OK, I had the chance to measure the width of the tires on my 48 Plymouth coupe on the Dakota frame today.
The frame is a 1990, the last year for the factory 5 lug wheels. The chassis is unmodified except the wheelbase was shortened 7" It retains the factory 8 1/4 3:55 limited slip, the 3.9 V6 (a 91 V6 was installed to replace the tired 150K original motor), the ax 15 5 speed, and the stock springs all around. The brakes were all replaced with new replacement parts. The cab and the motor & trans were moved back 7" and the drive shaft was shortened. The original cab floor and lower firewall were also retained.
The front wheels are the original Dakota 15" x 6" steel wheels and the tires are 225 75 R 15. The tire bulge exceeds the wheel width by 1 1/4" on each side of the wheel. The wheel backspacing is 3" (the hubs are actually centered, though they don't look like it).
I used the same method as before. A straight edge was set horizontally across the widest part of the tire bulge. A level was stood up with the bubble centered in the sight glass at the edge of the straight edge to represent the outer most point on the tire. A tape measure was set against the edge of the upright level at the ground level and goes across the ground at the front edge of the tire.
On the other side, the straight edge was placed across the tire bulge, the level stood up with the bubble centered in the sight glass and the edge of the level marks the tape measure.
Outside the tire bulge to outside the tire bulge measures 67". The tires have been on the front end of the car for 20,000 miles with no abnormal wear. I see no reason the rear edge would need to be measured as well, and the rear of the fender would be an issue with standing up the level.
If we take the 1 1/4" per side bulge measurement away from the 67", we have the wheel edge at 64 1/2". The track width is generally considered to be measured from the center of the tire tread width to the center of the tread. We can assume the tire will be centered on the wheel width, so we can take 1/2 of the wheel width from each side, or 6" in this case.
67" (bulge to bulge)
- 2 1/2" (bulge on each wheel)
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64 1/2 outside of wheel to outside of wheel (tire mounting edge)
- 6" (1/2 of each wheel width added together to subtract)
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58 1/2" the track width, as normally measured. Gene
