OFFSET and BACKSPACING EXPLAINED - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Sir Nuke · 10-19-2010, 07:26 AM

I have seen this question ask many times recently, WHAT IS OFFSET? or BACKSPACING? or the terms used incorrectly, for they are not the same thing....SO with that in mind, here is an explanation of these two terms.

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Wheel Offset

Offset is measured from the centerline of the barrel of the wheel to the hub mounting surface. If that hub mounting surface were in the exact center of the barrel of the wheel the offset would be “0". If the mounting surface is away from the center of the wheel the offset is POSITIVE, if the mounting surface is towards the center, the offset is NEGITIVE. Offset is measured in millimeters. There are 25.4 millimeters to an inch. So if the mounting surface is 12mm from the centerline of the wheel it has a 12mm offset. That would also mean that it is about ½ inch. If the mounting surface is moved away from the vehicle that is a positive offset. The picture shows a wheel with the positive offset. A positive offset will cause the wheel to set in or tuck into the vehicle. Originally you found positive offsets on just front wheel vehicles. Due to that some people refer to positive offset wheels as front wheel drive offsets. Currently there are many rear wheel drive cars and trucks with positive offsets. The higher the positive offset the less it sticks out from the vehicle and it will have a higher Backspace. If the mounting surface is moved in toward the vehicle past the centerline, that is a negative offset. A high negative offset will produce a lower Backspace. Once again the measurement in millimeters is how far away from the centerline the mounting surface is. A -24mm offset means that the mounting surface is located 24mm or 1 inch from the centerline toward the vehicle. The wheel will come out farther from the vehicle and will have that deep dish look.

Width

The width of a wheel is measured inside the beads which are usually ½ inches. If you measure on the outside of the beads an 8 inch wheel will measure 9 inches

Backspace

Back spacing is measured from the inner edge of the wheel to the hub mounting surface. It is a convenient measurement in that, as long as the back spacing remains the same, the clearance to the suspension also remains the same. If you know the width of the wheel and the offset you can compute the backspacing. For example if you have an 8 inch wheel with a +24mm offset. An 8 inch wheel is actually 9 inches wide so if the offset were 0 the mounting surface would be right on the centerline and the backspacing would be 4.5 inches. With a positive offset the mounting surface moves off center 24mm or 1 inch toward the outer edge of the wheel. This will make the inner edge go more inside which will result in a 5.5 inch backspacing.

Centerbore

This is the diameter of the center of the wheel. The centerbore must be equal to or larger than the hub of the vehicle for the wheel to seat. If the wheels centerbore is the same as the hub on the wheel then that wheel is hub-centric and uses the hub to center the wheels. If the centerbore is larger than the hub then the lugs will center the wheel and that is lug-centric. When using a lug-centric wheel be sure and snug the lugs up slowly and tighten them in an opposite or star pattern.

Bolt pattern

A bolt pattern of 5x120 mm means it has 5 lugs and if there were a circle through the center of all the lugs the diameter of that circle would be 120 mm.

oldfriend · 10-19-2010, 09:39 PM

It can't get any clear than this , very simple and clean explanation !!!

Sir Nuke · 10-19-2010, 11:15 PM

That was what I was going for......glad you liked it.

Jay_LHD3 · 10-20-2010, 10:04 AM

Let me see if I’m using this terminology correctly.

"The reason we don’t see really deep concave wheels on the new Camaros is because there is too much positive offset."

??

Sir Nuke · 10-20-2010, 10:23 AM

actually no, its because the Brembo brake calipers are so big, diameter wise, that they rub on the wheel.

Tallboy · 10-20-2010, 10:23 AM

Very well written and explained.

JFR1 · 10-20-2010, 12:55 PM

Thanks Sir Nuke - I learned the hardway - testing Cragars - I did all I know to do to get them to fit but the 1LS has 6"+ of backspacing needed to clear the caliper - Cragar is only 4.5". Thanks again for the lesson. JFR1

Bad Jewel · 10-29-2010, 04:05 AM

Now all I need to know is what width and backspacing 18" wheel will fit on my RS SS so I can mount stickies with a sidewall.

