Ttod

J P Stein · 08-20-2002, 12:28 AM

OK, gurus, I gots a question.

A couple of the local hot dogs of the Portland AX scene
showed up at yesterdays PCA AX. A former National champ in his Z06 and a BP 65 Vette (TTDO with a 30.9 to my 33.5)with tires the size of a steamroller's....er, rollers.
The course was pretty quick.....6k (or so....who has time to look?) in 3rd in 2 places.

Even with my semi-sucky driving (I've improved from sucky), they were only 10% faster. That last 10% is gonna be tough. I'm thinkin about bringing on a "hired gun" for driving.....I'll be the "tire warmer" in the first run group. I know this fella can almost (that's a real "almost", not a Muller "almost")run with these guys "as is" in my car......but we wanna whup em'.....who says oldfarts aren't dangerous?

I presently have stock alignment settings.
Stock front bars, 165 hp :-) progressive rear springs, and an adjustable front anti roll bar. 205 & 225 Kuhmos......LSD would be nice but I'm bucks down at the moment....and for the forseeable "moment". I've been told the inside front tire is lifting ......no pics, sorry. Ride height is about 5 inches at the doughnuts....both ends. Bilsteins at both ends....er, standard typos.

I (naturally) have a few ideas, but I need your "hot set-ups"
to bounce off mine. I can run 10 inch slicks in my class, BTW, but the rear fenders are gonna limit them to about 9 inch.

Presently the car is traction limited at the starting line. Lack of power doesn't concern me....at least for now. It hazes both tires, BTW.

Whatcha got?

John Rogers · 08-20-2002, 06:22 AM

I'd recommend the following: Goodyear 9x23x15 cantilever slicks (23# air) on 7 inch wheels on all 4 corners, Koni adjustable sport shocks all 4 corners, large front sway bar, hook up the rear sway bar, 200# rear springs, 23mm front torsion bars, BMW brakes on front, no prop valve and you won't have to use the brakes much at all and it should take 3 to 4 seconds off your fastest time minumum. Not cheap, but going real fast never is! Good luck.

Jeroen · 08-20-2002, 08:52 AM

Hey JP,

Try to get the most from what you got before shaking more money at your car...

Get a more aggressive alignment (dunno what you got now)
Zero toe in front is a nice compromise for a street / track car and for AX you might even wanna try a little toe-out
(if IIRC from your earlier post, you're already at max neg. camber)

If the inner front wheel is lifting, loosen up the front swaybar a bit.
If that softens your front end too much, you need bigger torsion bars.
With your current set up (stock t-bars) a bigger swaybar would only make things worse

What kind of Bilsteins are you running, standard or sports?
Koni's have the advantage of being adjustable, but since you're running Bilsteins, you'd need different front struts as well...

Cheers,

Jeroen

J P Stein · 08-20-2002, 09:34 AM

Thanks, John.

I'd never considered the same size tires, front and rear. I will now. I'd prolly have to massage the front fenders, some.

I know zip about slicks.
What kind of camber settings do those tires like?

Jeroen:

You don't understand........winter is coming. It is REQUIRED that I tear apart my car and thow money at. This ain't just for fun....it's.....er.....tradition. Not only that, the "Olefarts, NARP, Rattle Can Primer Racing Team" has little time left on this earth.
We need more speed and we need it NOW......well, by spring 03
anyhow.

The alignment settings are stock. Right now, I'm using only 2/3 (or so) of the tire width, according to the tire wear pattern.

John Rogers · 08-20-2002, 11:47 AM

The cantilever slicks like zero (0) camber front and rear and about 1/2 inch toe in rear, straight ahead on the front. There are couple of brands but the Goodyear bias plys are about the best if you get the soft compound. You can check their website for info but they are close to $200 per tire! If you use a tire with that much "stick" then the rest of the suspension is going to have to be very stiff since the body of the car will tend to get thrown when the car turns and you'll have tremendous body roll. Good luck.

Jeroen · 08-20-2002, 12:24 PM

Hey JP,

If you insist on throwing money at it, John's suggestions sound pretty good to me

Maybe also:
Treaded collars for the rear shocks, so you can get it corner balanced and perhaps new rear springs, to compliment the bigger front t-bars
Spherical bearing top strut mounts
A good seat (FIA approved full shell)

And if you have uneven wear paterns on your tires (is that 2/3's on the inside or outside?), get a good alignment

Cheers,

Jeroen

campbellcj · 08-20-2002, 12:39 PM

You could always pull out that wimpy 2.7 and drop in a 3.6

Brad Roberts · 08-20-2002, 12:51 PM

DOH !!

