Matt, Did you do any special break-in for the Rivals? On tire tests they seem to be the best alternative to DOT tires. Dwight Mitchell recommends eliminating and checking for any sway bar binding...he also has 10 other recommendations I should send you...I can't remember them now.

Is Dwight still around? I remember autocrossing with him in the early '90's. I beat him in his ASP 911 a few times with my '78 Targa. Fun times!

Also, consider Jae Lee here in San Diego ( he Builds the 3.8s for Singer) as he is a suspension guru, and Bilstein is located here.


Sent from my iPhone using Tapatalk

This Dwight Mitchell?
http://lh3.ggpht.com/-xq16tv61Mz8/Sq...4/DSC_5073.jpg

I was told to seek him out waaaay back when I started my project.

As far as the Rivals, no special break in. Bolted them on, drove a few hundred miles, ran them, then drove back. The small diameter kind of sucks on the freeway so I bring them separate now if I'm going to try them at an event.

I had HUGE swaybar bind that I found and eliminated. I wonder what those other tips are...

Lots of chatter in this thread, some useful and some not so much. That said, I use this sheet plenty and I'm surprised it hasn't been shared in the thread yet.

http://forums.pelicanparts.com/uploa...1438701062.jpg

I've seen that chart several times and it's pretty helpful. My car oversteers sometimes, understeers sometimes, and others is perfectly neutral. I would say that statement is true for almost every fast race car ever.

The next derivative in the equation is in phases of the corner.

- Corner entry is very dependent on the front end of the car. I run a touch of toe out up front to build slip angle in the tires to speed turn in. I run a large front bar to transfer weight quickly.
- Mid corner is spring rates and alignment. My car leans a fair amount, so I run big camber. The TBs and bars work together to create a certain balance of loads on the tires for a certain grip balance.
- Corner exit transfers some focus to the rear. I have a touch of rear toe in for stability in power down and to keep it from being too "snappy" should I overwhelm the rears.

Then the next derivative beyond that is transition.

An AX car spends a HUGE amount of time in transition. A car on a race track sees transition as well, but the percentage of time in transition is much lower. This is where my car needs help. It's control of the rate of weight transfer. A good example of where this is supremely important in AX is a slalom:

http://www.sccawiregrass.org/images/slalom.JPG

An AX car never reaches steady state in a slalom, it's constantly transferring loads from the left tires to the right and back again. This is where shocks (dampers) become extremely important. They can control the speed at which those loads move from one of those little tire patches to another. Compared the the STR cars I've driven, my car is as lethargic as molasses. So much lag time between input and reaction. The ways to speed that is by either more spring rate, more bar, more compression damping, or a combination of those.

What's worse, there's virtually no free lunch. Every change has both an upside and a potential downside. There's no perfect car, there's no perfect setup. And everything changes with every surface, every course, even the weather. Oh, and every driver is different - driver A may be faster with a loose car, where driver B may be faster in a tight car.

Like Captain Ahab, we're all chasing a white whale that is both a curse and an adventure.

Still love this thread, and thank you Matt for maintaining it and being so open to discussion.

Just did my 4th event ever (all 4 in the 911), and finally put down times that were encouraging. Just ordered 225/45/16 Z2 Star Specs for my 7s and 8s (the cheapest option for me right now) to see if I can get anywhere in CS. Strong likelihood I will join you in STR sooner than later because I want to add STR bits to the car in general (Recaros, SW chip, etc).

This is why having at least one adjustable sway bar is really important. When I autocrossed, I was adjusting a sway bar at just about every event. No two courses were the same and the car needed to be adjusted so it did not have too little or too much oversteer.

!!!

Awesome!

Not that I've thought about it, but if I were to play by C Street rules I would get really creative with the bumpstop rules the way they are written and factory ride height adjustment...

I am operating at a lower level (CS for SCCA and Production for PCA) but working on making my car and myself better at A/X. The latest improvement I made was to install Koni Sport (Yellow) shocks with external adjusters. I am running stock TBs (18 and 25 mm), stock sways and have a strut brace. Front toe is zero, front camber is -1.4, rear toe is +.30, rear camber is -2.0 and caster is +5.8. I have run BFG Rivals 225/45-15 on 7&8x15 Fuchs and I have Hankook R-S3v2 225/45-17 and 255/40-17 on 7&9x17 Euromeisters. Tires make a huge difference, alignment makes a huge difference.

