speedometer and fuel economy figures - not true

Dear All,

The speedometer and fuel economy figures shown in the instrument cluster is not true...
When the speedo shows 80km/hr - the actual speed is only between 70-72km/hr.
Also, if the fuel economy shown is 16km/lt - but when calculated from full tank to full tank
gives only about 14.5km/lt. !!!

Whereas, my 10 year old palio shows exactly the same speed as the GPS!!!

Has any one experienced this?

regards,
Krsna V

Basically it logs a number of lat/long points, and the GPS (atomic based) time it was at those points, and does the maths to calculate the distance between points, and the time it took to travel between those points. From there the rate can easily be calculated.

I think it is reasonably accurate. However, I think a proper speedometer is more accurate, provided the original sized tires are used, or the computer programmed to the actual tire size and all that.

On fuel economy part there would always be +/- errors in manual full tank to full tank and one shown on panel. Figure shown on panel is from time of last reset till that date while, full tank to full tank is for one full tank trip. Not necessarily would one get same kmpl in all full tanks. Also lesser one resets the panel more is the accuracy.

thankyou.
krsna

My Dacia is at least 10km out and this is normal ! which is good for speed cameras and stuff

Generally it is 10 Kms out of sync with GPS and I guess it is due to smaller rim sizes(14 inches against 15 in higher end versions in Europe) that we run here in India.

yes DIS is grossly out of sync with Kmpl and with fuel consumed to the amount of fuel present in the tank.

It is wanted here in Europe ! it is wanted that the Tacho shows more than you are driving for obvious reasons Just do this ! It is the best piece of advice I can give you and this is

DO NOT DRIVE FASTER THAN YOUR GUARDIAN ANGEL CAN FLY

means if speedometer shows 80 KMPH , then your exact speed is 70 KMPH? right?

vabs1981 wrote:

means if speedometer shows 80 KMPH , then your exact speed is 70 KMPH? right?

Could be the case. Does not stand true with all Logans. So not a general conclusion.

99.09 % of Logans have this difference ! In fact most cars do !

I wonder why there is this perception about error in the distance calculation. It is a simple math of multiplying the circumference of the tyre with the number of revs. It could go wrong by a few meters if there is a change in circumference of the tyre due to air pressure variations, but cannot be a 10% error. If you divide that with time, which again is not difficult to measure, you get speed. I am sure that the folks who engineered this master-piece would not be so naive to faulter on such simple math.

I agree with Mir..., GPS calculations cannot be accurate as the odometer. If you find a difference, you should assume that GPS is wrong, not the odometer.

I do agree that there is error in the fuel volume measurement. I have noticed that when I use up 45 ltrs of diesel, the meter actually shows only 38. This is definitely a big error. This introduces error in all calculations related to fuel consumption. Values such as: mileage, distance to empty etc. are all wrong.

That is why we should always measure using tank-full to tank full. There also there is big room for error. I go to a fuel pump where the pump is located on a ground that has a slight slope. When I park my car east-west for filling it takes as much as 49-50 ltrs, when I park west-east it cannot take more than 45 ltrs ! That is the kind of error due to the slope. So when you want to do an accurate measurement of a tank-full, always park in same position and direction at same pump everytime you fill.

If a GPS was not accurate it would not take you direct to the door !! Or the Americans could not place a rocket down the chimney of a House after being launched from sea could it !
You fill the tank and the filler pipe and you will get 5 ltrs more ! and i do not think you will have any filling stations on hills big enough for you to notice any difference in filling !!!a forward or backward slope would not make any difference at all only slope leaning in the direction of the filler cap would !

I think i have take out my fuel tank out & see how much diesel is left in it. coz everytime i fill up it never goes more 49 ltr in tank. May be i clean the tank for that would be useful. coz in my last car esteem i did the same & lot of rust,water i found at the bottom of fuel tank.

It really made a lot of diference in the feel of driving that engine was much smoother than earlier. I'll try this in logan also.......

What do you suggest experts...?

Vaibhav

Maybe Your tank has a dent in it !!!!

no dear...

I've observed the car recently under its body for any leakages & dents. My neighbours always appreciating how much care i took of car.

MY Answer:

Take care of your car when standstill.

She will take care of you when crusing.

BTW.. i didn't observed any dent on the tank. But can a single dent can deduce so much fuel space.? Is it?