jledford

iTrader: (1)

Due to my other tire rub thread and about half the people I know saying they wouldn't run the RE71R tire that had rubbed I purchased a set of Rival S tires as they were all that was available in the correct size, 275/35R18.

Now my car has become very loose in transition and corner exit. I've done one event on them and during a fast slalom that was offset the easy way there was no confidence in the tires. Myself and my co-driver both felt the same way. The old RE71R tires would have been flat through this slalom and trying that with the Rival S tires resulted in a few DNF runs were the car was so loose we had to abort the slalom.

To add to that it seems to be very tail happy on corner exit when transitioning back on the throttle. Yes this helps the car rotate but the grip compared to the RE71R is not there.

I know the tires potentially require a different setup but shock changes did not help much. In fact going to stiff on the shocks caused braking issues and I got a lot of ice mode problems. Taking the shocks back to the softer settings resolved the brake issues.

I'm looking at the following as potential solutions:

• Check rear toe - make sure it's still toe-in between 1/16 and 1/8th
• Possibly install the stock rear bar (running no rear bar right now) as there is also a slight entry to mid-corner push
• Raise the rear ride height

Any help, suggestions, or general discussion about this topic would be appreciated.


Some youtube vids from last weekends short course at a local event:


Co-driver loose #1:




Co-driver loose / push #2:




Myself loose and push:




Myself with an ice mode:

guitman32

iTrader: (15)

You didnt mention tire pressures. I assume that is the first place you went?

If so, then you probably do need to change your setup. Or sell the Rivals and get RE71Rs again. Or get tire warmers ha. Im not sure which is faster as I havent run the Rivals, but I know the RE71s are regarded as being the sharper, more responsive tire of the two.

Mind you, you are essentially running on cold tires (2x second autocross course) and that is definitely a large factor in how they perform.

jledford

iTrader: (1)

Yes, the co-driver and I were adjusting tire pressures without much difference in grip.

I would have bought the Bridgestone tires but the expected arrival date is middle of August or later and I needed tires for this weekends National Champ and Match Tour events in Bristol.

The tires were not cold at all. It might have only been a 23 second course but with 2 drivers and temps in the upper 80s we were having to spray the tires with water to keep the tire temps controllable and not get greasy. So I know they were getting hot enough.

I have checked the rear toe and it's still good from my last alignment. I can go more toe-in but would be over 1/8" total so not sure if that's a good idea.

I also re-installed the rear sway bar. I'm doing the Evo school on Friday (tomorrow) before the event so I will get some testing with the bar on the car. If it doesn't work I can just disconnect one end link and be back where I was before.

Finally I had the car dyno'd yesterday. So on top of the loose condition from the tires I now have a good 10-20+ ft-lb more torque from 3k to 6.5k rpms. That should make for an interesting time.

carbuffguy

Did you break in the new tires - 3/4 hundred miles? - it makes a big difference. If so, what tire pressure ranges did you try?

jledford

iTrader: (1)

Have you had experience breaking in the new crop of auto-x tires? Everyone in the auto-x community says that they don't need miles on them, just the mold release scrubbed off.

Having said that I had TireRack heat cycle them then I scrubbed them in before taking them to the event.

I went to the SCCA Champ and Match Tours in Bristol, TN over the weekend and the car still had the same issues. I had a chance to do quite a few changes to the car including rear toes changes, rear sway bar changes, and shock changes (compression and rebound) and talk to quite a few people about it. The major conclusion from this weekend is the car is sprung too stiff in the rear. I'll be looking for lower rate rear springs to test in the near future.

Myself and my co-driver believe the RE71R tires were just grippy enough to mask the issues with the car so even though we didn't do well at the event I believe it will help make the car faster in the long run. Hopefully that will be a good thing as I still PAX'd 19th out of 265 on the 2nd day of the Champ Tour with all the issues the car was having. That was about the only good point of the weekend.

carbuffguy

"Have you had experience breaking in the new crop of auto-x tires?"
Ya I have the RE71 and like to put 100 miles on them before hitting the course. It's easy for me though cus the alignment place i go to is 100 mile return trip. And your right, nothing will scrub it off better than the course.
Anyway, it was just a shot in the dark, but the tires masking the suspension issues seams very logical...imagine the grip with a better setup and back to the 71r's next time you need new shoes

How's the understeer with the new tires?

guitman32

iTrader: (15)

Keep us posted on how it goes.

What dampers and what rates are you running?

jledford

iTrader: (1)

Penske 8300's from Guy Ankeny and 1000f/900r as of now. Looking to try both 800 and 700 in the rear for testing. I've been told 700 is the way to go but I want to try both.

https://my350z.com/forum/autocross-r...ro-thread.html

guitman32

iTrader: (15)

I recently switched to a 12kg (672) rear and it feels pretty nice paired with a 16kg front. Overall I think the setup is on the soft side but the tracks I run like it. Spoke with BJ Zacharias and Brad Jaeger a few years back at Sebring and picked their brain. Dont really autox much anymore though.

justint5387

Hopefully you made the rival work. If it did, what kind of changes did you make?

jledford

iTrader: (1)

Well after the Bristol event I was frustrated and a little burnt out. The car has literally sat in the garage since then. Hopefully I'll feel like working on it again in the next few weeks and can pull the rear springs off to figure out the size I need to order for new springs. I'm thinking a lower rear spring rate will solve the problems. At the same time I think I might drop the front spring rate a bit to keep the frequency closer front to rear.

jledford

iTrader: (1)

As an update to this I went to 700 springs in the rear and the grip got better on the Rival S tires but still not as good as the RE71R. I did the math on the wheel rates and it seemed the front was quite a bit higher than the rear after the spring change so I dropped the front rate to 900 to get things to line up better. I also put RE71R tires back on and the car has been great.

I did a test n' tune locally and played with air pressure, front sway bar settings, connecting / disconnecting the rear bar, and shock settings. I've got a good baseline now for asphalt lots and am somewhat happy with the car again.

eye-5

Good that you like the car again. I've heard that the Rivals may have the ultimate time but the RE71Rs are easier for most drivers to be fast on. I like the RE71Rs a lot.

guitman32

iTrader: (15)

Good update...not too surprising the RE71Rs are great tires.

If I were you, the next thing I would look for is a stiffer front sway bar. Even the Hotchkis at full stiff isnt stiff enough IMO. Isnt it amazing how much the car leans even with a 1k front?

And just re-read your post and remembered tha I also had transitional oversteer issues when I was autoxing, I kept dropping the rear rebound click by click until I found a setting that settled the rear end down. Worked like a charm.

NA&CH

iTrader: (74)

Are you running a rear bar with those spring rates? A few guys locally are running around that setup no bar. They both seam to like the rival-s 1.5 over the re71. Are you using the rival s 1 or 1.5? I was going to try them for the next tire for test and tune setup.

Chris

PS let me know if you don't like your penskes… I know a buyer

jledford

iTrader: (1)

Rear bar is on the car but disconnected. I've tried reconnecting and it becomes loose, not terrible so I left the bar on the car in case I need more rotation on certain surfaces.

The S 1.5 doesn't come in sizes bigger than 255s. So if you're running 275s you're on the normal Rival S, which is what I tried.

Love the penske setup, but if I decide to change cars or classes I'll let you know. Still got the stock suspension so that would be the easiest parts to sell.