goofygrin

iTrader: (5)

It was SAE weekend at UTA, so they had two autocrosses on Saturday and then came out to play at ER on Sunday before heading home.

The course was so setup for the mod cars that the top 10 pax positions were mostly FSAE/BM cars with a couple of ST, ESP, and SS cars thrown in the mix.

Fair

Vail Valley National Tour update - the battle of scrub: Amy and I went to the Vail Valley National Tour with the EVO last weekend. We got back on Tuesday but have been playing catch up all week, so I'm just now adding our event report. It was a tow from hell getting there... 16 hours straight thru, after working a full day. Towing over several mountains including an 11,000 foot high pass wasn't fun in our truck, either. We got there Friday morning at 7:30 am, and Amy was entered in the EVO school at 8:30 am. So we grabbed an hour of sleep, our only rest for 2 days, and spent the next 3 days testing and racing.



Weather couldn't have been better - it sure beat the 100°F heat we had in Texas! Beautiful mountain views surrounded the Eagle Airport site as well. We had been battling some serious understeer the past several weeks, which I will touch on in a bit. Amy got a lot of test runs during the Evo school, but I think she could be teaching at these things by now (she has instructed at several driving schools in the past and has more wins at Nats than many of her former Evo teachers), but she says "it never hurts to get an outside perspective" and she got a good number of laps in before a freak downpour at 11 am. It dried quickly and (co-driver) John Scheier and I started taking laps at around 2 pm. The car was pushing as badly as ever, so we quickly headed for the pits and made some big changes between the many test n tune runs we made for the next several hours.

We swapped rear swaybars (from a Cobb hollow to a Works solid), adjusted all of the shocks, changed the front camber by a full degree, tweaked the front toe, and made laps in between changes. Nothing helped. We could get the turn-in right but as soon as the front wheels turned more than a few degrees the front end would wash out. The tires were howling, and we had no front end grip. Front tires were SO hot, rears were dead cold. Frustrating! Slaloms felt OK but the many 180 degree turn-arounds we had to drive through all weekend on the narrow airstrip courses were murder. Losing so much time in the big turns!



We've been playing with all sorts of adjustments on the car of late to try to re-discover some seriously missing front end grip. Ever since we switched from the 265mm AD07s we've been fighting a serious push, but the lack of performance wasn't as apparent at higher speed events (time trials/HPDE) nor at local autocrosses, where we still seemed to be doing well overall (but slowly slipping back in PAX). Too many spring rate changes to count, ending up with 700# fronts and 1000# rears, which seem a bit extreme because they are. On top of this push, the formerly flawless SST S-Sport automatic shifting mode was acting funny at this event for the first time ever, probably due to the 7000 foot elevation of the site? It needed coaxing to hold a gear and not upshift at odd times. Never done this to us before, so this was a mystery. We went to full manual shifting on some runs.


285 Yokohamas and 18x10s on an E36 M3!? Mayfield was FAST

At this Tour event we had a lot more competition (19 cars in STU!) and it was fairly obvious that the car was off the pace with all 3 of it's drivers. It wasn't until we got back that one of the obvious deficiencies was found - tire pressure. Look at this picture:



That outside front tire looks like it is about to come off the rim. We were running the sub 30 psi pressures that had worked so well on the wider 265mm AD07s. We'd noticed odd tire wear on the 245s lately though - it as wearing the insides more then the outsides up front. WTF? There was something else going on that was masking the lack of tire pressure that is so obvious from these pictures. We're running 40 psi up front on future testing, starting today. 3700 pounds with fuel and driver is too much for 29 psi. It may have worked on the 265s, but not on these 245s. We also noticed a lack of dynamic camber in higher angle turns, not readily apparent until you study multi-sequence pictures from the same turn. It needed more caster.