Better shocks make at least as much of a difference in raw times. At the last PCA A/X I was struggling to run decent times. Suddenly I remembered that I had forgotten to readjust the shocks from full soft (for driving on the street). I cranked the front and back shocks to full stiff and dropped 2+ from a 60 sec run. The difference was CLEARLY in transition. The car changed direction right now instead of leaning, grabbing and then changing direction. I need to add an item to my A/X prep list. Check the shock adjustment.

Better dampers help a stock setup but they can only do so much and are not better than changing the spring rates and sway bars to something more appropriate.

As far as alignment goes, I want a little bit of toe out at the front and a little bit of toe in at the rear. Camber settings all depend on the tire being used.

=================
I'm sure you are right. I plan to upgrade the t-bars and add an adjustable rear sway bar for next season. Those are things I can do and not move to a tougher class like STR or Improved. I will install better bushings when I replace the t-bars.

I don't think TB changes (or bushings for that matter) are allowed in Street? Just one swaybar.

I've read the rules many a time, but not sure what you're referring to about bumpstops. I definitely take advantage of ride height adjustment, a nice advantage we have over cars w/ coil springs.

If I understand it right, the digressive valving gets you a good tradeoff. AX lots are often much less smooth than race tracks, so stiffer springs aren't always the answer. Big low speed compression with a heavy digressive cut nets you a boost in spring rate when you want it, while allowing you to retain a softer spring for bump compliance when you don't.

I guess the super pimp top of the line race car tech these days is regressive valving:
http://qrgarage.ca/wp-content/upload...ivepiston2.jpg

Tremendous low speed control that somehow softens at high velocities. Idea is race drivers can just blast curbing and the suspension frees up enough to soak it up. No idea what kind of piston witchcraft they do to pull that off.

Wow that is cool, I wonder when the Regressive will filter down to mortals? I wonder if it would even be pleasant in a street/DE car? seems like it would.

Speaking of Witchcraft recently Ford released some track videos of the forthcoming Mustang GT 350 R (I think thats what its called). I believe thats a 3600 pound car with the new flat plane crank V8. Anyway, it has the magnetic particle shocks, the flat cornering and ability to absorb bumps by that thing is amazing. They show it coming over a big hump in the track and it just eats it up and takes an set in the next corner at huge speed - no drama. Really amazing. Worth a look.

I had adjustable bars on both the front and rear when I ran my 911 seriously. The goal was to just slightly lift the inside wheel. Maybe an inch at some point in the turn. I usually adjusted one bar or the other after each run. Today with data acquisition this should be a walk in the park.

I'm reminded that marque folks have alway had a really rough time in SCCA Solo competition. The fast guys just buy whatever is the fastest car in the class. They set it up the same way the fastest guy in the class sets his up. They win a lot.

People with marque loyalty spend a ton of money and never win. They do though have a lot of fun. That might be the real point.

Richard Newton
My 911 in Action

Looks like Penske sells a regressive piston for consumers now:
Penske Shocks / Accessories / ASSM, REGRESSIVE VALVE COMPRESSION
Not clear if that's one or a pair, but $500 on top of a $2000 per corner shock, before tuning, is pretty big money.

MR is nuts. I guess when you turn on an electromagnet it changes the effective viscosity of the oil. So in theory you can have whatever damping you want at any time. As that tech develops further, sensors get more accurate, processing power gets faster, and algorithms get better, that'll be pretty gnarly.

I run a Flowmaster spun cat. Light, high flow, meets the rules.

http://2.bp.blogspot.com/-CMxceo-kq3.../642-54959.jpg

The MR dampers react so fast that they change the damping dependent on suspension travel, not just the speed. I think it was one of the new GM cars that I read can adjust the damping every inch of travel for a bump at 60 mph.

FYI, the pic posted earlier is not normal cornering attitude for my car, just a well timed shot from a talented photographer. Here's immediately before and after. Either a bump or in transition it goes all awesome.

https://lh3.googleusercontent.com/-U...eels%2Bbro.jpg

Matt, Mitchell recommends 30/23 or 29/22mm T-bars for AutoX depending on the surface ...smaller for slicker surface bigger for smooth more grippy concrete. This was according to an article published in mid 90s but I don't think it will change much. He was also using 2 degrees of negative camber in front.

