Tires vs speedometer

[Warpious]

I think with prices going up on everything as quickly as they are I'll be buying tires in the next day or two. I know going from the stock 225 to 245s will affect the speedometer, not dramatically but at least a bit, there's not a way to tell the car what tires it has on it to adjust is there? I think it's only 1.2 mph so it's not a big deal but I'm curious.

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[GulfCoastBronco]

I think with prices going up on everything as quickly as they are I'll be buying tires in the next day or two. I know going from the stock 225 to 245s will affect the speedometer, not dramatically but at least a bit, there's not a way to tell the car what tires it has on it to adjust is there? I think it's only 1.2 mph so it's not a big deal but I'm curious.

You have to get it calibrated. And here in Texas I believe if you have it calibrated you have to get some official documents on it. Mine is about 2mph off. Find an area with a speed limit read out. Like school zone or construction zone. And drive by a few times to see how off you are.

 

[Major Kong]

Try this calculator
plug in your current tire
match against proposed tire
scroll on down towards the bottom for rotation/mile calcs
https://www.wheel-size.com/calc/

 

[BravoAlpha]

It’s a percentage based on speed. ie 3.2%. There’s a calculator out there on the internet.

 

[Warpious]

Yeah I did a calculator earlier, looks like it will only be 1.2 mph off, just wasn't sure if there was away to adjust or if it'd even be worth it

 

[RSH]

Just as the computers in our vehicles calculate MPG, they have been proven to be inaccurate to some extent. People rarely think about the accuracy of the speedometer, they are typically inaccurate as well. Have you ever driven on a hiway that has mileage markers? that is one way to check the accuracy, another way would be to use a smart phone that has GPS.
I have 245/65/17's on my Badlands, the speedometer is off a couple of miles per hour depending on the speed and the air pressure in the tires.
Overall it's not a big deal and after awhile you don't even think about it, you just drive.

 

[Warpious]

Just as the computers in our vehicles calculate MPG, they have been proven to be inaccurate to some extent. People rarely think about the accuracy of the speedometer, they are typically inaccurate as well. Have you ever driven on a hiway that has mileage markers? that is one way to check the accuracy, another way would be to use a smart phone that has GPS.
I have 245/65/17's on my Badlands, the speedometer is off a couple of miles per hour depending on the speed and the air pressure in the tires.
Overall it's not a big deal and after awhile you don't even think about it, you just drive.

It's funny you say that, I've given a lot of thought to that actually. How do we know they're correct from the factory I've never tested a vehicle for accuracy before other than the speed signs in a neighborhood or something, even then how do we know those are accurate.

 

[Mark S.]

It's funny you say that, I've given a lot of thought to that actually. How do we know they're correct from the factory I've never tested a vehicle for accuracy before other than the speed signs in a neighborhood or something, even then how do we know those are accurate.

Many mapping apps like Google Maps and Waze display your current GPS-derived speed on the screen while using the app. If you're in an area with weak GPS coverage the indicated speed may jump around. If you're cruising on flat ground and the displayed GPS speed is steady you can be fairly confident it's accurate.

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