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Old 07-11-2016, 05:25 PM   #1
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Default 225 Rival S or 245 VR1 (autox)

Hey Guys,

Hopefully, you could give some insight on which tires I should get.

Issue: Wheels/tires are not wide/sticky enough to handle boost (instructor's advice). I'm able to spin the rear tires and cannot get the power down without the rear end becoming super twitchy or spinning out.

Tweaks: Decreased tire pressure down to 25psi in the front and 23psi in the rear, disconnected the rear sway bar, and ran full soft on the rear damper and four clicks in the front.

Results: The car was a lot more stable, and the tires didn't spin as much (unless I smash on the throttle and not roll into it. Previously, it would spin when I roll onto the throttle). I was able to bring my time down by 24sec.

Current car setup:
  • FFD evo1 15x8 +32 w/ 205/50 NT05
  • 949's dual duty configuration (close to it)
    • Front
      • Camber: -2.0
      • Caster: 4.0
      • Toe: 0
    • Rear
      • Camber: -2.0
      • Toe: +1/8"
Proposed plan:
  • Kosei K8R 15x9 +35 (TireRack currently has a sale on them. $105 per wheel)
  • 225/45/15 Rival S or 245/40/15 VR1
  • Same alignment?
The car runs in SCCA's CST (California Street Touring) class (I think SSM is the national equivalent?), which is unlimited, the only restriction are tires, the tread wear cannot be below 200. Forgot to add, the car does not have p/s or abs.
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Old 07-11-2016, 09:46 PM   #2
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245s may hook better, but the 225 Rival S will undoubtedly be faster on an autocross course.
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Old 07-11-2016, 09:52 PM   #3
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Rivals will be faster, vr1s more durable
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Old 07-11-2016, 10:18 PM   #4
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Check out 949racing.com's alignment recommendations. You will want more camber all the way around, and a bit of positive rear toe (1/8 total) I'm assuming you have over 200whp.
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Old 07-11-2016, 11:15 PM   #5
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The car has over 200whp, and it's just a nightmare to drive fast. The car is currently trying to hit 949's dual duty settings, but my alignment bolts are maxed out (at least that's what the alignment shop said). I do have the extended lower ball joint I need to install. Hopefully, that will get me into -3 in the front.

Is there a reason why the rivals would be faster? Better compound?
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Old 07-11-2016, 11:28 PM   #6
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GRM did an instrumented tire test in the latest issue, according to their numbers the 2016 Rival S are what you want.

(edit) never mind about class. I haven't seen CST before -- SSM is Hoosier territory.

--Ian
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Old 07-12-2016, 12:16 AM   #7
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Quote:
Originally Posted by thumpetto007 View Post
Check out 949racing.com's alignment recommendations. You will want more camber all the way around, and a bit of positive rear toe (1/8 total) I'm assuming you have over 200whp.
Read.

Quote:
Originally Posted by .one lane View Post
Current car setup:
  • 949's dual duty configuration (close to it)
    • Front
      • Camber: -2.0
      • Caster: 4.0
      • Toe: 0
    • Rear
      • Camber: -2.0
      • Toe: +1/8"
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Old 07-12-2016, 12:42 AM   #8
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Not disagreeing with previous posts, but wasn't the GRM test on a ~2min track not autocross? Be curious to see an autocross specific comparison...
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Old 07-12-2016, 01:03 PM   #9
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I'm going to stop by Barns and Noble to see if they have a current issue of GRM, I'm interested in reading their article.

I found this review over on the frs forums:
Maxxis VR-1 (New 200TW tire) - Scion FR-S Forum | Subaru BRZ Forum | Toyota 86 GT 86 Forum | AS1 Forum - FT86CLUB

Looks like rivals or re71r are popular for autox
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Old 07-12-2016, 01:47 PM   #10
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Sway bar diameters?
Pinch weld heghts?
Spring rates?
Coilover model/brand?
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Old 07-12-2016, 01:59 PM   #11
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Sway bar: Stock
Pinch weld heights: Roughly 4-13/16"
Spring rate: F 12k / R 7K
Coilovers: AST 5100 w/ helper springs
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Old 07-12-2016, 02:24 PM   #12
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Quote:
Originally Posted by .one lane View Post
Sway bar: Stock
Pinch weld heights: Roughly 4-13/16"
Spring rate: F 12k / R 7K
Coilovers: AST 5100 w/ helper springs
You have too much rear roll couple bias. Add front roll stiffness. Your car NA or NB?
If you need to run stock sway bars, then run 16kg front springs. If you can run sway bars then run 1.125" x .187" wall front and solid .562 /14mm rear.
Lower the car 1/2" also
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Old 07-12-2016, 02:42 PM   #13
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The car is an NA.

Thanks for the information, Emilio! I'll incorporate your recommendations on the sway bar and lower ride height.
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Old 07-12-2016, 03:18 PM   #14
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Old 07-12-2016, 10:10 PM   #15
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Leave that rear bar off, and get the RB race bar into the front of it. That will help. But that kind of power in 2nd gear on silly tires is going to require the use of more than 2 throttle positions.
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Old 07-12-2016, 10:12 PM   #16
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Quote:
Originally Posted by Leafy View Post
Leave that rear bar off, and get the RB race bar into the front of it. That will help. But that kind of power in 2nd gear on silly tires is going to require the use of more than 2 throttle positions.
Wait throttles have more than 2 positions?
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Old 07-12-2016, 10:21 PM   #17
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99% and allofit from my understanding

Yeah, the 205 are just silly now.
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Old 07-13-2016, 09:37 PM   #18
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Quote:
Originally Posted by Leafy View Post
Leave that rear bar off, and get the RB race bar into the front of it. That will help. But that kind of power in 2nd gear on silly tires is going to require the use of more than 2 throttle positions.
Or RaceLogic TC?

--Ian
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Old 07-13-2016, 10:21 PM   #19
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MS3 does have a traction control feature. Been trying to read more about it.
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Old 07-13-2016, 10:22 PM   #20
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Its not that great for turning stuff. Only has 2 wheel speed inputs. I have it all hooked up but have yet to tune it.

I need more power. Or less traction.
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