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Thread: Liftís recommended tire size

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    Been Around the Block scoobycarolanNC's Avatar
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    Liftís recommended tire size

    Hey there! I have a Sahara & youíre lift is the way to go for me. Iím thinking a 305/70r18 will be a good size since Iím keeping my stock wheels. If not what size are you running?

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    Administrator wayoflife's Avatar
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    Quote Originally Posted by scoobycarolanNC View Post
    Hey there! I have a Sahara & youíre lift is the way to go for me. Iím thinking a 305/70r18 will be a good size since Iím keeping my stock wheels. If not what size are you running?
    305 is a true 35" tire and I know that this kit can run as big as a 315 which is a big 35 and without any problems.

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    Been Around the Block scoobycarolanNC's Avatar
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    Quote Originally Posted by wayoflife View Post
    305 is a true 35" tire and I know that this kit can run as big as a 315 which is a big 35 and without any problems.
    Hey Eddie. Iím less concerned about the diameter than I am the width. With the Saharaís narrower axle than the rubicon Iím worried about rubbing at full lock. Or am I way off base?

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    Administrator wayoflife's Avatar
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    Quote Originally Posted by scoobycarolanNC View Post
    Hey Eddie. Iím less concerned about the diameter than I am the width. With the Saharaís narrower axle than the rubicon Iím worried about rubbing at full lock. Or am I way off base?
    315 is what Dynatrac is running on their Sahara.

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    Caught the Bug Shots's Avatar
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    My stock Sahara tires (with the optional rims/tires) is 255 wide, so I assume yours are the same width. A 305 wide tire is 50mm wider than the stock tire, which works out to roughly 2". That means 1" closer to the suspension and 1" sticking further out (which makes them closer to the fenders when you turn). A 315 wide tire is only 10mm (.39") wider than that, so the difference between a 305 and 315 isn't likely to be an issue. That said, you can measure the tire's gap between the suspension, and fenders to assure you've got at least an inch of clearance (or 1.25 if you plan to use the 315). If you do, you're fine.
    Of course the easy way, is to check with people who have them mounted already like Dynatrac. Just keep in mind if they have different rims, you'll want to see how their backspacing compares to yours to make sure you have clearance.
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    Administrator wayoflife's Avatar
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    Good point about the rims. Are you wanting to run these on factory wheels? If so, that could be an issue. I'm pretty sure that Dynatrac is running wheels with 4.75" of back spacing. I'm quite certain you can get by with as much as 5.5".

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    Caught the Bug Shots's Avatar
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    I believe the stock rims are 18 x 7.5 +44.45, which puts them at a 5.5 backspace. Using the stock 255 wide tire on the stock rim, the inside edge of the tire will be roughly 10.5" inboard of the mounting face. If Dynatrac is using a 4.75 backspace with a 315 wide tire, their inside edge will be roughly 11" inboard of the mounting face. That's a lot of confusing numbers to some people, so what does that mean to you scoobycarolanNC? Simply that Dynatrac's setup puts the tire approximately .5" closer to the suspension than the stock rim/tire combo. Therefor using the stock rim, you can mount a 275 wide tire and have the same inboard clearance as Dynatrac's 315 on aftermarket rims. The nearest size that comes to mind is 285/70/18 which is actually 34" rather than 35" if that matters to you. However this size is still bigger than stock (1.7") and available in the BFG T/A KO2, which is a great tire.

    If you want to calculate any of this the math isn't that hard.
    1. First calculate the backspace of the rim. This number represents the distance to the inside edge of the rim, in relation to the mounting face against the suspension. To do this take half your rim width (7.5 / 2 = 3.75), and add the offset (44.45mm = 1.75"). Total backspace is then 5.5 for this rim. (3.75 + 1.75 = 5.5")
    2. Now you can take the tire width and convert to inches. The first number on your tire is the width in mm. Stock is 255. To convert to inches from mm divide by 25.4. (255 / 25.4 = 10.04")
    3. With the tire width in inches you can divide it in half (because on the rim half goes inboard, half goes outboard). (10.04 / 2 = 5.02")
    4. Lastly take the 1/2 tire width from the last step, plus the backspace from the first step and you get where the inboard edge of the tire is in relation to the mounting face. (5.02 + 5.5 = 10.52")


    If you want to see how different width tires will compare on the same rim replace the orange numbers with those from the new tire. So for example a 315 tire would be 6.2" (follow steps 2 and 3). Replace the orange 5.05 with the new tire's size of 6.2. The new tire will be 11.7" inboard from the mounting surface, or 1.18" closer to the suspension than the stock tire (11.7 - 10.52 = 1.18").
    The same thing can be done to experiment with different rims by adjusting the green numbers, which will change the red number.

    Okay, math class over. I hope that helps though.
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    Administrator wayoflife's Avatar
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    Quote Originally Posted by Shots View Post
    I believe the stock rims are 18 x 7.5 +44.45, which puts them at a 5.5 backspace.
    Sorry, I'm sure it was all well thought out and said but the factory wheels have 6.25" of back spacing. At least, last I checked.

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    Caught the Bug Shots's Avatar
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    Is that factory Rubicon rims with 6.25" backspacing?

    The stamp on the Graytech rims show 7.5" width and 44.45 offset. That works out to 5.5" backspacing. Unless I'm messing it up of course, which is certainly possible.
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    Administrator wayoflife's Avatar
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    Quote Originally Posted by Shots View Post
    Is that factory Rubicon rims with 6.25" backspacing?

    The stamp on the Graytech rims show 7.5" width and 44.45 offset. That works out to 5.5" backspacing. Unless I'm messing it up of course, which is certainly possible.
    Like I said, "last I checked". Granted, they aren't 18" wheels either or on a narrower axle.

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