Speedometer/Odometer accuracy for factory Sasquatch 35s?

[BulldogBear]

How accurate are the speedo/odo from the factory for a Sasquatch Bronco?

At 45mph on the Bronco Speedometer, the various stationary radar speed warning signs around town and my own GPS tracking tell me I'm going between 42-43mph. 5-7% off doesn't seem to great - with 13k on the odo, that could be an inaccurate increase of 900 miles on the dial…

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[Ducati1098]

There’s quite a few different threads on this. Most cars are up to 10% off. It’s pretty normal. There are ways to adjust it if you want to though.

 

[RagnarKon]

Yeah the speedometer programming isn't 100% accurate. Ford (and most other manufacturers) tend to over-predict on the speedometer in an attempt to account for tire wear, normal variation on tire sizes, etc. In general, it is better to over-predict than under-predict because... well... you don't usually get speeding tickets for going under the speed limit.

The over-predicting becomes more obvious on larger tires with bigger tread depth... which... obviously is what the Sasquatch package is all about.

You can reprogram your vehicle in Forscan to be more accurate, you just have to remember to periodically re-program as your tires wear.

 

[da_jokker]

Would correcting you speed improve your MPG? Seems like if the vehicle is going further then it thinks it's going, you're getting lower MPG numbers (Even if calculating by hand) than real world

 

[Ducati1098]

Would correcting you speed improve your MPG? Seems like if the vehicle is going further then it thinks it's going, you're getting lower MPG numbers (Even if calculating by hand) than real world

No, it would be opposite. You’re getting less mileage on a tank of gas than the odometer says you are, so it’s over exaggerating your fuel mileage.

 

[freetors]

One thing to keep in mind is that speedometer and odometer accuracy are not necessarily linked 1:1. I would bet that you're odometer, with the factory installed tire size, is likely accurate to within about 2% or so. However the speedometer really doesn't need to be that accurate and can be quite a bit off.. You'll have to determine for yourself whether you value speedo or odo accuracy more when you recalibrate. Personally I'd rather have a more accurate odometer because it's easier to not have to apply a correction factor when calculating my gas mileage and the numbers are larger. I can estimate my actual speed pretty well while driving with the simple two digit speeds and a known percent error.

 

[Lcubed]

One thing to keep in mind is that speedometer and odometer accuracy are not necessarily linked 1:1. I would bet that you're odometer, with the factory installed tire size, is likely accurate to within about 2% or so. However the speedometer really doesn't need to be that accurate and can be quite a bit off.. You'll have to determine for yourself whether you value speedo or odo accuracy more when you recalibrate. Personally I'd rather have a more accurate odometer because it's easier to not have to apply a correction factor when calculating my gas mileage and the numbers are larger. I can estimate my actual speed pretty well while driving with the simple two digit speeds and a known percent error.

since both the odo and the speedo are using the same basic input for their calculation (that is, distance travelled for a single revolution of the tire), they are very tied together.

both change when a single value is changed within FORSCAN.

 

[Ducati1098]

since both the odo and the speedo are using the same basic input for their calculation (that is, distance travelled for a single revolution of the tire), they are very tied together.

both change when a single value is changed within FORSCAN.

I agree with this. I would say they are 100% linked 1:1

 

[freetors]

since both the odo and the speedo are using the same basic input for their calculation (that is, distance travelled for a single revolution of the tire), they are very tied together.

both change when a single value is changed within FORSCAN.

I'm not saying that they are or aren't 1:1 percent errors, I don't even have a Bronco. I'm just saying that it's possible. If you've ever ridden a Japanese motorcycle from the last 20 years you'll see what I mean. They almost always come with odometers that are VERY accurate but their speedometers often read up to 10% higher than actual. They get their inputs from the same sensors, but they are intentionally programmed differently.