Sir Nuke · 10-29-2010, 06:14 AM

the best thing you can do, is when you see or find a wheel that LOOKS like what you want, ask the people that actually sell them, and if they don't kniow what fits what, they don't know their business and I would to elsewhere.

Dr Jkel · 11-04-2010, 12:31 PM

So a negative offset gives you a deeper dish look, with more lip so to speak?

Sir Nuke · 11-04-2010, 06:01 PM

yes, you would most likely have more LIP, so to speek

boomskeet · 11-10-2010, 01:33 PM

you deserve an award for that explaination

Fallen Angel · 11-12-2010, 10:53 AM

Great Explanation, thank you!

Revo1 · 11-26-2010, 01:09 AM

Extremely helpful, thanks Nuke!

10-19-2010, 07:26 AM	#1
Sir Nuke Master of All Things Drives: '20 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,323 View My Garage	OFFSET and BACKSPACING EXPLAINED I have seen this question ask many times recently, WHAT IS OFFSET? or BACKSPACING? or the terms used incorrectly, for they are not the same thing....SO with that in mind, here is an explanation of these two terms. Wheel Offset Offset is measured from the centerline of the barrel of the wheel to the hub mounting surface. If that hub mounting surface were in the exact center of the barrel of the wheel the offset would be “0". If the mounting surface is away from the center of the wheel the offset is POSITIVE, if the mounting surface is towards the center, the offset is NEGITIVE. Offset is measured in millimeters. There are 25.4 millimeters to an inch. So if the mounting surface is 12mm from the centerline of the wheel it has a 12mm offset. That would also mean that it is about ½ inch. If the mounting surface is moved away from the vehicle that is a positive offset. The picture shows a wheel with the positive offset. A positive offset will cause the wheel to set in or tuck into the vehicle. Originally you found positive offsets on just front wheel vehicles. Due to that some people refer to positive offset wheels as front wheel drive offsets. Currently there are many rear wheel drive cars and trucks with positive offsets. The higher the positive offset the less it sticks out from the vehicle and it will have a higher Backspace. If the mounting surface is moved in toward the vehicle past the centerline, that is a negative offset. A high negative offset will produce a lower Backspace. Once again the measurement in millimeters is how far away from the centerline the mounting surface is. A -24mm offset means that the mounting surface is located 24mm or 1 inch from the centerline toward the vehicle. The wheel will come out farther from the vehicle and will have that deep dish look. Width The width of a wheel is measured inside the beads which are usually ½ inches. If you measure on the outside of the beads an 8 inch wheel will measure 9 inches Backspace Back spacing is measured from the inner edge of the wheel to the hub mounting surface. It is a convenient measurement in that, as long as the back spacing remains the same, the clearance to the suspension also remains the same. If you know the width of the wheel and the offset you can compute the backspacing. For example if you have an 8 inch wheel with a +24mm offset. An 8 inch wheel is actually 9 inches wide so if the offset were 0 the mounting surface would be right on the centerline and the backspacing would be 4.5 inches. With a positive offset the mounting surface moves off center 24mm or 1 inch toward the outer edge of the wheel. This will make the inner edge go more inside which will result in a 5.5 inch backspacing. Centerbore This is the diameter of the center of the wheel. The centerbore must be equal to or larger than the hub of the vehicle for the wheel to seat. If the wheels centerbore is the same as the hub on the wheel then that wheel is hub-centric and uses the hub to center the wheels. If the centerbore is larger than the hub then the lugs will center the wheel and that is lug-centric. When using a lug-centric wheel be sure and snug the lugs up slowly and tighten them in an opposite or star pattern. Bolt pattern A bolt pattern of 5x120 mm means it has 5 lugs and if there were a circle through the center of all the lugs the diameter of that circle would be 120 mm. __________________ Last edited by Sir Nuke; 10-19-2010 at 09:46 AM.

