1959 GMC 100 Tires

[Sammy4358]

Does anyone know what modern tire size a new GMC 100 truck would have had in 1959?

[dsraven]

go here to get the spec
http://chevy.oldcarmanualproject.com...to/59tld09.htm
this is a great site if you go to the year specific index page you can pick another year that is the same style of truck and possibly glean more info if that page is missing or whatever from your particular year.

then go here to get the tire dimensions
https://www.cokertire.com/firestone-...ll-670-15.html

then go here to get a modern comparable size for height/width/rim size/etc
https://tiresize.com/comparison/

then go here for the engine rpm associated with your diff gear ratio, trans final drive ratio and tire diameter. then you can figure out the cruising speed engine rpm with a particular tire size compared to another tire size.
https://www.ringpinion.com/calculators/Calc_RPM.aspx


looks like it came with a 6.70 x 15 tire with a 4" wide rim and a 7.01 section width. the overall diameter is 28.58 so that would be something like a 235/75r15 (common size but a tiny bit taller) which is 9.3" wide or a 245/70r15 (closer to the right diameter size but maybe not as common) and it is 9.6" wide.

hope that helps

[DA68]

I'm running a 225/75/15 on my 59 GMC and they look perfect. I can PM you some pics.

[northerngmc]

I am pretty sure I went with 215 75 r15 on mine.

[SanJosesSteve]

I too am running with the 215's..... the previous tires were bigger and about 10 years old. Amazing what difference a new thinner tire makes when parking at Home Depot!

[dsraven]

sammy, are you looking for a stock diameter tire or just curious to see what other guys are using?
a smaller diameter tire is a better fit for the wheel opening if you are lowering the truck at all, because it may stop a front tire rub condition on turns over bumps, but a smaller rear (if keeping all 4 the same size) tire is going to make the engine rpm's climb at a given speed compared to the original diameter.
if you have a plan and let us know we could be a better help.

[Sammy4358]

Thanks for the help, I am restoring a 59 GMC back to factory specs but I can't bring myself to put a 4" wheel on it. I am putting a 6" X 15 smooth wheel with the small GMC chrome lug cover. I like a bigger tire and the new springs really picked the frame up, so I ordered some Bridgestone Dueler A/T Revo, they are 235/75R-15 and are about 29". I'll put the black side out.

[dsraven]

that should give you a stock height look, maybe a bit wider, and a stock rpm at road speeds like the old tires would.

[northerngmc]

Before my 59 was restored it ran 235 75 15's and a small wooden steering wheel. It was tough steering at slow speeds and real tough when parking. When stored I went with 215's and the original steering wheel. What a difference driving it. I think the steering wheel was the bigger issue.

I should clarify that I went with 215 75 r15 to try and replicate the original tire size.