Speedo Calibration

**wayz** · 23-11-2006, 04:18 PM

Hi guys, long time reader... (great forum!)

Ive just had 17" wheels put on the car (from the stock 14") and i think its put the speedo out of whack, anyone know where i can get the speedometer re-calibrated?

Dont want to stand there arguing with the boys in blue about how i WASN'T speeding

Cheers guys

syncro · 23-11-2006, 04:39 PM

Originally Posted by wayz

Hi guys, long time reader... (great forum!)

Ive just had 17" wheels put on the car (from the stock 14") and i think its put the speedo out of whack, anyone know where i can get the speedometer re-calibrated?

Dont want to stand there arguing with the boys in blue about how i WASN'T speeding

Cheers guys

Check it first as it may be within limits.
They normally read about 5-10% fast.

**wayz** · 23-11-2006, 04:54 PM

How would i go about checking it? (forgive me ignorance

)

i normally do about 550 nearly 600km a full tank and now im doing only 450 or so a tank? This happened immediately after i had changed the wheels. Would anything else be wrong?

**golf3** · 23-11-2006, 04:59 PM

Heavier wheels = more unsprung weight = more power required to make them/the car move = more petrol = more $$$

**wayz** · 23-11-2006, 05:04 PM

Arhh, yes.. i thought about that, but these wheels are actually lighter and the car feels like its driving with greater ease

**golf3** · 23-11-2006, 05:21 PM

Rolling diameter will be different every time you change tyres, even when still the stock size of 185/60R14. Tyres are all different. However, with 17's you should be running a 205/40R17 or similar to keep diameter to around the same...

**wayz** · 23-11-2006, 05:34 PM

Originally Posted by golf3

However, with 17's you should be running a 205/40R17 or similar to keep diameter to around the same...

I am running 205/40R17's
But im pretty sure they're a larger diameter tyre, and that would make the difference im guessing/hoping, otherwise im baffled and my car is in desperate need of a tune-up

syncro · 23-11-2006, 05:35 PM

Check your odometer on the M5 speedo check.
Drive next to someone and have a look at their speedo.
Drive really fast through a speed camera and wait for the photo.
Use a GPS.

**golf3** · 23-11-2006, 06:19 PM

http://www.miata.net/garage/tirecalc.html

Using stock of 185/60R14 to 205/40R17
Speedo reading with non stock tyre is 3.2% too slow...
You are actually doing 61.9mph when the speedo reads 60