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11-03-2010, 05:52 PM
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#1 |
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70+ ( Old Skool Club )
 
Join Date: Nov 2003
Location: Saskatoon, Saskatchewan ,Canada
Posts: 9,108
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Checking Speedo with a GPS
I got in a " see who can go faster" on the Highway last year with a rice rocket and when I backed off my speedo showed 95mph. Everything is tight on my truck and I have added a front sway bar but I figured a 38 year old truck would have a shake or shimmy at that speed, which mine didn't and it didn't feel like I was going that fast. Today I took my truck out for a last stretch before tucking her away for the Winter and took my GPS to see how accurate the speedo is. I'm running P235/70R15 tires which I believe are a little shorter ( or maybe taller?) than the originals ( H78-15) on my truck. When my speedo showed 60mph the GPS showed 58mph and at 70mph the GPS showed 68 and at 85mph the GPS showed 82mph. I didn't take it up to 95 this time but I'm sure I was doing over 90mph when I was playing with the rice rocket. This truck continues to amaze me. Oh yea, I was the one who backed off at 95 mph.
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1972 C10 Custom/Deluxe 613 Highlander 406/700R4 1999 White Tahoe LS 4x2 with Z56 Police Package 1992 K1500 GMC Suburban Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601 " Circumsatances Do Not Change Responsibility " " The Sky is not the Limit, Your Mind is." Marilyn Monroe .. RIP Charlie Watts 1941 - 2021 |
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11-03-2010, 06:00 PM
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#2 |
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Registered User
Join Date: Jun 2010
Location: Jefferson, MD
Posts: 2,397
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Re: Checking Speedo with a GPS
I've GPS tested before, mine's inaccurate the other direction. When my speedo indicates 50, I'm actually 53-55 (seems like the speedo isn't real precise, either). At an indicated 60, I am actually nearer to 64-65. Might have to be concerned with the police with this one.
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'68 Dodge Dart 270, 225, 904, 2.76--"Lucy" 1996 Gmc 1500 Z71, 350, 4l60e, 3.73s 1995 Jeep Wrangler Rio Grande 2.5, AX5, 4.10s 1989 Toyota Pickup 22re, auto, 3.73 |
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11-03-2010, 06:34 PM
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#3 |
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its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: Checking Speedo with a GPS
These trucks, esp the 1/2 ton/coil 2 wheel drive, are very stable at high speed. I've had the burb up to 95 or so, my old GMC I had the needle turned to the M on MPH, and my longhorn was flirting with 100. All of them were stable and true.
Remember, the rear suspention design is still used today, under some of the stock car classes, and they go a little faster than even us speed demons. |
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11-03-2010, 08:51 PM
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#4 |
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Registered User
Join Date: Jan 2010
Location: GREENEVILLE TENNESSEE
Posts: 1,310
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Re: Checking Speedo with a GPS
The GPS is not accurate north of the border..in mph ..it.should be in kph....
 Trust the truck speedo...they are right!!! The north pole messes with the magnetic field of the GPS
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11-03-2010, 09:01 PM
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#5 |
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Back in the sticks
Join Date: Jan 2001
Location: Fordland, MO
Posts: 3,188
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Re: Checking Speedo with a GPS
What I've noticed is that at 100, she just FLOATS along. Not that I've spent much time at that, its scary. But, ya, its a nice feeling.
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1971 Cheyenne C-10 w/700R4 and Tuned Port Injection 1969 K5 Blazer w/Tuned Port 2010 2SS/RS Flaming Orange Camaro 2011 K1500 Suburban 2014 K1500 Pickup 2008 Nissan Altima? The wifes' hoopty |
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11-04-2010, 12:13 AM
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#6 | |
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70+ ( Old Skool Club )
Join Date: Nov 2003
Location: Saskatoon, Saskatchewan ,Canada
Posts: 9,108
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Re: Checking Speedo with a GPS
Quote:
__________________
1972 C10 Custom/Deluxe 613 Highlander 406/700R4 1999 White Tahoe LS 4x2 with Z56 Police Package 1992 K1500 GMC Suburban Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601 " Circumsatances Do Not Change Responsibility " " The Sky is not the Limit, Your Mind is." Marilyn Monroe .. RIP Charlie Watts 1941 - 2021 |
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11-04-2010, 08:43 AM
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#7 | |
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Registered User
Join Date: Jan 2010
Location: GREENEVILLE TENNESSEE
Posts: 1,310
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Re: Checking Speedo with a GPS
Quote:
Last edited by 70BLAZERX2; 11-04-2010 at 08:44 AM. |
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11-04-2010, 09:55 AM
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#8 |
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yes, i do
Join Date: Jun 2007
Location: Spokane, wa
Posts: 2,734
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Re: Checking Speedo with a GPS
i know my speedo is off by at least 10 mph at highway speeds. while doing 70 cars that normally are doing 60 would be passing me and going up to 80 would get me right along with everyone that was doing 70. i know shorter tires make your speedo faster that you are actually going.
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ERROR 404....... SNAPPY COMEBACK NOT FOUND  _______________________________________________________________________________________________ -60 Chevy C10, dead 350/good th350 combo, sitting on a 76 c10 blazer frame, built from 11 different vehicles "the abomination" -07 gmt900 silverado 1500 lt xcab z71, granite blue -81 suzuki gs650g "shelah"- current project -81 kz1000m1 csr "sarge" -next project (just beautification) -07 kawasaki vulcan classic vn900 |
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11-04-2010, 11:57 AM
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#9 |
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Registered User
Join Date: May 2009
Location: Motor City
Posts: 9,192
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Re: Checking Speedo with a GPS
Mine is off by 5 mph at highway speeds (ie, GPS shows 65, truck speedo shows 70).
Everything is stock (stock tire size, gears and speedo adapter) but I just never noticed before. I wondered why everyone was giving me dirty looks as they flew by -
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Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ |
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