FYI - Wheels and Tires

Discussion in 'OEM Wheels/Tires' started by XrunnIT, Aug 5, 2007.

  1. XrunnIT

    XrunnIT Active Member

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    X-Runner Stock Wheel/Tire Specs:
    Bolt pattern is 5x4.5", 5x114.3mm
    Lug nut size is 12mm x 1.50
    Offset is +30mm.
    18 x 8 wrapped with Bridgestone Potenza RE050A 255/45ZR18
    Center Bore is 60mm
    Wheel weight is 31lbs - 32lbs (as advertised)
    Tire weight is 30lbs
    (as advertised)
    Wheel/Tire weight as weighed with 34lbs of tire pressure - 58.2lbs (as weighed on a scale)

    Extended Tire Info -
    Bridgestone Potenza RE050A 255/45ZR18
    Treadwear: 140
    Traction: A
    Temperature: A
    Max load: 1709
    Max Inflation Press: 44psi
    Tread Depth; 10/32"
    Tire Weight: 30lbs
    Rim Width Range: 8-9.5"
    Rim Width: 8.5"
    Sect Width: 9"
    Tread Width: 8"
    Overall Diam: 26.9 "
    Revs Per Mile: 774


    Here is a little bit of knowledge on wheels and tires. This info was originally documented on Ranger Power Sports (LINK & LINK).

    *EDIT* -
    I found this link in one of the other threads. It is a very good website that will give you a full visual as well as details regarding wheel and tire size in comparison to the stock fitment. Wheel & Tire Calculator (NOTE - Site works better using IE or IE tab for Firefox).

    Understanding Tire Sizes:
    Tire sizes are stated in usually one of two ways. The first (and most common for street use) is the metric way - 255/45R18. First number denotes the Section Width (in mm), which is the widest part of the tire, not the tread width. Second number is the Aspect Ratio. This is the percentage of the section width that tells you how tall the sidewall is. Third number is the Rim Diameter (in inches).

    To come up with the OD of a tire from the metric size, multiply the Section Width by the Aspect Ratio. This gives you the sidewall height in mm. Divide by 25.4mm/inch to get teh sidewall height in inches. Multiply by 2, and then add to the rim size. This will give you a close approximation to the OD of the tire, as it doesn't take into account tread wear.

    The second common way of stating tire size is by Height, width, then rim size, like 35x12.50R15. All are in inches. These are also approximations, some tires will be taller than others even though numerically, they are identical. There is also a variation on this style of measure. Some times tires will have the Width, thne Height and Rim size, as in 21/49-16.5. Also note that if there is no R infront of the rim size, it is not a Radial tire.

    There are other ways of denoting tire sizes, like 12-16.5 or 11R24.5, which only give you width and rim size, but those are rarely used in street applications on light trucks and cars.

    Diameter: The diameter of the the rim/tire between seats/beads. Do not try to mount a tire on a different size rim.
    Width: The distance between the bead seats on the rim. The lip of the rim is not counted in this calculation, so an 8" wide rim will be wider if you're measuring from outside of the lip.
    Backspacing: The distance from the wheel mounting surface to the back plane of the wheel. Commonly in inches (SAE)
    Offset: The distance from the wheel mounting surface to wheel centerline. Commonly in millimetres (Metric)
    1"=25.4mm

    Backspacing and offset are related to one another. You must know 2 variables in order to find the third, the 3 variables being Width, Offset and Backspacing.


    Backspacing - (Width/2) = Offset
    Example: We have an 8" wide rim with 5" of backspacing. Divide 8" by 2 gives us 4". Using the formula, 5" minus 4" equals 1" of positive offset, or 25.4mm of offset.

    Offset + (Width/2) = Backspacing
    Example: We have a 10" rim with -48mm of offset. Divide 10" by 2 gives us 5" Divide -48mm by 25.4mm/inch gives us -1.89" of offset. Using the formula, -1.89" offset plus 5" equals 3.11" of backspacing.

    2(Backspacing - Offset) = Width
    Example: We have a rim that has a backspacing of 4", and an offset of 12mm. 12mm divided by 25.4mm/inch gives us roughly 0.5". 4" minus 0.5" equals 3.5". Multiply that by 2 equals 7" The rim is 7" wide.


