Wheels and Tires Need help with wheels or tires? Got fitment issues? Have questions about tire performance and handling? Ask all of those questions here!

18x9.5 back spacing info

Thread Tools
 
Search this Thread
 
Old Jan 23, 2017 | 11:34 AM
  #1  
bk2life's Avatar
Thread Starter
Senior Member
Veteran: Army
5 Year Member
Loved
Community Favorite
 
Joined: Jul 2016
Posts: 805
Likes: 213
From: az
Car: 91 WS6 GTA
Engine: 5.3
Transmission: 4l60e
18x9.5 back spacing info

did a bit of searching, found all sorts of info, one says 5.5, one says 6.5, and just about everything in between.

91 GTA, stock suspension, but will be lowered. Not afraid to modify inner fender wells.--want 9.5 on all 4 corners, same tires if possible for easy rotation. daily driver, no track time, stock axle width.

don't want to stick out of fenders.

thank you for any info, or pointing me in the right direction.
Reply
Old Jan 23, 2017 | 03:25 PM
  #2  
Beater79TA's Avatar
Senior Member
20 Year Member
 
Joined: Aug 2004
Posts: 991
Likes: 24
From: Peoria, AZ
Re: 18x9.5 back spacing info

We did 18x10.5 on all 4 corners. 6 inch backspacing in front. 6.5 inch in the rear. Not sure this helps you though since you want to use a narrower wheel.
Reply
Old Jan 23, 2017 | 08:59 PM
  #3  
paul_huryk's Avatar
Supreme Member
25 Year Member
 
Joined: Jul 1999
Posts: 2,756
Likes: 10
From: Ahead of you...
Car: 1984 LG4 Camaro
Engine: 350 Roller Motor
Transmission: Level 10 700R4
Axle/Gears: Strange 12 bolt 3.42
Re: 18x9.5 back spacing info

5.25" for flush with fender, a bit more to tuck in in a bit.
Reply
Old Jan 24, 2017 | 09:15 AM
  #4  
QwkTrip's Avatar
COTM Editor
25 Year Member
iTrader: (22)
 
Joined: Mar 2001
Posts: 10,431
Likes: 2,093
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: 18x9.5 back spacing info

Originally Posted by paul_huryk
5.25" for flush with fender, a bit more to tuck in in a bit.

Think you got a typo in there. Did you mean 6.25"?


To the OP, when you're playing with such wide wheels and tires you really need to measure out clearances on your car. There isn't any room for error and things have to be dead nuts on. Better to be a little too much backspacing and have to apply a small spacer than to be too little backspacing and poke out too far.
Reply
Old Jan 24, 2017 | 12:59 PM
  #5  
paul_huryk's Avatar
Supreme Member
25 Year Member
 
Joined: Jul 1999
Posts: 2,756
Likes: 10
From: Ahead of you...
Car: 1984 LG4 Camaro
Engine: 350 Roller Motor
Transmission: Level 10 700R4
Axle/Gears: Strange 12 bolt 3.42
Re: 18x9.5 back spacing info

Nope, 5.25" brings the wheels flush on all 4 corners in 18" x 9.5". This of course assumes one is running a 3rd gen rear.


Originally Posted by QwkTrip
Think you got a typo in there. Did you mean 6.25"?


To the OP, when you're playing with such wide wheels and tires you really need to measure out clearances on your car. There isn't any room for error and things have to be dead nuts on. Better to be a little too much backspacing and have to apply a small spacer than to be too little backspacing and poke out too far.
Reply
Old Jan 24, 2017 | 11:18 PM
  #6  
QwkTrip's Avatar
COTM Editor
25 Year Member
iTrader: (22)
 
Joined: Mar 2001
Posts: 10,431
Likes: 2,093
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: 18x9.5 back spacing info

Oh, I see, somehow I got 10.5" wide on my mind, probably from Beater's post. Didn't notice the OP was asking about 9.5"
Reply
Old Jan 26, 2017 | 05:35 PM
  #7  
bk2life's Avatar
Thread Starter
Senior Member
Veteran: Army
5 Year Member
Loved
Community Favorite
 
Joined: Jul 2016
Posts: 805
Likes: 213
From: az
Car: 91 WS6 GTA
Engine: 5.3
Transmission: 4l60e
Re: 18x9.5 back spacing info

outstanding, thanks guys. There are soooooo many threads and info out there, and it all says something different.

