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Considering 35s? 34s? 33s? 32s Here's some tech info for you...

Discussion in '1Gen Wheels & Tires' started by Sal R., May 3, 2017.

  1. Sal R.

    Sal R. Active Member

    This thread is meant to provide some general information regarding some things to consider when adding larger than stock tire sizes and/or aftermarket wheels with specs different stock.

    Here is a general infographic of where interferences will occur with the addition of larger tires/varied wheel offsets:
    backspace.jpg

    First, let's talk suspension and suspension lifts. The suspension is meant to go up and down and are designed to have a max upward travel distance and downward travel distance. OEM tire sizes are designed to clear all the surrounding suspension components and structure at full compression steering lock to lock. The bumpstops located just above the lower control arms are the absolute limiting component of suspension upward travel.

    While suspension lifts (strut spacers, spring/strut combo, coilovers, etc.) are an easy way to gain some clearance between wheel & tire and the surround components and structure AT static ride height, it does nothing for clearance when the suspension cycles upward completely. You'll still get the same max allowable upward travel with stock suspension with all the same interferences from lock to lock at full compression. And when you're off-roading, your suspension WILL cycle upward all the way.

    Naturally, when putting on larger tires, you are effectively reducing the amount of clearance between the tire and the suspension components, fender, inner fender liner, firewall, and frame. How much reduction in clearances that will occur depends on the wheel AND tire combination. And I say wheel AND tire because the specs of the wheel will determine the placement of the tire at static ride height and the tire specs affects the steering turning travel area that is covered from lock to lock.
    OEM-LargerTires.jpg

    The two characteristics that determine wheel & tire placement are wheel backspacing and wheel offset. The lower the backspacing, the more the wheel & tire is pushed AWAY from the wheel hub (wheel sticks out more). The higher the negative offset, the more the wheel & tire is pushed AWAY from the wheel hub (wheel sticks out more).

    Low backspaced and high negative offset wheels create clearance away from SOME surrounding components and structure, but effectively, it only moves the interferences to another location.

    Wheel spacers reduces wheel backspacing (e.g. 4.5" backspace + 1.25" wheel spacer = 3.25" backspace).
    wheeloffset.jpg

    Body lifts create vertical clearance by lifting the actual sheet metal body AWAY from the frame and suspension.
    bodylift2.jpg

    To create clearance for larger tires using a body lift, a good rule of thumb is 1in for every 2in tire diameter change (e.g. OEM 30s > 35s = +5in diameter change ->2.5-3in body lift).
     
    Last edited: May 3, 2017
  2. Sal R.

    Sal R. Active Member

    For reference, 265/75R16 (31.25" Tire) 1" from full compression:

    Based on measurements taken when I tubbed for 34s, the wheel upward travel has a ratio of 2:1. Basically, for every 0.5" of travel between the lower control arm to the bumpstop equates to 1" of upward travel at the wheel.

    In the pic below, I still had +2" of usable upward wheel travel before fully cycling the suspension.
    IMG_20170503_093844.jpg
     
    Last edited: May 3, 2017
    Jim Smola and 02SR5SoccerMom like this.
  3. Sal R.

    Sal R. Active Member

    For reference: 295/70R18 (34" Tire) 0.5" from full compression

    Based on measurements taken when I tubbed for 34s, the wheel upward travel has a ratio of 2:1. Basically, for every 0.5" of travel between the lower control arm to the bumpstop equates to 1" of upward travel at the wheel.

    In the pic below, the wheel can travel upward +1", but as you can see, it would interfere with the fender.
    IMG_20170503_094311.jpg
    IMG_20170503_094338.jpg
     
    Last edited: May 3, 2017
  4. Jim Smola

    Jim Smola Administrator Staff Member Founding Member

    I simply love this post. Thanks so much for all your great input.
     
    Sequoia4WD and Sal R. like this.
  5. 1down4up

    1down4up New Member

    Just installed some new shoes on the tree. 275-70/17. Fitment is pretty much maxed for tire size. Stock suspension with rear airbags. Just an addition to the thread![​IMG][​IMG][​IMG][​IMG]

    Sent from my SM-G955U using Tapatalk
     
    Sal R. likes this.
  6. 1stgenoffroad

    1stgenoffroad New Member

    That looks good? Are you getting any rub with the factory wheels? It that last photo showing us the full turn?
     
  7. SR54WD

    SR54WD New Member


    Any more pics? I would love to see the whole truck if possible.
     
  8. 1down4up

    1down4up New Member

    SR54WD likes this.

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