Anyway, we fought the car all weekend, barely maintaining our mid-pack finishes in this field of STU heavy hitters (driving our butts off to get 10th an 13th places in Open). Amy still won STU-L somehow, but she was struggling more than normal to stay in front. She had a "mystery cone" assigned to her fastest Saturday run that knocked a cool second off her next best time (I watched that run from start to finish - it was bogus) which made it too close for comfort. We tried all manner of changes all weekend, even adding as much as 1/2" of toe out in the rear to try to get this thing to rotate. Nothing made a difference, which just didn't make sense. Something else was fundamentally wrong. We finished our runs, taking our licks, then packed it up for an 18 hour tow back to Dallas (record traffic jam at the Eisenhower tunnel made for an extra 2 hours getting from Vail to Denver - yay!)

On our way home we were scratching our heads, looking for answers. The video and data showed what we already knew - there was no front end grip. We had plenty of static camber and tested there with the the extremes. Hanchey called another engineer/racer friend of ours (Matteucci) and they keyed in on the many changes we've made to the car this year. We went from 4200s to 5200s (to test both AST strut designs), changed spring rates many times, played with various camber and toe settings, multiple swaybars, and more importantly used 3 different sets of wheels and 4 sets of tires in 2 widths. We also went back and forth from track to autocross setups, sometimes week after week. The problems seemed to follow the 245mm tires, and more specifically the 18x10" Enkei front wheels we've settled on lately.


Kazera 18x9.5" wheels are 3 pounds heavier, but reduce front track width by a full 2", reducing scrub!

Remember from earlier posts in this thread that the Enkei RPF1's we have on the front (6.7" backspace) had even less offset than the 18x10.5" NT03's we've been running for track events, and these RPF1s also needed 15mm of spacer to clear the calipers. The black CCWs on the back had more backspace as well (7") but couldn't clear the 14" front brakes with any amount of spacer. Well this weird offset issue with the front wheels was causing a terrible scrub condition, moving the centerline of the tire further away from the Kingpin angle defined scrub radius. I rechecked the toe at the event and noticed the front track width was alarming wide... nearly 74 inches! By contrast our old STU car, an E36 M3 with 18x10" wheels, has only a 67" front track width. Even our V8 powered E36 race car with 315mm tires has only a 72" track width! WTF?

There are ways to improve weird kingpin angle/scrub issues, namely adding more positive caster. We already had a much improved over stock +5.6° of caster, but our three previous BMW racecars have always been able to achieve +7 to +9 degrees of caster, with the steering feel and dynamic camber that were much better than what you typically see on the AWD cars. They come with much more caster to start with, and we improve on that with our plates. So the first thing I did when we got back from Vail was to make a new High Caster version of our camber-caster plates. We had also just made a short production run of new HC1 plates for the GD Subaru and EVO 5-9, some of which are already on testers' cars. This EVO X version made this week was hand built and adds .400" of more caster offset, which should add another degree and a half of caster, getting us closer to +7° (we will verify with a laser alignment soon).



We also dumped the RPF1s and CCW wheels this week, as they just are not the right fit for this car at all (CCWs are sold, the two RPF1s are for sale). The 10.5" wide NT03s are too wide for the little 245s we're restricted to for STU class, so we went looking for an 18x9.5" ET30 offset wheel... and found them from one of our employees! Stuart here at Vorshlag had a (discontinued) set of Kazera 18x9.5" ET30 wheels from an S197 chassis Mustang and they fit the Evo nearly perfectly. We're using a 5mm spacer in front (to clear the tender spring we need to run for use with a test sensor - a shock pot) and no spacer in back. The width change alone knocks out a full inch of track width plus losing a total of 20mm of spacer width is another inch less track/scrub... so track width in front is a full 2" narrower now. This is a HUGE change, and a GOOD thing when you are trying to slalom around cones. Every inch removed from track width can make significant time improvements in autocrossing.



These wheels aren't the lightest thing we've ever run (21 pounds) but they clear the brakes better than anything other than the NT03s, and due to the proper backspacing they fix much of our scrub problems. The added caster from the new plates was obvious on our first test drive, with improved steering feel and the most important improvement - the car rotates now! I could saw the wheel and break the rear tires loose at speed, which is so much better than before. No more howling front tires, as the scrub problems in front seem to be fixed with the new wheels, and the increased tire pressures feel better as well.

