anyone know, do they over or under read?

 

I don't know about in general, but mine showed when tested

Steady speedo reading: 70mph
Steady GPS reading: 66.5mph

Ratman,
MY98 Wagon

 

anyone else?

 

When tested against a Garmin E-trex GPS, my MY97 Turbo is reading 100 kph against a GPS indicated speed of around 90 kph, a variance of 10%, which gives an added safety margin against speeding,lol.

 

If you have changed the wheels/tyres, it will depend for starters how close they are to the OEM fit rolling diameter.

 

i'm guessing GPS tracking devices are 100% accurate

 

Not quite 100% accurate, but very close. Especially with DGPS.

 

i'm asking because i need to set up my blitz turbo timer properly, it does 0-60, 1/4 miles etc. and wanted it fairly accurate

i need to drive along at a steady 40kph to calibrate it, guess i need to drive at 44 or something then

 

Hey FLAT4 how are you?

Sorted my spluttering out today.

Solenoid?????????????

No!!

Gaps in sparkplugs incorrect.

Oh well, almost running 100% now

Nick

P.S. are you out on this Vodka Bar do beginning of June?

 

we'll see, i've posted my interest

 

Using a SPA micro-processor & standard tyres my 95 WRX over read by 9.4per cent. I am happy that this was a very accurate comparison as I was able to check this against marker posts on the motor-way to within 176yds or less in35km.

 

From 50 up to an indicated 100mph Subaru's are normally about 5mph put - ie 90 on the clock is a true 85.

Allegedly at an indicated 140 you'd be doing about 131/2

 

is it 10% from 0 upwards or is it a steady increase upto 10%? can't believe at an indicated 90 your doing 81!

plus; bigger wheels, does that put it even further out (can't be arsed to work this one out)

 

Going from 205X50X16 to 215X40X17 actually shortens the gearing slightly & so increases the error. ie. The standard speedo tells even bigger porkies.
Sorry but it is true.

 

the speed tracked by my origin blue-i seems to be pretty concurrent with the speedo of my MY01 up to about 120 (private roads, of course!)
simon

 

We've got 17" - but surely the whell radius is still the same due to tyres etc.

Ours read 63 @60 .... MY98 UK

 

Hi Jen,
If you get a tyre company technical data book listing rolling circumferences you will find interesting information.
My 205x50x16 tyres were 1865mm rolling circumference.
215x40x17 1846
For some tyre manufacturers and size changes the difference is much greater.

 

Surely it depends where the needle is alined with n all as i had to b carefull when changing dials 2 make sure i new where it was at rest b4 changing, but if i new it was innaccurate i kud always change it if unhappy Although u r allowed +10% i'd rather no the true speed shud i get pulled Looking at getting the defi HUD VSD2 n all which, i kud b rong, but mayb more accurate
Si

 

looks like its over by 5-10% depending on model, looks like the new shape might be accurate

 

Harvey - that's interesting!

 

U got wot the original standard rolling circ is i wana no how much i can push it b4 i is liekly 2 get seriously busted on 215/40ZR17's
Si

 

I have an Ultra Digital Speedo installed on the dash.

Generally i am seeing a difference of just over 5% (less than 10%) between the two with the digital one reading lower. Thats obviously the one I look at most.

My car is box standard with out-the-shop wheels and tyres.


brian

 

PTMW! recorded 134 @ an indicated 149

That was with some type of specialised timing device at a magazine shoot-out @ Alconbury Airfield...

 

Er that's over 10% then & technically illegal, not 2 mention the speed although obviously u'd never do the on her majestys highways
Si