[grd777]

Originally Posted by 71GP76TA

Yes

nice ,how does it drive with the 245 on the front

[importsmasher]

Originally Posted by Held for Ransom

Stop the misinformation. "Steelies" were 15x7. What was the price on the Y99?
https://forums.maxperformanceinc.com...d.php?t=772622

I completely forgot that I had posted that! I did a search before I posted this current thread, and didn't find that either.

Importsmasher

[importsmasher]

Originally Posted by Held for Ransom

Stop the misinformation. "Steelies" were 15x7. What was the price on the Y99?
https://forums.maxperformanceinc.com...d.php?t=772622

In answer to your question, the Y99 package was $157, per the PHS.

Importsmasher

[71GP76TA]

Originally Posted by grd777

nice ,how does it drive with the 245 on the front

Drives great.

[Held for Ransom]

Originally Posted by importsmasher

In answer to your question, the Y99 package was $157, per the PHS.

Importsmasher

Original tires would have been GR70-15 w/o space saver spare.

[72projectbird]

Originally Posted by grd777

nice ,how does it drive with the 245 on the front

I have 245s in the front and 275s in the back of my 71, and everything clears and handles great.

My 77 has 225/70s on all 4 corners, and that also rides great and cleats everything.

[Formulabruce]

There was Y99 before Radials... fyi..

[Held for Ransom]

Correct. In '73, the F60-15 was the other 15" option, at a different cost.

[unruhjonny]

interesting.
This thread made me look it up - for 1973 the Y99 did NOT require Rally II or Honeycomb wheels - that is a new revelation to me!!

But back to the question at hand.

F70-14 or GR70-15 would have been the (non-radial) tires used on a Formula Firebird;
For 1970-1972 the standard and optional tires were F70-14 or F60-15.

My understanding to this point is that although the letter sizing used on bias ply tires was in essence supposed to convert across, but it less than perfect; This is my understanding of cross reference from old to new tires (taking more into account the diameter once installed and aspect ratio):
F70-14 = 225 70 14*
F60-15 = 235 60 15
GR70-15 = 225 70 15

* = Some sources cite a 215/70/14, but if you dig further, it's a bit too short.

I believe that all these sizes when mounted on 7" wide wheels, were roughly the same overall diameter.

E78-14 (blackwall) was the n/c tire for base and Esprit;
Optional on the base or Esprit was E78-14 whitewall, F78-14 (blackwall or whitewall), and F70-14 (blackwall or whitewall).

The E78-14 tire was mounted on a 6" wide wheel.
The F78-14 & F70-14 were mounted on a 7" wide wheel.

The n/c tire for the Formula was F70-14 (blackwall);
Optional on the Formula was F70-14 whitewall, or GR70-15.

All of the Formula tire sizes were mounted on a 7" wide wheel.

The tire predicated the wheel - not the other way around, and this is why there is virtually no mention of wheel width.

[importsmasher]

Originally Posted by Held for Ransom

Original tires would have been GR70-15 w/o space saver spare.

Thanks! So using that information and unruhjonny's conversion, I'll be putting 225/70-15s on it. Now to find some steelies and dog dishes.....

Thanks everyone for the input! Good information, and I learned a lot!

Importsmasher

[Held for Ransom]

Here is the info on 1973 Formula's and tires.

[Formulabruce]

Originally Posted by unruhjonny

But back to the question at hand.

"F70-14 or GR70-15 would have been the (non-radial) tires used on a Formula Firebird;" << GR70 Is a Radial)
For 1970-1972 the standard and optional tires were F70-14 or F60-15.

My understanding to this point is that although the letter sizing used on bias ply tires was in essence supposed to convert across, but it less than perfect; This is my understanding of cross reference from old to new tires (taking more into account the diameter once installed and aspect ratio):
F70-14 = 225 70 14*
F60-15 = 235 60 15
GR70-15 = 225 70 15 << actually its 225/ 70R -15 ( yup " R")

My mention of 6 inch wide wheels comes from a 1st gen background as Chevy ran them on 15's and many cars had 6 inch wide spares as I recall.
Wheel / hub cap / wheel cover Choices brought about some of the confusion, But Customers started this asking for wheels/ tires that were NOT available on the model they want. There are a bunch of 15" tire cars in 71, 2 and 3 that did Not have Y99. I owned a 71Esprit 400 with 15 Honeycomb wheels and white line tires..
Anything to sell a car..

[importsmasher]

Thought I'd follow up on this thread. I found a set of dog dishes on ebay, and bought a new set of 15x7 steel wheels from Summit. Got them painted body color (Admiralty Blue) and mounted a set of 225/70-15s on them. I know some people don't care for the dog dish look, but I love it. And my son is happy cause he got my old Honeycombs for his 69 Firebird.

Thanks for all the input!

Importsmasher

[71GP76TA]

My Formula originally had GR-70x15 radial tire option on steel wheels and moon caps.. I am currently running 245/60R15's on 15x7 Rally II's.

[unruhjonny]

Although the sizing doesn't convert across, I like the following:

Bias Ply "F" tread width = 235(mm) radial tread width

Unfortunately to get the proper portions of contact width and diameter you have move things around so that they are not generally accepted tire conversion sizes.

Bias ply tires (at least to me) have a better look because of a flatter side wall and wider contact width;
while radial tires have a more rounded sidewall and with a smaller contact width.

On 7" wide Rally II wheels, I like a 235/60R14 in place of an F70-14, and a 245/60R15 in place of either a F60-15 or GR70-15.

245/60R14 are too wide for a 14x7 Rally II, and 255/60R15 are too wide for a 15x7 Rally II - both wear from the center out... I have learned this from personal experience.
But they both looked great!