I would absolutely love to see this car in the trophies at some point. I think it is an uphill battle but, most of the good fights are.

I think LSD will be worth alot of time as well.

Likewise.

LSD is on my list, precipitated by the recent demise of our transmission.

That's too bad. In San Diego the autocrosses at Qualcomm are legendary, with average attendance around 100 cars and the track is over a mile long.
https://plus.google.com/photos/105776011673223522600/albums/6017151612314142481?banner=pwa

I'm now in Nor Cal which has a fun venue at Sonoma airport. Last AX we got 15 laps.
http://forums.pelicanparts.com/uploa...1404229777.jpg
As far as exhaust options for your Carrera, you may want to post something in the AX forum.

Just remembered there is a guy in SD with a Carrera that has had his Ring and Pinion replaced with the 7:31 from the earlier cars. He is wicked quick. Might be something to consider if rules allow it.

Also, you may want to research the LSD. Some say it hurts turn in on autocrosses.

I've followed this thread with interest for awhile now. I just started autocrossing my '86 coupe in C-Street (RMS region). It's relatively heavy @ 2700# (1/4 tank of fuel w/ full Griffiths A/C, original Carrera tail, sunroof, power seats, etc) but it does have a factory LSD, short shifter, and seems to be a strong engine even at 135k original miles.

Moving up slowly in the C-Street ranks, but still behind (from a driver perspective, not the car's fault) the top 370z/Toyabaru twins/RX-8s. Only done two events so far and I'm also on Continental DWs, while everyone else has ~200 TW tires. I only have one set of wheels for now and the weather in CO is pretty unpredictable.

I am considering a switch to STR primarily to use Recaros for headroom (1st priority) and weight reduction, so your thread is perfect inspiration. I don't have the money to properly prep for STR this season, but it's in the cards.

Keep it up! :cool:

^Thanks, that's much appreciated. That's been my goal with this thread.

Also: I need to move to California.

Same here^

Except I haven't done any events yet. My car only has 25k on it but everything is old, even the tires (22yrs)

I lowered it, spaced the rack and did a dynomax exhaust.

Re11s asap

I'm fairly certain it has 7s, 8s and LSD, otherwise optioned the same as yours.

Matt,

You seem to know how to drive the car...that is half the battle. I reduce weight down to 2500 lbs without driver. I also did all of the basic maintenance items along with a fuel injection clean and balance by Marren. The engine is now putting out over 250 HP at the clutch.

My suspension rebuild is progressing with new rear T-bars, all new bushings and rear monoball by Rebel Racing. I will replace the rear sway bar and then try to see how it is improved. I think I can get the body roll down to the 3-4% range.

Thanks for the kind words all. I'm working on a few tricks this off-season. SCCA national schedule just came out and looks like I may do as many as six national events this coming season.

The diff is awesome, but needs some setup changes to take advantage of fully.

For autocrossing, I would not get an LSD. I would get a torque biasing differential from Guard Transmission.

I wanted the locking in off throttle, car was super unstable in braking while turning. I couldn't attack certain elements like I wanted to. Helical lsd couldn't give me that.

I went with a kaaz. Reverse 1.5 way, 1 set of plates disabled, softest preload springs.

Really stabilized the car, I can push it much harder. Picked up some push in slow corners though, conditions match to much preload.

I'm hoping the diff will break in as I can't lower the preload any more. I have a larger rear bar I'm going to try next season as well.

Unfortunately the off-season is long.

Ok, so STR rules allow for up to 9" wide wheels and up to 255 width tires. I've been running 225s on 7" Euros so far, which is obviously leaving time on the table.

Biggest I can find under a stock Carrera flare is 245s on 8" wheels. And even then it has to be perfect.

I have a friend who lent me a 17x9 ET55 Cup wheel for some test fitting. He had a Michelin 255 width tire on it. Took 20mm of spacer to make it fit, so 17x9 ET 35 equivalent:

https://lh6.googleusercontent.com/-K...o/IMAG1108.jpg

Virtually zero strut room. I removed my metal cans and have 4x4 offroad boots.
https://lh4.googleusercontent.com/-e...o/IMAG1104.jpg
Spins totally freely though. It actually turned with 15mm of spacer, but rubbed the boot audibly.

https://lh4.googleusercontent.com/-5...o/IMAG1110.jpg

It's hard to capture in a picture, but with camber and rolled fenders looks like I have plenty of clearance on the outside. That's with the front torsion lever cranked all the way down. Proof of concept success?

So question is - do I go full nutjob and have my front wheels widened to 9", or do I just so mostly stupid and go 8.5"? If the 9" looks like it fits, 8.5" should be a cakewalk, no?

