too much understeer now!

vortrex · 11-16-2010, 02:13 PM

neither of those sizes are good though for the wheel though. a 275 on the front is going to be bulging like crazy and a 285 on the rear is going to be stretched quite a bit. my 295's on the rear are already too small for the wheel.

Quote:

Originally Posted by s30z

I think you should change the tire size to one of these combo.

F 255-40-19 R 285-35-19

or

F 275-35-19 R 305-30-19

I prefer the first one since 2nd combo is way too much in my onpinion for the stock setup and power.
Generally speaking, if you over size the tire too much, you might get a nicer look, but you not only eat at your power but it also can also tend to numb the feel of the vehicle.

vortrex · 11-16-2010, 02:14 PM

Quote:

Originally Posted by m4a1mustang

More negative camber up front should help with the turn-in, but really it's going to be difficult to overcome that amount of tire stagger. Ideally you would maintain the OEM ratio or decrease it.

FWIW, you can fit up to a 275 width tire on a 9" wheel.

You could also leave the OEM sway bar up front and run a stiffer rear bar, but that will mostly help center-off.

question, how do other makers get away with an even bigger stagger? porsche has a huge stagger in the 997 and it obviously handles very well.

m4a1mustang · 11-16-2010, 02:16 PM

Quote:

Originally Posted by vortrex

question, how do other makers get away with an even bigger stagger? porsche has a huge stagger in the 997 and it obviously handles very well.

The Porsche needs that stagger as it has the weight of the engine over the rear wheels.

Over the years the 911s have always been notoriously "loose" cars due to their rear-engine design. Porsche engineers have done a lot to balance the car out with each redesign, and part of that includes quite a large stagger.

vortrex · 11-16-2010, 02:30 PM

it seems like 275/35 and 305/30 would be a combo made in Hankook that keeps the diameters in sync, but that's only gaining me 10mm less of a stagger. wonder how much of a difference that would make?

m4a1mustang · 11-16-2010, 02:40 PM

It should feel better. You'll have 40mm more contact area up front for better turn in. You still might want to run a little more negative camber but I think you'll have a much better base than you do right now.

ChrisSlicks · 11-16-2010, 02:47 PM

Yeah, the weight distribution of the 911 Carerra is 38% front, 62% rear. The large stagger is designed to induce understeer and stop people from going sideways into the nearest tree. There is a reason they used to call the 911 Turbo the "Widowmaker". For the Z you want a 20mm to 30mm stager at most.

vortrex · 11-16-2010, 02:49 PM

anyone have pics of a 275/35 on a 9" wheel? it seems like that will be bulging like crazy. a 255/35 is a perfect fit. I thought I saw pics of a 265 on a 9" and even that looked like too much.

ChrisSlicks · 11-16-2010, 02:54 PM

Quote:

Originally Posted by vortrex

anyone have pics of a 275/35 on a 9" wheel? it seems like that will be bulging like crazy. a 255/35 is a perfect fit. I thought I saw pics of a 265 on a 9" and even that looked like too much.

Check my picture gallery.

s30z · 11-16-2010, 03:11 PM

Quote:

Originally Posted by vortrex

it seems like 275/35 and 305/30 would be a combo made in Hankook that keeps the diameters in sync, but that's only gaining me 10mm less of a stagger. wonder how much of a difference that would make?

It is difficult to say, but if your only mods are Eibach springs and tires, then the only thing that I can think of that messes up the handling characteristics of the vehicle is the tire size. Non Nismo Eibach spring rate in my opinion is fairly balanced out and I dont think that is the cause of the difference in performance. Now I have never seen an eibach springs I can only tell your from numbers. But for example if your rears are progressive and your fronts are more linear of a spring then that can also be the cause of the understeer.

s30z · 11-16-2010, 03:12 PM

Quote:

Originally Posted by ChrisSlicks

Yeah, the weight distribution of the 911 Carerra is 38% front, 62% rear. The large stagger is designed to induce understeer and stop people from going sideways into the nearest tree. There is a reason they used to call the 911 Turbo the "Widowmaker". For the Z you want a 20mm to 30mm stager at most.

WhiskeyHotel · 11-16-2010, 03:35 PM

Yea, good advice above. I really think the way to balance the Z is to run as close to square as you can get with some adjustable sway bars to tweak that balance. Some of us (me) still prefer to go off the corner frontwards as opposed to backwards.

m4a1mustang · 11-16-2010, 03:36 PM

Quote:

Originally Posted by WhiskeyHotel

Yea, good advice above. I really think the way to balance the Z is to run as close to square as you can get with some adjustable sway bars to tweak that balance. Some of us (me) still prefer to go off the corner frontwards as opposed to backwards.

