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#1 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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.
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#2 |
Senior Member
![]() Join Date: Jan 2011
Location: Hayes Va
Posts: 4,569
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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 |
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#3 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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
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#4 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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
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#5 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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?
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#6 |
60-66 Nut
![]() ![]() Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,247
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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.
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#7 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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?
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#8 |
Registered User
Join Date: Jun 2013
Location: joshua tree ca.
Posts: 1,484
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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
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#9 |
Registered User
Join Date: Jun 2013
Location: joshua tree ca.
Posts: 1,484
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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. |
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#10 | |
67-72 parts collector,…
![]() Join Date: Nov 2002
Location: Mid-MO
Posts: 22,698
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Re: Larger tires and wheels back spacing help
Quote:
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.
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Keith Convert to disc brakes. http://67-72chevytrucks.com/vboard/s...d.php?t=444823 |
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#11 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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!
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#12 |
Registered User
Join Date: Oct 2004
Location: Calgary, AB
Posts: 80
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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?
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#13 | |
Moderator
![]() ![]() Join Date: Aug 2011
Location: China Spring, TX
Posts: 7,280
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Re: Larger tires and wheels back spacing help
Quote:
Your revs per mile will be only 4.16 revs less. Your speedo will read .39mph difference. http://www.americastire.com/dtcs/infoTireMath.do
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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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#14 |
Moderator
![]() ![]() Join Date: Aug 2011
Location: China Spring, TX
Posts: 7,280
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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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