Pontiac GTO Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
19 Posts
Discussion Starter #1
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?
 

·
64-67 Expert
Joined
·
8,569 Posts
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!!
 

·
Registered
Joined
·
1,116 Posts
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.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #4
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.
 

·
Super Moderator
Joined
·
5,146 Posts
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.
 

·
Registered
Joined
·
1,116 Posts
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.
 

·
64-67 Expert
Joined
·
8,569 Posts
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.
 

·
Registered
Joined
·
19 Posts
Discussion Starter #8
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. :confused
 

·
Super Moderator
Joined
·
5,146 Posts
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
 

·
64-67 Expert
Joined
·
8,569 Posts
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!!!
 

·
64-67 Expert
Joined
·
8,569 Posts
I have to say, I hold MT in very high esteem. I also have no doubt the tires change shape as speed increases. I just don't buy the 3 or 4 degree changes in the other article. There has to be a middle ground here, somewhere. Somebody must have done an actual scientific study with real data. That would be interesting, IMO. Good stuff!
 

·
64-67 Expert
Joined
·
8,569 Posts
Great basic article that sums it up. Back in the day, the caster/camber/toe settings on our cars was set to facilitate easy parking and low speed manuevering with manual steering and low-tech tires. Advances in tire and suspension technology can be applied to our cars to increase their performance and handling. If you want to see crazy caster angles, close to 10 degrees, check out a Mercedes turning next time you see one in a parking lot. You can see the caster, literally. I am still not convinced that my caster will change from say, 0 degrees to 4 degrees simply with a tire change. Even at 100mph...
 

·
Registered
Joined
·
3 Posts
Goodyear tires

My 69 Judge came with G70X14 Goodyear Polyglass GT tires.
I have seen many cars with Firestone Wide Oval so they are proably
correct as well
 

·
Registered
Joined
·
19 Posts
Discussion Starter #16
My 69 Judge came with G70X14 Goodyear Polyglass GT tires.
I have seen many cars with Firestone Wide Oval so they are proably
correct as well
Thanks for the help. I ordered the Firestones Tuesday and arrived today.
 
1 - 16 of 16 Posts
Top