Chris that was bad.

So far I havent heard anything out of JP about what the car is doing.

Think of it as chassis engineering/setup:

What is the car doing in low speed corners

What is the car doing in high speed corners

What are my cold tire pressures

What are the hot tire pressures.

Tire temps ?? anyone ?? IMO *inside,middle,outside*

This is the only way I can tell you to set the alignment for what you have now. If the outside temps are 50 degrees hotter than the inside...you need more negative camber.

Is the car grossly understeering in low speed corners or oversteering in high speed corners ??

I can throw parts and tires at all day, but is the current setup optimized ?? I'm guessing not.

Here is the real pisser for JP: Can either of you (drivers) give this kinda feedback when I ask what the car is doing ?? I'm running across more and more "Drivers" that have NO idea what their car is doing. Makes it real difficult to make suggestions or changes when they cant communicate.

B

sammyg2 · 08-20-2002, 01:08 PM

1/2" toe in on the back? Please tell me that is a typo. I would have thought 1/8" maybe.

But, (insert disclaimer here) I know nothing about slicks and have never driven a real race car. It's very possible there's something to this I haven't heard about.

John Rogers · 08-20-2002, 01:36 PM

The rear toe is total or about 1/4 per side. The slicks cause the suspension to work a lot harder and under braking that much just about goes to zero, at least on mine which also has plastic rear bushings? I agree with the post about what is the car doing, as an example at a recent San Diego auto-x a stock class 914 driver was having troubles. I asked what his tire pressures were with his new Khumo tires and he said approx 35#! I said that was a little too high, especially since the car was pushing terribly and sliding too. I suggested about 26# hot so after a couple of timed runs we dropped the pressure to 26# front and rear and guess what, he took a SECOND off his best time! Did not cost a cent!

campbellcj · 08-20-2002, 01:38 PM

Here's a dumb question -- are the 9" slicks really 9" wide or is that one of these fuzzy measurements like on regular metric DOT tires, where there's variation from mfr to mfr and model to model?

It sure would suck to order up some new tires based on measurements, and have 'em not fit.

Not that I am gonna run slicks at this point; just wondering.

J P Stein · 08-20-2002, 02:05 PM

Brad:

This is AX. After 5 passes, I can hold my hand on the tread......maybe 110/120 deg tops. Parking lots are neither smooth nor do they have a high (or even ) coeificent of traction.
High speed sections are the slaloms. Neutral to mild osteer......
Our only "sweeper" has a giant hump in the middle.....A nice (albeit short) drift becomes a real mess when ya come down off that hump.

Wait 15 minutes for the tires to cool down(?) and go do it again.
Pressure is 29 front and 31 rear, cold. The wear pattern on the tread shows consideribly less wear on the inside 1/3.

The car handles quite nicely. Slight tendency towards oversteer. Some corners will cause the car to push (see parking lots, above), but a tap on the brakes will nail the front and the loud pedal takes care of the rest (when I remember to get the sequence right;-).

I would like to maintain the current handling balance. I know the alignment is not optimized. Could be why I'm asking the Q, eh?
What I want is more grip.

As for feed back, that's it. If I had any effin' idea what I was doing maybe I could more help.......wait, I'M looking for help.

Mr. Rogers:

Hummm......stiffer is realativly cheep. It's a good thing, too as those tire prices are a heart stopper. Like sammy said 1/2 INCH toe?

campbellcj · 08-20-2002, 03:03 PM

If you're gonna stick (sorry) with the current Kumho DOT-R's, it is probably best & cheapest to play around with alignment and pressures for starters. Like B says a pyrometer is the way to go, but in general it sounds like dropping the height a bit and putting a little more neg. camber might help. I don't think the Kumhos need/want a whole ton of neg. camber IIRC but a 'stock' alignment spec has virtually 0 camber, right?

Dropping the pressures might get you more stick, although also more sidewall flex/roll. But you're right that at an autox you're never gonna get enough heat into the tires to make them happy-happy and pick up 5-8 psi like you would in sustained lapping.

