Hey guys, do the Octavia Speedometer is exactly on the speed it shows?

I have run my 1.8T at 240 KMs :eyecrazy: (Speedometer reading) but, do I was REALLY doing that speed???

BTW, My car has factory 16 inch wheels with 205/55/16 tires. Do this influence something with the Speedometer?

What about you RS guys with 17 inch wheels?

Try this one

http://briskoda.net/forums/showthread.php?s=&threadid=1578&highlight=speedo

my vRS over reads by 2-3 mph according to the gps...

Varies according to speed on mine.

Originally posted by TaviaRS in this post

Varies according to speed on mine.

put 19" wheels on then.. it will be perfect!

im sure mine varies as well but havent paid that much attention

19s? Nope, to big, to fragile. 18s, quite possibly if I ever considered modifying my car from its pristine and unblemished standard condition.

The speedometer accuracy on my new 1.9 TDi Octavia Elegance is the only disappointment on an otherwise great car. According to my GPS the speedo overreads throughout the range by about 10%. This is right on the legal limit for accuracy! Does anyone know if it can be adjusted or is likely to improve with use? I presume the fuel consumption displays are also affected by this or do they use a different speed sensor?

Jim - Change the rolling radius of your wheels by 10%. If you're on something like 225/50 R16, maybe a change to 245/50 R17 would get the speedo reading better. Although rubbing may become an issue (and if you can't see I'm joking - I am.)

My new wheels have thrown all my readings out a bit, but only by about 3%.

Think they use a different speed sensor.

Wasn't aware there was any restriction on overreading, I thought the only regulation was that it can't underread. Not that I ever really bother using the speedo anyway...

Rob.

I too have the same issue where the speedo reads over by 10% (standard Wheels & Tyres).

I spoke to Thatcham Research Institute, who said "depending upon which type of Electronic System it is will depend upon which Standard VAG build to", "Should not be that high on a modern car!"

So, contatced Skoda Customer Servs, Spoke to one of LadyLoki's Colleagues (M.M.) who checked & said

"Skoda does not concede that there are any accuracy issues, the speedo should be accurate. Our retailers can check it on their Rolling roads (?)."

When we had the discussion on GPS being different, stock response was "GPS could be more accurate !!", but Skoda still claim that the speedo is accurate & therefore give no %age error margins (or give out the standard to which they work.)

"Speedo is accurate, but GPS is MORE accurate" ??? = Speedo is not accurate !!!

:confused:

Graham

The speedo isn't accurate on the Octavia! Period. Interestingly, when I was in Holland this summer I used my GPS in brother-in-law's VW Sharan to check his speedo and it (the speedo) was out by only 1kph at 130kph. If VAG can fit accurate speedos to the Sharan they should be able to do the same for the Octavia.

According to my GPS, my speedo is 5mph out at an indicated 70mph (GPS Speed = 65)

At an idicated 30 mph the difference is 1 or 2 mph, so near enough.

I did a simple calc using the revs (assuming the tacho to be accurate:rolleyes: ) and mine isn't anymore than 3mph over at 70mph.

Probably not very accurate.

The relationship between the tachometer and speedo is determined by the gear ratios so you can't deduce anything from this. The problem is most likely related to the assumed rolling radius of the tyres (tyre pressure and wear has a marginal effect). I am beginning to suspect that the speedo was designed to be used with a different wheel and tyre combination than is actually fitted. The tyres are quite low profile - maybe there has been a design change and they forgot to modify the speedo!

Jim,

we know what speed is expected a 1k rpm in fifth.

So if 1krpm = 23mph in fifth gear can I not assume that 3krpm = 69mph (expected) in the same gear?

Just interested.

Cheers.

Adrian.

You are correct but if your tacho reads 3000 and speedo reads 69 this does not mean the speedo is accurate. You may only be travelling at 60 mph. You need an accurate independent means of measuring your speed. Either GPS or timing over a measured distance.

I think I get it now....although you're speedo read 69mph you may be actually doing something else due to diameter of wheels.

I think speedo reading comes off gearbox so although the gearbox reads one value the actual reading at the wheels may be different.

Ta.

Adrian.

Adrian, either borrow a GPS to check your speedo or else use the distance markers beside the road together with a stopwatch. It might also be worth looking for the special markers that police forces use to check their speedos whilst out on the road. I will try and find a picture of what they look like.

They start off with a single yellow disc, next one is 1/4 red 3/4 yellow, then 1/2 red 1/2 yellow, then 3/4 red 1/4 yellow, last one is full red. At a guess I'd say they were approx8-10" diameter. You see them by the side of motorways.

I can see it now.....

so how di you acutally come to have your accident Sir?

well officer I was looking out for these coloured disks to check out my speeding reading? Quite clever them disks...I was doing 100mph!

Sometimes they have painted squares on the road too.

Oh, and the discs are 1/4 mile apart.

The painted squares on the road are for police cars following you (or even driving ahead of you) to check your speed between the squares using VASCAR, ie by carrying out a simple time/distance measurement.

Just out of interest what type of devices are you using for your GPS measurements?

Garmin eTrex Vista (with windscreen mount and in-car power lead). Velocity accuracy is 0.05 meter/sec steady state.

Thats a serious peice of kit, very usuful if you are a mountaineer. I would have thought a Origin b2 radar detector might also do the same job too (in speed terms), although maybe not as accurate.