Offset Reference Ranges - "Will it Fit?" - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 1261 (permalink) Old 11-19-2009, 02:16 PM Thread Starter
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Offset Reference Ranges - "Will it Fit?"

I scoured both Boards and analyzed dozens of threads and hundreds of posts to compile a list of wheel offsets based on rim width that seem to be working for people. Looking for larger and/or wider wheels & tires myself, I know how challenging this can be.

I was able to find 30-40 posts that mention complete wheel & tire measurements and had photos. I did not include anything where the pictures looked like the tires sat at or outside of the fenders. I eliminated almost every mention of fitments that rub, except where I note it.

Now, when I look for wheels, depending on the rim width I'm looking at, I can see if the offset I'm looking at falls into a generally accepted range that has been proven by other members.

Hopefully others will find this useful. All offsets are +

Front Wheels

8" 35-48 Stock is +48 (18" & 19")
8.5" 30-45 Majority are running 35-40.
9" 38-51 Majority are running 38.
9.5" 34-40

Front Tires

Stock is 245/45-18 or 245/40-19 Front and Rear.
245 & 255 are most common. Even 265. Now 275. Some have tried 285.
45-18 and 40-19 are common.
245/40-19
255/35-19
265/35-19
245/35-20
255/35-20
275/35-19 on 19x9.5 w/+40 offset or +35 w/5mm spacer

Rear Wheels

8" 48 Stock is +48 (18" & 19")
8.5" 42
9.5" 35-57 Majority are 42-45
10" 40-55 Majority are 45, also 20x10 +60 with a 295/30-20 tucked and did not rub!
10.5" 46-47 50 seen now too.
11" 54

Rear Tires

275 & 285 are most common; up to 305 on lowered vehicle which required cutting & rolling.
40-18 and 35-19 are common.
275/35-19
285/35-19
305/30-19 (cutting & rolling)
285/30-20
245/35-20
295/30-20 (tested only on 20x10 +60 so far - no cutting or rolling and it tucked)

If anyone has any additional known fitments that do not cause rubbing issues OR if anyone sees any mistakes in here, please let me know and I'll add/change/delete to this list.

Warning: I can't guarantee these fitments - they are only as good as the person who posted the result and my interpretation of the pictures...

Approx. Measurements which might be helpful when looking at larger rear wheels & tires:

- Inner Wheel Well Wall to Wheel Mounting Surface = 8.715"
- Shock Bump-Out to Wheel Mounting Surface = 8.215"
- Inner Wheel Well Wall to OS Edge Fender = 12.75" = 324mm
- Shock Bump-Out to OS Edge Fender = 12.244" = 311mm
- Inner Wheel Well Wall to OS Edge Fender Minus a .125" Rolled-up Flat Lip = 12.625"
- Shock Bump-Out to Rolled-up Flat Lip = 12.125"
- Shock Bump-Out Plus extra .125" Clearance to Rolled-up Flat Lip = 12.000"
- Inner Wheel Well Wall to IS Edge of Non-Rolled Lip = 11.875"
- Shock Bump-Out to IS Edge of Non-Rolled Lip = 11.375"
- Shock Bump-Out Plus extra .125" Clearance to IS Edge of Non-Rolled Lip = 11.25"

2009 GT, Kooks 1-7/8 Mids, RPM Tune, Borla, Vararam, HSRK, P&P TB, UPR CCan, Mobil 1, Speedhut Gauges, FE3, Whiteline, Pedders, Summer MRR on 255/295, Winter Beyern on 245, CTS-V Fr Brembos, SS Rotors, Akebono Pads, Rolled/Pulled Fndrs, BMR Sways, Spohn Links & Arms, Sprt Pedals, Pont Shifter, Camaro Trans Pan, Pont Mats, Glove Box Light, MSM Lower Grills, CF Tail, GXP Diff, VG Fin, 20% Tint, 6000K HIDs, LED Fogs, GrafxWerks, Black Trim/Mirrors/Grills, Diffusr Lens/Amber Lens/Lowr Tails Tint

Last edited by SpeedRacerX; 01-02-2014 at 10:35 PM. Reason: Typo
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post #2 of 1261 (permalink) Old 11-19-2009, 02:20 PM
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Stock G8GT 19" Rear Wheels:
19"x8" +48mm Offset

Stock HSV 19" Rear Wheels:
19"x9.5" +57mm Offset

1 inch = 25.4 millimeters

I like these kinds of threads


Here are some helpful links


http://www.1010tires.com/tech.asp

http://www.onlineconversion.com/tire...conversion.htm

http://www.miata.net/garage/tirecalc.html

http://www.tiresizecalculator.info/




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Last edited by SRG963; 03-11-2010 at 03:55 PM.
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post #3 of 1261 (permalink) Old 11-19-2009, 02:57 PM
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17x8 +40 is my winter set... not on the car yet w/235-55R-17 tires

Last edited by karl f; 11-19-2009 at 03:02 PM.
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post #4 of 1261 (permalink) Old 11-19-2009, 03:25 PM
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Quote:
Originally Posted by SRG963 View Post
Stock G8GT Wheels:
19"x8" +48mm Offset


I like these kinds of threads
So do I. Thanks for your effort in providing helpful info for the community SpeedRacerX. I'll sticky this thread.
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post #5 of 1261 (permalink) Old 11-19-2009, 03:51 PM Thread Starter
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Quote:
Originally Posted by Rich-n-Texas View Post
So do I. Thanks for your effort in providing helpful info for the community SpeedRacerX. I'll sticky this thread.
My pleasure, thanks.