So now we're sort of back to the drawing board on the rest of our Autocross setup... we've started by resetting the adjustable swaybars on both ends, changed camber again (from -4 to -3°), and have to settle in on the spring rates now that we have the other fundamental issues improved (but it feels pretty damn good with 700/1000 - corners flat!). This scrub issue has probably been holding back performance for a couple of months. Good grief - we've only got a few weeks until Nationals, too. Today Brian also swapped back to the RacingBrake pads after he opened up the struts and put them back on with the new plates. This moved the car away from the ultra-hard race compound HTC-70 Hawk pads in front, as they take too much time to get up to working temperature. Great for the track but not so good on your first autocross run (we can't just "drag he brakes coming to the start line" due to the SST trans, either).

We've already scheduled two more test events in the next 3 weeks, so we've got some work ahead of us. If we can regain some of the performance we had earlier this year we think the STU competitiveness will return. To top off the week we have also had to pull the trans from our V8 powered BMW, as the input shaft decided to leave the bellhousing at 155 mph at TWS last weekend. Brian was racing it at a NASA Time Trial... good times.

Tune in for more test results soon...

griceiv

iTrader: (2)

removing scrub radius and decreasing track width will not shift the cars balance towards oversteer. Decreased scrub radius is equivalent to decreased caster, decreased track width is equivalent to increased roll stiffness. Both of which will increase understeer.

From your description it sounds like you have an unidentified source of front roll stiffness, ie suspension bind. I'd check swaybar bushings and end links first, followed by a redyno of the front struts to verify they still are what you think they are.

that's assuming you're actually running more appropriate 40ish tire pressure up front.

hancheyb

All that you mentioned has been done multiple times. I've rebuilt and dyno'd the shocks multiple times. BTW, shock performance is not going to dramatically affect steady state cornering unless the car is hopping over bumps which it is not. We've taken the bar loose and verified it was not binding.

The issue is obviously roll stiffness or more fundamentally lack of mechanical grip at the tire contact patch. The things we can control are tire pressure or camber since we have to run a 245. Most likely the issue is tire pressure, but we wanted to rule out all the changes we made to the car that changed from earlier this year. Earlier this year the car had different wheels and tires along with AST 4200s which have a more stock-like king pin inclination vs. the larger 5000 bodies. The higher caster plates are something we wanted to develop anyway as it has been requested by RobiSpec and it could help with camber gain at higher steering angles. As Terry points out, we had more tire under the car too and at 3700 pounds, every bit matters. Most if not all cars I've ever setup with Yokohamas do not require 40 psi in the fronts unless they are on stock suspension. I agree most tires need 40+ psi to autocross, but Yokohamas usually don't. This car with 245s under it obviously needs some help regardless of sidewall stiffness. Certainly running the Evo X MR on 245 DOT tires is not your average setup.

Frankly, this is our mistake for not *starting* on a skidpad when the AD08s showed up. It is a good reminder and lesson that sometimes the simple things matter most. Now, where can we find a skidpad in the middle of the week that doesn't end with jail time?

goofygrin

iTrader: (5)

Mineral Hells... but then you'll need new tires

Fair

Here's the in-car video from the Vail Valley Tour. This is my 3rd run from Day 2, and the time was almost exactly what John ran in the same car. Warning - it does not sound good, as the front tires are really howling:


click for video

Stuart is out test driving the Evo on one of our secret test locations, but so far Brian and I both feel like its 100% better. SCCA practice next weekend and TAMSCC practice the week after will shows us what we need to see.

GTB/ZR-1

iTrader: (30)

^^^

Fantastic course...

What is the car weighing these days?

TIA...

RaNGVR-4

iTrader: (4)

I was wondering why you guys were down in the middle of the pack at the tour. (I had to move that weekend, so I just watched the results online)

Im suprised you guys ran that low of pressures. Steering response had to suck! I dont even run that low on my 2500 lb ST Impreza.

Fair

Yea, Kevin Youngers (FStock Mustang driver) made a helluva course on Day 2. Loved it. Wish the car would have been working right because that's the kind of AWD course we dream for.

