CHEVROLET TRUCK TIRE SIZES

[STEVE POLLARD]

The tires on my 1969 Chevrolet 3/4 ton Custom Camper are starting to show signs of dry rot. The current tire size on the truck is LT 235 / 85R 16. I want to replace them with the correct factory specification tires, so I purchase a original 1969 Chevrolet Truck catalog with the specifications for 1969 model year. They have the following tire sizes listed for the 3/4 ton series:  8.75 - 16.5 , 9.50 - 16.5 , 10.00 - 16.5.  I'm guessing that the tires were bias ply back then, but I'm leaning towards  keeping radials on the truck.  I would appreciate any help in determining how to convert the original sizes over to today's truck tire sizes.

 

Thanks

 

 

[Bloo]

I remember seeing 16.5" tires on trucks years ago. 16" does not interchange. If the manual says 16.5", someone probably changed the rims to get to a size they could easily buy tires for. That was done quite a bit.

 

The first number in the tire size is the section width, or the width at the widest point on the tire when mounted on whatever width of rim the tire manufacturer chose to measure them on. This is also true on metric tires, but the measurement is in mm. Figuring the section width out is the easy part. Just multiply by 25.4 .

 

8.75"=222.25mm,

9.5"=241.3mm,

10"=254mm.

 

Your current tires, at 235mm, are right in the ballpark for section width.

 

Perhaps more important is the overall height. I paid little attention to pickup tires back then, so I am going to have to guess. On a passenger car tire from the same period as your truck, it is generally assumed that the aspect ratio is about 80 if it is not specified. Aspect ratio is the percentage you multiply the section width by to get sidewall height. Very few tires measure exactly what they "should". This will get you close. I am gonna go with 80.

 

8.75" * 80%(aspect ratio) = 7" * 2(sidewalls) = 14" + 16.5"(rim height) = 30.5" tall tire

9.5" * 80%(aspect ratio) = 7.6" * 2(sidewalls) = 15.2"+ 16.5'(rim height) = 31.7" tall tire

10" * 80%(aspect ratio) = 8" * 2(sidewalls) = 16' + 16.5"(rim height) = 32.5" tall tire

 

235mm / 25.4 (convert to inch) = 9.25" * 85%(aspect ratio) = 7.86" * 2(sidewalls) = 15.72" -+ 16"(rim height) = 31.72" tall tire

 

You are already close, if not right on. If the height is wrong, that will show up on the speedometer. If the truck is unmodified, and you want to take a guess at which of the three sizes it had, drive 10 miles (or 20 or 30) on a road that has mile markers, and find out exactly how much your odometer is off. Apply the percentage of error to the tire height. There is only about 3% to 4% difference in height between the sizes above. It should already be real close unless I guessed wrong on the aspect ratio of the original tires.

 

 

 

 

 

Edited April 20, 2018 by Bloo (see edit history)

[J.H.Boland]

That's a great looking truck ! When I bought my "72 Chevy C20 ,it had 9.50 x 16.5 tires on it. The nylon "early morning thump" never went away. One day when towing my car trailer on the freeway, one of the tires lost a big chunk of tread. When I arrived at my destination, I found a tire store that had a set of 8.75R16.5 radials and had them installed.The difference in handling and ride was amazing- lumber wagon to country Cadillac !.

That being said, trying to find 8.75R16.5 radials now may be difficult, and you should likely stay with 16". If you want to go back to original 16.5,I have a set of rims cheap !

 

Jim

[STEVE POLLARD]

Bloo, thanks for the information, I really appreciate it !

 

Thanks Jim for the kind remarks... I'll probably stick with the 16" rims, but thanks for the offer...by the way, that's one beautiful truck...I always liked the '67 thru '72 model years and when this '69 came on the market last year,  I could not resist ! 

 

Steve

[TerryB]

Great trucks!  I once owned a 1967 C10.

[mike6024]

Found this info:

 

Numeric Tire Sizing System
The first system developed for tire sizing was used until the late 1960s, but provided only the cross section width of the tire and the rim diameter in inches. If the section width ended in zero (e.g., 7.00-14 or 7.50-14), the tire has a common aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15), the tire was considered "low profile" with an aspect ratio of about 82.

 

and

 

The numeric method is the oldest tire sizing system for automobile tires. This system only provides the cross-section width of the tire and the rim diameter in inches. Two versions of numeric tire sizes were used as original equipment on vehicles between 1949 and 1970. The early numeric tires had the equivalent of a 90-series aspect ratio, while later tires offered a "lower" profile equivalent to a 80-series. These tires typically featured tread widths ranging from 3.5 inches for the smallest 13 inch rim diameter tires to about 5.5 inches for the largest 15 inch rim diameter tires. If the section width ended in zero (e.g., 7.00-14 or 7.50-14) the tire had an aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15) the tire was considered "low profile" with an aspect ratio of about 82. For example, a tire labeled 7.00-14 has a section width of 7 inches, a rim diameter of 14 inches, and an aspect ratio of 92. The low profile equivalent size tire with an aspect ratio of 82 would be 7.35-14.

 

Was the above the same system used for light truck tires? It seems to indicate the aspect ratio could have been 92.