I have trouble getting much more than 2 degrees front or back. I was going to go to camber plates from Elephant.

That seems soft - I'm 23/33. When did bars bigger than 30mm come out?

I'm also above those camber levels. I'm about -2.5° up front (offset, small diameter bearing camber plates) and have more than -3° in the rear using Elephant Camber Max (which I now realize aren't needed to get that high.)

Dwight Mitchell was the man. I would start with his setup and work from that point. The technology hasn't changed that much. Ok, the new tires seem to like a little more negative camber but that may be it.

http://forums.pelicanparts.com/uploa...1438965027.jpg

Always copy the fast guys. That can save you a lot of time.

Richard Newton
Gauge Restoration

That looks like a true stagger, 16" up front and 17" out back. I almost ran that combo, but felt I barely have enough power at 5280ft to spin a sticky 225...

I got the 225/45/16 'Lops mounted, they fit w/ zero issues around "Euro" ride height. Interestingly, the 225/45 Z2 Star Spec I have has a narrower section width, but 0.5" wider tread width than 225/50. Top speed in 2nd should now be ~64mph.

SCCA auto-cross tomorrow, though I don't have enough time to really break these in properly. First auto-cross on real sticky tahrs!

His car is much lighter than yours so maybe a heavier Tbar is not so bad. I have not been able to get more than 2.5 degrees from the rear suspension. I guess it depends on the shop doing the aligning.

Well, I've been autocrossing for 18 years now and finally took my first trip out to the Big Show - SCCA Solo Nationals.

I made a promise to myself long ago never to have a car that needs a trailer. My Dad and I hopped in the 911 and drove the 800 miles (each way!) to Lincoln, Ne. Other than wearing earplugs to reduce fatigue, car was a treat. This country is beautiful, that was my first trip to the plains.

SCCA Autocross Nationals is the largest motorsports competition in the world, with over 1,200 competitors this year. The event is split into four days, STR was scheduled to run the last two. We showed up on day 2 to get acclimated. Let me tell you, it's a sight to behold. I'm used to a big event being 200 people, 6x that is tough to take in at first. Once getting checked in we wandered over to the area of the courses - there's two. On one course we saw (and heard!) an Audi R8 V10 and a McLaren 12C. Big dollar CAM cars were running on the other course - including Mary Pozzi's car that was modeled in GranTurismo 6, Al Unser Jr and Robbie Unser, and a legitimate, real Shelby Cobra. What have we gotten ourselves into? Who cares! It's awesome!

That evening I purchased some runs on the practice course, which is intended for people to dial their cars into the surface. I had elected to switch rear tire brands - from RE71R to Rival-S - just before the event. I wanted full tread tires in case we hit rain on the trip (which we did) for safety. I preferred driving on the Rival-S due to their more progressive nature, but mixing brands was a bad idea. The car was slightly loose at steady state, where it's been mild understeer all year. I've had transitional issues with the car since day 1, which I've learned to drive around. But the big issue was turn in. The car was spooky there. In retrospect, I think the more responsive Bridgestone was reacting much faster than the laggy Rival, making the car feel very unsure of itself. Coupled with the mild oversteer, I more was fighting to survive runs rather than being able to attack the course. I decided to run a little extra front pressure to try and reduce the oversteer, I have no other adjustments on my car easily available.

The event itself works like this:
Day 1 you do 3 runs on one course.
Day 2 you do 3 runs on the other course.
Best run on each side are added.

So yes, I basically drove 1600 miles for 6 minutes of seat time. And I can't wait to do it again next year.

Run day 1 arrived. Pulling into grid with 62(!) STR entries is insane - that's a lot of competitors! Mostly S2000s, a lot of 3rd gen Miatas, and only a few oddballs - 1 Z3 coupe, an MR-S, 2 370zs, and a few older Miatas. My car was the oldest in STR by 13 years. The West course on day 1 was tight, narrow, and technical. I went out on a "recon" first run to make sure I had a clean one in the books. The car was even more twitchy and loose than it was on the practice course. Good thing I did the recon run, as I hit cones on runs 2 and 3. Wait, it's half over already?

https://lh3.googleusercontent.com/-I...PB1_2828-1.jpg

Day 2 was a much faster and wide open course. Car was still spooky loose, I spun my first run. Then I spun my 2nd. 1 run left to get a clean one - popped the safety chute and got through the course slow and conservative, but clean.

https://lh3.googleusercontent.com/-C...PB1_2834-1.jpg

Video of my runs.

