Speedo inaccurate before or after or always?

[HeyBales]

Because this issue of different sized tires needing at the least an option set on many cars to even use an alternate tire size - some tire shops will have a scanner that has ability to reach those settings. Had 2005 Rav4 that had 2 options, shop had ability to change it if I needed it. (used lot put on wrong size, wanted to confirm setting was right when I got replacements later)

You might check with the place you got the wheels if they do that service.
Otherwise dealership.

To the point in comment above, I do recall seeing the short list of alternate sizes available to choose from in that programming service - make sure they pick from the list rather than option of manual entry.
That may cause it to stick thru a reprogramming that occurs with a recall update down the road. Or you'll need to remember to mention that whenever an update is done.

ETA: 3 off at 70 seems about right for every car I can recall, older Ford at 3 at 60 off.
I think 1 Vehicle Speed Sensor reading was about 70 while another was matching the speedo below that - test on my way home tonight.
OBD VSS matched the speedometer - the cruise control reads 1 higher than that even at 40 mph.
There are 4 total VSS readings from different control modules. The cruise must be using another one for it's value. Kinda flakey design.

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[BeardedMarine]

Before I got my tune on my f150 I used a superchips flashcal to calibrate the speedo. They make one for the bronco sport 2.0 ecoboost buy not the Maverick. Maybe I'll just get a tune to correct it + other things with the tune.

 

[BeardedMarine]

To the point in comment above, I do recall seeing the short list of alternate sizes available to choose from in that programming service - make sure they pick from the list rather than option of manual entry.
That may cause it to stick thru a reprogramming that occurs with e recall update down the road. Or you'll need to remember to mention that whenever an update is done.

When you say 'they' are you referring to a ford tech or the wheel shop?

 

[BrianA]

I wish I had checked the speedo before I got new wheels and tires. I replaced the 17in wheels with 18in. At first I tried 235-60-18 but didn't like them with a 7in wide rim, but the speedo was somewhat accurate with them. So I put some 225-60-18 tires on which are the same height as the 225-65-17 but now the speedo is off by 3mph at 70mph. Has it always been off? I dunno. Anyone else have this problem? Are there and speedo correction units available?

Tread wear, PSI, vehicle load - all change the loaded radius of the tire and thus the indicated MPH (Unless the maverick has some sort of road sensing laser system - which I highly doubt.) What are you doing that you need better than 3MPH accuracy at 70 MPH? Especially when you know about how far it is off. A little Kentucky windage and you are good. Also wondering what you are measuring it with? Not something to even worry about in my opinion, but then it's your truck, so worry away!

 

[Fred Piering]

I have a 2024 XLT with 1500 miles. The speedometer is off 2 MPH at 25-30 MPH. Have not yet checked at 70. Standard tires as delivered on the vehicle.

 

[MakinDoForNow]

It reads low, so the GPS says 70 the speedo says 67.

GPS can vary depending on number of satellites used to calculate positions and if you have access to military precision or civilian precision. There is an accuracy ellipse which can be reduced depending on angle of travel to angle of satellite. Also the main difference is that of roundoff to arrive at 70mph. In all likelihood the displayed 70 calculated to 69+ to 70 on the nose but could be 69.5 to 70.5- plus adjustment for number of decimal places to satellite error allowance. All taken into consideration for Ford not to show something that could get operator a ticket.

 

[HeyBales]

When you say 'they' are you referring to a ford tech or the wheel shop?

Whichever one can do it that you decide on.

 

[Flyangler]

Coincidentally, my 22 Mav XL Hybrid had some trouble pulling my light weight trailer and raft out of a sandy river landing a couple days ago and I was thinking of replacing the stock Continentals again. I think about it every time I read a tire post here. But the dealer said my tread looked good when the truck was in the shop (during that tire sale that ended in June), and I didn’t replace them.

Then, driving home in the rain yesterday, I was annoyed to hydroplane a bit. Shortly thereafter, I went through this little town with a speed wagon on the side of the highway that clocked me at 38 in a 40mph zone. So I set the (aftermarket) cruise for 42, (the meaning of life) and was golden.

Thinking of going with Toyos or Nittos. If I don’t change size, but try to get a more aggressive, all-season tread, will that affect either that speed blip or the gas mileage? Also, what kind of margin of error does one of those speed trailers have? If I adjust the cruise control through forscan, is some other device, like the state trooper’s hand held radar going to read my speed differently?

 

[Rick65]

Glad someone brought this subject up. I have a 2024 FX4 with 4K tow. Stock tires were 225/65 r17 but right away I put 245/65 r17 tires on it expecting it to throw my speedometer off. Unfortunately I didn't test it before I replaced the tires but I have several of those roadside speed check radars all around me that I pass on city streets where I am going between 35 and 45 MPH. They all show that I am going about 1 MPH slower than my speedo says. I was expecting the opposite. Makes me wonder if every one of these roadside speed checkers is wrong or was my speedo a couple MPH off to begin with. I tried to test it with a GPS app and also with Waze but those constantly jump up and down by a couple MPH so I gave up trying to check with those.

