Tires and wheels

According to my handy 1976 service manual, U.S.-bound F10s wore 155-80-13 tires on 4-1/2J wheels with a 40 mm offset. Hatchbacks came standard with 165-70-13s, but if I read the manual right you could evidently de-option to use the 155s. Why anybody would do that is a mystery to me. Of course, Arnelle arrived on 155s that were rock hard after sitting for some number of years of Arizona sun and squealed unmercifully around anything but the slowest corners.

Now, these two stock sizes are significantly different in diameter. According to the Miata.net tire calculator, the 165 is about 0.7 inches smaller, which yields a nearly 3% speedometer error. Presumably, Nissan figured they were okay as long as you weren't going any faster than the speedo says, so I'm guessing the calibration is for 155-80-13 tires. (Could they have had two different speedo gears? Yes, but I seriously doubt it. And if they'd calibrated for 165s the speed would read lower than actual with 155s, which is not the direction you want errors to go.)

The bolt pattern is the now uncommon 4 x 114.3 mm, or 4 x 4-1/2 inches. At one point, I onsidered a hub conversion to give myself more options, but decided instead to see what I could find. Minilites? Something interesting from the 70s?

While browsing eBay a few weeks ago, I found what I was looking for: A set of 15 x 6-1/2J wheels with dual 4 x 100 and 4 x 114.3 bolt patterns. These wheels, in fact:

They have a resolutely un-metric 38 mm offset, but that's close enough to 40 as to not matter. A set of four from Discount Tire Direct was under $300 with free shipping, so I jumped on them.

A quick test fit of a bare wheel on the rear worked fine, so I went over to the local America's Tire and bought a Kumho Ecsta AST in a 205-50-15 size. That's about a half inch larger in diameter, but it looks like there's room. I only bought the one though, to lessen my humiliation if I have to turn around and sell all this stuff because it won't fit ... nothing to do but get out the floor jack and see.

1/7/9 UPDATE: They fit on all four corners, completely filling the wheel wells, but with no interference with anything, at least on the Sportwagon. Pictures to follow when I get a chance, but if I had to do it over again I might look for 15x6 wheels instead. The speedo has no noticeable amount of error, but I think the extra unsprung weight is finishing off the 30-year-old CV joints ... I can hear them clicking on high-G turns. Maybe it was just their time.