Tires: Tires that will fit 9.00 x 18 rims, marmon herrington, rim widths

Question
QUESTION: I am restoring a 1941 Ford RCAF airport crash tender with Marmon Herrington 6 wheel drive . The rims are split ring and the existing tires are Firestone bus/heavy truck 9.00 x 18 tires. I cannot find this size of tire. Can I use a 9 x 16 . Where can I find a 9 x 18 .I have looked for years for old military tires to fit.Any suggestions?

ANSWER: John,

First, your tire size is 9.00-18.  That means the tire is about 9" wide at its widest point, it has a 90 aspect ratio (the ".00" indicates that), it's a bias ply tire (the "-") and fits on an 18" diameter rim.  A 9.00-18 fits on a variety of rim widths, but most likely the rim width is 7.00", so the rim would properly be called a 7.00 X 18 rim.

Given the age and application, this is likely a tubetype tire.

But somewhere on the tire ought to be some info about ply rating.  It will say "X ply rating", where the "X" will be a number in the 10 to 16 range.  See if you can find that.

The info that I would like to see on the "post back" is:

1)  Ply Rating

2)  Tubetype or tubeless

3)  Any load info on the sidewall

4)  The rim width if it is stamped (might not be)

And lastly, are you sure this is the original tire size for the vehicle.  I would suspect that these might be replacement tires that happen to fit the rim.

OK, maybe one more thing:  It is important that if there are letters that appear immediately in front of or immediately behind any of the info I requested (and the tire size, which I didn't request), that you include that as well.  Sometimes these are clues as to what we may be dealing with.

---------- FOLLOW-UP ----------

QUESTION: The tires are stamped 10 ply and they are tubetype. Patented in 1936 made in Canada. A number H113349AN is stamped on the sidewall as well as H63987S Ground grip Gum Dipped. Free rolling apply to rotate (with directional arrows)this direction .

ANSWER: John,

At the moment, I am having trouble accessing some older tire load and dimension tables.  Those will help me with the load carrying characteristics and such dimenions as overall diameter and allowable rim width range.

They are currently locked in a storage room and the key to the room is with a person on vacation.  It may be as long as 2 weeks before I can get into the room.  When that happens, I'll post a followup to this post.

Please be patient.

********************************************************

Good news!  I found someone who had a key!!

I pulled out the 1950-51 Tire and Rim Association yearbook and a 9.00-18 10 ply rating had a load carrying capacity of 3225# at 65 psi.  It fit on a 7" rim and a section width of 10.1" with an option of 6.50" rim width and a minimum dual spacing of 12.2".  

But I looked the same size up in a 1960 yearbook and the load/pressure is different - 3690 @ 70 psi.

So I am in a bit of a quandry - but I think in the big scheme of things it probably doesn't matter.  Your intention is to be able to drive the vehicle, and not to put it into service.

So doing a little math, I think a 9.00-18 had an overall diameter of 27.1".  I don't think you are going to be able to match that.

BUT - I see that Bridgestone has a 255/70R18.  It's a passenger tire tire used on pickup trucks, but has a max pressure of 44 psi with a max load of 2469#.  It fits on a 7" rim, however it is 32.2" in diameter and it is tubeless, so you would need to find a tube.

I am afraid that you may need to upgrade to a 20" rim to find something that is currently available.

---------- FOLLOW-UP ----------

QUESTION: Would it be difficult to upgrade to a 20" rim . How would I find one that fits properly . ( I need  "wheels for dummies").

Answer
John,

Wheels is a little out of my league, but bolt circle diameter, and offset are important.

But you are dealing with a very unusual situation - and I would suggest you find some partners who have done this type of thing before,

The obvious place to start is an on line club for folks that restore old military trucks - or just plain old trucks.  I am sure you are not the first person who has run across this problem - and I am sure THEIR experience is much more valuable than mine.  I can help sort out some of the technical issues, but I just don't have the background for things like what parts are available, where to get them, what fits, etc.

Good Luck.