Need some help, - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Trailrider95 · 09-02-2011, 04:59 PM

Trying to figure out the stock tire size of a 1972 gmc longbed 2wd sierra grande? We recently put some tires on, and have a speedometer problem, it's off by about 15 miles an hour. Still haven't replaced the speedo gear, but this truck has the original engine/trans still.. looking for stock factory tire size

cdowns · 09-02-2011, 07:21 PM

1/2 or 3/4ton?? you do realize theywere bias ply tires that came on these trucks?

C10 - C90 Bill · 09-03-2011, 05:31 PM

If it's a 1/2 Ton, in today's modern day Radials, 235-75R-15's seem to work.

Bill

wilbilt · 09-03-2011, 08:00 PM

Quote:

Originally Posted by C10 - C90 Bill

If it's a 1/2 Ton, in today's modern day Radials, 235-75R-15's seem to work.

P235/75R15 is a good fit. The rough equivalent to an L78-15.

The stock tire size indicated in most manuals is a bit smaller, though. G78-15 or H78-15, which equate to P215/75R15 and P225/75R15.

A comparison chart with diameters and revolutions/mile here:

http://www.angelfire.com/on/geebjen/tires.html

Longhorn Man · 09-03-2011, 10:43 PM

at what speed is the speedo off by 15 MPH? I doubt you'll find a tire to make up that much.

Trailrider95 · 09-04-2011, 02:21 AM

Seems to be right round' 30, it says i'm doin 40-45ish. Could be the speedo gear though.Thanks for the help guys!

09-02-2011, 04:59 PM	#1
Trailrider95 Registered User Join Date: Jul 2010 Location: PNW (Washington) Posts: 75	Need some help, Trying to figure out the stock tire size of a 1972 gmc longbed 2wd sierra grande? We recently put some tires on, and have a speedometer problem, it's off by about 15 miles an hour. Still haven't replaced the speedo gear, but this truck has the original engine/trans still.. looking for stock factory tire size

09-02-2011, 07:21 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Need some help, 1/2 or 3/4ton?? you do realize theywere bias ply tires that came on these trucks? __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

09-03-2011, 05:31 PM	#3
C10 - C90 Bill Registered User Join Date: Nov 2001 Location: Moneta, VA USA Posts: 3,082	Re: Need some help, If it's a 1/2 Ton, in today's modern day Radials, 235-75R-15's seem to work. Bill __________________ '60-'72 Chev/GMC Fan GMC 9500 Fan Detroit Diesel Fan

09-03-2011, 10:43 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Need some help, at what speed is the speedo off by 15 MPH? I doubt you'll find a tire to make up that much.

09-04-2011, 02:21 AM	#6
Trailrider95 Registered User Join Date: Jul 2010 Location: PNW (Washington) Posts: 75	Re: Need some help, Seems to be right round' 30, it says i'm doin 40-45ish. Could be the speedo gear though.Thanks for the help guys!



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