froggy47

I have good neg camber for the a6's I usually run & I get the tire sidewall scrub mark right where it should be. I am usually about 4-5 psi differential. Maybe needing the rear toe in more than the psi.

May try 1/4 inch total toe in rear just to see.


Thx

93Rubie

I've ran the numbers on the gearing its only slightly better.

The front wheels are wider, I personally plan on running 285/30/18's at all fours next year on my 93 Z07. Weight will hurt me, my 93 is heavily optioned (I didn't buy it with auto-x in mind at all, wasn't even on the radar, now here we sit......) Its heavy at 3300lbs (questionable scale accuracy) with full fluids, roof in, stock wheels, etc...I might be able to get it closer to 3200 on a good day with less fluids, lighter wheels,etc...

Keep in mind C4's handle better and won't have fuel starvation issues with a full fuel tank and with spare tire on the car.

My personal opinion is someone will try 275's or something on the stock 8.5" wide wheels and make it work on a C5. I personally also think B-Street will wind up being C5 and AWD boost buggy land. C4's and S2000's while close to each other don't have the power and traction of the other cars. I think the Z0K's and MSR's are going to get pounded.

Time will tell. Thanks for this thread, if and when I upgrade to a C5 this will come in handy. Good Job BTW last weekend.

AND0

This is very interesting, and warrants more discussion. Do you have a theory as to why this is? Less weight up top? More compliance in the frame and body? This would have implications for suspension tuning.

Emdsd7

Thank you for a very interesting thread. Even though I have been autocrossing for a while I don't know much about this subject. My C5Z has a pfatd adjustable front bar and DA shocks. How do I help cure a slightly loose rear end mid corner? Penske shocks currently have one click of compression adjustment. Also, some mid corner under steer with 30 run or more A6s. Is there an adjustment for this? Front shocks are 15 out of 30 clicks rebound. Compression is 4 out of 6. Shocks have Koni valving. I notice this on concrete and front bar is on middle adjustment.

ltborg

Compliance isn't necessarily a bad thing. My thinking is that the extra compliance is just enough to help keep the car settled center-off. The possibility exists that running with the roof in and adjusting the suspension some other way to compensate for the balance could be a faster combination, but in Stock/Street there isn't too much tuning to be done. In STU or SSP trim, I would retest because the stiffness could be beneficial. It's the same thing as Stock/Street cars running weird tire sizes for the rim or weird damping curves. You do what it takes to get pace.

ltborg

If it's truly mid-corner (and you're not hitting the throttle at little harder than you think) then you can't fix it with shocks. You might be able to make some changes to the canister pressures to simulate adding or subtracting spring rate, but I think the change to the damping curves would be more significant than the spring rate change. Mid-corner (or steady-state) is controlled by the springs/bars. Get that balance sorted first in a skid pad (or similar) then worry about the dampers to tune corner entry and exit.

theseal

Cool. What kind of alignment spes are you running?

ltborg

I'll update the original post if I make any changes.

passons

Good job.

ltborg

OK, time for the first real update. At the Mineral Wells ProSolo, Jerry Centanni was nice enough to let me compare tires with him. At my recommendation, Jerry bought the 285 Hankooks instead of the 275s that I'm running. Here are the specs from Tire Rack:



As you can see, the specs claim that the 275 is 0.1" wider, 0.3" shorter, and 3 lbs lighter; all good things for the car. At the College Station Tour, I heard rumors from some of the STU guys that the 285 was actually wider on the same size rim. Since Jerry bought these tires, I decided to find out. Here's what we found at the Mineral Wells ProSolo:







The actual measurements between edges of the tread pattern for the 275 were 9-7/8" and for the 285 were 10-5/8". Both of these tires were mounted on 18x9.5" wheels. There was a minor (0.25") height difference between the tires. The 275s weigh 29 lbs. The 285s weigh 30 lbs.

As you can see, despite the specs stated on Tire Rack, the two sizes are VASTLY different. Jerry said his car handled great on the new tires. For the record, Jerry bought the version 2 of the Hankook while mine are version 1.

Going forward, I will clearly be using the 285 in the rear paired with the 255 in the front, both on 18s. We did not compare the 255R17s Jerry used compared to me 255R18s.

gunluvS14

nice update

parkerracing

That has to be a misprint from Tire Rack. I've never seen a 285 be smaller than a 275 from any brand. My .02

ltborg

Every now and then you get something off like that. It depends on the tire brand and the tire line, but I've seen little things like that. I would have figured Tire Rack would have had that covered, but I guess in this case, not so much.

I'm working on a Mineral Wells report to follow up the College Station one. Hopefully I'll have it done before Spring Nats...

talon95

From the Hankook USA site, 10.2" for the 275 and 10.1" for the 285,

275/35ZR18
95 W 9.5 9.0-11.0 25.6 10.9 10.2 8.8 813 SBL 51 1,521

285/35ZR18 XL
101 W 10.0 9.5-11.0 25.9 11.4 10.1 8.8 803 SBL 50 1,819


I'd link to it but it's a stupid flash site. Not TR's fault.

dale3guy

I'm curious, why is there no A-street class when I look up the Mineral Wells results?

ltborg

A-Street is grouped into the indexed Street-RWD (SR) class.

bsalie99

I feel you pain with the overdriving, I made the switch to Rivals and hit the 1st event the same way I did with A6's, lets just say it was interesting. I had real power down issues, but I am hitting them alot harder and they rear really wanted to come around. I will be backing down the dampening on the Koni's for the next event and seeing if that helps.

rkdc5z06

Thanks for sharing!!
Awesome Driving!!

talon95

I think this tracks with what I've been saying about the RS3V1 > Z2,

http://www.roadraceautox.com/showthr...=1#post1419669

If you assume Rival >= Z2 which is generally what I've seen from tests.

bsalie99

It was My car that Grant drove in the post on the other forum. I rode along. He was very fast in the car, the Rivals felt like they were all ways on the edge of letting go in the rear, I may try softening the shocks even more to try and tame the rear. The extra power in my car seems to upset the cat more then help it with the Rivals. I still need to do a ton of work on my driving, esp when you get beat in your own car by 5 sec.