Tire rolling over - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Big-B · 08-02-2013, 12:44 PM

I wasn't sure where to post this, but this section should get the most informed answers. I wasn't racing or on a Autocross, but might as well have been with the speed I have taken this corner.

I noticed the other day what appeared to be some curb rash on my right rear tire. Odd since I haven't parallel parked or been near any curbs lately. This morning I felt it; I took a corner, on the way to work, (90 deg left hander with slight bank) and I felt the the RR tire roll over. Sure enough I cheked the tire and more scuff marks below the tread to the side wall.

I have changed the crap factory tires and wheels and have Enkei Fujin 17x7.5 with 40 mm offset and Goodyear Eagle F1 Asymmetric 2 225/45-17. I'm running at 36 psi cold and the RR has (as best I can measure) about 1.2 deg camber.

The new setup has greatly increased grip, to the point where the car is perfectly neutral without the snap oversteer that it had before.

So what do you all think? Tire pressure to low? Bad tire?

CSG Mike · 08-02-2013, 12:49 PM

Tire is too wide for the rim for the way you're cornering

That's the real fix.

Additional fixes include more camber and some coilovers with higher spring rates.

mit_peid · 08-02-2013, 01:53 PM

I have me some Goodyear Eagle F1 Asymmetric 2s as well, but in 225/40/18s on 18x7.5s. So far I've been amazed & happy at how much stickier they are over the stock tires. I haven't quite pushed them to the limit quite yet since they so far have clung onto every turn I've thrown at them. Good to know 7.5" wide rims might be too wide (didn't think it was wide at all) in extreme cases for 225s?

CSG Mike · 08-02-2013, 02:08 PM

Quote:

Originally Posted by mit_peid

I have me some Goodyear Eagle F1 Asymmetric 2s as well, but in 225/40/18s on 18x7.5s. So far I've been amazed & happy at how much stickier they are over the stock tires. I haven't quite pushed them to the limit quite yet since they so far have clung onto every turn I've thrown at them. Good to know 7.5" wide rims might be too wide (didn't think it was wide at all) in extreme cases for 225s?

I actually meant that the 225 was too wide for the 7.5". Technically it's in spec, but putting it on a wider wheel (8" or 8.5") will reduce this rollover, give you a larger contact patch, and improve feedback.

mla163 · 08-02-2013, 02:28 PM

I don't think the section is too wide. 225 on a 7.5" is pretty square. I mean the car comes with 215s on a 7" and I don't think that's too much width. Sure, you'll get less squirm with a narrower tire on a wider wheel, but this size isn't too crazy. Maybe that tire has really weak sidewalls. I don't know, but I find it hard to believe that a tire with 3.5" of treadwall would flatten down to the wheel.

I'd bet that the tire was either very low on air, or maybe you (or someone else) curbed it parking somehow. I've done a lot of autocross with a lot of tire and wheel combos and have never heard of anyone rubbing a wheel across the pavement.

celica73 · 08-02-2013, 02:31 PM

Add more air and see what happens.

7thgear · 08-02-2013, 02:41 PM

Quote:

Originally Posted by mla163

I don't know the section is too wide. 225 on a 7.5" is pretty square. I mean the car comes with 215s on a 7" and I don't think that's too much width.

you ask for opinions and you get the best answer from one of the more qualified individuals... and you're dismissing it.

why ask for help in the first place?

Dezoris · 08-02-2013, 03:27 PM

I can't believe the tire is rolling that much. Ramp up pressures in front by 2lbs.
Are you sure you are just driving it FWD and forcing too much understeer?

mla163 · 08-02-2013, 03:29 PM

Quote:

Originally Posted by 7thgear

you ask for opinions and you get the best answer from one of the more qualified individuals... and you're dismissing it.

why ask for help in the first place?

I'm not the OP.

I'm just giving my opinion.

raul · 08-02-2013, 04:00 PM

Quote:

Originally Posted by Dezoris

I can't believe the tire is rolling that much. Ramp up pressures in front by 2lbs.
Are you sure you are just driving it FWD and forcing too much understeer?

I'm not sure, but it seems fishy to me that he's describing the stock nature of the car as having snap oversteer. The stock behavior of the car is progressive oversteer. The only snap oversteer you'll get is if you yank the wheel and floor the gas hard. And typically a grippier tire will make oversteer even snappier so the OP's description sounds backwards to me.

brz7400 · 08-02-2013, 04:43 PM

maybe a defective tire?
you can try swapping RR and LR wheel/tires and see if the same thing happens.

Big-B · 08-02-2013, 07:12 PM

Quote:

Originally Posted by raul

I'm not sure, but it seems fishy to me that he's describing the stock nature of the car as having snap oversteer. The stock behavior of the car is progressive oversteer. The only snap oversteer you'll get is if you yank the wheel and floor the gas hard. And typically a grippier tire will make oversteer even snappier so the OP's description sounds backwards to me.

