Need offset advice for RIMS

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Apr 3, 2011 | 09:18 PM

joe blow

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Need offset advice for RIMS

Hi,

I am looking at buying some 20" rims in the future and am not to sure what offset I would need....IF ANY. Can anyone offer some advice on 20's they have purchased and offset they went with?

Thanks

Apr 5, 2011 | 09:55 PM

Acer

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What year is the truck, and what width are the wheels?

Assuming an '08+ and 20"x9" wheels, we generally suggest +0mm to +12mm, depending on the width tire you plan to run.

Thanks,

Acer Engineering

Apr 5, 2011 | 10:30 PM

joe blow

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The truck is 2004 and the width of the wheel is 9"...The rims I am looking at only come in 5" backspacing.

I have a question:

How is backspacing determined...measurement from outer lip to center?

What is offset? Is it the same as backspacing....need clarification from someone...

thanks

Apr 5, 2011 | 10:41 PM

Acer

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If you lay a straight edge across the back of the rim and measure to the Wheel mounting surface, that is the backspacing.

Offset is the distance from the centerline of the wheel to the wheel mounting surface.

The conversion is approximately:

Backspacing - [ ( wheel width + 1" ) / 2 ] * 25.4 = Offset (in mm)

For instance, for your 20"x9" with 5" backspacing:

(5" - [ ( 9" + 1" ) / 2 ] ) * 25.4
= [ 5" - ( 10" / 2 ) ] * 25.4
= ( 5" - 5" ) * 25.4
= 0 mm

And:

( 4.5" - [ ( 9" + 1" ) / 2 ] ) * 25.4
= [ 4.5" - ( 10" / 2 ) ] * 25.4
= ( 4.5" - 5" ) * 25.4
= -0.5" * 25.4
≈ -13 mm

For a leaf sprung truck, 5" of backspacing is borderline excessive. We generally suggest 4.5" of backspacing to avoid any rubbing on the leaf springs.

Thanks,

Acer Engineering

Apr 5, 2011 | 10:54 PM

joe blow

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Thank you for the great and detailed explanation, it does make sense....I suddenly feel dumb after seeing all the equations you provided

Just kidding.....I currently have a bit of rubbing at full lockout which I am ok with....this truck is a pavement queen and I am ok with that....so 5" may be ok for my application?

Thanks