B arry's Tire Tech

This is a series of articles on the technical aspects of tires, their care and usage.

My primary purpose in these articles is to help people understand tires and thereby reduce the risks we all face every day.

..........and since tires is just about the only thing I know about..........

Please drop me a note if you have a topic you want to see:

Barry@BarrysTireTech.com
16.5 tires

  • DO NOT MOUNT A 16" TIRE ON A 16.5" RIM!

  • DO NOT USE MORE THAN 40 PSI WHEN SEATING A BEAD!

    Serious injury or death may result in failure to follow the above instructions.

    This is the full warning


    I've started this web page with a warning. This is such a dangerous issue that it bears repeating every opportunity.

    16.5" tires are commonly known as 15° taper tires. This is because the taper of the bead is 15°, as opposed to the normal 5°.

    While it is possible to put a 16" tire on a 16.5" rim, the bead can not be stretched to fit the bead seat diameter. However, the tire can seal against the rim, and pressure can be applied to the tire. Applying additional pressure will only cause more stresses within the tire and if enough inflation pressure is applied, the tire will burst. Many people have been killed when this has happened.

    The 40 psi beat seat pressure limitation is to prevent the tire from bursting. If you EVER encounter a situation where the bead does not seat by the time you get to 40 psi ON ANY TIRE:

    STOP!

    Examine the whole situation and find out why the bead is not seating. Look at the rim diameter, the tire size, the lube, etc. Dismount the tire off the rim if you can not find a reason and start again.



    I've developed the chart below in answer to a question about converting a truck from 16.5" to 16". I have not personally done any changeovers. I have not heard the results of such a changeover. So I can not guarantee this will work. It is a best guess based on published data.

    There are several issues I can not know about:

  • Brake Clearance
  • Availability of rims with the right offset
  • Clearance on the vehicle - both vertical and side clearance


    The worst clearance condition is usually when the steering wheel is fully turned AND the suspension is fully compressed. There is just no way the average guy can know what will work - and experience is a great teacher!

    I recommend you work through a retailer who is willing to insure that the fitment is right. I would appreciate a note if a correction to the chart below is in order.

    Special Note: It has been pointed out that it isn't obvious from the above that to convert from 16.5" tires to 16" requires the purchase of 16" rims. So let me state it clearly:

    The chart below is to assist folks who are making a switch from 16.5" tires and rims to 16" tires and rims. That requires the purchase of both tires (in the size indicated) AND the purchase of 16" rims with offsets that will work with the vehicle.

    As I said earlier, I can not know all the possibilities, and I have not done any conversions myself, so I recommend you work with a retailer who is familiar with everything that is involved.



    • Placard Tire Size Radial or Bias New Tire Size New Rim Width Pressure compared to Placard Diameter Single Tire Side Clearance? Dually Spacing and Side Clearance Minimum Dual Spacing Needed
    8.00R16.5LT Radial LT215/85R16 6" 10 psi less 1" more vertical clearance needed 1/4" more clearance needed on each side 1/2" more clearance needed on each side and wheels need 3/8" more offset 9.88"
    LT225/75R16 6" 10 psi less 1/2" more vertical clearance needed 3/8" more clearance needed on each side 1" more clearance needed on each side and wheels need 5/8" more offset. 10.2"
    8.00-16.5LT Bias LT215/85R16 6 5 psi less 1" more vertical clearance needed 1/4" more clearance needed on each side 1/2" more clearance needed on each side and wheels need 3/8" more offset 9.88"
    LT225/75R16 6" 5 psi less 1/2" more vertical clearance needed 3/8" more clearance needed on each side 1" more clearance needed each side and wheels need 5/8" more offset 10.2"
    8.75R16.5LT Radial LT215/85R16 6" Same 1/2" more vertical clearance needed No side clearance issues No side clearance issues and no spacing issues 9.88"
    LT225/75R16 6" Same No vertical clearance issues No side clearance issues No side clearance issues and no spacing issues 10.2"
    8.75-16.5LT Bias LT215/85R16 6" 5 psi more 1/2" more vertical clearance needed No side clearance issues No side clearance issues and no spacing issues 9.88"
    LT225/75R16 6" 5 psi more No vertical clearance issues No side clearance issues No side clearance issues and no spacing issues 10.2"
    9.50R16.5LT Radial LT235/85R16 6 1/2" 5 psi more* 5/8" more vertical clearance needed No side clearance issues No side clearance issues and no spacing 10.75"
    LT245/75R16 7" 5 psi more* No side clearance issues 1/8" more clearance needed on each side 1/2" more clearance needed on each side and wheels need 3/8" more offset 11.34"
    9.50-16.5LT Bias LT235/85R16 6 1/2" 10 psi more* 5/8" more vertical clearance needed No side clearance issues No side clearance issues and no spacing issues 10.75"
    LT245/75R16 7" 10 psi more* No vertical clearance issues 1/8" more clearance needed on each side 1/2" more clearance needed each side and wheels need 3/8" more offset 11.34"

    * - CAUTION: This additional pressure may exceed the maximum pressure of the tire. If that is the case, you can not make this change! I know of no substitute!



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