Speedometer Vs Odometer
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Cross-Country
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Speedometer Vs Odometer
Forgive my ignorance but I’m trying to think this through. I decided to check my speedometer the other day against a couple different apps on my phone and best I can tell I’m actually doing 48 when my speedometer shows 50 (4% difference right?) Then I checked my odometer on my trip to work- truck odometer recorded 20.2 miles and the gps recorded 20.0 miles (1% difference right?) Now I get that these readings may not be super accurate but before I tested the odometer my initial thought was to upsize my tires from the factory 265/75s to 285s which would correct the 4% speedometer difference. I’m just not sure of where the truck gets the readings for the speedometer vs the odometer and how they would be affected by possibly larger tires?
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Cross-Country
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Ahh so just one sensor for both. Then if I were to upsize the tires 4% to correct the speedometer my odometer would be recording 3% less miles than I’m actually traveling (current 1% over actual miles then subtract 4% for larger tires = 3% under actual miles travelled) or is the math not that straight forward? I’m probably overthinking this
Lead Driver
Joined: Oct 2005
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From: Ponca City, OK
Not sure but can't Forscan make speedo corrections for tire size changes? Would be cheaper than new tires, but if you're just looking for a reason to get bigger tires then math be damned and I'll butt out.
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Cross-Country
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I’m only partially looking for an excuse for bigger tires… (but I’m pretty conscious of fuel mileage so I still need to weigh pros and cons)
I need to get setup on forscan that would be helpful. Also any idea why the odometer would be more accurate than the speedometer coming from the same sensor? Or am I expecting too much accuracy out of a 20yr old truck
I need to get setup on forscan that would be helpful. Also any idea why the odometer would be more accurate than the speedometer coming from the same sensor? Or am I expecting too much accuracy out of a 20yr old truck
Lead Driver
Joined: Oct 2005
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From: Ponca City, OK
I would guess it's more about trying to take a live reading while driving mixed with a little lag in the satellite stream to your phone versus a combined measurement over the span of a 20 mile trip that is the cause of the discrepancy. I mean the data of both reading originate from the same source so how could they actually differ all that much? Unless Ford programed the speedos to read slightly low for some safety purposes or something. Human nature is to push the limits and the only way we would normally have of monitoring our speed is from the speedo. So if we think we're riding the line but actually not who would be the wiser? Conspiracies may be afoot.
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Cross-Country
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Hmm interesting thought about safety with the speedometer. After reflecting on some responses I think I should do further testing between the odometer and the gps. If 1 or 2% is all it’s off by then maybe that’s not too bad. Plus I’d rather have the odometer as accurate as possible I think. Also the argument against bigger tires- every bit of fuel mileage and acceleration comes in handy on these trucks
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Frmr Ford Trans Engr
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The signal going to both is exactly the same. The difference is that the speedos are just not as accurate as you expect.
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Lead Driver
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From: Ponca City, OK
Hmm interesting thought about safety with the speedometer. After reflecting on some responses I think I should do further testing between the odometer and the gps. If 1 or 2% is all it’s off by then maybe that’s not too bad. Plus I’d rather have the odometer as accurate as possible I think. Also the argument against bigger tires- every bit of fuel mileage and acceleration comes in handy on these trucks
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Cross-Country
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Yeah I ran the 285's for a set and switched back to a 235/85. The only thing I did notice between the 2 was MPG. Didn't preform better in the slop and the height difference is negligible really. We can kid ourselves all we want but that extra inch or so isn't going to change the game. Now if acceleration is what you want put that tire money down on some injectors and tuning. They're still bringing a smile to my face after almost 2 years.
Cargo Master
Joined: Aug 2003
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From: Eastern Washington
I got a good deal on some 285/75r16 when I needed some tires. Originals were 265/75r16.
I didn't think about it too much as they are so close in size, but my truck would read a few mph low at 60, now it's spot on.
I didn't notice any difference in MPG.
I didn't think about it too much as they are so close in size, but my truck would read a few mph low at 60, now it's spot on.
I didn't notice any difference in MPG.
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Cross-Country
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Notice any difference in acceleration? The 285s I’ve looked at are several pounds heavier
Cargo Master
Joined: Aug 2003
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From: Eastern Washington
No difference noted. You can probably figure with a 1% change a 1% difference in performance, but its not like we're drag racing. The wind direction probably makes a bigger difference than 265 to 285.
Mountain Pass
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Excursion 2001 PSD 4x4 3.73
Going from 265/75/16 to 285/75/16 changed the speedometer reading and now indicates speed as follows:
After change speedo is almost correct. Was reading about 58 mph with the 265's (gps speed was 60)
With the 285 tires 60 indicated is about 61-62.
On my truck the fuel milage is about the same, but the tires seem to last longer. (no towing or hauling)
I would not go back to the 265's personally. But the 235/85/16 seem interesting. I did not check but guess the 265/85/16 are not a common size. I don't drive in snow but wonder if the narrow tires would be better in the snow. (My truck never has been in winter conditions as I live in FL and rarely drive out of state.)
Going from 265/75/16 to 285/75/16 changed the speedometer reading and now indicates speed as follows:
After change speedo is almost correct. Was reading about 58 mph with the 265's (gps speed was 60)
With the 285 tires 60 indicated is about 61-62.
On my truck the fuel milage is about the same, but the tires seem to last longer. (no towing or hauling)
I would not go back to the 265's personally. But the 235/85/16 seem interesting. I did not check but guess the 265/85/16 are not a common size. I don't drive in snow but wonder if the narrow tires would be better in the snow. (My truck never has been in winter conditions as I live in FL and rarely drive out of state.)