The Evo weighs 3510 with fuel but without driver. Yea, its HEAVY. Mitsubishi went to a lot of trouble to get it this light, too: aluminum hood, roof, trunk, control arms, subframes, 2-piece rotors, etc. Its just so BIG. When Brian parks his Evo next to my M3 it just dwarfs the BMW.

We were down in the pack due to a lot of issues, not just tire pressures. We've run Yokohama AD07s in the past this low and they worked great. Those were 265mm sets that we used on our E36 M3 and even this heavy Evo. Great steering response, wear, etc. Apparently 245s are a bit overwhelmed on this car at those pressures... oh well, we've learned.

RaNGVR-4

iTrader: (4)

^ could be slightly different sidewall construction from the larger tires to the 245's as well.

I know the dunlops on my car and the dunlops on our ST Beater subaru have a totally different feel at the same pressures, and the sidewall heights are simmilar (not identical).

Fair

Got a test session planned for this Saturday (SCCA practice @ Pennington Field) with a race on Sunday. Another 2 day test the following weekend at Texas A&M (also concrete). We'll be eying our PAX results compared to other "known" entrants/National champions, people like Andy Hollis and Mark Maderash, to see if the Evo's performance has indeed improved. The data we collect and driving feel will tell us a lot, too.

Fair

Amy and I spent most of Saturday at an SCCA practice event, testing new settings, alignment, tire pressures, and new parts. Pennington Field's high grip concrete is a great test site, even if not that big. Brian came out for a few hours to help and we all drove the car in several iterations. We had some other known drivers there to compare to, namely Chris Ledbetter's STX prepped E36 and Andy Hollis' ST prepped Civic (Andy took an unusual number of runs, prepping not only for Nationals but also doing a test for an upcoming magazine article).

There was a timed ~23 second practice course that we could take 1-2 laps on at a time and we tested a lot of theories and setup changes, finding 1 full second from tuning by day's end. The skidpad was also helpful when coupled with our pyrometer tests, which showed us that the low camber (-2.5°) setup we had aligned to last week needed another degree of camber after all. The increased tire pressures helped considerably as well, going from the 29-30 psi range to 40-45 psi up front by days end. Big car, little tire, needs more pressure.

We had one more test to try but the event was shut down abruptly at 3 pm, so we left that setup and packed up the car/trailer/truck and headed back home until Sunday, when the competition event would be held at the same site.

Results: PAX - Final - Raw (overall)

Andy Hollis and the other fast ST Civics have made a habit of bumping up to STU at our Regionals as they have a good shot of beating the "Faster" STU cars on this smaller site's tighter layouts. On Sunday's event I started out with that last, untested change from Saturday, which proved to not be beneficial. My first run was 1 second slower than 2 of the faster STU drivers, so I quickly changed back to the last, proven setup. I made changes after almost every run yet again, but kept finding time. In the end my times were bested by 3 other STU drivers... Andy Hollis had me by .6 sec and Jason McCall in an '08 STI (that we've done a lot of work on) and Ken Orgeron's E46 M3 both had me by a little over .1 sec (they were .005 sec apart). As I was changing things between each run this made for more of a test event than a competition, and by my 4th run I felt like the car was handling pretty well, without looking at the car from outside or seeing data.


The front end looks higher because it is... we were testing another theory that didn't hold water. Its going back down by 1/2"

Amy ran in in the last Heat of the day (temps were hovering around 99°F by that time), running in the local PAXed Womens class and starting with the setup I finished with. Her first run started out quicker than mine did but while watching her on course I saw some things going on in the front end and changed the rebound yet again, and she kept improving her times throughout the heat. By her 4th and final run she had bested my time by .01 sec and won her class by 1 sec, so she was happy.


Then Amy skirted me by a fraction of a second...

We've come to realize that this 3700 pound car (with driver and fuel) is probably limited more by the 245mm section width than most other competitive STU cars, none of which are this heavy. The trick is to get the car to the limit of the tires' adhesion (a slight push in steady-state) and then keep it there, or it moves into a loud and ugly push. It doesn't feel fast around sweepers and at this overall weight it may never be. The SST transmission did work flawlessly in S-Sport auto mode at this site for both days, so the odd shifting issues we saw at Vail had to be altitude related, we think.


