Tires: Minimum dual tire kiss spacing, dual applications, tire and rim association

Question
Hi Barry===I have a 2002 RV which came with LT225/75R16/D, OE tires on rims with a dual spacing of 10.0 inches. The original OE tires have been discontinued, and the replacement tires being placed in the dual applications with 10.0 inch dual spacing have a stated section width of 8.8  ( on a designated 6.0 rim ) and require a minimum dual spacing of 10.2 to 10.4 inches depending upon the tire. In most cases the mounted section width is actually 9.0 inches  ( still within the 4 percent tolerance ). The only tire that is reported to be a replacement for the OE tires requires a minimum dual spacing of 10.4 inches according the the tire manufacturers specification. This results in a mounted unloaded tire space of 1 inch and a loaded radius space of 5/16 inch. The tire dealers don't seem to be paying attention to the minimum dual spacing for replacement tires. They are only going by the Placard size and the load requirements.... My question is what is the minimum space at the loaded radius that can be considered safe ( kissing, heat dissipation, rock collection, etc...Thank you Johnny

Answer
Johnny,

I am having a great deal of difficulty understanding your question.  It's not that I don't know what it is you want.  It's that the set up seems to be wrong - and if that's wrong, then my response will also be wrong.  So let's clear that up.

1)  I don't think a vehicle manufacturer would choose to use a set of rims with a dual spacing less than the minimum specified by the Tire and Rim Association - and for an LT225/75R16, that is 10.2".  

2)  Further, tire makers would also be aware of this limitation and adjust for it.  I am puzzled by your statement that there was only one tire reported to be a replacement - and it lists a width of 9" and a dual spacing of 10.4"  I went to Tire Rack to see if I could sort this out.

While Tire Rack doesn't list dual spacing, it does list section width - and for practical purposes, width controls dual spacing.    I found a total of 19 tires that I consider to be suitable replacements - and none of them had a listed width of 9.0"  One of them had a width listed as 10" (an obvious error!) and 2 of them listed their widths as 8.9".  Given that they know about the minimum dual spacing, I assume they checked to see if there was enough clearance when under load.

But most importantly, I didn't see any tires with a 9.0" width.  So what brand was that?

3)  It is little wonder that tire dealers don't pay attention to dual spacing.  The vehicle manufacturer is supposed to do this correctly - and to my knowledge they all do.  So I think the next step is to check the dual spacing on your RV:

Take some masking tape and put it across the face of both treads.  Unless you have room in the fenderwells, you'll have to do this near to the ground.  

Next, mark the centerline of each tread.  Measure the distance between the 2 marks - and that is the dual spacing!  I am going to bet it is more like 10.4"

Please post back with the results.  If it turns out the dual spacing is only 10.0", then we could explore changing the tire size to LT215/85R16, but that requires more room vertically - and more measurements!

And one last thought:  I hope you realize that you can use Load Range E tires in place of the Load Range D tires that came originally.  Load Range E tires behave exactly like Load Range D's except that you can use more inflation pressure to get more load carrying capacity.