2009 GT, Kooks 1-7/8 Mids, RPM Tune, Borla, Vararam, HSRK, P&P TB, UPR CCan, Mobil 1, Speedhut Gauges, FE3, Whiteline, Pedders, Summer MRR on 255/295, Winter Beyern on 245, CTS-V Fr Brembos, SS Rotors, Akebono Pads, Rolled/Pulled Fndrs, BMR Sways, Spohn Links & Arms, Sprt Pedals, Pont Shifter, Camaro Trans Pan, Pont Mats, Glove Box Light, MSM Lower Grills, CF Tail, GXP Diff, VG Fin, 20% Tint, 6000K HIDs, LED Fogs, GrafxWerks, Black Trim/Mirrors/Grills, Diffusr Lens/Amber Lens/Lowr Tails Tint
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post #6 of 1261 (permalink) Old 01-04-2010, 10:57 AM
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I am looking for replacement wheels right now and this type of thread is so useful, especially because the wheels on the car currently were not my doing (20 x 8.5 aftermarket).
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post #7 of 1261 (permalink) Old 01-12-2010, 07:36 PM
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Great job SpeedRacer, thanks for taking the time to do this!
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post #8 of 1261 (permalink) Old 01-17-2010, 06:51 PM
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Looking for some input here and verification of my math!

According to the "Monster Meats" thread, they fit 19x9.5ET34 up front. If I go with 19x8.5ET20, this would stick out towards the fender about 1.3mm further (0.05") compared to the 9.5ET34. Am I right here? Then going with a smaller tire compared to "Monster Meats", I shouldn't expect any rubbing but good concavity.

Any input would be much appreciated.
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post #9 of 1261 (permalink) Old 01-18-2010, 07:15 AM
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Great Post thanks.
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post #10 of 1261 (permalink) Old 02-23-2010, 11:59 AM
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im jus making sure but a 19x9.5 with a 35 offset in the rear with 275.35.19 is ok right?
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post #11 of 1261 (permalink) Old 02-23-2010, 12:06 PM
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Quote:
Originally Posted by Tommy6188 View Post
im jus making sure but a 19x9.5 with a 35 offset in the rear with 275.35.19 is ok right?
+35 is too small an offset for a 9.5" rear wheel IMO.

It may work as long as you don't load up with passengers or lower your car any.



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post #12 of 1261 (permalink) Old 02-23-2010, 12:22 PM Thread Starter
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Quote:
Originally Posted by Tommy6188 View Post
im jus making sure but a 19x9.5 with a 35 offset in the rear with 275.35.19 is ok right?
Quote:
Originally Posted by SRG963 View Post
+35 is too small an offset for a 9.5" rear wheel IMO.

It may work as long as you don't load up with passengers or lower your car any.
I know it says +35 for a 9.5" is OK in the data above but it was the lowest positive one that didn't stick out of the fender well and ALL the above (unless noted) safely assumed no lowering. Some were lowered but it wasn't my intention to try and decipher lowering and rubbing scenarios.

There's a reason why most of those I found for rear 9.5" are in the +42 to +45 (even +47) range as SRG963 has pointed out.

I'm not saying it can't work - because clearly it did for other people - but I agree with SRG963. I would be careful. IMHO.

2009 GT, Kooks 1-7/8 Mids, RPM Tune, Borla, Vararam, HSRK, P&P TB, UPR CCan, Mobil 1, Speedhut Gauges, FE3, Whiteline, Pedders, Summer MRR on 255/295, Winter Beyern on 245, CTS-V Fr Brembos, SS Rotors, Akebono Pads, Rolled/Pulled Fndrs, BMR Sways, Spohn Links & Arms, Sprt Pedals, Pont Shifter, Camaro Trans Pan, Pont Mats, Glove Box Light, MSM Lower Grills, CF Tail, GXP Diff, VG Fin, 20% Tint, 6000K HIDs, LED Fogs, GrafxWerks, Black Trim/Mirrors/Grills, Diffusr Lens/Amber Lens/Lowr Tails Tint
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post #13 of 1261 (permalink) Old 02-23-2010, 08:28 PM
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Quote:
Originally Posted by SpeedRacerX View Post
I know it says +35 for a 9.5" is OK in the data above but it was the lowest positive one that didn't stick out of the fender well and ALL the above (unless noted) safely assumed no lowering. Some were lowered but it wasn't my intention to try and decipher lowering and rubbing scenarios.

