Polybias Tires ? Alignment Specs


#1

I’m looking to align my 1971 Mach 1. According to the original specs which are for Polybias Tires and not today’s radials, can anyone shed some light on this topic. Seems like a vast degree of difference. After researching I have Chamber at 0, Caster at 2 degrees Positive and 1/8" Toe In. Does anyone have any suggestions?


#2

Are you putting on radials? Or repo bias-ply tires. “Polybias” is just a marketing thing. Polyglas plus bias ply = Polybias

For radials, I’d only change the settings you posted by changing the camber from 0 to 0.10 to 0.25 degrees negative. A little more caster would be good but you probably can’t get a bunch more. 3 degrees positive would help the steering wheel return but only if you have power steering. If it is manual, leave it at 2 degrees.


#3

Radials are going on…with power steering, thanks for the help


#4

Have you posted this on classic Mustang forums? Not that I doubt Mustangman’s advice, that is…


#5

It may not mean anything but I took a look at an old manual (circa 1972) I have and it shows the preferred setting on caster at 0, preferred camber at 1 degree positive, and toe at 3/16 in +/- 1/16.

I’d stick with that but the toe in kind of bugs me a bit as that is a lot even if the plus/minus was bumped back to 1/8. You could try 1/8 or 1/16 in and keep tabs on the treadwear pattern while adjusting as necessary if need be.

I can’t attest to the accuracy of that info but there it is if you can use it.

Neat cars. A local guy has a 71 Boss 429 with 30k actual miles on it along with the manuals, window stickers, and all. It’s as new and selling it at auction is being considered at the right point in time based on the economy. My guess is 200 grand or maybe more. That lets me out… :frowning:


#6

Stick with the OEM alignment specs and monitor the wear. If you begin to see uneven wear, start with the assumption that you have worn suspension components and/or tired springs and diagnose it based on that assumption. When and only when you determine that everything is back to “like new” and you still have uneven wear should you begin to introduce adjustments to the OEM alignment specs.


#7

A few (about 800) Boss 9 Mustangs were made in 1969 and 1970 but I don’t think any were made in 1971…At least not by Ford…


#8

I’m probably mistaken on the year then. The car is in a local museum and my head was under the hood while the info spiel was going on.


#9

“it shows the preferred setting on caster at 0, preferred camber at 1 degree positive, and toe at 3/16 in +/- 1/16”

0 degrees caster?? That is a bias ply manual steering number if I ever saw one. Nothing but the pneumatic trail is returning the steering to center. Positive 1 degree also seems very high. It would wear out the outer tread on the tire and @ok4450 is right. Too much toe-in. Radials don’t need or want that much toe-in


#10

I have never heard of a Boss 9 Mustang, but the Mach 1 was made in 71. But as a general rule, radials have slightly less drag than the bias belted tires that were standard equipment on vehicles of that era. The toe would be set to 1/16th less than the spec for bias belted. Other than that all else remained the same.

Keep in mind that the radials that were on the market in that time frame are not the same as the ones we have today. Back then you were probably looking at a G70 14 which would probably be equivalent to a 215-70 14 today.


#11

ok4450 Ford did make a Boss 351 in 1971. The only difference between the Boss and my standard 1971 Mach 1 was graphics and functional ram air.


#12

Apparently the 1971 Boss 351 had quite a bit more than my standard Mach 1! Including 35 more hp! I apologize.

The 1971 Boss 351 Mustang was the last of the true muscle cars of the era. It replaced both the Boss 302 and Boss 429 from the previous two years as the performance mustang in 1971. The Boss 351 Cleveland engine stocked 330 horsepower and featured a four-bolt man block, large port cylinder heads and valves, a solid lifter camshaft, an 11.7:1 compression ratio and aluminum valve covers. Also standard on the Boss 351 was Ram Air, 3.91:1 rear axle with Traction-Lok, Competition suspension, four-speed manual transmission, power front disc brakes, front spoiler, lower body side paint treatment and Boss 351 decals in place of the Mach 1 decals.
A chrome front bumper, instead of the rubber bumper found on the Mach 1, could also be found on the Boss 351. The black or argent paint, in the shape of a rectangle, covered most of the hood which differed from the Mach 1 hood scheme.

Standard wheel were 15 x 7 with trim rings/hubcaps. Optional were the chrome Magnum 500s, also measuring 15 x 7. Either way, tires were Goodyear F60x15 RWL.

The Boss 351 had much better low-end response than the previous Boss 302 and Boss 429 models, and its equal weight distribution made for better handling as well as better braking.


#13

about that time I was a fan of the Mach 5, driven by Speed Racer…

…and kimba the white lion…