Wheels go round and round

Not much time for work today.  There were a couple of critical things I needed to get done.  I want to get some new wheels ordered and I needed to double check the wheel specs.

There is really a lot to wheels, more than I wanted to know, bore size, offset, backspace, width, load rating, it goes on and on.  And it’s critical to get it right.

The first thing I know is the tire size is a ST225/75R15.  The ST is Special Trailer, the 225 in milimeters tells you how wide the tread is that will contact the road.  The 75 is a ratio of the 225 number and tells you how high the tire is from the rim to the tread.  So in my case the height is 75% of 225mm or 168.75mm high.  The R designates a Radial tire, and the 15 is the size of the wheel in inches.

I went surfing the net to find a place to help explain the wheel specs. I came across this site: Wheel Technical Information.

After pulling the wheel off the trailer, I cut a stick just long enough to fit into the wheel to measure the Backspace.  I got 3.5″. 


For the bolt pattern I simply needed to count the number of bolt holes.  There are six on my wheel.  When the number of holes are even you mesure across two of them center to center to get the spec.  I measured 5.5″.  So I have a 6 on 5.5 bolt pattern.


Next is bore size.  I’m not sure about this one.  I know it’s the center hole on the wheel.  Mine measured 3-5/8″.  I assume this will depend on your axle.  If you know, send me a note and fill me in :-).


So, now I know I need a 15″ wheel, with 6 on 5.5 bolt holes, 3.5″ backspace, and a 2600lb load rating since thats what Airstream uses.  Hopefully I have enough info to get the correct wheels coming.

The only other thing I had time for was lining the TwinTemp Jr. box with ceramic insulation.  This will help keep the heat transfer down when the Jr. is running with the cover on.


I have not put the cover back on yet there are a few items I want to tiddy first regarding the Jr.  Hopefully I can finish it up soon.

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