The unusual Figure 8 course layout made for lots of loooong sweepers.

In the end we PAXed well enough (15th and 16th out of 126) but its not where we like to be right before Nationals. The grip was good (1.2g lateral and 1.13 under braking) so basics are there. As you can see above the course layout was laid out with a LARGE emphasis on long sweeping turns, having a huge figure 8 dominating the course design. There wasn't much room to accelerate as it looks, either, as there was a transition at the start of one of the long stretches in the "X" and a transition at the end of the other. This emphasis on sweeps does not exactly play to the 3500 pound EVO's strengths, which are: braking, acceleration, large speed changes (where we'd see lots of up/down shifting) and transitions. Not to take anything away from their driving, but the cars that outpaced us in STU were a good bit lighter (Civic is ~1960, STi is ~3150) and/or had much wider tires (E46 M3). Excuses - I've got a million of em!


Hollis was on fire and PAXed 4th


Ken O was fast in his STU prepped E46 M3 on D-Force 18x10s & 275mm tires


Paul and Jason are getting quick in the 08 STi on ASTs


Todd M's Civic was one of the ones that didn't beat us...

Anyway, we don't think these Pennington courses are indicative of what we'll see at Nationals, from what we've heard from the course previews by Howard Duncan. Our setup has changed drastically from the Vail Tour 2 weeks ago and hopefully the Lincoln site will play to this car's strengths... and hopefully Amy and I can drive well enough to show the car's performance. We'll be taking lots of laps at the Nationals Practice Course looking for the right setup.

Until next time...

Silencer

iTrader: (4)

This sounds familar back before the car hit the dealer floors. Weight > 245mm. Same reason that the Lancer Ralliart has no chance in STU much less be competitive in STX against the 300 lb. lighter WRX.

Good luck at Nationals.


Dave

Fair

Yea, well we thought we could get a lot of the weight out, and we did drop a lot, just not nearly enough. The DSG trans is heavy, as is the crazy rear diff. And the car itself... is just SO BIG. The crappy fuel tank design doesn't help either, as we have to run nearly full or face fuel starvation in left handers. All that said we still had really good results on 265mm AD07 tires, both on track and in Solo, which we ran until the AD08s came out. Then we switched to the class 245mm limit for AWD cars and the car has struggled in sweepers - which, if you think about it, it should be slower.

Just found out that Hollis was running the 225mm Hankooks on the front of his Civic at yesterday's event... so a ~1960 pound car on 225s beat our 3500 pound car on 245s, on a course with tons of sweepers. If you scale up that Civic's "tire width - to weight" ratio for the Evo, we would need a 400mm wide tire to have the equivalent grip level. I don't feel so bad anymore.

hancheyb

I figured I'd provide an update for the Evo. Now that the season is winding down, the Evo will be used as a test platform for new products, product revisions, and general street and track testing. I'll be publishing our results on the AST blog (third entry down) hopefully on a monthly basis. My first addition is here and includes a link to one of the faster laps that day.

These results are from the NASA event at Eagle's Canyon last weekend. I ran TTA. NASA TX is a little slow on the results, but I think I won for the day. Hard to say, but I was fastest and then it started raining so I'm pretty sure the time wasn't beat.

Keep in mind this is my daily driven street car. I drove it to the event with a tool box, jack, and a cooler. It has very few mods besides the suspension and Cobb AP. I was running Yokohama AD07s and the competition weight of the car is around 3700 pounds with driver and safety gear. We have to run it full of gas of course.

The car's peak lateral g's was 1.33, sustained was 1.2g. Not bad for such a porker! It ran a 2:03.7 as well. That's on par with 2600 pound Prepared class BMWs on Hoosiers. Again, not bad! Car still has some push steady state that we'll continue to work on, but it was a blast to drive!

Special thanks to Cobb Tuning Plano for all the last minute help prepping the car. Cobb aligned it and flushed the brakes the day before. The car never overheated, never detonated, and provided nothing but 320 whp all day long!