G78-15 equivalent

[Mike80D]

Sorry to beat a dead horse, but I’m wanting to find a tire size as close as possible to the G78-15 that came on the truck originally. I thought I had found the pot of gold at the end of the rainbow when I saw a truck at the Southeast truck nats that was being restored. It was sporting a set of bias ply G78-15 white walls from Royalton. Well, they were the last set made as when I called the company they told me there wasn’t enough interest to keep up production. Even though they had the perfect look, I like to get out on the open road with my truck so I will be sticking with a radial. I’ve seen a truck with 225/75/15s that looked good, but I’m getting conflicting reports that a 215/75/15 is also an equivalent. I haven’t seen a truck in person with that size however. I currently have a set of Firestone LR78-15 bias style tires from Coker on my original 15x6 wheels. I am not satisfied with the ride, and wanting to replace them. Attached is a pic of the Royalton tires, and the truck with the 225s.

[Stocker]

Found on the web:

The Metric equivalent of the G78-15 load range C trailer tire is a 205/75-15 tire which is designed to fit up to a 6-1/2 inch wide rim.

Tire Size Overall Diameter Section Width
G78-15 28.0" 8.4"


http://www.vintagecarconnection.com/...sion_chart.htm

[SCOTI]

A 205/75-15 is only 27" tall mathematically.

Originally Posted by Mike80D

Sorry to beat a dead horse, but I’m wanting to find a tire size as close as possible to the G78-15 that came on the truck originally. I thought I had found the pot of gold at the end of the rainbow when I saw a truck at the Southeast truck nats that was being restored. It was sporting a set of bias ply G78-15 white walls from Royalton. Well, they were the last set made as when I called the company they told me there wasn’t enough interest to keep up production. Even though they had the perfect look, I like to get out on the open road with my truck so I will be sticking with a radial. I’ve seen a truck with 225/75/15s that looked good, but I’m getting conflicting reports that a 215/75/15 is also an equivalent. I haven’t seen a truck in person with that size however. I currently have a set of Firestone LR78-15 bias style tires from Coker on my original 15x6 wheels. I am not satisfied with the ride, and wanting to replace them. Attached is a pic of the Royalton tires, and the truck with the 225s.

The two sizes are so close it would be hard to tell them apart. They'll both fit on a 6-7" wheel. The 215 = 27.7; the 225 = 28.3".

[cericd]

I realize this is an old thread but I too am trying to find a tire that is closest to the original tire listed in my 1970 brochure for my C10 which was the G78-15B. My initial research lead me to this site for vintage tire conversion which says 215/75R15 or 225/70R15. I have also used these online tire size comparison sites, here and here which are pretty handy. I see that a popular size tire to use with stock wheels is 235/75R15 but it has a 28.9" overall diameter as opposed to the 215/75R15 which has an O.D. of 27.7". Also the 235 is almost an inch wider. The first set of radials I bought for my truck were the 215/75R15's. I arrived at that decision by measuring the overall diameter of the bias-ply tires that were still on the original rims which were included when I bought my truck from the previous owner. I then looked online for a tire with the closest dimensions. I chose Cooper Trendsetter SE tires because I had seen them used on several classic vehicles online. I also like the fact that it had a thin whitewall on one side which was similar to what was used on trucks that ran the full wheel covers from the factory back then. Unfortunately those tires are no longer produced. I really like the taller/skinnier look of bias-ply tires instead of the more rounded/flatter look of radials but am sure radials ride and drive better. I'm still on the lookout for a radial tire with the "taller tread" look of a bias-ply, preferably from an American tire manufacturer to replace my Coopers when it's time.

Here are the dimensions I got when measuring one of the G78/15 bias ply tires on my factory 6-lug wheels.

27.93" O.D. - no air
28.09" O.D. - 32 psi

7.5" cross section width
5.25" tread width

Here are some pics of my truck with 15x6 5-lug OEM square body wheels and the Cooper 215/75R15 tires since Mike said he hadn't seen that size before. Probably not the best to determine the look due to the shadows of the fender wells.

[cericd]

Here's a "new" tire by Coker, the Coker Classic Star Series | 1.30 Inch Whitewall | 215/75R15 which is listed as being, " a direct replacement for 710-15 and G78-15 bias ply tires". Still has that "rounded" shape of a radial though but it's another data point of a 215/75R15 being the modern P-Metric size equivalent of the old G78-15.

[chevmn]

Watch the load range, as originally a 1/2 ton originally came with 4 ply (load range b now). I know many put a load range c (old 6 ply) due to hauling heavier loads, but unless you plan on loading or pulling a fairly heavy trailer the tires will ride quite a bit more harsh. Even on my C20 running 16x7 wheels I run a load range b tire, since I never plan on doing any heavy hauling. A P215 should be about right on a 6 inch rim. I have a 72 C10 and put OBS wheels on which are a little wider, and run P225-75-15 whitewalls, and it fills the wheel wells a little better, and since I use P01 full wheel covers the look is the same.

Hankook whitewalls
https://simpletire.com/brands/hankoo...ctPos=3&rad=BD

[Already Gone]

Here is a conversion chart I had booked marked on the computer.

http://www.vintagecarconnection.com/...sion_chart.htm