Road Trip Observations (Speedo error)

The Long Ranger

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I did a 200 miler yesterday (one way) and returned today. Three observations. #1: My Ranger does NOT like 25-35 MPH crosswinds. It was all over the place. I shut down the Driver Assist cause it was driving it crazy. #2: My analog speedometer and my digital speed readout don't match. The digital reads 3-4 MPH faster than the speedometer dial. #3: I was getting "Speed Trap Ahead" alerts on the sound system. I assume they were generated by Android Auto but not sure. And I averaged 26.5 MPG. (by the trip computer)
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Definitely interesting. I know my speedometer read faster than actual speed with stock tires, and after I went up 1” in diameter both are dead on accurate after testing with my phone GPS.
 

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The "Speed Trap Ahead" sounds like a Waze warning "Police Reported Ahead".

Waze Pro tip: Set the voice to Kate-British. The clearest and most easily understood of the voices I've tried.

I always run Waze when on a road trip if for no other reason than the traffic, road debris, and hidden revenue generation opportunities that it mentions (I rarely go 5 over the limit but I still like to know when they are around)
 
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The Long Ranger

The Long Ranger

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The "Speed Trap Ahead" sounds like a Waze warning "Police Reported Ahead".

Waze Pro tip: Set the voice to Kate-British. The clearest and most easily understood of the voices I've tried.

I always run Waze when on a road trip if for no other reason than the traffic, road debris, and hidden revenue generation opportunities that it mentions (I rarely go 5 over the limit but I still like to know when they are around)
Not familiar with Waze.
 

Dr. Zaius

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Langwilliams

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I've heard of it but never installed it, until reading this post. I haven't verified my speedometer with my phone gps yet. I did on my fusion an it read about 2 mph faster than I was actually going. I had the base car with the 16" wheels an wondered if it because they use the same speed calibration for all models, some have 17 an 18" wheels.
 

P. A. Schilke

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I've heard of it but never installed it, until reading this post. I haven't verified my speedometer with my phone gps yet. I did on my fusion an it read about 2 mph faster than I was actually going. I had the base car with the 16" wheels an wondered if it because they use the same speed calibration for all models, some have 17 an 18" wheels.
Hi Langley,

Back Story. Way before electronic speedometers. The speedometer was cable driven off the rear of the transmission up to the instrument cluster. We were for ever swapping axles/ transmissions and even engines. So determining speed for following test procedures was problematic. Thus we used the bicycle 5th wheels that you use to see in testing photographs. Now getting a 5th wheel installed was a PITA, so we resorted to all sorts of work arounds. There were three drive gears on the output of the Transmission and about 17 driven gears on the speedo cable. When testing, the speedo was always suspect. The Dearborn Police knew this and cut us huge slack as they understood this when we were on public streets and even the freeways. What we did mostly to "calibrate the speedo" was to drive the high speed test track at an indicated 60 mph over the measured mile on the high speed test track If it timed out to one minute, the the speedo was correct...if not we had a rule of thumb that that one tooth on the driven gear was good for 3mph, so we could roughly calculate the need for increase or reduction of the driven gear vs what was installed in the truck. So if the truck had a 17 tooth and was too fast, we needed to increase indicated speed by two teeth, a 15 toothed gear was good. Or conversely if we needed to slow the indicated speed, as the truck was below the 60 minute mile we could go with a 19 tooth gear. Sometimes this would not work as the trans drive gear was wrong, so in these cases we had "cheater" cards that showed us about 6 speeds. eg. 50 indicated is 46.4 mph which gave us an idea of what speed was needed for testing.

Then with the development of radar guns for speed, we could home in on the speedo gear change very quickly and so we had acces to radar guns. The downside was when we were on the freeways and hit the radar gun, we faced tons of brake lights as all the folks on the freeway (or many of them) had radar detectors, so we learned very quickly to not use the radar guns on the public roads as it could cause inadvertent traffic jambs.

Best,
Phil Schilke
Ranger Vehicle Engineering
Ford Motor Co. Retired
 

charwest

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did anybody get back to you about the dial/digital discrepancy? mine also runs 2-3mph slower on the dial and i’m wondering which is accurate and why there might be a discrepancy in the first place?

i was assuming the dial is an analog interpretation of the same input. i can’t imagine a truck with this much electronic gadgetry has a speedometer cable.



I did a 200 miler yesterday (one way) and returned today. Three observations. #1: My Ranger does NOT like 25-35 MPH crosswinds. It was all over the place. I shut down the Driver Assist cause it was driving it crazy. #2: My analog speedometer and my digital speed readout don't match. The digital reads 3-4 MPH faster than the speedometer dial. #3: I was getting "Speed Trap Ahead" alerts on the sound system. I assume they were generated by Android Auto but not sure. And I averaged 26.5 MPG. (by the trip computer)
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The Long Ranger

The Long Ranger

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No Char. Still don't know why the discrepancy but I don't notice it anymore. I rarely drive the Ranger now. It hasn't been on the road in over a month.
 

charwest

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did anybody get back to you about the dial/digital discrepancy? mine also runs 2-3mph slower on the dial and i’m wondering which is accurate and why there might be a discrepancy in the first place?

i was assuming the dial is an analog interpretation of the same input. i can’t imagine a truck with this much electronic gadgetry has a speedometer cable.



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image.jpg
I brought my gps along this weekend. On a straightaway with the cruise control on 55mph and the digital speedo saying 55 and the gps saying 55.5mph (+/- ~0.2mph) the dash gauge dial comes up around 52-53mph.

So I’m convinced the dial is the outlier as everything else matches up. It annoys me a little there is a discrepancy but ultimately doesn’t matter. I’m happier now knowing which to trust (digital, not dial).
 

rang19ca

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I always wondered if manufacturers purposely ran the calibrations low to slow people down. I have no inside info on this, maybe Phil has some ?
 

slowmachine

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I always wondered if manufacturers purposely ran the calibrations low to slow people down. I have no inside info on this, maybe Phil has some ?
I have read that to comply with USA laws, the actual speed of the car cannot be faster than the indicated speed on the gauge. To ensure compliance, the actual speed will always be a bit less than indicated.

An interesting aside - German engineering is a source of national pride, and the speedometers on my BMWs indicate just about exactly 3 MPH faster than actual speed with the OE tires. When you dig into the software configuration for the car (similar to Forscan) there is an option to disable the 3 MPH discrepancy, but it will not work for USA-market cars.
 

rang19ca

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I have read that to comply with USA laws, the actual speed of the car cannot be faster than the indicated speed on the gauge. To ensure compliance, the actual speed will always be a bit less than indicated.

An interesting aside - German engineering is a source of national pride, and the speedometers on my BMWs indicate just about exactly 3 MPH faster than actual speed with the OE tires. When you dig into the software configuration for the car (similar to Forscan) there is an option to disable the 3 MPH discrepancy, but it will not work for USA-market cars.
Now that sounds like something the German automakers would do.
 

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My speedo is about 1 mph off per 10mph in speed. No idea why 33" tires put it so far off.

At 77mph per GPS (which was cross-check in a different vehicle as +1/-1 accuracy) my Ranger is showing 70mph.

I have appointment Friday for shudder TSB at cold start going to tell them to re-calibrate speedo since THEY are the ones who installed the tires before I came along and bought the truck.
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