Correct tires - Pontiac GTO Forum
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post #1 of 16 (permalink) Old 10-01-2012, 03:43 PM Thread Starter
 
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Correct tires

I want to change out the tires on my car from modern tire tothe original tires. What was the standard tire that would have come on the 1970 GTO Judge? Size was G70x14, but was it the Firestone Wide Oval or Goodyear polyglas?
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post #2 of 16 (permalink) Old 10-01-2012, 06:29 PM
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Pretty sure it was the Goodyear Polyglas GT. Be prepared for a significant drop in ride and handling quality. I ran nothing but bias ply's on my GTO's until the late 1980's, and was amazed with the improvement when I installed radials. I had a '66 Coronet in the '90's that I ran both on, bias plys on factory steel rims, and radials on slot mags. The car felt like it was worn out with the bias ply's installed, and then I'd swap wheels and it felt and handled like a new car. Nothing looks as cool as bias ply's on an old car, though!!
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post #3 of 16 (permalink) Old 10-01-2012, 07:35 PM
 
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Standard tire for all 1970 Judge models was G70x14 blackwall bias-ply. Raised white letter G70x14 Firestone wide oval tires were optional. G78x14 blackwall, white lettered were also options for all 1970 GTO's.


67 Post Coupe,
69 RA III Judge
06 BOM, M6, 18's
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post #4 of 16 (permalink) Old 10-01-2012, 08:11 PM Thread Starter
 
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Looking at my build sheet box 106 it's says G70x14 2x4 WL FUYR. Below in the options codes it says PK5 G70x14 WL FG. Window sticker says PK5 G70x14 White LTR Fiberglass. So am I correct that it should be the Firetone Wide Oval tire?

Not worried about the handling of the car, just want it back to original. I have a LS6 Chevelle that is restored like the day it rolled off the line 42 years ago.

Thanks for the help.
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post #5 of 16 (permalink) Old 10-01-2012, 09:37 PM
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advag,

FWIW, a bias-ply tire will distort while traveling down the highway placing the contact patch in a positive caster situation, if your car's caster is set for a radial tire you will have 3 or 4 degrees more positive caster than needed for bias ply tire.

If you notice poor handling have your alignment set to factory specs, radial tires are usually set with more positive caster.

Randy


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post #6 of 16 (permalink) Old 10-02-2012, 07:20 AM
 
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Originally Posted by advag View Post
Looking at my build sheet box 106 it's says G70x14 2x4 WL FUYR. Below in the options codes it says PK5 G70x14 WL FG. Window sticker says PK5 G70x14 White LTR Fiberglass. So am I correct that it should be the Firetone Wide Oval tire?

Not worried about the handling of the car, just want it back to original. I have a LS6 Chevelle that is restored like the day it rolled off the line 42 years ago.

Thanks for the help.
Yes that is correct.


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06 BOM, M6, 18's
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post #7 of 16 (permalink) Old 10-02-2012, 09:08 AM
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05, I respectfully disagree. In my ecxperience, tires don't distort enough to change hard settings of the suspension components. Different tires DO have different alignment settings they like to run at due to their construction. Most Pontiacs can't be set at a lot of positive caster with stock parts because the A arm bolts aren't long enough for all the shims you'd have to stick behind the front bolt. (and the engine is too wide...BTDT with F body spindles!) These cars were designed with negative caster so they would steer easier at lower speeds and park easier with manual steering. Set to specifications, Bias ply tires are no comparison to radials in ride or handling, and especially tracking. Since advag is going the show car route, not an issue.
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post #8 of 16 (permalink) Old 10-02-2012, 10:05 AM Thread Starter
 
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I posted this question on the yenko site and they said with build date of my car being 2-24 that it could have either Goodyear or Firestone. Now I'm confused.
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post #9 of 16 (permalink) Old 10-02-2012, 11:11 AM
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Originally Posted by geeteeohguy View Post
05, I respectfully disagree. In my ecxperience, tires don't distort enough to change hard settings of the suspension components. Different tires DO have different alignment settings they like to run at due to their construction. Most Pontiacs can't be set at a lot of positive caster with stock parts because the A arm bolts aren't long enough for all the shims you'd have to stick behind the front bolt. (and the engine is too wide...BTDT with F body spindles!) These cars were designed with negative caster so they would steer easier at lower speeds and park easier with manual steering. Set to specifications, Bias ply tires are no comparison to radials in ride or handling, and especially tracking. Since advag is going the show car route, not an issue.
Here is a thread that goes into greater detail regarding my above post;

GMCnet: GMCnet => [GMCnet] Summary of the Align it Right! presentation made at GMCWS Casa de Fruita rally

Randy


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post #10 of 16 (permalink) Old 10-02-2012, 12:24 PM
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Thanks for posting the article! The writer is in error on his theories of tires egg-shaping and changing caster by 3+ degrees. He writes a very well written article, but it's nonsense. I don't know it all, but I did work for a tire manufacturer for 14 years and have been aligning cars for almost 30, and I have never heard of such a thing and neither have any of my technician colleagues, whom I have been asking in case I missed something. Interesting to read, but simply not true. I could be wrong, and have been before. But I really don't think so!!!
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