 

[Jdc]

I'm not saying that they are or aren't 1:1 percent errors, I don't even have a Bronco. I'm just saying that it's possible. If you've ever ridden a Japanese motorcycle from the last 20 years you'll see what I mean. They almost always come with odometers that are VERY accurate but their speedometers often read up to 10% higher than actual. They get their inputs from the same sensors, but they are intentionally programmed differently.

Unless you're very meticulously tracking miles driven how would you know that the odometer is off?

Also, the wife drives a Mazda CX-5 and I've compared the GPS speed to speedometer and it's pretty damn accurate. I'd say with a couple percentage points of each other if not dead on quite often.

 

[freetors]

Unless you're very meticulously tracking miles driven how would you know that the odometer is off?

Also, the wife drives a Mazda CX-5 and I've compared the GPS speed to speedometer and it's pretty damn accurate. I'd say with a couple percentage points of each other if not dead on quite often.

You have to do the legwork. Best way to do it is on a roadtrip on a long highway or interstate and zeroing your trip odometer and starting a gps odometer at the same time. Note the mileages at the end of the drive and do the math for percent difference. You can also count mile markers but the gps is a lot easier. The more miles you can drive on that trip the better the accuracy will be. 20 is ok, 50 is better, 100+ will be really good. Also avoid doing this on really hilly or curvy roads to avoid gps errors - gps distance tracking works on dropping points at certain time intervals and then makes straight lines between them so curvy roads can report shorter distances than you actually travelled.

You might be surprised at the results...

 

[Lcubed]

I'm not saying that they are or aren't 1:1 percent errors, I don't even have a Bronco. I'm just saying that it's possible. If you've ever ridden a Japanese motorcycle from the last 20 years you'll see what I mean. They almost always come with odometers that are VERY accurate but their speedometers often read up to 10% higher than actual. They get their inputs from the same sensors, but they are intentionally programmed differently.

are you saying that if i were to tweak the FORSCAN tire variable to by 10%, the ODO and SPEEDO might shift by different percentage amounts?

i could only see that happening if the hardware supported using different (non-linear) lookup tables for calculating speed and distance.

or if the BRONCO was a top fuel dragster where the tire diameter depends on RPM

i don't see why FORD would use such a solution for this. makes sense for things like measuring airflow, etc since those may feed a N-dimension table for desired engine performance.

 

[freetors]

are you saying that if i were to tweak the FORSCAN tire variable to by 10%, the ODO and SPEEDO might shift by different percentage amounts?

i could only see that happening if the hardware supported using different (non-linear) lookup tables for calculating speed and distance.

or if the BRONCO was a top fuel dragster where the tire diameter depends on RPM

i don't see why FORD would use such a solution for this. makes sense for things like measuring airflow, etc since those may feed a N-dimension table for desired engine performance.

I don't have a bronco and I've never used forscan so I can only speculate, but my guess is that *IF* there is a percent error discrepancy between the the speedo and odo, then it's probably a hard coded difference and probably extremely unlikely to be adjustable by any readily available software like forscan. But like I said, it's only speculation, and it's a speculation based on a presumption that they might be programmed differently. It's going to take real world users to do the test and post their results to know for sure.

 

[lapazleo]

No, it would be opposite. You’re getting less mileage on a tank of gas than the odometer says you are, so it’s over exaggerating your fuel mileage.

Fuel mileage on most vehicles dashes are usually off any way. The fuel mileage on the dash of most vehicles is calculated buy fuel pressure and flow not the odo or speedo.

 

[Ducati1098]

Fuel mileage on most vehicles dashes are usually off any way. The fuel mileage on the dash of most vehicles is calculated buy fuel pressure and flow not the odo or speedo.

Fuel mileage is actually based on fuel alcohol percentage, fuel flow volume display, fuel level reading display, odometer count and fuel level input from the IPC.

That being said, I’m not sure how accurate it is on the bronco. I’ve never calculated it by myself on mine. I’m sure it’s relatively close however.

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