CompSyn
Well-Known Member
This is in regard to my 69 Road Runner. I know many will recommend the tried and true 275/60 15 (rear) and some other smaller tire up front combo, which looks great, but I’ve already done that with a 68 Charger I once had. With my Road Runner, I’m leaning towards something a little different.
Here are some of my thoughts:
I’ll probably go with modern BFG radial TAs. Not opposed to polyglas repros, but a little costly for my blood.
I also want the same tire size at all corners.
According to Kelsey Tire Inc., the F70/14 Goodyear polyglas tires that came factory on my Road Runner have a diameter of 26.45” inches.
According to BFGoodrich, the P245/60R 15 Radial T/As tires have a diameter of 26.6” inches, which is nearly identical to the diameter of the factory F70/14s.
Using the vexer visual speed calculator, at 65 mph, P245/60R 15 tires spin the rpms to 3240 with 3.91 gears. With the F70/14s, it’s about the same at 3250 rpms. Incidentally, an A12 Road Runner with 4.10 gears and G70/15 tires run the same 3250 rpms at 65. Maybe I’m reading into it too much, but perhaps this is a formula favored by the Chrysler engineers? I’m already liking this idea.
A couple questions:
I believe my parts manual calls for a 40 tooth speedo gear for the F70/14s, which I think is close for the P245/60R 15 tires. But I also saw a chart where at a 26.8” inch diameter tire, I should be at a 38 tooth speedo gear. Should I stick with 40 or go with a 38?
Also, BFGoodrich says the P245/60R15s can be mounted on 7”-8.5” inch rims. So should I go 7” inch or 8” inch?
Any other Suggestions/Comments?
Thanks!
Here are some of my thoughts:
I’ll probably go with modern BFG radial TAs. Not opposed to polyglas repros, but a little costly for my blood.
I also want the same tire size at all corners.
According to Kelsey Tire Inc., the F70/14 Goodyear polyglas tires that came factory on my Road Runner have a diameter of 26.45” inches.
According to BFGoodrich, the P245/60R 15 Radial T/As tires have a diameter of 26.6” inches, which is nearly identical to the diameter of the factory F70/14s.
Using the vexer visual speed calculator, at 65 mph, P245/60R 15 tires spin the rpms to 3240 with 3.91 gears. With the F70/14s, it’s about the same at 3250 rpms. Incidentally, an A12 Road Runner with 4.10 gears and G70/15 tires run the same 3250 rpms at 65. Maybe I’m reading into it too much, but perhaps this is a formula favored by the Chrysler engineers? I’m already liking this idea.
A couple questions:
I believe my parts manual calls for a 40 tooth speedo gear for the F70/14s, which I think is close for the P245/60R 15 tires. But I also saw a chart where at a 26.8” inch diameter tire, I should be at a 38 tooth speedo gear. Should I stick with 40 or go with a 38?
Also, BFGoodrich says the P245/60R15s can be mounted on 7”-8.5” inch rims. So should I go 7” inch or 8” inch?
Any other Suggestions/Comments?
Thanks!