Thanks again!
Reply
Old Jan 27, 2017 | 05:44 PM
  #8  
VincentZ28's Avatar
Supreme Member
iTrader: (2)
 
Joined: Mar 2002
Posts: 2,516
Likes: 5
From: San Antonio TX
Car: 1990 G92 IROC Z Miniram
Engine: 388cu 6.4 Liters
Transmission: G-Force T5
Axle/Gears: 3.73 Gears
Re: 18x9.5 back spacing info

I have 18x 9.5 all 4 corners and 2in drop all 4. I have 6in back spacing with no rubbing. The tires are just inside the fenders. Will not scrape on dips
Reply
Old Jan 28, 2017 | 08:34 AM
  #9  
paul_huryk's Avatar
Supreme Member
25 Year Member
 
Joined: Jul 1999
Posts: 2,756
Likes: 10
From: Ahead of you...
Car: 1984 LG4 Camaro
Engine: 350 Roller Motor
Transmission: Level 10 700R4
Axle/Gears: Strange 12 bolt 3.42
Re: 18x9.5 back spacing info

Indeed there is.

But there is only a narrow range of BS numbers that make that size wheel for a 3rd gen. From 5.25" to around 6" is the range.


Originally Posted by bk2life
outstanding, thanks guys. There are soooooo many threads and info out there, and it all says something different.

Thanks again!
Reply
Old Jan 28, 2017 | 11:56 AM
  #10  
bk2life's Avatar
Thread Starter
Senior Member
Veteran: Army
5 Year Member
Loved
Community Favorite
 
Joined: Jul 2016
Posts: 805
Likes: 213
From: az
Car: 91 WS6 GTA
Engine: 5.3
Transmission: 4l60e
Re: 18x9.5 back spacing info

Originally Posted by VincentZ28
I have 18x 9.5 all 4 corners and 2in drop all 4. I have 6in back spacing with no rubbing. The tires are just inside the fenders. Will not scrape on dips
what size tire are you running? and can you post a side pic of your car?
Reply
Old Jan 28, 2017 | 06:04 PM
  #11  
VincentZ28's Avatar
Supreme Member
iTrader: (2)
 
Joined: Mar 2002
Posts: 2,516
Likes: 5
From: San Antonio TX
Car: 1990 G92 IROC Z Miniram
Engine: 388cu 6.4 Liters
Transmission: G-Force T5
Axle/Gears: 3.73 Gears
Re: 18x9.5 back spacing info

Originally Posted by bk2life
what size tire are you running? and can you post a side pic of your car?
275/35/18 Front, 285/35/18 Rear
Name:  EBBF4009-4E5D-44D2-A4E8-3D78F9733EF5.jpg
Views: 4633
Size:  237.6 KB
Name:  MyIROCZ012.jpg
Views: 3563
Size:  106.0 KB
Name:  MyIROCZ011.jpg
Views: 3516
Size:  100.2 KB
Name:  40466bd8.jpg
Views: 3519
Size:  80.9 KB

Last edited by VincentZ28; Jan 28, 2017 at 06:13 PM.
Reply
Old Jan 30, 2017 | 08:05 AM
  #12  
bluegrassz's Avatar
Supreme Member
20 Year Member
Liked
Loved
Community Favorite
iTrader: (3)
 
Joined: Jan 2002
Posts: 3,449
Likes: 7
From: LONDON, KY
Car: Camaro
Engine: Carbed L98
Transmission: TH350
Axle/Gears: 3.73
Re: 18x9.5 back spacing info

Originally Posted by VincentZ28
275/35/18 Front, 285/35/18 Rear



Thats a real nice look.
Any modifications to the bump stops or wheel wells?
Reply
Old Jan 30, 2017 | 11:51 AM
  #13  
VincentZ28's Avatar
Supreme Member
iTrader: (2)
 
Joined: Mar 2002
Posts: 2,516
Likes: 5
From: San Antonio TX
Car: 1990 G92 IROC Z Miniram
Engine: 388cu 6.4 Liters
Transmission: G-Force T5
Axle/Gears: 3.73 Gears
Re: 18x9.5 back spacing info

No
Reply
Old Jan 30, 2017 | 04:53 PM
  #14  
jmd's Avatar
jmd
Supreme Member
25 Year Member
Liked
Loved
Community Favorite
iTrader: (4)
 
Joined: Jul 2000
Posts: 6,526
Likes: 93
From: Aridzona
Car: `86 SS / `87 SS
Engine: L69 w/ TPI on top / 305 4bbl
Transmission: `95 T56 \ `88 200-4R
Re: 18x9.5 back spacing info

