How accurate is your speedo

Hello all,

We have just returned from our holidays. During which time i took the lead in getting from one place to another infront of our friends. I told our friends that we cruise at between 55 - 60, however when we got to the camp site i was told that i only hit a max of 53 even though our speedo at the time showed just over 60 and most of the time we weren't even hitting 55 by quite a margin.

I have 185/70/R14 tyres i know these weren't the option when the van left the factory. Is the circumferance that far out that it would throw the speedo readings out by that much.

The other thing, going quite deep here but if it is showing 60 at the speedo the engine has obviously got to turn the wheel round more times to get to the distant end, is this putting more strain on the engine i.e. the engine believes it is going 60 instead of 53 and is revving high. If this is the case am i loosing a lot of MPG.

Your thoughts please or is there nothing to worry about

 

We have a lot of those roadside speed check displays at the side of the road round here, and I've tested my speedo against them. I'm pretty much bang on the same speed, whereas my Seat Ibiza daily overreads about 8%.

My van has 185R14C tyres, just like the ones it came out of the factory with, and on the motorway at 60mph indicated, it's about 58mph on the sat nav.

 

When my speedo reads 70 my sat nav reads 65 and when I go through speed cameras at 30 my sat nav says im doing 25

 

185 R14C tyres (std) are 82
you have 70's so your speedo under-reads.
Google tyre speed calculator and see how far it's out.
That of course assumes your speedo is accurate in the first place.

 

I drive now using satnav speed. It's the most accurate way to stick to speed limit. Regardless of what vehicle you are in.

 

Back in olden days, speedometers were less accurate and were usually set to err on the side of caution so that if you thought you were driving on the speed limit you wouldn't accidentally get done for speeding. Or so the bloke running that Speed Awareness Training session (that I had to sit through last year cuz I got done speeding) told us.

My speedo however vibrates across a range of more than 5 mph so it's anywhere between "about right" and "significantly fast" depending on how you want to interpret it.

 

Mine shows 55 mph for 50

 

According to both sat-naffs **mph is **mph and so on. It's very accurate.

 

Well i have to admit my speedo only reads 55mph max when im chasing down Woody.

However when out alone it seems to go a bit higher. reads 90mph when sat nav says 75mph. 8) :censored:

 

I've been on the tyre bible and now use sat nav to get an accurate reading and also marked the glass on the speedo for 30, 40 and 55 (wish i needed to mark higher but hey ho)

second part of the original post was the question is it putting any extra stress on the engine or working parts making the wheels and engine rev higher because it is actually going 55 but the wheels and engine are working at the equivalent speed of 60, if you understand what i mean!!! or does it not work like that.

As you can guess just lately i have had a bit of extra time on my hands to think of the van

 

yes if you have fitted wheels and tyres with a smaller over all height than stock ( on the rear) you are working your engine harder and using more fuel

 

If your tyres are smaller then I would think that it's effectively the same as running with a slightly lower gear ratio.
So on the -ive side, your engine will be revving higher for a given speed and usually using more fuel; but on the +ive side, hill starts should be a breeze!

 

i got van tyres on15'' and do 33 when speedo says 30... i think. lol
50-55 is a good speed....no worries of a AA or a RAC breakdown truck.

 

All speedos overstate the speed you are doing (up to 10%). This allows for setting errors and in case the dealer fits lower profile tyres. If they were the other way round you could defend a speeding ticket by countersuing the car's manufacturer. So they err on the side of caution. Some are closer than others. VW are (and were) no different.

And one for the mods why does the software on here highlight the word fact even when its part of the spelling of manufacturer?

 

Mine shows 46mph on sat nav when 50mph on the speedo.

 

more accurate than the fuel gauge ...

 

can your sat nav do that... :-[