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Wheel Backspacing Question Nbs


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#1 KCMO

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Posted 21 November 2008 - 05:34 PM

Is anyone running aftermarket wheels with 205/55/20's on them and having any issues with a 2" leveling kit? I wasn't sure if it would work or if you could change the backspacing and make it work? I dont have much experience on it. If not, im looking at getting 20" aftermarket wheels and want to get the biggest tire I can fit without doing a full suspension lift. Ive read that 275/60's fit with very little rubbing. If thats the case I will probably go with a factory backspacing and get those. any help on the subject would be appreciated.

Edited by KCMO, 21 November 2008 - 05:35 PM.

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#2 DV2000NJ

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Posted 21 November 2008 - 05:49 PM

Search, it has been covered EXTENSIVELY. And that's an understatement.

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#3 07SilveradoNoob

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Posted 21 November 2008 - 05:50 PM

205/55/20??? -->275/5520 maybe?

If you want to run a tire around 33" you will need to keep as close to stock backspacing as you can. . . and of course the wider the rim and wider tires will hurt you on the rubbing issue too.

It took me 3.5" of lift to clear my 33x11 on 20x9 with -12offset(4.5backspacing). . . this is a skinny 33" <--the only way I could get away without any trimming with that much backspacing.
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#4 Zembonez

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Posted 21 November 2008 - 06:53 PM

Search, it has been covered EXTENSIVELY. And that's an understatement.

Get "em Danno! :pimp:












I have 275-55-20s on 20x9 +25mm offset wheels and plenty of clearance all around. They look too little to me. I'm definitely going bigger. I understand that 275-60-20s require leveling to clear according to others in here.

Edited by Zembonez, 21 November 2008 - 06:56 PM.

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#5 KCMO

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Posted 21 November 2008 - 07:55 PM

Sorry, I meant to type 305/55/20. I think these are going to be just a bit big to fit with just a leveling kit. I searched through but i couldn't find exactly what i was looking for. Factory backspacing....but what is the offset you talked about? Sorry like i said, kind of a newb to this kid of stuff. Oh and how wide of wheel should I get? I think they are 20x9, is that going to be too big?

Edited by KCMO, 21 November 2008 - 08:02 PM.

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#6 Zembonez

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Posted 21 November 2008 - 08:02 PM

Sorry, I meant to type 305/55/20. I think these are going to be just a bit big to fit with just a leveling kit. I searched through but i couldn't find exactly what i was looking for. Factory backspacing....but what is the offset you talked about? Sorry like i said, kind of a newb to this kid of stuff.

No problem. You know can go back and edit that first post? I'd recommend it. Sounds like a leveling kit is a must for those tires.

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#7 Treasure

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Posted 21 November 2008 - 10:44 PM

search for "before and after pics" guys got a nice truck with 275/60/20 and 2" RC level kit
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#8 07SilveradoNoob

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Posted 22 November 2008 - 04:20 AM

Sorry, I meant to type 305/55/20. I think these are going to be just a bit big to fit with just a leveling kit. I searched through but i couldn't find exactly what i was looking for. Factory backspacing....but what is the offset you talked about? Sorry like i said, kind of a newb to this kid of stuff. Oh and how wide of wheel should I get? I think they are 20x9, is that going to be too big?


O ok, 305 is a pretty wide tire but it can fit if: you stick to factory backspacing/offset and use a 2.5" level kit or equal--but even with that there might be a little bit of trimming needed.

Backspacing(usually listed in inches-") and offset(millimeters-mm) are kinda the same thing: If you know one you can figure out the other-assuming the rim width is known.
-Backspacing= distance from the hub mounting area to the edge of the wheel (inner/suspension wheel side)
-Offset= distance from the centerline of the wheel(if split in half) to the hub mount. A postive offset (+) will tuck the wheel into the truck more resulting in a more flush look, while a negative (-) will push them out and give more of a deeper lip/dish.


A 20x8.5 would be ideal width for cleanance issues but you tire options will be limited. . . 20x9 will be great with the 305's. With that size rim(20x9) try and get the backspacing around +22mm/+26mm to keep the backspacing close to stock. There are several guys running a 305/55/20 with just leveling kits(most run the 2.5"), some have minor trimming will others say no trimming. . . mostly depends on wheel and tire widths.


Factory backspacing:
17x7.5=
+31mm offset(5.5" or 139mm)
18x8= +31mm offset(5.7" or 145mm)
20x8.5= +31mm offset(5.9" or 150mm)

Edited by 07SilveradoNoob, 22 November 2008 - 04:22 AM.

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#9 andymiller

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Posted 22 November 2008 - 09:52 AM

thanks
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#10 KCMO

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Posted 23 November 2008 - 04:27 PM

O ok, 305 is a pretty wide tire but it can fit if: you stick to factory backspacing/offset and use a 2.5" level kit or equal--but even with that there might be a little bit of trimming needed.

