Tires: tire dimensions, rear fenders, inch rims

Question

1945 GMC   QUESTION: Hi Barry.... I am restoring a 1945 GMC but not to stock. I would like to make it my daily driver, and have really doctored the thing up from when I first got it as a mess of parts. I inherited a set of turbine rims and it took a good week to clean them, and custom paint them, but they turned out really nice. The tires were shot so I stopped by the local small town station to ask if them had some "skins" I could mount and he looked at the rims and gave me some 31x10.50R15LT tires. I just finished the rear fenders and slapped on the new rim/tires only to find that there was clearance, but not nearly enough (about a quarter of an inch!). Now, I am really struggling with tire expertise, so I need to ask someone. I know the 31 is the diameter in inches. And I suspect that this tire has very little tread left on it, so the 31 is probably closer to 30.... and it is almost touching the front of the fender. I also suspect the rims are 10" inch rims? Have I got that right? So, the question. I can move, shim, adjust the fenders to make these tires work, but the time will come soon when I will have to replace the tires, so I thought now would be a good time. The truck was built for a top speed of 45 to 50 MPH on a good day, so speed is not important, and I am not going to haul much of anything in it so weight is not a consideration. I would prefer radials, but will listen to your advice. Obviously the most important problem is the tires hitting the front of the rear fender so I need to get that 31 part down to a ???? When I did my research I came up with P235/60R15 but have no clue as if this conversion would work, but I think it said the diameter was just a hair over 26 inches... which should work... will these fit and be mountable on a ten inch rim? Did I give you enough information? Too much? Too demanding? Also.... beggars can't be choosers, but I just love the raised white lettering on the old school truck.... and would like a tire that would fit, and yet have the possibility of raised white lettering too.... Thanks Barry... look forward to your suggestions..... Dennis

ANSWER: Dennis,

I can only help you so far.

First, we need to establish for sure what width the rims are.  We need to know this so we can be sure that the tire size will fit on the rims.  It might be stamped on the rim somewhere - and it might look like 15X10JJ - with 15 being the diameter, 10 being the width and JJ being the flange type.

By know you are probably aware that Tire Rack has a lot of information on every tire that they list.  Included would be the diameter (which may vary a bit from manufacturer to manufacturer) and the rim width (which won't vary from manufacturer to manufacturer).

Also, here is a web page that has calculated values, and rim width is one of those values:

http://www.1010tires.com/TireSizeCalculator.asp

Based on this a p235/60R15 has a rim width range of 6.5" to 8.5".

Overall this is going to be a problem in that large 15" tire sizes are rapidly disappearing.  So I would start looking at some tires in the "faux performance" category (This is my own category, which means that they look like performance tires, but aren't.)

Just for fun I did a little digging and came up with both Goodyear and Goodrich have 295/50R15's with are about 26½" in diameter and fit on 8" to 11" rims.

This might be a good starting point once you've establish the rim width.  Pay particular attention to the "specs" list and that has the entire range available in that particular brand / tire line.

BTW a 31x10.50R15 requires a rim width in the range 7" to 9".

Good Luck.

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

QUESTION: Hi again Barry... Like I said, I am a little ignorant in all this and need to ask a few more questions. First, I will look to see if any dimensions are stamped on the rim, but if not, I would have to measure with a tape... Do I measure from the inside of the rim or to the outside of the rim? Does that make sense? I suspect just getting the distance "close" is good enough since the tires seem to have a particular "range" as you pointed out with the Goodyear/Goodrich tires.... I will look today and this is the first step and I thank you for your advice so far... Now to spend some time "looking" all over the 'net....
Dennis

ANSWER: Dennis,

Coker tire has a brief write up on rim width:

http://resources.coker.com/wheel-tech/wheel-installation/how-do-i-measure-my-rim

If you search the 'net, I'm sure you'll find better drawings, but the essence is that it's best to have a bare rim, but if you can't take the tire off and can't find the stamping, then be aware that the rim flange has thickness and you'll have to compensate.

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

QUESTION: Hi Barry.... First, my apologies. I heeded your advice, and spent some time taking the new turbine rims off the truck and putting back the original wheels/tires.... ugly at best....so I do want to pursue this to get something that will work on the turbine rims. Next, took your advice a second time, turned the turbine rims over and then remembered and did the Homer Simpson "doh!" thing. I remembered that there were different size rims on the front and back. The front rims are 15x7 and the rear are 15x8.5 which fits what you said about the big tire skins that were installed (31x10.50R15). So can we start again? The main thing to keep in mind is that the 31 inch tires (30 inches when you consider that little tread was left) almost made contact with the fenders and I am open to suggestions as to what you think the clearance should be for the fenders (26 inch tire?). So I need a radial tire, hopefully raised white lettering, that will fit a 15x7 and 15x8.5 rim. Further, I would respect your opinion as to two different sizes, one size (smaller?) for the front, and a larger tire for the rear.... Does that make sense? I'll hit send now, and wait for your reply which I really appreciate! Barry, I'm learning and thank you.

Answer
Dennis,

For safety's sake, you need to put as large a tire on there as you can.  Plus it will fit the opening in the fender so the truck will look proportional.

So you need to start with the tire calculator:

http://www.1010tires.com/TireSizeCalculator.asp

Then run through some scenarios about what you think will fit.  That should lead you to a couple of tire sizes that might work.

I would use the same diameter tire (and if you can manage it, the same load carrying capacity) - and that should mean a narrow tire on the front with a wide one on the rear.

Then try Tire Rack for sizing within a line of tires to verify that the dimensions.