Barry's Tire Tech

16.5″ Tires

Posted in Types of Tires on December 2, 2021

Barry provides a chart to help folks changeover from 16.5" tires to 16". He also explains what 16.5" tires are, and why they are disappearing.

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 for failure to follow the above instructions.

Here’s the full warning: RMA Warning about 16.5″ Tires

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’s bead will fail. Many people have been killed when this has happened.

The 40 psi bead seat pressure limitation is to prevent the bead from failing. 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.

* – 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!