Changing Rim Backspacing. How To Measure My...
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Postmaster
Joined: Aug 2005
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From: Lancaster, MA
Changing Rim Backspacing. How To Measure My...
Currently I'm running 17" Ultra Rogue 175 black rims with 37x12.50 tires wrapped around them. I have plenty of room all the way around except at full lock thy rub the leaf springs a bit. It's a bit of an annoyance and I want my tires to stick out a bit more because I will be adding fender flares as well. The rims I have now (Ultra Rogue 175 Series 17x8, 8x170, 5.25" Backspacing at Carolina Classic Trucks) have a backspacing of 5.25" which just isn't cutting it. I'm wanting to go to a 4.75" or 4.5" backspacing to get the tires to stick out more. How can I measure around to make sure the tires will still fit and not hit the bumper in this case. I was going to turn the tires to the point where they get closest to the front bumper and measure how much room I have. If it's more than the difference in backspacing (like .75" or .5") then I should be ok, right? Or are my measurements off? My current wheels are 17x8 (I think 8). Will going to a 8.5" or 9" rim affect anything for the better or worse?
These are the new rims I'm looking at:
Fuel D509 Octane - Black-RH1
Pro Comp Xtreme Alloy Series 7047 - Flat Black-RH1
These are the new rims I'm looking at:
Fuel D509 Octane - Black-RH1
Pro Comp Xtreme Alloy Series 7047 - Flat Black-RH1
Cargo Master
Joined: Apr 2007
Posts: 2,659
Likes: 2
Spacers will not only change how far the wheel sticks out but also the arc that the wheel swings on when it turns. You'll lose clearance to the front and back of the wheel opening. Measuring out the front and making a theoretical assessment is a bit difficult because you have to account for the arc the wheel travels when turning, and suspension movement all the way to the bump stops.
I don't know what the pro's do, but this is my redneck idea... Get a piece of 1/4 inch thick aluminum bar stock from any hardware store. Cut short strips and stick to the hub where wheel mates. Mount your existing wheel with tire. The aluminum strips will space out the wheel 1/4 inch at a time. Keep adjusting until you're happy. Don't forget to account for changes in your tires when mounted on the new rim (diameter and width).
I don't know what the pro's do, but this is my redneck idea... Get a piece of 1/4 inch thick aluminum bar stock from any hardware store. Cut short strips and stick to the hub where wheel mates. Mount your existing wheel with tire. The aluminum strips will space out the wheel 1/4 inch at a time. Keep adjusting until you're happy. Don't forget to account for changes in your tires when mounted on the new rim (diameter and width).
Lead Driver
Joined: Jun 2007
Posts: 6,757
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From: Corvallis, OR
The more your tires stick out, the greater chance of having interference with the rear of the fender opening and the bumper valence. On a '99 with 37x12.50 tires, you would want about a -12 offset wheel to clear the frame and not stick out too far. -25 would work as well, but you might rub the back of the fender opening at full lock. The wheels you currently have are offset for '05 and later trucks, and they probably rub the leaf springs a lot more than "a little" since they are about 1.25" further in than they need to be.
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Postmaster
Joined: Aug 2005
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From: Lancaster, MA
OK, so maybe "a little" was "a little" off. They rub at about 70% of turning. Makes parking lots a nightmare. I don't understand why my girlfriend always wants to take my truck when we go grocery shopping or something, but anyway. What would a -12 offset as far as inches of backspacing. I'm sorry I'm such a noob at this. This is my first lifted truck.
Lead Driver
Joined: Jun 2007
Posts: 6,757
Likes: 5
From: Corvallis, OR
It depends on wheel width. On a 10" wide wheel, it would be 5" backspace. -12mm offset means the mounting surface is 12mm closer to the back of the wheel from center. Wheels are usually 1" wider than their bead measurement, so a 10" wheel is 11" wide. Divide 11" by 2 leaves 5.5" to center from the back edge. 12mm is about 1/2", so subtract 1/2" and that leaves 5" backspace.
So, for -12mm offset: (wheel width spec +1)/2 - 0.5 = backspace
Since the -12mm offset is the same as the bead width, you can essentially just divide wheel width by 2 and that is your backspace.
So, for -12mm offset: (wheel width spec +1)/2 - 0.5 = backspace
Since the -12mm offset is the same as the bead width, you can essentially just divide wheel width by 2 and that is your backspace.
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Postmaster
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Postmaster
Joined: Aug 2005
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From: Lancaster, MA
Makes sense. As long as the offset is a -12 or -25 like you said, I wouldn't have to worry about the width. Now to find some wheels with a -12 offset that I actually like. That'll be the fun part. Thanks cartmanea
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2008, assessment, backspace, backspacing, duty, f150, ford, measurement, mount, rim, rims, specs, stock, super, wheel
