# Speedometer: How fast??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BLzr4x4ngkid, May 8, 2000.

1. ### BLzr4x4ngkid1/2 ton status

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With 35's, about how much is the speedometer off?? I figured mine is off by about 7-15mph. I haven't had much time to check it. How much is your guy's speedo off?? HAHAHA Thanks again.

Alex
Wichita, KS
What me get stuck? NEVER!!(Famous last words)

2. ### Blazer791/2 ton status

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There's a calculator at http://www.4lo.com that helps you with that and other stuff.

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What the heck!...Drive it like gas is \$0.50/gal!!!
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3. ### 70jimmy3/4 ton statusPremium MemberGMOTM Winner

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On speedometer change with larger tires you need to realize that there is no specific amount that a speedo is off. As your speed increases you amount of error increases. You need to check it at different speeds. Easiest is of course 60 seconds at 60 mph to go one mile. Use a stop watch or second hand and the milemarkers. Also remember that if speedo is off so is your odometer. To figure out how long it should take at a given speed to go one mile use the following: Speed times 1.466 then take 5280 divided by answer and that will give you number of seconds to travel one mile. Example 75 mph times 1.466 =109.95 5280 divided by 109.95 =48.0218281 or just over 48 seconds. The 1.466 changes mph to feet per second and the 5280 is the number of feet in a mile. I will make it easy: 30mph = 120 seconds
35 mph= 102.90 seconds
40 mph =90 seconds
60 mph = 60 seconds
65 mph = 55.4 seconds
70 mph = 51.45 seconds
75 mph = 48.02 seconds
80 mph and up = you dont need to know
Once you know this you can put a little note on the dash as a reminder, Keeps you out of hot water with your signifigant other. All those who are worried about how fast you are going please raise your right foot.

4. ### BLzr4x4ngkid1/2 ton status

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I'm not too worried about the speed. I was just kind of curious. Basically, I don't care how fast I'm going as long as I get there safely without incident.

Alex
Wichita, KS
What me get stuck? NEVER!!(Famous last words)

5. ### CrazeeBush1/2 ton status

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Would this work?

Take a trip down the interstate and go say 10 miles, and record the miles on your odomenter, then use the actual vs. error to set up a ratio? Like I went 10 miles and odometer says 9.6.

Then 10/9.6=(Actual MPH)/(My Speedo Reeding)

Then do some cross multiplying and you get:

9.6*(Actual Speed you wanna go, say 80 MPH)=10*x

where x would be the value your speedo would say.

I dunno, I'm just rambling off stuff... I think that would work. Someone correct me if I'm wrong... That ould give you a percentage of error that would increase with speed.

6. ### walrus101Registered Member

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easiest way to get a good guess is when you are driving down the highway look at the mile markers as you go by. look at your odometer and compare. for every 10 mi. my odometer is off .5mi so every 20 i am off 1mi. so at 20mph i am doing 21 at 40 doing 42 and so on. this is not completely accurate but it gives you an idea. plus it gives you something to do while you are driving.

walrus101

goo goo gaju

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