Calculation of Speed and Kilometers

[Guest]

How accurate is the Challenger PC speedo?
A recent check compared to my GPS is
Challenger Speed 100kph GPS 93kph
Challenger Kilometers travelled 93.4kl GPS 92.1kl
Obviously two different methods are used to calculate the difference of speeds and kilometers travelled. So the question is which method is used to calculate the fuel economy and distance available?

[old Jack]

Kilometres traveled as displayed on the odometer.
Have you also checked your odometer against the km markers on the side of the road?

OJ.

[Dicko1]

Kilometres traveled as displayed on the odometer.
Have you also checked your odometer against the km markers on the side of the road?

OJ.

I,ve checked my NW,s speedo with the road klm markers Over a 5 klm stretch I reckon I,m about .2 over So thats roughly 4klm per 100klms over what I have actually travelld. I just dont understand some of the ultra low fuel usage some members on the forum get. They must drive at 85kph, with no passengers or accessories and drive like "old women"....




Either that or their figures are just plain wrong.

[nj swb]

How accurate is the Challenger PC speedo?
A recent check compared to my GPS is
Challenger Speed 100kph GPS 93kph
Challenger Kilometers travelled 93.4kl GPS 92.1kl
Obviously two different methods are used to calculate the difference of speeds and kilometers travelled. So the question is which method is used to calculate the fuel economy and distance available?

Not different methods, just different factors.

The transfer case has a "sender" that puts out pulses based on rotation of the output shaft. Each pulse effectively represents a small distance - maybe a few hundred mm. An ecu counts the number of pulses and multiplies by a factor for distance (odometer). The same ecu measures the frequency the pulses and multiplies by a factor for speed (speedometer). Because our ADRs have some strange requirements for accuracy of the speedometer, different factors are used for each calculation.

Fuel economy and distance available don't use speed in the calculations - only distance. I find my economy reading is surprisingly accurate, if a little high - my calculations typically return slightly better economy than the meter. Distance wise, compared against a gps and roadside markers, my odometer is accurate within 0.5km per 100km. About 0.5% error.

[NJV6]

my odometer is accurate within 0.5km per 100km. About 0.5% error.

That’s with your one size bigger tyres I take it? My NT says 100 on the dial, 97 on the ultragauge plugged into the ECU and 95 on the GPS!

[nj swb]

That’s with your one size bigger tyres I take it? My NT says 100 on the dial, 97 on the ultragauge plugged into the ECU and 95 on the GPS!

Yes, one size bigger tyres, but I'm talking distance, not speed. Multiple times, over a variety of distances in different places, I've compared what my odometer reports vs road side markers and OziExplorer trip meters. The difference typically works out at less than 500m error in 100km, but more than 400m. My odometer reports higher than the other methods. I think. With that level of error, it really doesn't bother me which way around it is.

Speed wise, its 2 - 3 km/h at 100km/h GPS i.e. 100km/h on the GPS is about 102 / 103 on the speedometer. I don't look at the "speedo" speed on Torque - I have it displaying GPS speed.

At times, I have 3 different GPS devices displaying speed - Torque, OziExplorer on an Android tablet, and OziExplorer on my Android in-dash head unit. It's not unusual for the readings to disagree by 1 or 2 km/h.

[BMN]

How accurate is the Challenger PC speedo?
A recent check compared to my GPS is
Challenger Speed 100kph GPS 93kph
Challenger Kilometers travelled 93.4kl GPS 92.1kl
Obviously two different methods are used to calculate the difference of speeds and kilometers travelled. So the question is which method is used to calculate the fuel economy and distance available?

I think by law speedo is not allowed to read under and they have a 10% error allowance meaning speedo can show 100kph but actual speed is 90kph. I think this is one reason people appear to be sitting on 100kph in 110kph zones. My PB reads over like yours by about 7-8% so happily sit on 118-120kph speedo reading in 110 zones and never get flashed.

[Guest]

Kilometres traveled as displayed on the odometer.
Have you also checked your odometer against the km markers on the side of the road?

OJ.

No I haven't. But an interesting suggestion. Not back home from overseas until mid Dec. Will give that a check. Interesting the comments from others

[BMN]

Worse than what i thought. They are allowed 10% +4kph.....no wonder many drive under the speed limit

https://www.racq.com.au/cars-and-driving/safety-on-the-road/driving-safely/speedo-accuracy

[nj swb]

Worse than what i thought. They are allowed 10% +4kph.....no wonder many drive under the speed limit

Yep. Safety first! Don't drive at the speed limit, drive under it. So people think they're "driving safely" at 95km/h, when they're really somewhere under 90, and glaring disapprovingly at everybody driving 10km/h faster - but still under the speed limit.

Ignorance may be bliss, but so many of the ignorant are still unhappy with their fellow road users.

[BMN]

Yep. Safety first! Don't drive at the speed limit, drive under it. So people think they're "driving safely" at 95km/h, when they're really somewhere under 90, and glaring disapprovingly at everybody driving 10km/h faster - but still under the speed limit.

Ignorance may be bliss, but so many of the ignorant are still unhappy with their fellow road users.

All while they sit in the right hand lane.

[Dicko1]

All while they sit in the right hand lane.

And do 5kph over the speed limit when they hit the overtaking lane...bastards!!