How to determine tread depth (tire percentage)

Discussion in 'General Tech' started by jeepinmatt, May 8, 2009.

  1. jeepinmatt

    jeepinmatt Detonnified

    Mar 24, 2005
    Stanley, NC
    As with all things, this is subject to interpretation, but given the range of values I see given to worn out tires, I think it would be worthwhile to have a general basis to compare with.

    Step 1. Determine what brand, model and size of tire you have. For example, Interco makes a TSL SX in a 35x15.50 for a 15" wheel. BF Goodrich makes an All Terrain in a 315/70 for a 17" wheel.

    Step 2. Measure and record the tread depth on each tire in 32nd's of an inch. This can be done with a tape measure or ruler by noting if it is a 16th, plus half or minus half. It should be measured along the center of the tread. This is a good time to note any irregularities in the tread. If a tape measure will not fit, use any object that works, put a mark on it, and measure the distance. It is important to be accurate with your measurement. Typically, the front tires will be of similar depth and the rear tires will be of similar depth.

    Step 3. Go to the manufacturers website and locate their tire charts. They will have the tread depth for each and every model and size of tire. To help out, I've put a list of links at the bottom of the page.

    Step 4. Take the tread depth you recorded (step 1), and divide it by the manufacturers tread depth (step 3). For example, if you measured 8/32" and the manufacturers tread depth is 24/32", then divide 8 by 24 (8/24) whichs equals .3333, or 33% tread remaining.
    Since tape measures and rulers are only graduated in 16th's, heres how to convert to 32nd's. You just double the top and bottom numbers until you get the bottom number you need. 1/2"=2/4"=4/8"=8/16"=16/32".
    For example, if you measured about halfway between 5/16" and 3/8", that is 11/32". 5/16" is equal to 10/32", so a little more is 11/32". if the tread depth is 20/32, or just 20, then you would do 11 divided by 20, which give you 0.55. That means that 55% of the tread is left.

    If you have any questions or need help with the math, post up or shoot me a PM.
  2. GubNi

    GubNi 8 lug disc brakes?

    Mar 20, 2005
    Jonesborough, TN
    This needs to be a sticky at the top of tires for sale section!

    Always measure in the very center of the tire. We know there's great tread on the edges.

    Measure all 4 tires. If you haven't rotated often a front tire may have 1/2 tread and a rear might have 1/4

    A tape measure often will not fit, but use a stick. Then mark the stick and measure the stick.

    Make note of unusual wear on the edges caused by an alignment problem.

    Make note of any cuts in the tire in the tread area or especially in the sidewall.

    Always mention the size of the tire with three numbers. 33x12.50x15 means 33" tall 12.5 " wide and fits a 15" rim. Often people leave off the rim size.

Share This Page