You're right in that the stock setup tended to be progressive oversteer, but the stock tires tended to have inconsistent grip. Once you went past their happy point, they REALLY wanted to slide. But, with the gripper tires it's hard to get the back end to step out at all. I get slight understeer, get on the gas, and she hooks up nice and neutral.
I will probably swap the tire to different corner to see if it happens again, before I mess with tire pressures. But, CSG Mike is probably correct that the wheel is too skinny. I was vacillating between 7.5" and 8" but went for the lighter weight.

raul · 08-02-2013, 07:16 PM

I think CSG Mike said your tire is too wide not too narrow.

CSG Mike · 08-02-2013, 07:55 PM

Sorry, please let me know if I need to clarify... I was up till like 2AM last night studying datalogs, and was at my day job by 7AM this morning.

Need more coffee.

Count for the day:

1 Drive energy drink
4 shots of espresso over ice
2 20oz diet cokes
4 shots of espresso over ice (currently drinking)

I expect another iced coffee before the day ends...

08-02-2013, 01:53 PM	#3
mit_peid Boosted Noob Join Date: Nov 2012 Drives: '13 FRS MT KW SC, '05 4Runner 4WD Location: SoCal Posts: 883 Thanks: 353 Thanked 343 Times in 175 Posts Mentioned: 7 Post(s) Tagged: 0 Thread(s)	I have me some Goodyear Eagle F1 Asymmetric 2s as well, but in 225/40/18s on 18x7.5s. So far I've been amazed & happy at how much stickier they are over the stock tires. I haven't quite pushed them to the limit quite yet since they so far have clung onto every turn I've thrown at them. Good to know 7.5" wide rims might be too wide (didn't think it was wide at all) in extreme cases for 225s? __________________

08-02-2013, 02:28 PM	#5
mla163 Overthinking it Join Date: May 2012 Drives: BRZ in CS Location: DC Posts: 271 Thanks: 27 Thanked 81 Times in 48 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	I don't think the section is too wide. 225 on a 7.5" is pretty square. I mean the car comes with 215s on a 7" and I don't think that's too much width. Sure, you'll get less squirm with a narrower tire on a wider wheel, but this size isn't too crazy. Maybe that tire has really weak sidewalls. I don't know, but I find it hard to believe that a tire with 3.5" of treadwall would flatten down to the wheel. I'd bet that the tire was either very low on air, or maybe you (or someone else) curbed it parking somehow. I've done a lot of autocross with a lot of tire and wheel combos and have never heard of anyone rubbing a wheel across the pavement. Last edited by mla163; 08-02-2013 at 03:30 PM. Reason: me talk better

08-02-2013, 03:27 PM	#8
Dezoris Senior Member Join Date: Aug 2012 Drives: FR-S Location: IL Posts: 2,857 Thanks: 519 Thanked 2,998 Times in 1,095 Posts Mentioned: 159 Post(s) Tagged: 1 Thread(s)	I can't believe the tire is rolling that much. Ramp up pressures in front by 2lbs. Are you sure you are just driving it FWD and forcing too much understeer? __________________ SAVAGEGEESE

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08-02-2013, 12:49 PM	#2
CSG Mike Join Date: Jul 2012 Drives: S2000 CR Location: Orange County Posts: 14,562 Thanks: 8,942 Thanked 14,211 Times in 6,854 Posts Mentioned: 970 Post(s) Tagged: 14 Thread(s)	Tire is too wide for the rim for the way you're cornering That's the real fix. Additional fixes include more camber and some coilovers with higher spring rates.

08-02-2013, 02:31 PM	#6
celica73 Senior Member Join Date: Jun 2012 Drives: '13 BRZ / '11 Outback / '06 Tundra Location: Durham NC Posts: 510 Thanks: 6 Thanked 155 Times in 104 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	Add more air and see what happens.

08-02-2013, 04:43 PM	#11
brz7400 Senior Member Join Date: Jun 2012 Drives: Subaru BRZ Location: Los Angeles, CA Posts: 138 Thanks: 84 Thanked 30 Times in 22 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	maybe a defective tire? you can try swapping RR and LR wheel/tires and see if the same thing happens.

08-02-2013, 07:55 PM	#14
CSG Mike Join Date: Jul 2012 Drives: S2000 CR Location: Orange County Posts: 14,562 Thanks: 8,942 Thanked 14,211 Times in 6,854 Posts Mentioned: 970 Post(s) Tagged: 14 Thread(s)	Sorry, please let me know if I need to clarify... I was up till like 2AM last night studying datalogs, and was at my day job by 7AM this morning. Need more coffee. Count for the day: 1 Drive energy drink 4 shots of espresso over ice 2 20oz diet cokes 4 shots of espresso over ice (currently drinking) I expect another iced coffee before the day ends...

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