too much understeer now!

Jessobear · 11-16-2010, 09:29 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.

vortrex · 11-17-2010, 01:12 PM

wow, those fronts are really bulging.

s30z · 11-17-2010, 02:34 PM

Yes, they are.

ChrisSlicks · 11-17-2010, 03:57 PM

No there not. It is just the design of the tire lip.

djpathfinder · 11-17-2010, 01:51 PM

No they're not.

Nikon FM · 11-18-2010, 05:47 PM

Quote:

Originally Posted by vortrex

I put 9x19 and 9x11 wheels with 255/35 and 295/30 hankooks with eibach springs and now have too much understeer. the alignment specs post spring install show -1.3deg and -1.4deg camber in the front.

can I get more negative camber out of the front with the stock bits? if so, what is suggested to relieve the understeer based off the tire sizes I am running? also, at what point do I start getting tire wear because of too much negative camber?

would sway bars help my situation at all?

thanks.

I run the OEM wheels with
255x30 Front
295x30 Rear
Toyo R888 tires on the track. I haven't experienced any understeer with the OEM suspension whatsoever. Pretty much point and go. With the springs and different wheel sizes there are a bunch of changes happening at once. If you still have your OEM wheels I'd swap out and see if the problem persists. Try and fix this by very small adjustments at a time…..just my 2 cents.

vortrex · 11-18-2010, 09:21 PM

I turned VDC off tonight and believe it or not that made a noticeable difference for the better. it's still not great, but much better than it was. I'll do some more testing with it to be certain.

djpathfinder · 11-18-2010, 10:22 PM

I'm puzzled...how would turning VDC off improve understeer?

vortrex · 11-18-2010, 11:38 PM

no idea, but I take the same route every day and it seemed better to me with it off.

Jessobear · 11-19-2010, 07:01 AM

The VDC system uses the brakes (I believe) to try and compensate for things like wheel spin. If he changed tire diameters significantly from stock, the VDC system may rear that as wheel slip due to differences in the rotational speed of the tires.

Next, try raising the front tires a bit and lowering the rears.

djpathfinder · 11-19-2010, 08:00 AM

Yeah, but with VDC on, are you noticing the slip light flashing, hearing/feeling the ABS go off, or feeling the car not keeping its speed during a turn? I thpught a 0.6" difference in tire diameter was acceptable. I know others have run a similar difference. How about slightly deflating the front (since the diameter is larger) and see if that equalizes front to back?

Jessobear · 11-19-2010, 10:06 AM

Reducing air pressure in the front tires reduces grip. It causes the tire to roll more in a corner.

corner3garage · 11-19-2010, 12:11 PM

i think a camber kit for the front with 2-2.5 degrees of negative camber would help a little bit, but you can also run a 255/285 combo to try and see if the rear doesnt push as hard.

vortrex · 11-19-2010, 12:23 PM

maybe the VDC thing is just my imagination then...

what air pressures should I be running?

my setup:

Hankook V12's

9x9 255/35
9x11 295/30

front = -1.3/-1.4 camber, .04 toe
rear = -1.6/-1.6 camber, .10/.08 toe

Jessobear · 11-19-2010, 01:08 PM

Not sure what the factory alignment specs are, but you have twice as much total toe in the rear than the front. I'll take a look at the settings later.

As far as tire pressures, take the factory spec and try +3 in the front and -3 in the back.

11-17-2010, 02:34 PM	#3 (permalink)
s30z Base Member Join Date: Aug 2010 Location: usa Posts: 21 Drives: 73 240z 10 370z Rep Power: 15	Yes, they are. Last edited by s30z; 11-17-2010 at 02:37 PM.