 

[BeardedMarine]

Tread wear, PSI, vehicle load - all change the loaded radius of the tire and thus the indicated MPH (Unless the maverick has some sort of road sensing laser system - which I highly doubt.) What are you doing that you need better than 3MPH accuracy at 70 MPH? Especially when you know about how far it is off. A little Kentucky windage and you are good. Also wondering what you are measuring it with? Not something to even worry about in my opinion, but then it's your truck, so worry away!

After I installed new rims and tires I just wanted to check it, curious. I checked it with 2 different apps on my phone. But like others have said, that might not be all that accurate. Never said I was worried, just curious.

 

[BeardedMarine]

I have a 2024 XLT with 1500 miles. The speedometer is off 2 MPH at 25-30 MPH. Have not yet checked at 70. Standard tires as delivered on the vehicle.

Thank you, I guess it's to be expected. Other vehicles I've had have been pretty spot on.

 

[BeardedMarine]

GPS can vary depending on number of satellites used to calculate positions and if you have access to military precision or civilian precision. There is an accuracy ellipse which can be reduced depending on angle of travel to angle of satellite. Also the main difference is that of roundoff to arrive at 70mph. In all likelihood the displayed 70 calculated to 69+ to 70 on the nose but could be 69.5 to 70.5- plus adjustment for number of decimal places to satellite error allowance. All taken into consideration for Ford not to show something that could get operator a ticket.

Interesting, thanks for the response.

 

[BeardedMarine]

Coincidentally, my 22 Mav XL Hybrid had some trouble pulling my light weight trailer and raft out of a sandy river landing a couple days ago and I was thinking of replacing the stock Continentals again. I think about it every time I read a tire post here. But the dealer said my tread looked good when the truck was in the shop (during that tire sale that ended in June), and I didn’t replace them.

Then, driving home in the rain yesterday, I was annoyed to hydroplane a bit. Shortly thereafter, I went through this little town with a speed wagon on the side of the highway that clocked me at 38 in a 40mph zone. So I set the (aftermarket) cruise for 42, (the meaning of life) and was golden.

Thinking of going with Toyos or Nittos. If I don’t change size, but try to get a more aggressive, all-season tread, will that affect either that speed blip or the gas mileage? Also, what kind of margin of error does one of those speed trailers have? If I adjust the cruise control through forscan, is some other device, like the state trooper’s hand held radar going to read my speed differently?

Damn that's a pretty trout in your avatar.

 

[Phimosis]

So I put some 225-60-18 tires on which are the same height as the 225-65-17 but now the speedo is off by 3mph at 70mph. Has it always been off? I dunno. Anyone else have this problem? Are there and speedo correction units available?

I always run a gps enabled radar detector, so I am looking at actual and indicated speed every time I drive. With stock 225/65R17 tires (2024 fx4 4K tow) and cruise control set to 80, my gps would always show 79 mph.

This is exactly where I want to be, 14 mph over the limit. In my state, fines are different for 1-15 mph over, 16-25 mph and 26+ mph over.

Then I went to a 255/65r17 tire (30.1” and 708 revs per mile, VS 28.5” and 729 revs per mile). Now, when my speedo reads 76, my gps shows 79 mph.

So my maverick was reading 1 mph fast from the factory and now it is reading 3 mph slow because of the larger tires.

If your truck is reading 3 mph slow on stock sized tires, I would take it in to the dealer. Reading a little fast is ok. It prevents you from getting tickets. Reading a lot slow is not ok.

 

[Phimosis]

Glad someone brought this subject up. I have a 2024 FX4 with 4K tow. Stock tires were 225/65 r17 but right away I put 245/65 r17 tires on it expecting it to throw my speedometer off. Unfortunately I didn't test it before I replaced the tires but I have several of those roadside speed check radars all around me that I pass on city streets where I am going between 35 and 45 MPH. They all show that I am going about 1 MPH slower than my speedo says. I was expecting the opposite. Makes me wonder if every one of these roadside speed checkers is wrong or was my speedo a couple MPH off to begin with. I tried to test it with a GPS app and also with Waze but those constantly jump up and down by a couple MPH so I gave up trying to check with those.

im going to bet that the roadside radar detector is wrong and that you are indeed traveling faster than your speedo indicates. Every mile I’ve spent in my Mav has been with a gps enabled radar detector, either a Uniden R4 or an Escort max 360c. With stock tires, the Speedo read 1 mph fast. Now I run 255,65R17’s and the Speedo reads 3 mph slow.

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