What Size? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

PhoneTruck · 12-08-2002, 06:05 AM

I bought a 1967 1/2ton Southern Bell 2 speed pick-up with 6 lug 15" rims and the speedometer is approx. 7 miles fast! Can some please tell me the wheel and tire size that the fleet truck came with? Its a 2 speed,so I would like to get the correct size because I believe it would lower R.P.M. also!
Thanks

ChevLoRay · 12-08-2002, 12:22 PM

I imagine the stock size tire in '67, for a half-ton truck was either a 6.70, or a 7.10, maybe even an 8.00X15.

Then, there were the 7.75 series that came out.

Your tires would have to smaller than the original size to cause your speedometer to be overly optimistic. The gear in the transmission tailshaft that drives the speedometer may not be correct. The gearing in the differential may not be the one that it left the factory with. Oh, one more thing....mechanically-driven speedometers of old were notorious for being inaccurate. Yours may be just like it always has been, which is why the police had "Certified" speedometers in their vehicles.

Electronics has provided us with accurate speedometers, especially since so many factors for the engine computers are dependent on the speed of the vehicle, for one of the inputs.

Mine is pessimistic, by approximately 5MPH, when I am going approximately 65MPH, i.e, it shows me to be doing 60MPH, more or less, or thereabouts. So, I kinda rely on "Pacing" to keep me in check, or out of trouble.

So, bottom line, having the original size of tire may not provide you with the accuracy you want. In fact, it may be difficult to achieve without taking your speedometer to a shop that specializes in them and can certify it, knowing your axle ratio and the gear in the transmission that drives it.

Capitol68 · 12-08-2002, 12:40 PM

mine had 16" orig.

PhoneTruck · 12-08-2002, 09:04 PM

Thanks guys for your help and Capitol68 what was the tire size of the 16"? Thanks again!

*67/72junkie* · 12-09-2002, 11:08 AM

Ride behind friend with vehicle known to be correct to find out how far youre off. Remove speedo gear from transmission and count teeth . Each tooth added or subtracted is approximately 5 mph . Two or three bucks at gm parts counter.

Southpa · 12-09-2002, 11:19 AM

I guess that goes for the odometer too. Hmmmm...maybe thats why I'm only getting 7.4 mpg... tires are 31" high.

Capitol68 · 12-09-2002, 12:33 PM

I dont remember what was on it before,friend had it before me,He changed to 15',with 10 x 31.5.\
I found you drive next to one of those new fangled vehicles with electronic display, you can look in their window and see that way.I think mine is off like 5 mph

PhoneTruck · 12-09-2002, 11:32 PM

Thanks to all of you that have responded to my question. I think now that it did come with 16" wheels and it is not all the speed thing of 7 miles per hr. faster with the 15" instead of the 16".but I was thinking the engine R.P.M. would also be lower running the larger wheel by several hundred. What do you think? Thanks again.

Longhorn Man · 12-10-2002, 12:39 AM

Look in your glove box. There should be a sticker that will read 16 inch rims if it was so equipped.

PhoneTruck · 12-10-2002, 01:04 PM

The glove box was missing,but thanks anyway. I was hoping someone had a 67 GMC Owners Manual that might list the size!

solidaxel · 02-27-2003, 01:35 PM

Count the teeth on the speedo gear ( in the side of the transmission) like he said and go to one that has 2 teeth less!

12-08-2002, 06:05 AM	#1
PhoneTruck Registered User Join Date: Dec 2002 Location: Foothills of Brushy Mountains,N.C. Posts: 4	What Size? I bought a 1967 1/2ton Southern Bell 2 speed pick-up with 6 lug 15" rims and the speedometer is approx. 7 miles fast! Can some please tell me the wheel and tire size that the fleet truck came with? Its a 2 speed,so I would like to get the correct size because I believe it would lower R.P.M. also! Thanks Last edited by PhoneTruck; 12-08-2002 at 06:26 AM.

