Freelander 1 Speedo accuracy & odometer readings

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htr

htr

Well-Known Member
Posts
1,522
Location
Central Otago, Southern New Zealand
My speedo reads faster than my actual speed according to the digital speed signs along some of our main roads here in NZ. I guess that's because I'm running slightly smaller tyres than what the FL1 came out with: 205/70/15 as opposed to the original 195/80/15. This works in my favour as I'm unlikely to get done for speeding. According to those digital speed signs when I think I'm travelling at 100km/h they show about 94/5 km/h, so that's about 6% out.

However, I would assume that my odometer reading will be out too. It will record a lesser distance that what has actually be covered and I guess that will also be 6%.

So does that mean that when I do a fuel economy calculation I should increase the distance travelled by 6% to compensate for that inaccuracy?
 
If your tyres have a smaller circumference then it will take more wheel revolutions to get anywhere than the car expects. Your car will think you have gone FURTHER. Your odo will report 6% too high.
 
htr said:
My speedo reads faster than my actual speed according to the digital speed signs along some of our main roads here in NZ. I guess that's because I'm running slightly smaller tyres than what the FL1 came out with: 205/70/15 as opposed to the original 195/80/15. This works in my favour as I'm unlikely to get done for speeding. According to those digital speed signs when I think I'm travelling at 100km/h they show about 94/5 km/h, so that's about 6% out.

However, I would assume that my odometer reading will be out too. It will record a lesser distance that what has actually be covered and I guess that will also be 6%.

So does that mean that when I do a fuel economy calculation I should increase the distance travelled by 6% to compensate for that inaccuracy?
Click to expand...
If you are running 205/70/15 tyres rather than standard 195/80/15, at an indicated 60 MPH your true road speed will be 57.8 MPH. So for ever 60 miles recorded on your odometer you will only have done 57.8. So you are adding 2.2 miles to your overall recorded mileage for no reason every 60 miles. That will also cock up the fuel computer.
 
Really? If I put skateboard wheels on then the axles would have to spin, say, 100 times more then with stock wheels. The car doesn't know I have toy wheels on so it will report that I have done a distance equivalent to many 100s of revolutions of the stock wheels.
 
davidsmith1307 said:
Really? If I put skateboard wheels on then the axles would have to spin, say, 100 times more then with stock wheels. The car doesn't know I have toy wheels on so it will report that I have done a distance equivalent to many 100s of revolutions of the stock wheels.
Click to expand...

Yes really. If you fit tyres with a smaller rolling radius the the actual road speed will be less than indicated. If you fit tyres with a larger rolling radius the actual road speed will be higher than indicated.
 
wammers said:
If you are running 205/70/15 tyres rather than standard 195/80/15, at an indicated 60 MPH your true road speed will be 57.8 MPH. So for ever 60 miles recorded on your odometer you will only have done 57.8. So you are adding 2.2 miles to your overall recorded mileage for no reason every 60 miles. That will also cock up the fuel computer.
Click to expand...
The speedo and odometer are electronic so I guess both will be out by the same. I added 5% to the distance travelled when doing fuel usage calculations to try and get a more accurate result. Have I done that the right way?
 
htr said:
The speedo and odometer are electronic so I guess both will be out by the same. I added 5% to the distance travelled when doing fuel usage calculations to try and get a more accurate result. Have I done that the right way?
Click to expand...

I have just posted an answer to this problem on another thread. For every 60 miles registered on your odometer you have only travelled 57.8. Because the odometer and speedo are over reading by 2.2 miles every 60 miles. It won't make a vast difference to the fuel calcs but it will make a difference. If you put a gallon of fuel in the car and drove for an hour at an indicated 60 MPH then ran out of fuel. In theory you have done 60 miles to the gallon. Actually you have done 57.8 miles to the gallon because the speedo is over reading the actual road speed. If that makes sense.
 
Speckydude said:
Were you coasting ? :cool:
Click to expand...

Idling in gear coasting down the hill. Most i had seen before was 66 MPG gallon same thing down a hill in Blackburn. Average for the trip 45 miles there 45 miles back was a shade under 34 MPG. Three adults two kids and a boot full of cases.
 
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