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Tire Sizes the same?

Discussion in 'Wheels & Tires' started by MD4x4 Fireman, Oct 23, 2007.

  1. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

    Right now I have P235/75/R15 tires on my truck now, my friend has some tires that are 30x9.50r15. How close are they in size? Will it throw off my spedo alot? Please dont laugh cause I dont know anything about tire sizes.
     
  2. finalday7

    finalday7 Epic Member 5+ Years ROTM Winner 1000 Posts

    The 30x9.5x15 are about 1.12"'s bigger than your current tires resulting in about a 2.5mph diffrence in your speedo. So if your doing 60 your speedo is only reading 57.5. Hope this helps
     
  3. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

    that answer was PERFECT, the rim width is the same right?
     
  4. finalday7

    finalday7 Epic Member 5+ Years ROTM Winner 1000 Posts

    Are you getting new rims with the tires or are you just using the same? Either way they will fit.
     
  5. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

    using the same rims
     
  6. TahoeFever

    TahoeFever Epic Member 5+ Years 500 Posts

    Officer I was only doing 57.5 in a 55 zone! :lol:
     
  7. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    If you use the tire size calculator at redrock4x4 you get this:
    Result:
    235/75/15 = 28.9x9.3/15


    If you use the online calculator at onlineconversion.com
    You will see that if you speedo shows 60mph you will actually be traveling at 62.3mph
     
  8. FireRed

    FireRed Rockstar 100 Posts

    One thing most do not consider is that bigger tires require more power at all speeds, present a larger profile to the wind at speed. They cost you in lost fuel mileage and more wear and tear on suspension parts but yes they do look cool!!
     
  9. MD4x4 Fireman

    MD4x4 Fireman Epic Member 5+ Years 1000 Posts

    im just adding them so i have traction, i plan on buying a cheap set of rims from the junk yard to use for them so if i wanna go offroading or when it snows.
     
  10. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    When I dropped from 305's to 265's I noticed much better pulling power and it is much easier to turn at low speeds. Of course, you can change the gearing to improve pulling, but that is expensive with 4x4 since both diffs have to be the same ratio. When increasing tire sizes more than 3% the increased loading on the brakes is dangerous.
     

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