Track with 245/35/18 on the front

Master Apex · 08-30-2010, 02:52 PM

Has anyone tried/track 245/35/18 on the front ?
245/35/18 is 24.8" diameter so about 1" smaller than the stock size 225/45 or 245/40 which are about 25.8" diameter.

My 245/40/18 is needing replacement after 5 hot track days and it rubs a little.

So thinking about using 245/35/18 next but wondering if the 1" diameter drop will have negative impact in weight transfer in case the distance between "new CG" and "new roll center" will be longer than current setup since the lower arm will tilt downward due to smaller tires diameter.

Thanks.

a_riddler · 08-30-2010, 05:04 PM

What camber are you running in the front?

Master Apex · 08-30-2010, 08:02 PM

-3.5 camber

crfine88 · 08-30-2010, 08:05 PM

where are you rubbing?

Master Apex · 08-31-2010, 06:06 PM

nlink720 · 09-06-2010, 09:55 PM

That's odd. I have run 255/35-18 and 245-40-17 (both Dunlop Z1's like you too) on the front both with no problems. What are your spring rates? Does it happen on the track? My guess is that this occurs on the street, and that you have softer springs or something.

I would put some tape or markings where it is rubbing, and try to isolate when it is occurring.

DerekSelmanRacing · 09-09-2010, 02:54 PM

We run 245/35x18 on all 4 corners so I can't address weight xfer issues but they clear on 9.5" wheels. Not sure of offset.

Master Apex · 09-11-2010, 12:59 PM

nlink720,

Your 255/35/18 has 25" diameter
Stock 225/45/18 has 25.9" diameter
My 245/40/18 has 25.7" diameter

My setup rubs at the track, not on the street.
I usually run with the Red group and instructors.

Your 0.7" smaller diameter translates to 0.35" clearance on the upper half so if both cars have the same ride height, your car has extra 0.35" clearance..so this explains no rubbing on yours.

I read your post too late and have already installed 245/35/18 (24.8") diameter because I was not sure 255/35/18 will clear the KW CS body with my front wheel offset at 38mm.
What wheel offset you have on the front with 255/35/18?

With 245/35/18, I am able to lower the front perch even more so my air dam is now at 4.75" clearance and the underbody tray is at 3.5" clearance.

08-30-2010, 02:52 PM	#1
Master Apex Private 17 Rep 99 Posts Drives: '17 F80 M3 '07 Z4M '06 E60M5 Join Date: Apr 2010 Location: Austin, TX iTrader: (0)	Track with 245/35/18 on the front Has anyone tried/track 245/35/18 on the front ? 245/35/18 is 24.8" diameter so about 1" smaller than the stock size 225/45 or 245/40 which are about 25.8" diameter. My 245/40/18 is needing replacement after 5 hot track days and it rubs a little. So thinking about using 245/35/18 next but wondering if the 1" diameter drop will have negative impact in weight transfer in case the distance between "new CG" and "new roll center" will be longer than current setup since the lower arm will tilt downward due to smaller tires diameter. Thanks.
	Appreciate 0 Tweet Quote

08-30-2010, 05:04 PM	#2
a_riddler Bimmer Noob 30 Rep 566 Posts Drives: 08 Z4MC;08 MBZ E350 4Matic Join Date: May 2010 Location: Seattle, WA iTrader: (6)	What camber are you running in the front? __________________ 08 Z4MC /// DKF Exhaust, Stoptech 6/4 BBK, TCK Coilovers, Strong-Strut, Apex EC-7's, APR Splitter/Wing, AFE Intake, Underdrive pulleys, AS SSK, Jaffster, UUC Tranny Mounts, Matte Grill, RPI Scoop, CF Badges
	Appreciate 0 Quote

08-30-2010, 08:02 PM	#3
Master Apex Private 17 Rep 99 Posts Drives: '17 F80 M3 '07 Z4M '06 E60M5 Join Date: Apr 2010 Location: Austin, TX iTrader: (0)	-3.5 camber
	Appreciate 0 Quote

08-30-2010, 08:05 PM	#4
crfine88 Colonel 442 Rep 2,747 Posts Drives: E86M Join Date: Jan 2009 Location: Cave Creek AZ. iTrader: (19)	where are you rubbing? __________________ LINK TO 07 IR PHOTO JOURNAL:http://www.zpost.com/forums/showthread.php?t=1303735 LINK TO 06 IB MOD JOURNAL:http://www.zpost.com/forums/showthread.php?t=403119
	Appreciate 0 Quote

08-31-2010, 06:06 PM	#5
Master Apex Private 17 Rep 99 Posts Drives: '17 F80 M3 '07 Z4M '06 E60M5 Join Date: Apr 2010 Location: Austin, TX iTrader: (0)
	Appreciate 0 Quote

09-06-2010, 09:55 PM	#6
nlink720 Second Lieutenant 20 Rep 231 Posts Drives: 2004 BMW Z4 Roadster Join Date: Jan 2008 Location: Maryland iTrader: (3)	That's odd. I have run 255/35-18 and 245-40-17 (both Dunlop Z1's like you too) on the front both with no problems. What are your spring rates? Does it happen on the track? My guess is that this occurs on the street, and that you have softer springs or something. I would put some tape or markings where it is rubbing, and try to isolate when it is occurring.
	Appreciate 0 Quote

09-09-2010, 02:54 PM	#7
DerekSelmanRacing Second Lieutenant 8 Rep 222 Posts Drives: 05 Z4 3.0 SMG, 01 530 Join Date: Jul 2008 Location: Lake Havasu City, AZ. iTrader: (0)	We run 245/35x18 on all 4 corners so I can't address weight xfer issues but they clear on 9.5" wheels. Not sure of offset.
	Appreciate 0 Quote

09-11-2010, 12:59 PM	#8
Master Apex Private 17 Rep 99 Posts Drives: '17 F80 M3 '07 Z4M '06 E60M5 Join Date: Apr 2010 Location: Austin, TX iTrader: (0)	nlink720, Your 255/35/18 has 25" diameter Stock 225/45/18 has 25.9" diameter My 245/40/18 has 25.7" diameter My setup rubs at the track, not on the street. I usually run with the Red group and instructors. Your 0.7" smaller diameter translates to 0.35" clearance on the upper half so if both cars have the same ride height, your car has extra 0.35" clearance..so this explains no rubbing on yours. I read your post too late and have already installed 245/35/18 (24.8") diameter because I was not sure 255/35/18 will clear the KW CS body with my front wheel offset at 38mm. What wheel offset you have on the front with 255/35/18? With 245/35/18, I am able to lower the front perch even more so my air dam is now at 4.75" clearance and the underbody tray is at 3.5" clearance.
	Appreciate 0 Quote