Backspacing(usually listed in inches-") and offset(millimeters-mm) are kinda the same thing: If you know one you can figure out the other-assuming the rim width is known.
-Backspacing= distance from the hub mounting area to the edge of the wheel (inner/suspension wheel side)
-Offset= distance from the centerline of the wheel(if split in half) to the hub mount. A postive offset (+) will tuck the wheel into the truck more resulting in a more flush look, while a negative (-) will push them out and give more of a deeper lip/dish.


A 20x8.5 would be ideal width for cleanance issues but you tire options will be limited. . . 20x9 will be great with the 305's. With that size rim(20x9) try and get the backspacing around +22mm/+26mm to keep the backspacing close to stock. There are several guys running a 305/55/20 with just leveling kits(most run the 2.5"), some have minor trimming will others say no trimming. . . mostly depends on wheel and tire widths.


Factory backspacing:
17x7.5=
+31mm offset(5.5" or 139mm)
18x8= +31mm offset(5.7" or 145mm)
20x8.5= +31mm offset(5.9" or 150mm)



thanks man, that makes a lot more sense that it did. So I think i need to look for a little bigger leveling kit. I had checked out the rancho quick-lift and the truxx lift that other people on the board have posted about. They run a little over 300 for each of them. I didn't plan on doing any shocks but if I get too big of a leveling kit my shocks are going to wear out pretty premature right? Im just trying to do everything right the first shot.

My list of parts ive been looking into:
20x9 KMC Rockstars
305/55/20 or 275/55/20
Rancho quick-lift (Havnt read a lot of reviews from NBS owners) OR
Truxx lvl kit (seems to be pretty nice from what ive read.

What all trimming are you talking about? I dont have mudflaps on it (yet) and I really dont wanna take a rubber mallet to my brand new truck :cheers: If that what its going to come down, i'll sacrifice for a little smaller tire I guess.
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#11 07SilveradoNoob

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Posted 23 November 2008 - 06:19 PM

thanks man, that makes a lot more sense that it did. So I think i need to look for a little bigger leveling kit. I had checked out the rancho quick-lift and the truxx lift that other people on the board have posted about. They run a little over 300 for each of them. I didn't plan on doing any shocks but if I get too big of a leveling kit my shocks are going to wear out pretty premature right? Im just trying to do everything right the first shot.

My list of parts ive been looking into:
20x9 KMC Rockstars
305/55/20 or 275/55/20
Rancho quick-lift (Havnt read a lot of reviews from NBS owners) OR
Truxx lvl kit (seems to be pretty nice from what ive read.

What all trimming are you talking about? I dont have mudflaps on it (yet) and I really dont wanna take a rubber mallet to my brand new truck :cheers: If that what its going to come down, i'll sacrifice for a little smaller tire I guess.


No problem. I used to run the CCMoffroad 2.5" leveling kit off ebay(about $85), worked great and alot of other guys on GMFS use that same kit. $300 is way too much for a leveling kit. . . and no need for additional shocks from just adding the CCM spacer.

The trimming, would consist of pulling the plastic liners back with zip-ties or such on the front side, and cutting(trimming) some
of the metal on the bottom rocker thus allowing you to pull the plastic liner on the cab side in more. Theres a sticky thread over on GMFS that has how-to/pics.

If you go with the 20x9 RockStar's and keep the backspacing/offset close to stock you would be able to run the 275/55/20 with a 2" kit, or with a 2.5" kit you could run the 275/60/20 with probably zero trimming or 305/55/20 with possibly a bit of trimmage.

Also the 305/55/20(33x12) will be the widest/tallest and weigh the most-which will cause the biggest decrease in MPG-if that a concern, followed by the 275/60/20(33x11) the the smallest 275/55/60(32x11).

Edited by 07SilveradoNoob, 23 November 2008 - 06:20 PM.

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#12 JNP07CC

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Posted 24 November 2008 - 08:05 AM

For the 17" x 7.5" wheel with 31 mm offset :

7.5 width = 190.5mm / 2 = 95.25mm center - 31.0mm backspacing = 64.25mm offset - 190.5 width = 126.25 mm /25.4 mm = 4.97 backspacing

how did you get 5.5" ??
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#13 07SilveradoNoob

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Posted 24 November 2008 - 03:46 PM

For the 17" x 7.5" wheel with 31 mm offset :

7.5 width = 190.5mm / 2 = 95.25mm center - 31.0mm backspacing = 64.25mm offset - 190.5 width = 126.25 mm /25.4 mm = 4.97 backspacing

how did you get 5.5" ??


Theres your problem, stock offset = +31mm . . . try it again and you should see that the backspacing on the 17x7.5=139mm or 5.5"

Also you can't use 7.5" as rim width, you use the actual width which would be a bit wider :thumbs:
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#14 KCMO

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Posted 24 November 2008 - 10:38 PM

Thanks Jay, I appreciate all your help. Im going to do a bit more looking into the rancho quick lift as i can get a electonic ride controller for it, just gotta decide if it's worth it or not. If i dont end up going that way i'll probably go with the CCM. I'll be sure to post some pics up and show you the finished result.

Edited by KCMO, 25 November 2008 - 12:09 AM.

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#15 07SilveradoNoob

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Posted 25 November 2008 - 06:20 AM

No problem
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