You could always spring for those real "autox" tires...Hoosier A3S03 for instance. Gummy suckers, designed to get up to temp super fast, like .5-1lap supposedly.

Jeroen · 08-20-2002, 03:21 PM

Hey JP,

If the inside of the tire wears less, you either need more neg. camber or less toe-in (or both)

If I were you, I'd spend my money on a good alignment first (others can prolly get you some suggestions for the rear) and fiddle some with the front swaybar settings and tire pressures

Don't make too many changes at once (which is likely in a winter project) or you'll be clueless at what changes caused what...

Understeer in tight corners is usually not as much a matter of setup, but a matter of too high entrance speed or to early back on the throttle
Braking a little longer may feel slower, but you can make the corner without understeer and get back on the power earlier, which will make you faster

More seat-time will make you faster than spending money on go-fast-goodies (a fast driver in a slow car will always be faster than a slow driver in a fast car)

Cheers,

Jeroen
PS what's the size of your swaybars and rear springs

John Rogers · 08-20-2002, 06:47 PM

The 9 inch slicks really have a 9 inche contact witdh and they fit on a 7 inch rim. They were made when the SCCA had a rim width limit as they never figured anyone could make a tire with contact that wide and they are made by several companys although the Goodyears seem to work the best. At the auto-x I mentioned above, the rear tire pressure was actually going up due to all the heat coming off the engine while in line although in the San Diego sessions the wait is usually only a minute or three between runs.

Brad Roberts · 08-20-2002, 08:03 PM

We run R430 cantilevers on all of our EP and FP cars. We STILL have a 7 inch wide rim limit.

B

Ron Meier · 08-20-2002, 09:27 PM

Hey Brad

You're bein' nice.

I noticed that your previous post about pressures, temps, etc has gone largely ignored. It is difficult, if not impossible to determine if you have maximum print on the ground by the wear marks on a tire. Same with pressures. Rigid sidewall construction allows for pressure adjustments. A Pyrometer is a MUST tool for serious racing.

If your tires are heating up from engine heat or anything else, try filling them with nitrogen. Beauty is, once set, they stay (kinda - can't ever seem to displace all the air). They even don't expand that much running and that nitrogen cylinder will run your air tools.

As far as wider tires, there is an optimum. On our cars we ran the 8" Goodyears. Someone convined us that running 9" would make us stick that much better. Well, no stickier and the car was slower due to the increased rolling/wind resistance (or so we surmised).

Oh well - back to the cave - I've shot my nickel.

Brad Roberts · 08-20-2002, 09:40 PM

JP,

I cant tell if the "This is AutoX" statement was telling me to F-off or not...LOL

Every single race car engineer I know (over 20) learned 90% of what they know from having championship AutoX cars.

You even have one in your neck of the woods:

Greg Fordahl. Lead engineer on the Salleen ALMS cars and 5 or 6 time SCCA national AutoX champ in a 6 cyl 914.

Bottom Line.. dont give me crap about buying a 90$ pyrometer and finding out what the car is doing. You asked a serious question that I took seriously. I currently run setup on the SF region SCCA CSP 2.0 914 who happens to be leading the points with over 30 cars in his class. I have a clue.

Wanna win.. lets chat... or at least get the car cornerweighted before we chat.

B

campbellcj · 08-20-2002, 11:19 PM

Quote:

Originally posted by BRM9148
We run R430 cantilevers on all of our EP and FP cars. We STILL have a 7 inch wide rim limit.

B

This is starting to sound damn tempting. (Hey, if I'm gonna be completely outclassed, I might as well go down with class). How much rolling or pulling is necessary to fit these suckers under the fenders? I still don't know if I will run 5-lug fuchs or 4-lug panos or revolutions or ??? But they will be 15x7's most likely. I don't mind some serious rolling but don't want to cut the fenders quite yet.

si2t3m · 08-21-2002, 06:59 AM

JP,

I'm about sure that you have a digital multimeter so check this out for a <10$ pyrometer (can you say CSOB)

http://www.rennsport.ca/articles/technical/Rsr%20pyro.htm

Find a decent place to do some testing and start doing 8 figures...

HTH

Marc-Andre Morin
70 914-6 conversion 3.0L Webers