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#1 |
Registered User
Join Date: Sep 2016
Location: Brentwood CA
Posts: 180
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back spacing question
I don't currently have my truck to measure... so my question is, Does anyone know if a a 20x10 with a 5.5 BS on 275/45/20 tire will work on a 69 with 4'6 drop? I tried to do a search but can't find a definite answer.
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#2 |
Senior Member
![]() Join Date: Jul 2015
Location: Fairfax, Missouri
Posts: 1,049
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Re: back spacing question
Google it and most likely this site will pop up with results.
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#3 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,191
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Re: back spacing question
I believe anything over 8 1/2" - 9" width will have clearance issues on bed side areas.
6" drop will also need adjustable panhard bar... otherwise the axle will be forced out of alignment... |
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#4 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,200
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Re: back spacing question
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Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#5 |
Registered User
Join Date: Sep 2016
Location: Brentwood CA
Posts: 180
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Re: back spacing question
Yes, i have an adjustable panhard bar. I was also worried about the bed side. The rims I currently have are really close on the inner and I cant remember off the top of my head what backspacing I went with. the place where i want to order my rims from swears that the 5.5 will work but I am not sure that is totally true. I am only asking because these will be custom built and I want to be sure they fit the first time. Thanks for the replies!
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#6 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,191
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Re: back spacing question
How long before you can get to your truck?
I wouldnt order anything custom without measuring the clearance at ten times.... ![]() ![]() ![]() ![]() ![]() |
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#7 |
laying low
![]() Join Date: Mar 2001
Location: Searcy, Ark. USA
Posts: 13,200
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Re: back spacing question
Your truck could have the narrow axle or the wider axle. There is about 1 1/2" difference in width.
__________________
Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross |
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#8 |
Registered User
Join Date: Sep 2016
Location: Brentwood CA
Posts: 180
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Re: back spacing question
It will be about a week before I get the truck back. There is a deal on the wheels and it is due to expire. I believe I have the narrower rear end as the PO swapped it out. I found this out when I did the 6 to 5 lug conversion the axles were 17 spline. The guy I am ordering my rims from said the front on a 20x8.5 with a 5.25 BS and rear 20x10 with a 5.5 BS will work but I am thinking that the 5.5BS may be to close to the bed side.I would hate to have to get spacers.
Last edited by 1969 Project; 08-30-2017 at 09:32 PM. |
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#9 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,191
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Re: back spacing question
There are two different wheel mount to wheel mount dimensions:
The 70 1/2 and earlier width is 62-3/8" from wheel mount to wheel mount. The 70 1/2 and later width is 63-3/4" from wheel mount to wheel mount. So there is 1 3/8" difference in the width possible. Half that and we get 5/8" loss possible clearance if the rear end is the narrower style (early).... So do math...Internal short cross sill measure 50", you have two 5 1/2" backspaced wheels = 11" making a total of 61"...minimum axle flange to flange is 62 3/8"...leaving only 1 3/8" split to get each side clearance of only 5/8""....this is without any overhang of the wheel housings.... Even if you had the later wider rear axle, it is still too close to call. I simply cant see 5 1/2" backspace working unless you make changes to the bed and the wheel housings. I would not be ordering special wheels without making certain that they will not only fit, but will have sufficient clearance especially on the bed side area. I wont run anything less than 2" clearance unless you have replaced the panhard bar with solid rod end to absolutely control sideways movement of the rear end. Better to be safe than wrecked and out of pocket... ![]() ![]() ![]() Last edited by AussieinNC; 08-30-2017 at 10:06 PM. |
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#10 |
Registered User
![]() Join Date: Jun 2004
Location: On The Beach, S C
Posts: 613
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Re: back spacing question
Try this: rimsntires.com/specspro.jsp
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4oldcars Driving: 1971 Jimmy w/68 Chev front clip, 1953 Bel Air 2 dr hdtp, 1996 Roadmaster wagon, 2000 Eldorado The ones I let go: 1931 2 dr sedan, 1935 pick up, 1938 2 dr sedan, 1962 SS 454, 1963 409 wagon, 1970 short bed, 1972 short bed, 1972 sub, 1976 short bed, 1986 long bed, 03 short bed |
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#11 |
Registered User
Join Date: Sep 2016
Location: Brentwood CA
Posts: 180
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Re: back spacing question
Thanks! Most came up with a 5" BS. I am curious... would BS also depend on the style of the wheel?
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#12 |
Moderator
![]() Join Date: Jun 2017
Location: Cherryville, NC
Posts: 2,191
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Re: back spacing question
Backspace is defined as the distance between the wheel flange mounting surface and the outside of the tire mount bead.
It does not include any allowance for tire bulge outside of the bead. ![]() ![]() ![]() ![]() ![]() ![]() |
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#13 |
Registered User
Join Date: Sep 2016
Location: Brentwood CA
Posts: 180
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Re: back spacing question
I have confirmed that my Foose in the rear are in fact 5.5 BS so I should be good. Yes, the bulge from my tire is what makes it a close fit but it works. My truck should be finished getting painted next week and my rims are out 6-9 weeks so i'll be sure to post some pics when she's all finished. The paint guy is pretty cool so Ihave been stopping by frequently to check out the progress and I have been like a little kid at the candy store lately. lol Thanks everyone for the replies and advice!
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#14 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,717
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Re: back spacing question
I would think the 5.5" bs would work on the 10" rim on a fleetside truck even with the narrower axle.
17x9 on my 69 short step with the wider axle and 5" backspacce works. But the fleetside gives you quite a bit more room on the inside. Worse case scenario is you buy a later axle which may or may not work out being cheaper than buyin new wheels.
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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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#15 |
Registered User
Join Date: Jul 2015
Location: Alberta
Posts: 161
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Re: back spacing question
Tiresize.com is a great website to figure this stuff out.
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#16 |
Registered User
![]() Join Date: Feb 2004
Location: brownfield texas (west texas)
Posts: 1,936
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Re: back spacing question
For what its worth i run a 15x12 with 6.5 bs and 15" wide drag radials and they clear the outters but inner tubs needed to be wider. No I have since made room on the outer edge but its because i now have bags and i already had a 3" body drop. A stock truck with a narrow rear like yours should have shod have no outer lip issues even with a 6" drop. The longer panard bar will also help in the side to side movement..
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