Speedo Issue

[lyons]

hey all

so ive always thought my speedo is out and finally checked it with a couple gps's and they say the same thing im about 10% out (at 100 i lose 10, 80 i lose 8 so on)

my wheels are the same diameter as the stockos

im gunna get it checked on the dyno in a couple weeks when they have space, but the speedo is all driven by electrics arent they?

any1 had the ame problem or know how to fix it?

[lyons]

ive just looked at a size calculator thing and according to it with the profile i have my speedo should be 4% faster 104 at 100 not 10% slow so im really confused

[whtbox]

if the wheels is same as stock, what about the tyre size you using?

but at least the speedo is shown faster than you are going, means that you'll never get speeding ticket

Wipe off 5 got ruled

Edited September 30, 2009 by pw350gt

[lyons]

on the rear i have 295/30 18s and stock is 245/45 18

so its actually slightly smaller diameter which should send the speedo the opposite way

[V35_Paul]

mine is out only a little bit. It says 40 but i'm going 38.

I was testing it on one of those roadside workers "speed warning" signs

[MSKYO]

Most Australian delivered cars in the last 5 years or so are between 4-7% under. I've heard it is to comply with Australian standards. I know the J31 Nissan Maxima with the VQ35 is 7% under ie 93kph when speedo is 100, the latest BMW 3 series coupes are about 5% off as is the Honda Accord Euro. 10% sounds like a bit much though

[lyons]

see i wouldnt mind if it was only a small difference but being 10% i dont like to think about where to speed up to lol

and yeh 10% is really strange considering the fact the wheels i have should bring it closer to true speed

Edited September 30, 2009 by lyons

[rs73]

if your current tyres is slightly smaller than the std manufacturer's spec you will 'loose' speed.

e.g. if your Speedo is showing 100 km/h, in the real life you only travelled less than 100 km/h

from what you described with those sizes 295/30R18 is 6% circumference less than 245/45R18 so you will 'loose' about 6% on your speedo than what is shown.

if most cars by factory standard has their speedo reads about 3-7% higher than actual speed, then the way you describe you loose about 10% would be right, because if V35 has 4% speedo error, with your tyres, it will be 10% difference. So your speedo shows 100km/h but you only actually travel 90km/h in real.

[rs73]

ok - free plug, because of the numbers of this questions have popped up on the forum, i will attach an excel spreadsheet that i have created for my own purpose...

feel free to improve it. use the circumference difference as a guideline because circumference is the rolling surface of your tyres that will affect the actual distance you travel within 1 rotation of the tyre, and eventually affect the actual speed vs shown speedo speed in your car..

Tyre_Size.zip

[skygo2xs]

hey lyons,

Just to let you know, I have the same issue with my speedo, out by more than 10% the faster the speed, at 110km/h, speedo reads 124km/h. Very frustrating but as you say, not a simple fix, so as far as I know. I had the speedo into an instrument specialist, they had a good look but are unable to do anything with speedo alone stating its controlled by the can-bus and need the whole car to attempt calibrating/fixing it. This issue is with standard wheels.

Let me know if you come up with a solution, as will I.

[lyons]

yeh its quite annoying

cheers for ya help rs73 i had my size to speed around the wrong way, you dont know how to fix it? anything easier than getting a thicker profile tyres

the site that i looked at was the other way like i thought but now ive thought about it the way you put it makes sense lol. heres what the site listed

Stock Tire - 245/45R18 Tire 1 - 295/30R18

Section Width: 9.64 in 245 mm Section Width: 11.61 in 295 mm

Rim Diameter: 18 in 457.2 mm Rim Diameter: 18 in 457.2 mm

Rim Width Range: 7.5 - 9 in Rim Width Range: 10.5 - 11.5 in

Overall Diameter: 26.68 in 677.67 mm Overall Diameter: 24.96 in 633.98 mm

Sidewall Height: 4.34 in 110.23 mm Sidewall Height: 3.48 in 88.392 mm

Radius: 13.34 in 338.83 mm Radius: 12.48 in 316.99 mm

Circumference: 83.81 in 2128.7 mm Circumference: 78.41 in 1991.6 mm

Revs per Mile: 779.6 Revs per Mile: 833.3

Actual Speed: 60 mph 100 km/h Speedometer1: 64.1 mph 106. km/h

Speedometer Difference: - Speedometer Difference: 6.888% too fast

Diameter Difference: - Diameter Difference: 6.45%

or was i just reading this wrong?

Edited September 30, 2009 by lyons

[xscape237]

Even with the standard wheels on, mine reads 108km/ph when doing 100...

[rs73]

Speedometer Difference: - Speedometer Difference: 6.888% too fast

Diameter Difference: - Diameter Difference: 6.45%

or was i just reading this wrong?

that speedometer too fast means when it shows 106.88kph on the speedo you actually only travelled 100kph actual speed.

so yeah, you kind of 'loose' 7km/h

in addition to stock setting which can vary by about 5-10km/h, you could be around 10-20km/h off the actual speed...

either you change the tyres, or you drive faster with additional 10km/h in mind... e.g. if the road limit is 100kph u just drive

at your speedo showing 110kph. or move over to the left lane, no one would blame you for driving 5-10 under on the left lane.

[g33k]

I have the same problem, i just put up with it, let me know if you find a solution (other than changing tyres)

[mosoto]

on the rear i have 295/30 18s and stock is 245/45 18

so its actually slightly smaller diameter which should send the speedo the opposite way

With that size tyre on the rear your Speedo will be reading 6.4% too fast. When your doing 100kph the speedo will read 93.6kph.

I'm suprised you haven't had issues with VDC as it apparently only tolerates a variance of 3-4% over stock

[Stephen Thorpe]

wow, what a lot of detail... and good work on the spreadsheet RS73!

This has been covered so many times about speedo error...

From my own knowledge and unless it has changed, Australian Design Rules for Speedo Error allows 10% plus or minus in the reading, so there isn't a huge problem legally.

If you are really concerned, do a Tyre place ring around and find an accurate measurement of rolling diameter of the tyre that you are using and then look for a bigger version. They all have the capability to research the exact Profile height.

Or pump them right up!

[Son Gokou]

Hi guys,

I just bought my V35 sedan and its come with the factory 17" wheels with tyres size: 215/45R17.

When i'm on the fwy and doing 100km/hr, i noticed ppls are ovetake me or up on my ass!

What are the stock 17" tyres size?

As i suspect with the 215/45R17 tyres, my speedo is under read.

I dont have a GPS so cant really do a check.