Larger tires and wheels back spacing help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1963chev · 02-09-2016, 02:02 PM

I have 235 R75 15s on the original rims on my truck and in the rear they are centered almost exactly in the wheel weld between the fenders and the bed. I like the setup as far as steering and handling but need tires and want new rims (see pic) so I am moving to 16x8 rims and 255 R65 16s. What backspacing should I choose? 4.0 because I am centered now? Thanks for any help or advice.

**PGSigns** · 02-09-2016, 04:12 PM

I run 15X8 with 4" of back spacing on the rear of my 66 fleet with 275's with no issues.
Jimmy

1963chev · 02-09-2016, 10:56 PM

Thanks Jimmy. I have done so much customization like 72 rear end and 71 front end, lowered 2/3, ps, etc that I can't really make comparisons to stock trucks. What I need to find out is how to match the back spacing of what I have on the truck now. I just pulled one of the 15x7 rims off, measured, and found that with the rim face up, it measures 4 inches from the floor to the bolt holes. With the rim face down, it measures 3 inches from the floor to the bolt holes. So, does anyone know what back spacing that is? If I go to 16x8, what back spacing should I get to match what I have now? Thanks for any help

1963chev · 02-09-2016, 11:28 PM

Thanks Jimmy. I have done so much customization like 72 rear end and 71 front end, lowered 2/3, ps, etc that I can't really make comparisons to stock trucks. What I need to find out is how to match the back spacing of what I have on the truck now. I just pulled one of the 15x7 rims off, measured, and found that with the rim face up, it measures 4 inches from the floor to the bolt holes. With the rim face down, it measures 3 inches from the floor to the bolt holes. So, does anyone know what back spacing that is? If I go to 16x8, what back spacing should I get to match what I have now? Thanks for any help

1963chev · 02-09-2016, 11:40 PM

Yes I am well centered now with the 7 inch rims but I don't know their back spacing. With the measurements I gave, can you tell me what the back spacing is?

**Captainfab** · 02-10-2016, 01:23 AM

Wheel backspacing is measured from the inside of the wheel where it bolts to the drum/axle flange to the edge of the wheel. This does not include the tire. If you measured correctly it sounds like your current wheels have a 4" back spacing.

1963chev · 02-10-2016, 03:41 AM

Thank you for the help, that's a lot easier than I was thinking. If I understand, the back spacing is just the measurement from the bolt holes to the BACK (inner) edge of the rim. I am at 4.0 back spacing with the 7 inch wide rims I have now. Since I am moving to an 8 inch wide rim is it correct that I need to get 4.5 back spacing to keep the wheel and tire centered where they are now?

jtrichard · 02-09-2016, 11:14 PM

IF you are well centered now with 4" back spacing you will want 3-1/2 back and 2-1/2 on the face .... 1" wider wheel 7" now? vs 8" new

jtrichard · 02-10-2016, 04:13 AM

OPPS had my math bassackwards above yes it would be 4-1/2" backspace and 3-1/2 on the face with an 8" wide wheel

**lolife99** · 02-10-2016, 11:19 AM

Quote:

Originally Posted by jtrichard

OPPS had my math bassackwards above yes it would be 4-1/2" backspace and 3-1/2 on the face with an 8" wide wheel

Remember most wheels measure 1" wider than their advertised width.
This is because wheels are measured at the bead surface,... NOT the actual outside-to-outside width.
Look at a bare rim and you will see what I'm talking about.
You need to account for this when measuring backspacing.

1963chev · 02-11-2016, 09:59 PM

Man o man, thank you all for taking the time to help. I was about to make a mistake but I was saved!

1963chev · 02-24-2016, 11:13 AM

So the move from 15x7 rims with 235 75R15 tires to 16x8 rims and 255 65R16 went great as far as fit, handling, and ride quality but I notice my truck is not as zippy off the line and works harder pushing the bigger tires around. I'm surprised. Any thoughts?

**The Rocknrod** · 02-24-2016, 11:19 AM

Quote:

Originally Posted by 1963chev

So the move from 15x7 rims with 235 75R15 tires to 16x8 rims and 255 65R16 went great as far as fit, handling, and ride quality but I notice my truck is not as zippy off the line and works harder pushing the bigger tires around. I'm surprised. Any thoughts?