There's a reason why most of those I found for rear 9.5" are in the +42 to +45 (even +47) range as SRG963 has pointed out.

I'm not saying it can't work - because clearly it did for other people - but I agree with SRG963. I would be careful. IMHO.

o ok thanks so 45 would work better right?
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post #14 of 1261 (permalink) Old 02-24-2010, 07:19 PM Thread Starter
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Quote:
Originally Posted by Tommy6188 View Post
o ok thanks so 45 would work better right?
Better, yes.

2009 GT, Kooks 1-7/8 Mids, RPM Tune, Borla, Vararam, HSRK, P&P TB, UPR CCan, Mobil 1, Speedhut Gauges, FE3, Whiteline, Pedders, Summer MRR on 255/295, Winter Beyern on 245, CTS-V Fr Brembos, SS Rotors, Akebono Pads, Rolled/Pulled Fndrs, BMR Sways, Spohn Links & Arms, Sprt Pedals, Pont Shifter, Camaro Trans Pan, Pont Mats, Glove Box Light, MSM Lower Grills, CF Tail, GXP Diff, VG Fin, 20% Tint, 6000K HIDs, LED Fogs, GrafxWerks, Black Trim/Mirrors/Grills, Diffusr Lens/Amber Lens/Lowr Tails Tint
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post #15 of 1261 (permalink) Old 02-24-2010, 07:48 PM
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Excellent information.
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post #16 of 1261 (permalink) Old 03-08-2010, 04:32 PM
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Will a +45 work on a front 8.5" wheel?

I've done some calculations, and compared to the Intense offsets and widths. There is 2mm more clearance compared to the Intense G8 and there is 3mm less clearance than the stock 8" wheel.



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Last edited by SRG963; 03-08-2010 at 05:03 PM. Reason: cleared it up
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post #17 of 1261 (permalink) Old 03-08-2010, 04:49 PM
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According to the info here a 20x10" wheel with a 35mm offset has NO SHOT, so I am just curious as how all the staggered breyton gts wheels fit peoples cars? Tirerack has them in only 35mm offset, and some people even have their cars lowered yet it still works. Any info on how that is possible?

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post #18 of 1261 (permalink) Old 03-08-2010, 04:51 PM
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Quote:
Originally Posted by aekariotis View Post
Tirerack has them in only 35mm offset, and some people even have their cars lowered yet it still works. Any info on how that is possible?
Anything is possible If you don't ever load up the G8, you can get away with it.
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post #19 of 1261 (permalink) Old 03-08-2010, 05:23 PM
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Oh ok. So there is no mythical 20x10 45mm offset Breyton gts rim somewhere that I missed?

'09 Liquid Red GT

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post #20 of 1261 (permalink) Old 03-08-2010, 06:12 PM Thread Starter
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Quote:
Originally Posted by SRG963 View Post
Will a +45 work on a front 8.5" wheel?

I've done some calculations, and compared to the Intense offsets and widths. There is 2mm more clearance compared to the Intense G8 and there is 3mm less clearance than the stock 8" wheel.
Seems like it will work, after all, you can get a 255 to clear the inside on a stock 8" rim and that ends up adding 5mm to the inside (in affect a +43 offset).
All depends on the tire width and how true the brand of tire runs. what size tire?

Quote:
Originally Posted by aekariotis View Post
According to the info here a 20x10" wheel with a 35mm offset has NO SHOT, so I am just curious as how all the staggered breyton gts wheels fit peoples cars? Tirerack has them in only 35mm offset, and some people even have their cars lowered yet it still works. Any info on how that is possible?
10" wide and +35 has a "shot" it's just that (well almost any size tire) will sit completely under the lip and you risk rubbing badly when lowered or when weight is in the back plus when hitting big bumps UNLESS fenders are rolled or cut. It can be made to work if you are into that look and are willing to make the necessary sacrifices. Wasn't worth the headaches to me. To others, well worth it and quite frankly, most aftermarket wheels and tires enhance the looks of this car.

Quote:
Originally Posted by aekariotis View Post
Oh ok. So there is no mythical 20x10 45mm offset Breyton gts rim somewhere that I missed?
Not that we are aware of unless someone shaved 10mm off the back of their +35mm wheel.

2009 GT, Kooks 1-7/8 Mids, RPM Tune, Borla, Vararam, HSRK, P&P TB, UPR CCan, Mobil 1, Speedhut Gauges, FE3, Whiteline, Pedders, Summer MRR on 255/295, Winter Beyern on 245, CTS-V Fr Brembos, SS Rotors, Akebono Pads, Rolled/Pulled Fndrs, BMR Sways, Spohn Links & Arms, Sprt Pedals, Pont Shifter, Camaro Trans Pan, Pont Mats, Glove Box Light, MSM Lower Grills, CF Tail, GXP Diff, VG Fin, 20% Tint, 6000K HIDs, LED Fogs, GrafxWerks, Black Trim/Mirrors/Grills, Diffusr Lens/Amber Lens/Lowr Tails Tint
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