Radar vs Reality

So. I’m on 275/70/17

I passed by one of those speed limit signs that display your speed.

my truck and the sign were the same.

its a low mph, sign is for 25.

any insight would be insight.

also I’m wondering what everyone else’s says.

 

Road side radar is notorious for being out of calibration.
Use a GPS app. You'll get an accurate speed.

 

I've had several encounters and my speedo registers higher than what the radar says by about 3 MPH.

So when I'm doing 45 in a 45mph zone the radar tracks me at like 43.... which is fine by me... keeps me out of ticket trouble.

 

That’s what I figured. But I was also wondering if the Leo’s tech in the cruiser was the same.

 

They're supposed to calibrate those regularly

 

As far as I can tell, everything is working normally. The stock speedometer is off by about 3.5%, overstating the speed. Your current tires are 4.9% larger than stock, so your truck is actually only off by about 1.5%, understating the speed. Which, at 25 mph, is about 0.375 mph off. In other words, you’re traveling too slowly for your level of speedo inaccuracy to show itself.

If you were still stock, your dash would probably say 25 mph and the radar would probably say 24 mph.

 

Not off by as much as one would think.
While I'm not an LEO, they are trained, and learn, to know how to approximate speed.

In short, If you are getting pulled over for doing 5 over. You're getting a ticket anyways. For something....

I'm lucky enough to live in a county, and state, that doesn't typically give speeding tickets until you are 10 mph or over.
Even if the radar is off, it isn't off by enough to not have been pulled over.

 

For those interested, US Highway Safety requires +/-5 mph @ 50mph.

My truck is about 3 mph SLOWER than the speedometer says at 35 mph.

 

I’m lucky enough to live in a county where I rarely get pulled over.
I drove a ‘24 mustang as a rental car a little while ago, I’m not trying to speed in my taco anymore, just lusting for a newer model mustang to beat on.
I really am wondering for mileage purposes.

 

According to the magical tire calculator mine is 5.1% in the diameter/circumfernece dept. so at 20, it’s actually 21

 

I just went through a construction zone a couple of weeks ago, side by side with another vehicle, I was doing maybe 1-2 mph faster, barely creeping past. There was a radar sign on both sides and our displayed speed was nearly 10 mph different. Not real precise on either accounts, but you get the idea.

 

A fully stock truck does not have an accurate speedometer to begin with. Like I said, it overstates your speed by 3.5%. Meaning at 100 mph, you’re actually going around 96.5. Now you’ve added tires that are roughly 5% larger than stock. You’ve made the speedo become incorrect in the opposite direction (underreporting/slow), but the net difference is only about 1.5%. So at 100 mph, it’s like 101.5 now. But at 25 mph, which is how fast you travelled in this post, it’s too small of a difference to notice on a radar. Nobody can tell a difference between 25 or 25.375 mph. So your speedo and the radar reported the same.

The perfect speedo happens when you upsize tires from stock to only 1” larger. As in 265/70R16 to 265/75R16, 265/65R17 to 265/70R17, etc. You are slightly larger than those by 0.5” and so your speedo is slightly off still, but it’s underreporting instead of overreporting (like stock) and it’s not enough to notice at slow speeds. Hit about 40-50 mph and you’ll see it start getting closer to 0.5-1 mph off.

 

This is simple. If you have a cellphone, you have a GPS.
Unless you are the last of a dying breed and don't have a smartphone.
But I doubt you are, those guys hate technology. They wouldn't own a 3rd gen. A 2ng Gen would be too "new" for most.

 

I’m just too lazy to find a gps speedo. There’s all this “research” involved. But the 1st gens do turn my head.

 

ewwwww! You gonna get the Flippers fired up tonight!!

 

I'm old enough to remember what it was like without a cellphone.
And just about old enough to miss those days.

I'm 41.
I didn't get a cell phone until I was 24 or so.

Long lost are the youth to day.
They will never know what it's like to walk home.
I only ran out of gas ONCE in my life.

But I walked home a few times. Even hitch hiked once after I blew the motor in my Trans Am.
We don't talk about sneaking out an getting the truck stuck in High School. That was a LONG walk home. (in reality it was less than a half mile home.)

 

Same here for age and when I got a cell. Funny that I used to tell people that if wanted to be called I’d be home. Can’t even fathom leaving the house without my phone now days.

Back to the topic. Google maps will tell you your speed. So not that hard to find. Unless you don’t get data on your phone (then you’d have to download the maps ahead of time).

 

Well. I’m like 46 going on 27. Got my first cell phone at 24. Well aside from that bag phone thing that weighed like 15 pounds. I use Google maps. Never seen a Speedo on it.

 

My truck is stock down to the Firestone tires.

The analogue speedometer reads a bit fast, the digital display is usually right on with the road side speed displays.