Tire calculator shows a .17" difference in diameter, so I don't get it.
Your revs per mile will be only 4.16 revs less.
Your speedo will read .39mph difference.
http://www.americastire.com/dtcs/infoTireMath.do

**The Rocknrod** · 02-10-2016, 10:26 AM

The Wheel Smith has a great backspace diagram and you can download and print their sheet to work with.
http://www.thewheelsmith.net/WheelGeometry.html
Sheet:
http://www.thewheelsmith.net/images/...0spec-form.pdf

02-09-2016, 02:02 PM	#1
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Larger tires and wheels back spacing help I have 235 R75 15s on the original rims on my truck and in the rear they are centered almost exactly in the wheel weld between the fenders and the bed. I like the setup as far as steering and handling but need tires and want new rims (see pic) so I am moving to 16x8 rims and 255 R65 16s. What backspacing should I choose? 4.0 because I am centered now? Thanks for any help or advice. Attached Images

02-09-2016, 04:12 PM	#2
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	Re: Larger tires and wheels back spacing help I run 15X8 with 4" of back spacing on the rear of my 66 fleet with 275's with no issues. Jimmy __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

02-09-2016, 10:56 PM	#3
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Re: Larger tires and wheels back spacing help Thanks Jimmy. I have done so much customization like 72 rear end and 71 front end, lowered 2/3, ps, etc that I can't really make comparisons to stock trucks. What I need to find out is how to match the back spacing of what I have on the truck now. I just pulled one of the 15x7 rims off, measured, and found that with the rim face up, it measures 4 inches from the floor to the bolt holes. With the rim face down, it measures 3 inches from the floor to the bolt holes. So, does anyone know what back spacing that is? If I go to 16x8, what back spacing should I get to match what I have now? Thanks for any help Attached Images

02-09-2016, 11:28 PM	#4
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Re: Larger tires and wheels back spacing help Thanks Jimmy. I have done so much customization like 72 rear end and 71 front end, lowered 2/3, ps, etc that I can't really make comparisons to stock trucks. What I need to find out is how to match the back spacing of what I have on the truck now. I just pulled one of the 15x7 rims off, measured, and found that with the rim face up, it measures 4 inches from the floor to the bolt holes. With the rim face down, it measures 3 inches from the floor to the bolt holes. So, does anyone know what back spacing that is? If I go to 16x8, what back spacing should I get to match what I have now? Thanks for any help Attached Images

02-09-2016, 11:40 PM	#5
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Re: Larger tires and wheels back spacing help Yes I am well centered now with the 7 inch rims but I don't know their back spacing. With the measurements I gave, can you tell me what the back spacing is?

02-10-2016, 01:23 AM	#6
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,252	Re: Larger tires and wheels back spacing help Wheel backspacing is measured from the inside of the wheel where it bolts to the drum/axle flange to the edge of the wheel. This does not include the tire. If you measured correctly it sounds like your current wheels have a 4" back spacing. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

02-10-2016, 03:41 AM	#7
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Re: Larger tires and wheels back spacing help Thank you for the help, that's a lot easier than I was thinking. If I understand, the back spacing is just the measurement from the bolt holes to the BACK (inner) edge of the rim. I am at 4.0 back spacing with the 7 inch wide rims I have now. Since I am moving to an 8 inch wide rim is it correct that I need to get 4.5 back spacing to keep the wheel and tire centered where they are now?

02-09-2016, 11:14 PM	#8
jtrichard Registered User Join Date: Jun 2013 Location: joshua tree ca. Posts: 1,484	Re: Larger tires and wheels back spacing help IF you are well centered now with 4" back spacing you will want 3-1/2 back and 2-1/2 on the face .... 1" wider wheel 7" now? vs 8" new

02-10-2016, 04:13 AM	#9
jtrichard Registered User Join Date: Jun 2013 Location: joshua tree ca. Posts: 1,484	Re: Larger tires and wheels back spacing help OPPS had my math bassackwards above yes it would be 4-1/2" backspace and 3-1/2 on the face with an 8" wide wheel Last edited by jtrichard; 02-10-2016 at 04:22 AM.

02-11-2016, 09:59 PM	#11
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Re: Larger tires and wheels back spacing help Man o man, thank you all for taking the time to help. I was about to make a mistake but I was saved!

02-24-2016, 11:13 AM	#12
1963chev Registered User Join Date: Oct 2004 Location: Calgary, AB Posts: 80	Re: Larger tires and wheels back spacing help So the move from 15x7 rims with 235 75R15 tires to 16x8 rims and 255 65R16 went great as far as fit, handling, and ride quality but I notice my truck is not as zippy off the line and works harder pushing the bigger tires around. I'm surprised. Any thoughts? Attached Images

02-10-2016, 10:26 AM	#14
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Larger tires and wheels back spacing help The Wheel Smith has a great backspace diagram and you can download and print their sheet to work with. http://www.thewheelsmith.net/WheelGeometry.html Sheet: http://www.thewheelsmith.net/images/...0spec-form.pdf __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?



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