Result? 50th. Out of 62. Well, not last I guess. Against the best in the country, I guess I should be happy. Not quite. Pretty sure any 911 isn't going to have a shot at the title, but I'm not going to be satisfied until I earn a trophy. I think it's possible. For next year I'm bringing some real shock damping, some adjustability so I can tweak the car if needed, and, uh, matched tires. And more seat time. Hopefully that can bring me into the top half. Then onward and upward.

Goofing around with my 911 these last few years has far and away been the most challenging, rewarding, and fun I've had playing the autocross game. While going as far as I have with the car is up to you, I highly recommend at least getting out to a local event and playing with your car.

Matt it looked like a very wide open course. The spins seem to be on exit. Did you adjust anything day to day or run to run?

I was thinking of going to custom Bilstein adjustable shocks. Do you have a good choice for your shocks yet?

That was really a bit of my problem - very little on my car is adjustable. All I did (and really could do) was run higher front tire pressure.

You know, the car is temperamental. It seems pretty consistent on asphalt. On heavily weathered & cracked, relatively new, even sealcoated lots it's about the same. Concrete though is a crapshoot. At Toledo the car has never felt good - slightly spooky, inconsistent, usually either loose or snappy. Up at Oscoda, it was rather pushy. At Wilmington it's felt really good - on the push side of balanced, which is exactly where I want it so I can attack the course.

As for shocks, funny you should ask:
https://lh4.googleusercontent.com/-n...922_170432.jpg

These showed up at my door about 8:00pm just this Monday.

Nearly every single person that has driven my car has mentioned that it needs shocks. Well, that time has finally come, at least in the rear. Double adjustable. I put them in last night and drove a grand total of 15 minutes on them. All I know for sure is that both full soft is too soft, both full firm is pretty punishing on the street. But man, this is the body control I've been missing. Huge, HUGE improvement. Can't wait to see what they feel like in competition, though figuring out how to dial them in is going to be a tough process.

Great write up Matt and good job representing our cars. You know, if you want to solve your handling issues just switch to rallycross; all that stuff up there is irrelevant LOL

Did my first event on the Hotbits rear shocks yesterday and thought I'd drop a quick review.

I had a co-driver who is pretty good at setting up cars, but we only had 8 runs between the two of us.

First of all, holy cow, body control is amazing. My car was really, really bad in out-of-phase type maneuvers - that is, when putting an opposite input in from the way the mass is transferring. Aka slalom or lane change type maneuvers. I previously had to waste tons of time (and therefore sacrifice speed) waiting for the rear weight to stop moving before I could put in an opposite input and have any idea what the car would do. No more. In slalom type moves, the rear end set, planted, and stuck. Like a real, modern car. The effect was so night an day, it took me the whole event building confidence in the car and I still didn't reach the limit. Impressive!

The bad news is we threw the balance off everywhere else. The car picked up a LOT of understeer, in basically all three phases of a corner. That's confusing, as the stiffer shocks should have reduced rear grip. Best guess is that before the uncontrolled rear flopping around was upsetting the tires, causing oversteer.

We also found out what overshooting on compression damping does - creates a nasty oscillation / hop in sweepers.

Can't wait to get proper damping in my fronts.

I'm going to need a notebook.

hey checked your web site for more details on the shocks. did not see anything. Do you have link you would share?

their website is having some problems - will check back later.

Yeah, I haven't put up a blog post about them yet. I'm a slacker.

See this thread for more info about the Hotbits shocks.

Just to have some closure on this thread, I'm calling this project complete.

I got the car about where I want it handling wise. It's a riot to drive. It rotates at will, digs deep in sweepers, and plants and goes like a 911 should. It's fast enough to place well at local events.

Nationally, I'm still well off the pace of the S2000s, and the new ND Miatas that just got put into STR are already starting to supercede those with minimal development. So I'm getting further behind. The newer cars are much, much more stable and easy to extract speed at the 9.999/10ths you need to be at to be nationally competitive.