10-19-2010, 11:15 PM	#3
Sir Nuke Master of All Things Drives: '20 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,323 View My Garage	That was what I was going for......glad you liked it. __________________

10-20-2010, 10:23 AM	#5
Sir Nuke Master of All Things Drives: '20 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,323 View My Garage	actually no, its because the Brembo brake calipers are so big, diameter wise, that they rub on the wheel. __________________

10-20-2010, 12:55 PM	#7
JFR1 Drives: 2011 1LS. Garaged:Stock 69 Z28 Join Date: Sep 2010 Location: New Smyrna Beach FL Posts: 117	Thanks Thanks Sir Nuke - I learned the hardway - testing Cragars - I did all I know to do to get them to fit but the 1LS has 6"+ of backspacing needed to clear the caliper - Cragar is only 4.5". Thanks again for the lesson. JFR1

10-29-2010, 04:05 AM	#8
Bad Jewel Drives: 2010 RS SS Red Jewel Tintcoat 6M Join Date: May 2010 Location: Valencia, PA Posts: 11	Now all I need to know is what width and backspacing 18" wheel will fit on my RS SS so I can mount stickies with a sidewall. __________________ 2010 RS SS 6M Red Jewel Tintcoat THR Edition Delivered - 5/27/10 E-Force Rotofab Stainless Works Custom Tune 550 rwhp / 550 rwtq

10-19-2010, 09:39 PM	#2
oldfriend Drives: Fiat 500 E Join Date: Dec 2009 Location: 32.7607/N. 16.95947/W Posts: 7,816 View My Garage	It can't get any clear than this , very simple and clean explanation !!!

10-20-2010, 10:04 AM	#4
Jay_LHD3 Drives: 2019 F150 RCSB Abyss FX4 Join Date: Aug 2009 Location: Huntsville, AL Posts: 2,277	Let me see if I’m using this terminology correctly. "The reason we don’t see really deep concave wheels on the new Camaros is because there is too much positive offset." ??

10-20-2010, 10:23 AM	#6
Tallboy Say "when"... Drives: 11 2LT Join Date: Jul 2010 Location: Venice, FL Posts: 431	Very well written and explained.

10-29-2010, 06:14 AM	#9
Sir Nuke Master of All Things Drives: '20 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,323 View My Garage	the best thing you can do, is when you see or find a wheel that LOOKS like what you want, ask the people that actually sell them, and if they don't kniow what fits what, they don't know their business and I would to elsewhere. __________________

11-04-2010, 12:31 PM	#10
Dr Jkel and MR. HYDE Drives: 2010 2SS RJT/BLK 6Spd Man Join Date: May 2009 Location: Oxford, Alabama Posts: 4,375	So a negative offset gives you a deeper dish look, with more lip so to speak?

11-04-2010, 06:01 PM	#11
Sir Nuke Master of All Things Drives: '20 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,323 View My Garage	yes, you would most likely have more LIP, so to speek __________________

11-10-2010, 01:33 PM	#12
boomskeet Drives: 2010 Camaro 1LT - Cyber Gray Join Date: Mar 2010 Location: Los Angeles Posts: 216	you deserve an award for that explaination __________________ '10 1LT CGM V6 W/ mods all my mods done by myself and borrowing friends' tools Performance: flowmaster AT axle back exhaust Cosmetic: Matte Black Grand Sport stripes, Matte Black Powder Coated 18" stock rims, Matte Black Rear blackout panels, Matte Black Tinted rear lights, Carbon Fiber DiNoc emblems, Carbon Fiber DiNoc rear light surround bezels, GTS headlight black outs, Street Scenes rear spoiler, Decepticon gas cap AKA The "Decepticon" Camaro

11-12-2010, 10:53 AM	#13
Fallen Angel Drives: It's silver and fast! Join Date: Nov 2009 Location: Providence, RI Posts: 87	Great Explanation, thank you!

11-26-2010, 01:09 AM	#14
Revo1 Don't Like it? Suggit. Drives: 2010 2SS/RS Join Date: Aug 2008 Location: Fresno, CA Posts: 14,832 View My Garage	Extremely helpful, thanks Nuke! __________________ "Tops off, tach up baby- loud and proud!" A Camaro lover from day one- 1996 3.8 V6 Camaro, to 1996 5.7 LT1 Camaro Z28, to the sold 2002 5.7 LS1 Camaro SS, and NOW, a [I]6.2 L99 VR 2SS/RS: XS Power stainless full exhaust, Airaid CAI, BMR drop springs and sways, custom tune by Cal Speed- 411rwhp

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