sat nav mph and speedo mph quite different

[63rub]

2010 octavia 1.8tsi dsg7

when driving my satnav will say 70mph and my speedo says about 76

at 30 speedo says about 35

I am on factory 16 x 6.5 inch wheels with 205 50 16 toyo t1r

I have now tried three different sat navs now and i still get the same readings.

i am beginning to think that they may be the wrong wheels, but I'm not sure how to find out for sure

I didn't buy the car new so I don't know if they were changed at some point.

is thre a code no to look for or can vcds tell what the speedo is calibrated for?

[langers2k]

Think 205 55 r16 is standard.

Even with the right size I'd expect your speedo to over read slightly.

[deemack]

Your car's speedo is designed to overstate your speed so that when you get nicked you can't sue Skoda.

In straight and level flight with a good signal your sat nav unit will be displaying your actual measured speed.

I don't know what the Skoda over read factor is but it looks like about 10% if your wheels & tyres are OEM fitment.

[Bazzer1955]

My 54 plate 1.9 pd is exactly the same when comparing the speedo to my Tomtom and as far know it is on the original alloys, 44 mph registered on the speedo is 40 mph on the Tomtom

[WaveyDavey]

Perfectly normal.... Your speedo is designed to over read like this.

[ayouden]

My 2.0 TDi VRS 2010 reads 73mph speedo and 70mph on SatNav.

 

My old '09 Fiesta was around 80mph Speedo and 70mph SatNav!

 

Not sure if my SatNav is wrong, but I have compared to another SatNav make and that gives the same reading.

 

But all in all, yes, it is meant to over-read

[gav_is_con]

My 54 plate 1.9 pd is exactly the same when comparing the speedo to my Tomtom and as far know it is on the original alloys, 44 mph registered on the speedo is 40 mph on the Tomtom

Same on my 1.9 with 205/55/16 tyres.

Sent from my iPhone using Tapatalk

[Stoofa]

In the UK a speedometer must never show an indicated speed less than the actual speed.

The indicated speed must not exceed 110% of the actual speed plus 6.25mph.

 

So, for example.

Vehicle travelling at 50mph - the speedometer must show a reading between 50mph & 61.25mph

[brad1.8T]

I am on factory 16 x 6.5 inch wheels with 205 50 16 toyo t1r

 

Wrong size tyre.

OEM size is 205/55r16

 

50 profile would have to be a 225/50r16.

[labman1001]

I'm on 225/45/17 tyres and the difference between SatNav and Speedo is between. 2 and 4 mph ... At 30 on SatNav the Speedo is 32 and at 70 it's 74 on Speedo....

[KBPhoto]

I've found both my Skodas to be displaying 2-3 mph over at 30 and 3-4 mph at 60; and both had factory fitted wheels with correct tyre sizes.

With the Columbus I can see the CAN speed which is always lower that the speed displayed in the instrument panel.

It's no surprise that there is a discrepancy between the two. My dad's old Nissan Primera was way out - when doing 70mph the display would be about 85!!! At 30 it showed almost 40...

Edited 9 May, 2016 by KBPhoto

[Jevpls]

It's normal. Speedometers do that all the time and people in posts above have explained why.

By the way, I think that if you wish to compare speedometer readings to ones done by GPS device then you should have a professional GPS, not your mobile phone or some cheap device with doubtful accuracy. And yes, you should drive straight on flat terrrain.

[darius]

Yes normal - that why I set my cruse control to the GPS speed 70mph and not the speedo.

[logiclee]

Even tyres of the same stated size can be different diameter.

 

My Passat has 235/45x17's fitted. With Conti Sports fitted at 70mph the speedo reads 73mph. With Goodyear eagle F1's Assy 3's the speed reads 76mph.

 

Even though both tyres are the same size side by side the goodyears appear lower profile and wider.

 

Lee

[Jevpls]

About tyres: there is a little difference between new tyres and worn ones. I made some calculations and seems like there is like ~2 kph difference in speed between new tyres (I used 9mm tread depth) and worn ones (2mm).

Not much but if you want to be accurate...

[0ctavist]

...changed my wheels to the Scout size 225/50/17 instead the original 225/45/17...now my speedo shows nearly exact the speed of the SatNav

When I go 100km/h by SatNav the speedo shows a tick over 100...

 

The driving comfort is much better especially on our bad french country roads

 

Original old wheels Skoda Pegasus with 225/45/17

 

new wheels Keskin with 225/50/17

[63rub]

I have checked my tyre size again and they are actually 205 55 16, my bad on the earlier post.

and I have compared the speedo with a military sat nav with external transmiter / receiver.

now that I know everyone is getting similar readings my question is now answered, thanks everyone.

[brad1.8T]

...changed my wheels to the Scout size 225/50/17 instead the original 225/45/17...now my speedo shows nearly exact the speed of the SatNav

When I go 100km/h by SatNav the speedo shows a tick over 100...

 

The driving comfort is much better especially on our bad french country roads

 

Original old wheels Skoda Pegasus with 225/45/17

 

 

new wheels Keskin with 225/50/17

 

How were the 225/50r17 going around corners?  Any rubbing on the front?

 

I had 225/50r17 with 17x7.5 ET45 and Eibach Sportline springs and the front would get minor scraping if it hit a bump mid-corner.  It wasn't causing damage but the noise stopped you from attacking a corner.  If they didn't foul the bodywork they would have been ideal.  Agree, speedo was spot-on.

 

The other size that I liked (and it didn't foul the bodywork) was 225/55r16 on 16x7.5 ET50.  They were just a fraction smaller.  Speedo was out by maybe 3kph, which was fine by me.

 

I'm currently running 225/40r17 which are 5-6kph out and I tend to speed more as I know that there's some wiggle room available.

[0ctavist]

No problems with rubbing, my rims have ET48 instead the  ET54 of the Pegasus and rear I have additional a 15mm H&R spacer.

But I have other shocks and springs mounted. HD springs rear and  new Sachs gasshocks for towing all around makes the car 1cm higher.....more  load now possible without hanging on the wheels......very happy with that combination.... 

 

Ordered mud shields all around and will see this weekend, if they will cause  problems...

Edited 12 May, 2016 by 0ctavist

[brad1.8T]

I like it.  I might go back to the big tyres when I take the eibachs off (slowly putting car back to stock(ish) in preparation for giving car to daughter).  I really liked the way they filled the guards.