speedo out help needed

[mr ke70]

hey guys im upgraded my wheels from 16inch till 17inch and i think my speedo is out which is cool but which one will be correct the cluster or the gps speedo i didnt think it will much difference looking at bout 4-6k outs but only for 1ch is that strange to u guys

[Guest]

GPS is allways going to be a hell of alot more accurate than the speedo....

[Blind Kid Seeks]

rotational distance has changed, you could correct it by buying new tyres.

[DJKOR]

rotational distance has changed, you could correct it by buying new tyres.

That is making the assumption that he had increased wheel size WITHOUT changing the tire size appropriately. If he made sure to adjust the tire size, his variation in his speedo should only be about 1-3km/h.

To the OP: Did you pay attention to the speedo before the wheel change? Was it still off by 4-6km/h? If so, it's nothing much to worry about, so long as it reads under the actual speed. Your GPS will give you a closer to accurate to speed so you can see how much your speedo is off by.

Most cars can be up to 10% out and then to be on the positive side, that is, showing you a speed faster than what you are actually going.

[mr ke70]

before the wheel change the speedo and the gps were dead set spot on but now they are out as a said by bout 4-6ks. the tyres which are on the car now are not brand new bout 70 percent tread

[DJKOR]

On your tire placard on the drivers door area, what is the recommended tire size? Now what is the size of the 17 inch tires you have on it now?

They can then be entered into this calculator:

1010 Tires - Tire Size Calculator

[mr ke70]

the recommendation in the door says 205/60 R16

i have on the car now 215/55 R17

[CHA54]

you need 215/50/17's for it to be close to the originals.

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

[mr ke70]

thanks for that is that avaibable in aust that size

[mr ke70]

so what ur saying is that if u get that tyre size my speedo will be spot on

[mr ke70]

205/40/17

[Rolla Boy]

Or you can get your speedo calibrated to suit the new size...

Give General Auto Instruments at Lidcombe a call :)

[mr ke70]

is that expensive

[lateralus]

recalibration costs around $300, but theyre generally only willing to do it after a report is done to determine the exact error (which is around $50).

the way i see it is at some stage, youre going to have to replace the tyres anyway as part of general wear and tear. if it were me, i would just leave the tyres the way they are, and then when the tyres need replacing switch to the correct size, and leave the standard equipment the way it is without having to adjust settings, etc.

a bit more cost effective that way

Edited August 17, 2009 by lateralus

[mr ke70]

yeah thats wat im doing but every tyre place i ring they give me different reading which sucks