Matt, fascinating process you've been going through, sort of a Zen path of continuous exploration for the ultimate balance / performance. Must be fun and maddening in equal measures. Nice work. John in CT.

"obviously leaving time on the table".

Matt I am going t question that statement. I am all about big tires but I think racers want the least amount of tire they can get away with for their car weight, power, balance etc. Right??

Less weight, less rolling resistance, cheap way to get a better gear ratio? I remember reading one time a guy was running a solar racer with bicycle tires because for that race that was the sweet spot.


Not sure how you evaluate that? I guess it would be trying different sizes and comparing lap times?

I noticed that the performance on my 73 noticeably dropped off in every way when I went from 15x7,8 fuchs to 16x7,8 panasport imitations (heavier and taller and I was able to run a 245 tire and not a 225.

The 255 michelins might fit but ZII or Rival or R-S3 might not (or might fit better). Also the tires deflect under load and may rub if you are that dang close. 245 is a better bet. 8" or 8.5" should be enough for a 245 tire. TireRack has some pretty good info on actual tire dimensions.

I still think you would be faster on 15s. Faster accell, lower unsprung weight and lower car. Hard to get more 15" rubber on the road but still may be worth it. This year I will be able to compare 225/45-15 Rivals on 7&8 Fuchs to 225/45-17 & 255/40-17 R-S3s on 17x8&9 Euromeisters. My guess is the 17" setup will be slower despite the extra rubber. I will need to include more negative camber and rolled fenders up front before the 17"s fit properly. The 17" wheel and tire assys. are HEAVY.

Yeah, I'm not sure. Really entering uncharted territory. AX tends to favor pure mechanical grip. Acceleration is important, but not the end all be all. Otherwise 97hp Civics and 115hp Miatas wouldn't be as fast as they are. I figure why give 2" of wheel width to my competitors - they're all on 9" wheels all around.

At higher speeds, the fronts on a 911 don't seem to be quite as important. They more request slip angles for the rear tires. At AX speeds I'm really leaning on the fronts. I've been trying to tune around that, but I think I'm reducing rear grip to get my intended balance.

So I'm leaning towards trying the 9". Even if I drop down to a 245 or even 235 the much squarer sidewall should give me an advantage over the pinched 225 on the 7" wheel.

Euros are 7&9, not 8&9. That's the setup (including tire size) I run now. They fit on my car without any roll and stock camber plates maxed out with just barely grazing the LH fender lip. No issues with the spherical bearing camber plates.

If I could get a legal short 255 15" tire I'd totally rock it. Thrust charts look pretty awesome.

FWIW, Toyo makes the R1R in a 245/35-17. That's quite a bit shorter than the 255/40. It's been updated to 200tw this year, so legal for ST. Supposedly the compound didn't change though, so it would hate the back of a 911.

You've picked a really tough class. The S200s and Miatas are very difficult to beat. The fast guys usually pick the fastest car in the class if they want to win. I've seen national champions switch marques in the middle of the season. The fast guys have zero marque loyalty.

At least you're having fun. One problem you're going to encounter - if you haven't done so already - it the PCA rulebook. PCA and SCCA rules are different enough to require different approaches. Our local PCA finally threw in the towel and we now run SCCA rules.

Richard Newton

Matt knows, I think, that I fall in the camp of lower weight and lower gearing of 15" wheels and tires. That being said, Matt is optimizing his car purely for SCCA STR autocross while I'll throw my car at anything it's legal for including RallyCross.

FWIW I'm going up to 17" this year (not for rallycross) but not from a performance standpoint but to promote our new 17" replica wheels. Sorry about hijacking your thread for the blatant plug Matt but if you'll consider using a pair of our 17x9 at what ever offset you need rather than cutting up and welding up some other wheels (a dubious practice IMHO though I have seen no data to suggest it's not appropriate) I'll cut you a really good deal. There, now we are even LOL.

I saw a big difference going to a square set up using 16x7's running 225's. It made the car much more balanced and neutral than my previous set up of 205's and 225's. It probably improved my times by 1 second on a 60 second course. Alignment makes a big difference too. There is very little under steer during the typical autocross course.

BTW, Euro offers a 17x8, though it is rear fitment (et10.6).

I agree that the RS3, ZII, etc will run wider than the 255 Michelin (according to Tire Rack specs and friends who have compared), so I might go for a 245 up front. Then an 8.5J wheel would be perfect and give you a bit more breathing room.

I'll watch this with interest since I agree the lack of front tire (in autocross specifically) leaves performance on the table.

Since I'm probably not getting new wheels this year, I plan to go with 225 all around on my 7s and 8s, maybe the shorter 225/45/16 Dunlops, but I'm also limited in CS. I've been running 205/225 but want the extra bite up front the post above me is referring to.