Nice delivery of example pics, Vincent.
Reply
Old Mar 19, 2017 | 08:28 PM
  #15  
maroboytrell's Avatar
Junior Member
 
Joined: Feb 2012
Posts: 1
Likes: 0
From: I live under a car
Car: 92 RS VERT♡86 Z28♡88 GT
Engine: 305 Lm7 ???
Transmission: 700R4 T56 ???
Axle/Gears: 86' Z28 4:10...92' RS 3:42
Re: 18x9.5 back spacing info

Do you think a 10.5 or 11 inch rear wheel would fit with the same BS?
Reply
Old Apr 27, 2017 | 09:05 AM
  #16  
antman89iroc's Avatar
Supreme Member
 
Joined: Jun 2005
Posts: 1,440
Likes: 2
From: huntsville, al
Car: 89 IROC
Engine: 6.8 HSR N2O
Transmission: TKO 600
Axle/Gears: 9" Moser 3.50 True trac
Re: 18x9.5 back spacing info

Mine are 18 x 9.5 on rear with 6"BS and 1/2" spacers. (so 5.5 net BS) Without the spacer it fit but I thought the tire sat inboard too much.




Fronts are 18 x 8.5 but I don't recall the BS.

Reply
Old Apr 27, 2017 | 09:10 AM
  #17  
Beater79TA's Avatar
Senior Member
20 Year Member
 
Joined: Aug 2004
Posts: 991
Likes: 24
From: Peoria, AZ
Re: 18x9.5 back spacing info

Originally Posted by maroboytrell
Do you think a 10.5 or 11 inch rear wheel would fit with the same BS?
10.5 fit with 6 inch backspace on the front and 6.5 on the rear. With a 315 tire they are flush with the outside edge of the fender. It will also require some clearancing within the wheel wells.
Reply
Old Apr 29, 2017 | 04:57 PM
  #18  
tom86iroc's Avatar
Senior Member
15 Year Member
iTrader: (1)
 
Joined: May 2008
Posts: 867
Likes: 1
From: pawtucket RI
Car: 1986 iroc
Engine: alum. head 350 supercharged
Transmission: 6speed
Axle/Gears: ford 9in 3.90 35 spline moser axles
Re: 18x9.5 back spacing info

is that 6inch BS on all 4 rims? and did you use any spacers? ty those wheels look great
Originally Posted by VincentZ28
275/35/18 Front, 285/35/18 Rear



Reply
Old Jul 15, 2017 | 01:43 AM
  #19  
jonmcintyre's Avatar
Junior Member
 
Joined: May 2017
Posts: 10
Likes: 0
Re: 18x9.5 back spacing info

Originally Posted by Beater79TA
10.5 fit with 6 inch backspace on the front and 6.5 on the rear. With a 315 tire they are flush with the outside edge of the fender. It will also require some clearancing within the wheel wells.
would rolling the finders do enough for that? I wanna run 18x10s out back an wanna see if I can get a 315 on it
Reply
Old Jul 16, 2017 | 02:02 PM
  #20  
Beater79TA's Avatar
Senior Member
20 Year Member
 
Joined: Aug 2004
Posts: 991
Likes: 24
From: Peoria, AZ
Re: 18x9.5 back spacing info

Originally Posted by jonmcintyre
would rolling the finders do enough for that? I wanna run 18x10s out back an wanna see if I can get a 315 on it
I doubt it. You can try but I expect you'll need to trim some of the sheetmetal inside the wheel wells on both ends.
Reply
Old Jul 16, 2017 | 08:36 PM
  #21  
twinturrbo406's Avatar
Junior Member
 
Joined: Jan 2007
Posts: 25
Likes: 0
From: Lynchburg,VA
Car: 1987 Pontiac GTA
Transmission: Haven't decided yet ;)
Axle/Gears: 3.42
Re: 18x9.5 back spacing info

Originally Posted by VincentZ28
275/35/18 Front, 285/35/18 Rear






... that looks fantastic !!! ..
Reply
Old Jul 29, 2017 | 03:59 PM
  #22  
Watford91Z28's Avatar
Junior Member
 
Joined: Jul 2017
Posts: 1
Likes: 0
From: Georgia
Car: 1991 Z28
Engine: 6.0
Transmission: t56
Axle/Gears: 3.73 posi
Re: 18x9.5 back spacing info