11-17-2010, 03:57 PM	#4 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 654	No there not. It is just the design of the tire lip. __________________ Hotchkis ARB \| Stillen CAI \| Art Pipes \| Berk CBE \| Stillen AP Racing Brakes \| AE Performance Oil Cooler \| BC Racing ER Coilovers \| Doran Control Arms

11-17-2010, 01:51 PM	#5 (permalink)
djpathfinder A True Z Fanatic Join Date: Mar 2010 Location: Edmonton, Canada Posts: 12,910 Drives: 2012 GT-R BE Rep Power: 734	No they're not. __________________ 2012 GT-R Black Edition Jet Black 2010 370Z 40th Anniversary // SOLD

11-18-2010, 10:22 PM	#8 (permalink)
djpathfinder A True Z Fanatic Join Date: Mar 2010 Location: Edmonton, Canada Posts: 12,910 Drives: 2012 GT-R BE Rep Power: 734	I'm puzzled...how would turning VDC off improve understeer? __________________ 2012 GT-R Black Edition Jet Black 2010 370Z 40th Anniversary // SOLD

11-19-2010, 08:00 AM	#11 (permalink)
djpathfinder A True Z Fanatic Join Date: Mar 2010 Location: Edmonton, Canada Posts: 12,910 Drives: 2012 GT-R BE Rep Power: 734	Yeah, but with VDC on, are you noticing the slip light flashing, hearing/feeling the ABS go off, or feeling the car not keeping its speed during a turn? I thpught a 0.6" difference in tire diameter was acceptable. I know others have run a similar difference. How about slightly deflating the front (since the diameter is larger) and see if that equalizes front to back? __________________ 2012 GT-R Black Edition Jet Black 2010 370Z 40th Anniversary // SOLD

11-16-2010, 09:29 PM	#1 (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.

11-17-2010, 01:12 PM	#2 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	wow, those fronts are really bulging.

11-18-2010, 09:21 PM	#7 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	I turned VDC off tonight and believe it or not that made a noticeable difference for the better. it's still not great, but much better than it was. I'll do some more testing with it to be certain.

11-18-2010, 11:38 PM	#9 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	no idea, but I take the same route every day and it seemed better to me with it off.

11-19-2010, 07:01 AM	#10 (permalink)
Jessobear Base Member Join Date: Oct 2010 Location: Washington, DC Posts: 201 Drives: '10 370Z Tour/Sp M6 Rep Power: 15	The VDC system uses the brakes (I believe) to try and compensate for things like wheel spin. If he changed tire diameters significantly from stock, the VDC system may rear that as wheel slip due to differences in the rotational speed of the tires. Next, try raising the front tires a bit and lowering the rears.

11-19-2010, 10:06 AM	#12 (permalink)
Jessobear Base Member Join Date: Oct 2010 Location: Washington, DC Posts: 201 Drives: '10 370Z Tour/Sp M6 Rep Power: 15	Reducing air pressure in the front tires reduces grip. It causes the tire to roll more in a corner.

11-19-2010, 12:11 PM	#13 (permalink)
corner3garage The370Z.com Sponsor Join Date: Oct 2009 Location: Laguna Hills, CA Posts: 9,879 Drives: 240sx, 350z, 370z Rep Power: 35	i think a camber kit for the front with 2-2.5 degrees of negative camber would help a little bit, but you can also run a 255/285 combo to try and see if the rear doesnt push as hard. __________________ Corner3motorsports.com

11-19-2010, 12:23 PM	#14 (permalink)
vortrex Base Member Join Date: Nov 2009 Location: SF, CA Posts: 199 Drives: '09 370z 6spd Rep Power: 16	maybe the VDC thing is just my imagination then... what air pressures should I be running? my setup: Hankook V12's 9x9 255/35 9x11 295/30 front = -1.3/-1.4 camber, .04 toe rear = -1.6/-1.6 camber, .10/.08 toe

11-19-2010, 01:08 PM	#15 (permalink)
Jessobear Base Member Join Date: Oct 2010 Location: Washington, DC Posts: 201 Drives: '10 370Z Tour/Sp M6 Rep Power: 15	Not sure what the factory alignment specs are, but you have twice as much total toe in the rear than the front. I'll take a look at the settings later. As far as tire pressures, take the factory spec and try +3 in the front and -3 in the back.

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