysox stadium. I had one chance to win my class for the season: I had to beat my closest rival in the championship by two places. It was close, but in the end, the weather voted against me. The other two ran in the dry and my heat ran in a monsoon.
In the end the GeorgeCo BMW powered by Beano finished the season in a solid second place in the Modified 3 class. Here’s a little life lesson: Be sure to read the class rules carefully. You had to run 6 of 8 events to compete for a class win for the season, best 7 of 8 events counted for points. The previous year it had been best 6 of 8. GeorgeCo only ran 6 of 8 events in a best of 7 series, we lost on total points despite 4 class wins; 1 second place; and 1 third — the most wins in the class. We could have showed up for the event 7, came in last, and walked away with the title. D’oh!
Time to start planning for next season. Next year this will be the only series we’ll run so we won’t come up short on total points again. The car needs a few repairs: new clutch slave cylinder and a new final drive. It’s also time to start working on more power with new injectors, a header, free flow exhaust and a custom ECU tune. Ho, ho, ho, ho, ho. It’s also time to bite the bullet and buy some Hoosier A6 tires.
The GeorgeCo BMW powered by Beano put in a strong performance among higher horsepower cars this past weekend at Summit Point. The three-day school on the Jefferson Circuit was the last track weekend of the year for the National Capital Chapter.
We’re finally figuring out the skidpad and sustained oversteer. The key is to stay in second gear, dial in some mild understeer, as the front hooks up, wait, then blip the throttle. As the rear comes around, countersteer and hold the throttle steady.
Temperatures on the car were good all weekend. Tirewear has been fairly even. We’re getting some rubbing in the front on the new swaybar but that may be only an issue at full lock on the skidpad.
The biggest issue of the weekend is the ugly song the differential began singing on Saturday. We checked the fluid level and color and both were good. Temp was fine. It may just be in the last throws of death. Time to start checking craigslist.
Final Session, Part 1.
Final Session, Part 2.
Things to remember about this car on the Jeff counter-clockwise:
- Turn 1: max entry speed; stay on the crown; trailbrake; put in lots of steering input; carry speed up the hill; don’t worry so much about track position for turn 2, just be back on-line for turn 3.
- Turn 4: brake mid track; wait for the front to hook up; long apex; unwind the wheel on exit
- Turn 5: stay mid track to avoid dip on entry; trailbrake slightly; head for accessroad; lots of steering input at the apex; avoid the patch; full gas well before apex
- Turn 7: double apex. Brake late to carry speed up the hill, but don’t go deep; trailbrake; get on the throttle early; late second apex
Chapterfest marked the end of the Summer for the GeorgeCo BMW Powered by Beano. The annual event sponsored by the National Capital Chapter of the BMW Car Club of America brings together the diverse sub-groups of 6,000+ member chapter into one event. It features a swapmeet, shine & show, good food, and of course autocross.
There were some beautiful old cars in the show as well as quite a bit of questionable carbon fiber bits on newer cars. And this:
Not exactly my thing, but to each his own I suppose. I think that audio system costs more than my car. And it probably has more power too… There were some interesting non-BMWs too. I always like to find dubious aero bits:
No video from the autocross. Another autocross season down, another dead video camera I’m afraid. I’m going to have to invest in a solid-state recorder of some sort. The course was more challenging than it appeared during the course walk. The course designers decided to use the lower lot at Baysox Stadium this time. To get there and back, the course has to pass through a couple of islands in the parking lot. That risk means designing very slow sections before the entry to the pass through. This caught out a lot of people, but since going fast by going slow is what the GeorgeCo BMW Powered by Beano does best, it was no problem for us. Rain spoiled the times for the fourth heat runners, but running in the second heat, we managed to take first in class, solidifying our position going into the season finale next month.
Sunday brought the sixth championship event for the Washington DC Region of the SCCA at FEDEX Field. In this series, we’re running the GeorgeCo Gas-X MINI in the Street Mod class.
The only car on street tires as well as the only true daily-driver in the mod-till-you-drop Street Mod Class, the GeorgeCo Gas-X MINI has a significant disadvantage to the stripped-out, higher horse power cars in the class running on competition tires. That is, until it rains. We almost achieved greatness yesterday. Almost. It rained heavily during the fifth heat. At the start of the sixth and final heat, the course was very damp and slick. At the start of the second of four runs, the GeorgeCo Gas-X MINI was in the lead. Unfortunately, the sun was still shining and the course was drying and we saw our advantage slip away. Nonetheless, the car ran well and the course was challenging. Perhaps just as interesting were some of the other cars that were at the event.