Originally Posted by Beater79TA
I doubt it. You can try but I expect you'll need to trim some of the sheetmetal inside the wheel wells on both ends.
Did you have to do any trimming in the front with your 10.5s? I test fitted some US Mags 9.5s on the front with a 275/40R18 and have clearance issues when I went to turn. It would hit the ground effects on the lower part of the front bumper cover and the back of the wheel well.
Backspacing=5.25in
Reply
Old Jul 29, 2017 | 08:07 PM
  #23  
articwhiteZ's Avatar
Supreme Member
15 Year Member
iTrader: (56)
 
Joined: Sep 2009
Posts: 3,776
Likes: 101
From: Spokane WA
Car: 92 Lingenfelter Z28 articwhite
Engine: Aluminum 615BBC
Transmission: Th400wbrake/curri entps9" locker
Axle/Gears: 4.11/4.30/4.56
Re: 18x9.5 back spacing info

photo bucket sucks....

Last edited by articwhiteZ; Jul 29, 2017 at 08:13 PM.
Reply
Old Jul 29, 2017 | 08:18 PM
  #24  
tom86iroc's Avatar
Senior Member
15 Year Member
iTrader: (1)
 
Joined: May 2008
Posts: 867
Likes: 1
From: pawtucket RI
Car: 1986 iroc
Engine: alum. head 350 supercharged
Transmission: 6speed
Axle/Gears: ford 9in 3.90 35 spline moser axles
Re: 18x9.5 back spacing info

Originally Posted by articwhiteZ
photo bucket sucks....
yeah they changed their site around now
Reply
Old Jul 30, 2017 | 11:26 PM
  #25  
VincentZ28's Avatar
Supreme Member
iTrader: (2)
 
Joined: Mar 2002
Posts: 2,516
Likes: 5
From: San Antonio TX
Car: 1990 G92 IROC Z Miniram
Engine: 388cu 6.4 Liters
Transmission: G-Force T5
Axle/Gears: 3.73 Gears
Re: 18x9.5 back spacing info

Originally Posted by Watford91Z28
Did you have to do any trimming in the front with your 10.5s? I test fitted some US Mags 9.5s on the front with a 275/40R18 and have clearance issues when I went to turn. It would hit the ground effects on the lower part of the front bumper cover and the back of the wheel well.
Backspacing=5.25in
If you change the tire size to 275/35/18, you will have clearance. Look at the front of my car. No issues
Reply
Old Oct 28, 2017 | 11:45 AM
  #26  
tom86iroc's Avatar
Senior Member
15 Year Member
iTrader: (1)
 
Joined: May 2008
Posts: 867
Likes: 1
From: pawtucket RI
Car: 1986 iroc
Engine: alum. head 350 supercharged
Transmission: 6speed
Axle/Gears: ford 9in 3.90 35 spline moser axles
Re: 18x9.5 back spacing info

Originally Posted by VincentZ28
I have 18x 9.5 all 4 corners and 2in drop all 4. I have 6in back spacing with no rubbing. The tires are just inside the fenders. Will not scrape on dips
is that 6 inch bs on all 4 wheels ? thanks
Reply
Old Oct 28, 2017 | 04:16 PM
  #27  
articwhiteZ's Avatar
Supreme Member
15 Year Member
iTrader: (56)
 
Joined: Sep 2009
Posts: 3,776
Likes: 101
From: Spokane WA
Car: 92 Lingenfelter Z28 articwhite
Engine: Aluminum 615BBC
Transmission: Th400wbrake/curri entps9" locker
Axle/Gears: 4.11/4.30/4.56
Re: 18x9.5 back spacing info

your not tryn...lol
Reply
Old Oct 29, 2017 | 06:30 AM
  #28  
VincentZ28's Avatar
Supreme Member
iTrader: (2)
 
Joined: Mar 2002
Posts: 2,516
Likes: 5
From: San Antonio TX
Car: 1990 G92 IROC Z Miniram
Engine: 388cu 6.4 Liters
Transmission: G-Force T5
Axle/Gears: 3.73 Gears
Re: 18x9.5 back spacing info

Originally Posted by tom86iroc
is that 6 inch bs on all 4 wheels ? thanks
Yes!
Reply
Old Nov 19, 2020 | 06:26 AM
  #29  
bk2life's Avatar
Thread Starter
Senior Member
Veteran: Army
5 Year Member
Loved
Community Favorite
 
Joined: Jul 2016
Posts: 805
Likes: 213
From: az
Car: 91 WS6 GTA
Engine: 5.3
Transmission: 4l60e
Re: 18x9.5 back spacing info

such a great thread !
Reply




All times are GMT -5. The time now is 07:28 AM.