Good 'ole NASCAR explanation of oversteer/understeer:

Oversteer: You hit the wall with the rear end first.

Understeer: You hit the wall with the front end first.

vortrex · 11-16-2010, 04:29 PM

yeah I don't mind a little understeer but it's at the point now of performing quite a bit worse than a stock Z. I was on highway 17 (for the bay area folk) and it was a little scary going into some of those corners staring right at that center cement divide.

vortrex · 11-16-2010, 08:34 PM

would a .6" difference between tire diameter front to rear be an issue? I've heard with some cars it can play tricks with the ABS.

I'm wondering if I might just throw some 275's on the front and leave my rear 295's...

the front would be 26.6" and the rear would be 26" tall.

Jessobear · 11-16-2010, 10:29 PM

Try driving the car with the VDC on and off and see if it makes a difference.

But probably your biggest issue is simply that you have too much rear tire. You've actually increased the front track relative to the rear, which should reduce understeer. You could play with raising the front tire pressure relative to the rear pressure. Sounds like what you're doing currently is the opposite of what you're supposed to do:

Tire Tech Information - Air Pressure for Competition Tires

Also, take a look at your springs and see if you can't figure out their rates. Eibach often prints them on there. You should also be able to tell if they're progressively wound by looking at them. Progressive springs will have a non-uniform winding. There's a chance that the front spring rates were increased relative to the rear rates, which would increase understeer.

11-16-2010, 02:40 PM	#20 (permalink)
m4a1mustang A True Z Fanatic Join Date: Feb 2009 Location: Northern VA Posts: 55,385 Drives: on two wheels Rep Power: 6962	It should feel better. You'll have 40mm more contact area up front for better turn in. You still might want to run a little more negative camber but I think you'll have a much better base than you do right now. __________________ - Steve Zs & Coffee - Saturdays at 10AM in Fairfax, VA and Columbia, MD (Click the banner!) LIKE us on Facebook!

11-16-2010, 02:47 PM	#21 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 653	Yeah, the weight distribution of the 911 Carerra is 38% front, 62% rear. The large stagger is designed to induce understeer and stop people from going sideways into the nearest tree. There is a reason they used to call the 911 Turbo the "Widowmaker". For the Z you want a 20mm to 30mm stager at most. __________________ Hotchkis ARB \| Stillen CAI \| Art Pipes \| Berk CBE \| Stillen AP Racing Brakes \| AE Performance Oil Cooler \| BC Racing ER Coilovers \| Doran Control Arms

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11-16-2010, 02:30 PM	#19 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	it seems like 275/35 and 305/30 would be a combo made in Hankook that keeps the diameters in sync, but that's only gaining me 10mm less of a stagger. wonder how much of a difference that would make?

11-16-2010, 02:49 PM	#22 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	anyone have pics of a 275/35 on a 9" wheel? it seems like that will be bulging like crazy. a 255/35 is a perfect fit. I thought I saw pics of a 265 on a 9" and even that looked like too much.

11-16-2010, 03:35 PM	#26 (permalink)
WhiskeyHotel Track Member Join Date: Nov 2009 Location: Oklahoma Posts: 530 Drives: 2015 GT-R PW Premium Rep Power: 17	Yea, good advice above. I really think the way to balance the Z is to run as close to square as you can get with some adjustable sway bars to tweak that balance. Some of us (me) still prefer to go off the corner frontwards as opposed to backwards.

11-16-2010, 04:29 PM	#28 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	yeah I don't mind a little understeer but it's at the point now of performing quite a bit worse than a stock Z. I was on highway 17 (for the bay area folk) and it was a little scary going into some of those corners staring right at that center cement divide.

11-16-2010, 08:34 PM	#29 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	would a .6" difference between tire diameter front to rear be an issue? I've heard with some cars it can play tricks with the ABS. I'm wondering if I might just throw some 275's on the front and leave my rear 295's... the front would be 26.6" and the rear would be 26" tall.

11-16-2010, 10:29 PM	#30 (permalink)
Jessobear Base Member Join Date: Oct 2010 Location: Washington, DC Posts: 201 Drives: '10 370Z Tour/Sp M6 Rep Power: 15	Try driving the car with the VDC on and off and see if it makes a difference. But probably your biggest issue is simply that you have too much rear tire. You've actually increased the front track relative to the rear, which should reduce understeer. You could play with raising the front tire pressure relative to the rear pressure. Sounds like what you're doing currently is the opposite of what you're supposed to do: Tire Tech Information - Air Pressure for Competition Tires Also, take a look at your springs and see if you can't figure out their rates. Eibach often prints them on there. You should also be able to tell if they're progressively wound by looking at them. Progressive springs will have a non-uniform winding. There's a chance that the front spring rates were increased relative to the rear rates, which would increase understeer.