Google map distance v cars.

[Macadoodle]

I've found that my car tends to over report distance by around 2% compared to plotting precise points with GM.
Not sure which one will be more accurate, thoughts ?

Edit - sorry, UNDER report distance is what I meant to say, car says 98, GM says 100 .

 

[Ian Key]

I used to visit my auntie who lived in Cheltenham from where I lived in Derby. Coming back was a mile further because I was going round the outside of the bends and traffic islands.

 

[tsedge]

There's also the accuracy of the speedometer. Normally they over-read to comply with the law.

 

[Macadoodle]

There's also the accuracy of the speedometer. Normally they over-read to comply with the law.

Speedo seems to overread slightly, weird if the odometer does the opposite.
In Bjorn Nyland's vids he seems to quote google maps distances all the time, some cars do under report and I think the 4 he had on test did so.
Only wondering as it will mean our miles / kWh figures will be a little better than we're thinking

 

[Rolfe]

I've also formed the impression that my car is under-reporting mileage compared to my previous car doing the same journeys. I'm not wholly certain though.

I am certain that the speedo is dead on and is not over-reading, unlike any other car I have ever driven.

 

[pd2]

I am certain that the speedo is dead on and is not over-reading, unlike any other car I have ever driven.

I agree with this, i tested mine using waze on my wifes phone not connected to the car it was spot on with every mph change. So 70 on the gps was 70mph on the car. Tried with various speeds and all were the same.

 

[Rolfe]

There are 20 mph limits in my village and the surrounding ones, and there are real time speed readouts to warn drivers if they're exceeding this. Other cars, speedo had to be at least 22 to get a 20 readout. The MG4 is spot on the nail. So I hope that speed camera van in Edinburgh a week past Saturday wasn't looking because my speedo said 37 and the limit was 30.

 

[Alb]

I find those real time speed detectors usually read over rather than under or spot-on.

 

[Rolfe]

Well, they agree perfectly with my MG4.

 

[PeteC]

I've also formed the impression that my car is under-reporting mileage compared to my previous car doing the same journeys. I'm not wholly certain though.

I am certain that the speedo is dead on and is not over-reading, unlike any other car I have ever driven.

My MG is also reporting lower journey mileages than my previous car.

 

[Rolfe]

Does anyone know if these mileages are in synch with the odometer? If the odometer is inaccurate that's quite a serious issue.

 

[okohll]

I don't know how accurate they usually are but if it's only 2%, it doesn't sound like a big issue. There could be various sources of error I guess. The odometer is probably reading from motor/wheel rotations, translations to distance will depend on how pumped up tyres are (I'm assuming massive skids aren't a factor in most journeys). Similarly, Google maps may have small sources of error, e.g. if the sampling size for elevation changes isn't very small, bumps and dips could be missed etc. And as people have said, inside/outside lanes, or lots of weaving perhaps.

 

[tsedge]

Normally the speed and distance sources are the same, so they agree. But MG could be doing something weird.

 

[Rolfe]

It's odd that several people are mentioning it though. And since I'm suspicious of an inaccuracy on journeys of about 40 miles I think it could be more than 2%.

 

[spence7788]

My speedo is exactly & I mean exactly as per 3 different GPS devices & various real time speed signs which I've always found pretty accurate so pretty confident it's as per exactly the real speed, every other car I've had has over-read slightly so I was slightly surprised by this, I also do the same journey day in, day out & at a couple of points have noticed it's around a mile less than my old MG5, haven't looked on Google maps, & depending on tyre wear etc. Rolling radius I suppose there's always going to be certain variables but as a general rule I think they do under or more likely more accurately report milage. Just my unscientific experience. ?

 

[Rolfe]

I just did a rough test. There is a point on my journey home I had always pegged as being 8 miles from my house, give or take very little. I checked the mileage showing for that stretch this afternoon. 7.3 miles. That's some way shorter than "give or take". In fact it's nearly 9% short of the expected distance.

 

[Macadoodle]

I just did a rough test. There is a point on my journey home I had always pegged as being 8 miles from my house, give or take very little. I checked the mileage showing for that stretch this afternoon. 7.3 miles. That's some way shorter than "give or take". In fact it's nearly 9% short of the expected distance.

Wow, that's quite a discrepancy if it's accurate. Don't think my one is that far out but I have always felt that it was being modest with mileage.
In the decent heat today I recorded a surprising 5.6 miles / kWh after a moderately sedate 35 mile run on mainly B roads, a genuine 6 seems to be on the cards if it is under reporting.
Hyundai go home

 

[Rolfe]

I wouldn't put too much faith in a single observation. But it's an impression I get quite often, when I'm doing journeys I did frequently in my previous car.

 

[ukslim]

I read here that:

The UK law is based on the EU standard, with some minor changes. A speedo must never show less than the actual speed, and must never show more than 110% of actual speed + 6.25mph.

So if your true speed is 40mph, your speedo could legally be reading up to 50.25mph but never less than 40mph. Or to put it another way, if your speedo is reading 50mph, you won’t be doing more than 50mph but it’s possible you might actually only be travelling at 40mph.

Certainly the calibration will err on the side of over-reporting speed, so as not to end up on the wrong side of the law. But you'd hope that the MG would be pretty close, especially since many of us will be using TFA / CC set at exactly the speed limit.

 

[Macadoodle]

The need for a speedo to never under-read is understandable, not sure if there are any laws regarding odo accuracy though.