Speedometer not accurate

[ORRadtech]

Grew up in Indiana soo...
But small towns everywhere should be approached with care.

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[K4fxd]

Sunday evening, no traffic, the jerk was coming the other way, turned around and got me.
60 in a 55.

 

[ORRadtech]

Try living in the deep south. You learn which places use tickets to fund the town coffers locally. But if I'm more than 50 miles or so away from home I tend to be careful. The one stop light towns are the worst. I'll set my cruise control as soon as I see signs of a town.

 

[Austin1992]

Hey now, I live in a small hicktown in Indiana lol. My Speedometer is about 2mph off and usually set my cruise at 5-10 over the limit so I’m actually doing 3-8 over and regularly see local and state cops. Only ever been busted for a seat belt once and this year I didn’t get my plate renewal form in the mail so totally spaced it and was like 3 weeks past due lol. Belt was a 25$ ticket, plates were a verbal warning. During the belt stop I was late for work and doing 13 over, he just said to slow it down, speed wasn’t mentioned during the plates stop but I was only doing 3 over.

 

[K4fxd]

I live in a small hicktown in Indiana lol

It was Greensburg In. Rt. 46 just before it turns into a 4 lane, Deputy Sheriff in a pickup

 

[Austin1992]

It was Greensburg In. Rt. 46 just before it turns into a 4 lane, Deputy Sheriff in a pickup

Oh, I’m an hour or 2 west of there

 

[dgreene1]

So just to confirm the physics, assuming the speedo is based on wheel rotational rate... At a given "actual speed" if the the tire diameter increases, the wheel is spinning slower compared to a smaller tire diameter, hence the speedo will read slower. Bigger tire = slower speedo read. Smaller tire = faster speedo read. Correct?

 

[joe603]

So new tires put on, OEM size...speed still off by the same amount. Probably needs to be fixed in ECU by dealer or Forscan.

 

[ORRadtech]

Happened to go past one of those "watch your speed" radar things the other day while I had Waze and cruise control running and thought of this thread.
My speedo and Waze agreed but the radar thing flickered between 1 & 2 mph lower.
I'm OK with that.

 

[WICK MODE 21GT]

Yes could be tires, car out of line, etc. etc.. sat gps too slow... lol

 

[Garfy]

Personally I'd rather the speedo read 2 over than 2 under.

Also, I know that it's jurisdiction/ LEO dependant but I've never been ticketed for anything under 10 over. Hope that doesn't jinx me...

...unless you're driving a loud Mustang, Corvette, Ferrari, etc., especially if it's red

 

[Garfy]

Don't drive in Indiana, got popped for 5 over coming into some hick town.

The same will happen in NV going from Vegas to Reno as you pass these small "mining towns" with low speed limits. Perfect speed traps since before you hit the town you're doing 70+.

 

[Linkster1666]

So new tires put on, OEM size...speed still off by the same amount. Probably needs to be fixed in ECU by dealer or Forscan.

Speed is off by WHAT measurement? Is it within 2 mph? The ONLY way to fix this Bullshit is go to a SUPERSPEEDWAY and time it, otherwise STFU!!!

 

[Johnny Rockit]

Both my gps and radar detector show a faster soeed than my speedometer. Same when in cruise.

 

[CORNYOTE]

you can change your tire height in forescan to correct this. Pretty simple to do.

https://forscan.org/home.html

Link showing how to change tire size:

https://forscan.org/forum/viewtopic.php?t=15994

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