    Backspacing
    Backspacing is the distance from the wheel’s rear mounting surface (hub) to the edge of the rim. The best way to measure backspacing is to place a straight edge across the rims and measure to the mounting surface.
    Offset
    [​IMG]


    The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types.
    • Zero Offset - The hub mounting surface is even with the centerline of the wheel.
    • Negative Offset - The hub mounting surface is toward the front or wheel side of the wheel.
    • Positive Offset - The hub mounting surface is toward the outside of the rim. These are generally found on front wheel drive cars and newer rear drive cars.
    If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won’t work correctly.
    Example Formula
    offset = backspacing - (overall wheel width/2)
    wheel = 15×6.5
    backspacing = 4?
    overall width = 7.5?
    4? - (7.5? / 2) = 0.25? positive offset


    [​IMG]



    Aspect Ratio
    A term that describes a tire’s height-to-width proportion. If a tires sidewall height were 65% of its cross section width, its aspect ratio would be 65. In the tire size expressed as 205/65-15, the number 65 is the aspect ratio. (Section Height/ Section Width) x 100
    Balance
    The state in which a tire and wheel assembly spins with all its weight distributed equally. A wheel balancer is used to place weights compensating for static and dynamic imbalances that exist in all assemblies. Not balancing an assembly will result in extreme vibration.
    Bead
    A round hoop of steel wires, wrapped or reinforced by steel cords, placed at the very inside of the tire’s diameter.
    Deflection
    Free radius minus loaded radius.
    DOT Number
    The tires identification number, which is used if a tire is recalled. The last three numbers indicate the week and the last digit of the year the tire was manufactured.
    Footprint
    The portion of the tread that contacts the road during operation.
    Free Radius
    Radius of the tire and wheel assembly that is not deflected under load.
    Loaded Radius
    Distance from the wheel axis of rotation to the supporting surface at a given inflation pressure.
    Loaded Section Height
    Loaded radius minus half of the nominal rim diameter. Distance from the rim seat to the outer tread surface of a loaded tire.
    Load and Speed Index
    The maximum weight the tire can carry at its maximum speed rating.
    Maximum Load and Inflation
    Maximum inflation is not the recommended tire inflation pressure.
    Nominal Rim Diameter
    Diameter of the rim seat supporting the tire bead. Examples: 13, 15, and 16.5 inches.
    Overall Diameter
    Diameter of the inflated tire without any load.
    Overall Width
    Maximum width in cross section of unloaded tire including protruding side ribs and decorations.
    Plus Sizing

    [​IMG]


    Plus sizing your wheel & tire combination means that you are increasing the diameter of your wheel and lowering your tire profile. In other words you increase the wheel size. section width and lower the aspect ratio.
    Rim Width
    Linear distance between the rim flanges in contact with the tire.
    Section Height
    Distance from the rim seat to the outer tread surface of the unloaded tire.
    Section Width
    Linear distance between the outside sidewalls of an inflated tire without any load (exclusive of protruding side ribs and decorations).
    Treadwear Indicator
    Narrow bands, sometimes called “wear bars”, that appear across the tread when 2/32? of tread remains.
    Treadwear, Traction and Temperature
    Treadwear rates how long a tire is expected to last. Ratings start at 100 and go up to 500, with 500 lasting the longest. Tire wear is also determined by tire maintenance, and how and where you drive. “Traction” followed by a letter grade of A to C, with C being the lowest, rates the tire’s ability to stop on a wet road surface. “Temperature” grades the tire’s ability to withstand heat, from A to C, with C being the lowest.
    Tread Width
    The portion of the tread design that comes in contact with the road.
     
    #1 XrunnIT, Aug 5, 2007
    Last edited: Nov 11, 2008
  2. shook

    shook Active Member

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    Good info :top:
     
  3. Stevenredx

    Stevenredx New Member

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    Great info.. thank you for sharing that with us :top:
     
  4. XrunnIT

    XrunnIT Active Member

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    Maybe we could get this stickied in the FAQ section or something? I'll work on finding/writing some other FYI type posts as I always found them very useful/helpful.
     
  5. project-c2

    project-c2 New Member

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    18x 9 with zero offset would look PIMP, too bad it won't fit. LOL
     
  6. futurexman

    futurexman New Member

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    Do they make the stock rims any wider and chrome. It would be nice to fatten up the rear.
     
  7. XNU

    XNU New Member

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    Good too know. Thanks
     
  8. i_ski

    i_ski New Member

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    Great work! finally all of that information in one place.

    You can get the stockers widened and then chromed but it would be custom and probably expensive.
     
    #8 i_ski, Aug 22, 2008
    Last edited: Aug 22, 2008
  9. willrideanything

    willrideanything New Member

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    Thanks for the info.
     
  10. XRUNNAH808

    XRUNNAH808 Member

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    Very useful, will help me in the future!
     
  11. stan23

    stan23 New Member

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    I know this is an old thread, but many thanks to the OP. This is very helpful!
     

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