 

I seem to remember the early tires looking narrow and tall, maybe taller in aspect ratio than 80. I briefly had a new '73 C20 and it had the 16.5 inch with tires that seemed very tall. Also my Dad's half ton had 7.00-15 that were very narrow but seemed plenty tall.

[STEVE POLLARD]

Thanks for the info Mike.

[mike6024]

You could still get 9.50 by 16.5 tires if you wanted.

 

Firestone Transforce HT 9.50R16.5 E/10PR BSW, Set of 4 tires $ 748.44, free shipping.

 

This new Firestone Transforce HT 9.50R16.5 E/10PR BSW Tires. Manufacturer part number: 189820.
The Firestone Transforce HT tire  is a heavy duty light truck tire for all seasons that promises wet and dry performance along with a quiet, comfortable ride. This is a great tire for fleets because it has a special tread compound for low rolling resistance and a casing design that runs cooler.  Both these features contribute to the Firestone Transforce HT tire improving your fuel economy by 1% versus other Firestone tires.

In addition to having this superb fuel efficiency, this tire also provides long wear life and puncture resistance. This comes from an extra steel belt under the tread and polyester casing plies with extra tensile strength.The Firestone Transforce HT is designed to last, with durablity and toughness to keep you on the road.

 

https://www.tires-easy.com/9.50-16.5/firestone-tires/transforce-ht/tirecode/189820

https://www.tires-easy.com/

 

This website allows you to buy unusual size tires. They ship direct from the manufacturer, including sizes that are not commonly available in the USA. They ship to you, and you take them to the shop of your choice for mounting. I have bought high profile 80 series tires for my car, a size I could never have found at a local tire shop,

 

But since you already have the 16 inch rims I'd stick with those. If you still had the 16.5 on the truck I'd probably be looking for 16.5 tires.

 

[Bloo]

29 minutes ago, mike6024 said:

Numeric Tire Sizing System
The first system developed for tire sizing was used until the late 1960s, but provided only the cross section width of the tire and the rim diameter in inches. If the section width ended in zero (e.g., 7.00-14 or 7.50-14), the tire has a common aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15), the tire was considered "low profile" with an aspect ratio of about 82.

 

and

 

The numeric method is the oldest tire sizing system for automobile tires. This system only provides the cross-section width of the tire and the rim diameter in inches. Two versions of numeric tire sizes were used as original equipment on vehicles between 1949 and 1970. The early numeric tires had the equivalent of a 90-series aspect ratio, while later tires offered a "lower" profile equivalent to a 80-series. These tires typically featured tread widths ranging from 3.5 inches for the smallest 13 inch rim diameter tires to about 5.5 inches for the largest 15 inch rim diameter tires. If the section width ended in zero (e.g., 7.00-14 or 7.50-14) the tire had an aspect ratio of about 92. For section widths not ending in zero (e.g., 8.25-15) the tire was considered "low profile" with an aspect ratio of about 82. For example, a tire labeled 7.00-14 has a section width of 7 inches, a rim diameter of 14 inches, and an aspect ratio of 92. The low profile equivalent size tire with an aspect ratio of 82 would be 7.35-14.

 

 

This change probably occurred in 1965. Somewhere I have a wall poster detailing these changes from a major US tire manufacturer, probably Goodyear. It lists all the "new" sizes and which tires they would replace. I cant find it. I'm sure I put it in a safe place!  The copyright date was 1965.

 

What I wonder about is what happened in 1948 (1949 in the quote above). 1948 is a year I have often heard thrown about for an industry-wide tire size change, much like 1965. (can't be 1970, letter sizes existed by then). If the 92 aspect ratio began in 1948(49?), then what was the aspect ratio before 1948? 100?

 

If it was 100, that begs the question what changed when the tire sizes changed from tread diameter (31x4 for instance) to rim diameter (4.00x23) in the mid 20s (1924?)? Anything? If not, those 2 sizes would be the same.

 

The implication, I guess, is that all pre-1948(49?) tires are a 100 aspect ratio. If that is true, it sure goes a long way toward explaining why nobody can seem to get inflated tires in their sidemounts. Do any of you guys know for sure?

[bobg1951chevy]

Steve and J.H., beautiful trucks !

[bobg1951chevy]

950 x 16.5 bias are CLOSE to 235-85-16 or 265-75-16  radials, check the dimensions.

[STEVE POLLARD]

Interesting note, upon looking more into the specifications chart, the 3/4 ton & 1 ton also had a "Tube Type" size: 7.50 - 16....

[Bloo]

Maybe you have original rims after all....

[misterc9]

16.5 was tubeless while 16 in was usually tube type. Back then most 16s were the split rim type. Nobody wants to change the old split rim wheels so most of them were scrapped and replaced with one piece wheels. The tire's weight capacity is important when picking tires. Every modern tire has it's weight capacity marked on the sidewall. Example  2000 lbs @ 40 psi This is for each tire.  I don't know the truck's weight or if you are putting a camper on. Most trucks had a label somewhere stating the weight for front and rear axles. The tires need to meet or ideally  exceed this weight.