Watching video from my first runs with the car to today are hilarious. My car was pretty stock when I bought it, the thing could barely get out of it's own way.

The process of figuring things out for myself was super rewarding and a great life experience. The car is a magnet for people, I've met virtually everyone on the national circuit because of it. Pretty cool. So many compliments too.

Some shots of what will likely be it's 2nd to last National autocross:

https://lh6.googleusercontent.com/-6...sburghLift.jpg

This was a large bump on course that apparently threw the car in the air. Neat!

https://lh6.googleusercontent.com/-W...rghStaring.jpg

Found a track rat '86 and couldn't resist taking this photo. Talked to the owner for a minute, always cool to meet a fellow 911 driver.

And it's new retired self:

https://lh4.googleusercontent.com/-L...525_180204.jpg

I'll probably content the car a bit with slightly less aggressive torsion bars and the quieter OE exhaust, but the rest of the stuff is staying. I'll likely still drive the car at local events just because it's so darn fun (and challenging) to drive hard. I drove the car to and from every event as far as 800 miles away and back with minimal incidents (1 dead DME relay, 1 starter that stopped working when hot) which would be an accomplishment for many more modern cars, let alone a 32 year old classic. What a great, great car.


Final setup in case anyone wants to copy, in order of importance:
245-17 square Rival S tires on 9" wheels all around
23/36 torsions (would do 24mm fronts if I continued with the car. Just can't get enough spring for the grip of modern street tires.)
ER revalved front / Hotbits double adjustable rear shocks
Addco 22.2mm OE style big front swaybar
No rear swaybar
KAAZ limited slip
Modified cheapie eBay front camber plates
Delrin A-arm bushings and spring plate bushings
SW chip / homemade exhaust
Bunch of other stuff that's less important

What I would have liked:
Lighter wheels
A much shorter 2nd gear (illegal in STR)
About 200lb off the rear of the car (illegal in STR)
A bigger front swaybar (would have to be a custom STR legal piece)

So if anyone in the future stumbles on this thread, feel free to PM me or whatever with any questions. I'm more than willing to share anything I've learned along the way for autocross prep. Most likely I can say I've tried that to most of the common stuff.

Most of us are really too quick to start playing with shocks. Koni and Bilstein both feel that shocks are the final step in chassis tuning. You have to get the spring (torsion bar) package correct first. Shocks are precision devices and should be used for that final step.

Here's an article I wrote on all of this.

http://2.bp.blogspot.com/-wsoqhUFuKo...0/Shock+4w.jpg

Richard Newton

Thanks Richard. Pretty sure you're a bot that just searches for keywords and plugs your blog with marginally relevant things, but whatever. That pic isn't even a 911.

I asked Chuck @ Elephant to valve shocks to my specifications, which were quite a bit different than his canned tune. He told me to take a long walk off a short pier.

The double adjustable Hotbits I bought for the rear massively improved the car, plus gave me the ability to tweak to match surface / course / conditions. Adjustability is a two-way sword though, you've got to know what to do with it, and you have to be methodical, or there's a good chance you can make things really, really bad.

Especially with seat time in 60 second bursts, it was real work to get them dialed in. And that's just one end of the car!

And the blogs articles are mostly fluff and don't really provide much useful information.

You click on them? Shame on you.,

Wow I thought Richard New was legit..never took the time to go to his site....glad I didn't.

I wonder if part of the problem with STR for the air cooled 911 is that the rules wont allow you to add bracing and so the chassis is flexing as much as the T bars are deflecting?

Great fun to read about and watch your progress. Are you going to get a new car to campaign nationally?

Hey Matt, I'm very grateful to you for documenting the extent of this build and your experience, and especially following up with a sort of 'national-event wrap-up.' It's been a great read and very informative for a noob like myself.

Hey Matt,

It was nice to meet you last Sat. at Pitt Race. I have learned a lot about my similar car by following your threads and your Blog. You have put a major effort into making your car competitive in a Porsche Hostile class. You are not afraid to dig into technical stuff that uses actual math skills. BTW, I think you could earn a living as a writer.

Attached is a picture of your car hitting that same bump.
http://forums.pelicanparts.com/uploa...1468870745.jpg

and looking sharp at starting line.
http://forums.pelicanparts.com/uploa...1468870902.jpg