12-08-2002, 12:22 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	I imagine the stock size tire in '67, for a half-ton truck was either a 6.70, or a 7.10, maybe even an 8.00X15. Then, there were the 7.75 series that came out. Your tires would have to smaller than the original size to cause your speedometer to be overly optimistic. The gear in the transmission tailshaft that drives the speedometer may not be correct. The gearing in the differential may not be the one that it left the factory with. Oh, one more thing....mechanically-driven speedometers of old were notorious for being inaccurate. Yours may be just like it always has been, which is why the police had "Certified" speedometers in their vehicles. Electronics has provided us with accurate speedometers, especially since so many factors for the engine computers are dependent on the speed of the vehicle, for one of the inputs. Mine is pessimistic, by approximately 5MPH, when I am going approximately 65MPH, i.e, it shows me to be doing 60MPH, more or less, or thereabouts. So, I kinda rely on "Pacing" to keep me in check, or out of trouble. So, bottom line, having the original size of tire may not provide you with the accuracy you want. In fact, it may be difficult to achieve without taking your speedometer to a shop that specializes in them and can certify it, knowing your axle ratio and the gear in the transmission that drives it. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

12-08-2002, 12:40 PM	#3
Capitol68 Registered User Join Date: Sep 2002 Location: Austin,Tx Posts: 327	mine had 16" orig. __________________ '68 Fleet LWB orig 307 .030 over GM Hei/w Accel Super coil orig. stock TH 400. _______________________ “What we do for ourselves dies with us. What we do for others and the world remains and is immortal.” Albert Pine English author d.1851

12-08-2002, 09:04 PM	#4
PhoneTruck Registered User Join Date: Dec 2002 Location: Foothills of Brushy Mountains,N.C. Posts: 4	Capitol68 Thanks guys for your help and Capitol68 what was the tire size of the 16"? Thanks again!

12-09-2002, 11:08 AM	#5
67/72junkie Account Suspended Join Date: Oct 2002 Location: NC Posts: 1,129	speedo Ride behind friend with vehicle known to be correct to find out how far youre off. Remove speedo gear from transmission and count teeth . Each tooth added or subtracted is approximately 5 mph . Two or three bucks at gm parts counter.

12-09-2002, 11:19 AM	#6
Southpa Registered User Join Date: May 2000 Location: Victoria, BC, Canada Posts: 2,410	I guess that goes for the odometer too. Hmmmm...maybe thats why I'm only getting 7.4 mpg... tires are 31" high. __________________ 1970 GMC 1500 Custom Original 350/TH350 Victoria, BC, Canada You can wish in one hand and crap in the other. See which one gets filled first.

12-09-2002, 12:33 PM	#7
Capitol68 Registered User Join Date: Sep 2002 Location: Austin,Tx Posts: 327	I dont remember what was on it before,friend had it before me,He changed to 15',with 10 x 31.5.\ I found you drive next to one of those new fangled vehicles with electronic display, you can look in their window and see that way.I think mine is off like 5 mph __________________ '68 Fleet LWB orig 307 .030 over GM Hei/w Accel Super coil orig. stock TH 400. _______________________ “What we do for ourselves dies with us. What we do for others and the world remains and is immortal.” Albert Pine English author d.1851

12-09-2002, 11:32 PM	#8
PhoneTruck Registered User Join Date: Dec 2002 Location: Foothills of Brushy Mountains,N.C. Posts: 4	Thanks all again! Thanks to all of you that have responded to my question. I think now that it did come with 16" wheels and it is not all the speed thing of 7 miles per hr. faster with the 15" instead of the 16".but I was thinking the engine R.P.M. would also be lower running the larger wheel by several hundred. What do you think? Thanks again.

12-10-2002, 12:39 AM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Look in your glove box. There should be a sticker that will read 16 inch rims if it was so equipped.

12-10-2002, 01:04 PM	#10
PhoneTruck Registered User Join Date: Dec 2002 Location: Foothills of Brushy Mountains,N.C. Posts: 4	No Glove Box The glove box was missing,but thanks anyway. I was hoping someone had a 67 GMC Owners Manual that might list the size!

02-27-2003, 01:35 PM	#11
solidaxel Registered User Join Date: Dec 2002 Location: Cactus Patch So. Az Posts: 4,749	Count the teeth on the speedo gear ( in the side of the transmission) like he said and go to one that has 2 teeth less! __________________ 53 TuTone Extended Cab 350 4-Spd 3:08 (SOLD) 53 Chevy Moldy pearl green ZZ-4 4L60E 9" 3:25 55 GMC 1st Black Mll (ZZ4) ZZ6 TKO 600 5 sp 3:73 62 Solidaxle Corvette Roman Red (327 340hp 4spd 3:36) C4 & C5 suspension tube chassis LS 3 4L70E 65 Corvette Coupe 327 350hp 4spd 4:11 78 Black Silverado SWB (350/350) 5.3 & 4L60E 3:42 2000 S-Type 3.0 (wife cruiser) 2003 GMC SCSB 5.3 4L60E 3:42



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