GM Truck Club
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Results 1 to 7 of 7
  1. #1

    Join Date
    Aug 2008
    East of Branson, Missouri
    Blog Entries

    Default Is my math correct? This tire size MINUS an inch...?

    I am trying to get from one tire size to get an inch thinner tire. Please tell me if I have the math correct:

    305 70 16 is what I have on. I want to get an thinner tire because of some slight fender rub. Please tell me if I have this correct:

    305 70 16 = 33 x 12.01 x 16

    12.01 - 1 = 11.01

    33 x 11.1 x 16 = 285 75 16 (actually 280 77 16)

    So putting a 285 75 16 tire on my 10 inch rims should decrease the width of the tires by 1 inch, correct?


    Bonus question: I should be able to go one inch thinner still with a 16 x 10 rim, right? Will that give me too thin a look?

    "The Sarge"
    1999 Chevy Suburban LT- K2500
    7.4 454 Vortec, 4WD
    305/70/16 on Eagle Alloy

  2. #2


    Yes, this is as close to one inch as you will get. The only numbers you need to look at for width are the first series - 305 and 285. These are in millimeters, and each inch is 25.4 millimeters. A 20mm decrease is a bit over 3/4 of an inch. going down to a 275 would be slightly over an inch. Long story short. Your calculation was one of the 2 closest sizes. You should be able to stick with the 10 inch rim, without looking too narrow. hope this helps
    Last edited by pmf608; 04-07-2009 at 07:15 PM.

    2008 FORD F350. My new all-around truck.
    2001 Silverado Reg. Cab Not-So-Base -- SOLD
    2003 Avalanche Z71. No Cladding. Check out my Mod thread. - Crashed. Will be rebuilt soon.
    1974 Triumph Spitfire 1500 - Work in Progress
    2003 Sierra 3500 Duramax. The Newer, Better Work Truck -- FOR SALE

  3. #3


    Go back to school
    1998 1500 Silverado Z71
    2006 YFZ450

  4. #4
    Master Mechanic CarpenterGuy's Avatar
    Join Date
    Jul 2008
    Leeds, Alabama


    a kid at my school has 285/75/16's. his are thinner than my old trucks 33x12.5's. i'm sure it'll work for you.
    2006 Silverado Z71 - 97,000 - totaled, RIP
    2006 Silverado Z71 - 122,000 (K&N 77 Series CAI, PowerAid TBS, Magnaflow dual rear exit, 33x12.50 Mickey Thompson MTZ, Tuff Country Torsion Keys, Tuff Country Add-A-Leafs)
    1966 C10 swb stepside (Gen I 350, Turbo 400 trans, dual cyl power brakes, front discs)
    I'll keep my money, guns, and freedom. You keep the Change.

  5. #5


    it will work fine. the 285 tires are usually more like 11.5 inches wide and on the 10" wide rim they will look good. If you want to see what a 285 looks liek ona 16x8 rim look at my pics, that is the setup I ran
    95 GMC Sierra 2500
    3" Body Lift, 33" Goodyear MTR's
    5.7L 350 TBI Edelbrock SDT Exhaust, Flowtech Headers, K&N Intake
    Sold :(
    1999 Jeep Cherokee, 3" Rustys lift, 33" BFG MT's, locked, armored: Rolled :(
    2000 Jeep Grand Cherokee Limited. K&N Intake, Custom Kolak Exhaust

    Contact this GMTC Moderator for any problems or questions you may have :great:

    Join the GMTC Facebook Group!!! Join Here

  6. #6


    285's should be fine Throw the 305's on craigslist, I bet they'll sell pretty quickly.
    1999 GMC Sierra 2500 350 vortec
    1967 Jeep M725 ambulance 230 tornado
    1990 Cherokee Limited- 3 inch lift on 33's
    ...and every one of em has issues

    If you have any questions or problems don't hesitate to send me or any other GMTC moderators a PM

  7. #7

    Join Date
    Aug 2008
    East of Branson, Missouri
    Blog Entries


    Thanks for all the input. That's what I'll do then.

    Mindi- unfortunately they didn't teach tire size mathematics in my school! lol

Similar Threads

  1. Replies: 7
    Last: 09-20-2011, 03:10 PM
  2. gear size for 35 inch tires
    By Bowen26 in forum Wheels & Tires
    Replies: 8
    Last: 02-04-2010, 08:06 AM
  3. 34 inch tire with a leveling kit?
    By jbfireemt in forum Wheels & Tires
    Replies: 6
    Last: 09-20-2009, 12:54 PM
  4. widest tire on an 8,5 inch rim
    By DutchTBI in forum Chevy Tahoe Forum (GMC Yukon, Cadillac Escalade)
    Replies: 2
    Last: 04-09-2007, 11:31 AM
  5. 1999 k1500 ls tire no lift max tire size.....
    By ultramegabob in forum Chevy Suburban Forum (GMC Yukon XL)
    Replies: 2
    Last: 02-17-2007, 11:35 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts