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Speedometer Calibration

SHANE666
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SHANE666 Mentor

SHANE666

Posted
Posted

Hey guys,

as the topic suggests, WIll I need to calibrate my speedometer and some other parts to compensate for lagrer rims?

I have a R34 Non-turbo. Stock rim size is 16 inches. I have 17 Inch rims on at the moment.

I want to put 350z rims on them, which are 18 inches.

Thanks,

Shane

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Trav33 Mentor

Trav33

Posted
Posted

Rim size has nothing to do with it. It the overall wheel diameter (rolling diameter).

You'll notice that 18" wheels have a lower-profile tire, compared with 17/16/15" rims?

Any half decent tyre+wheel stockist will look at your tyre plakard to work out the stock rolling diameter, and then find a suitable tyre profile to maintain the diameter as close-as-possible.

You wont need to touch your speedo.

stenve Proficient

stenve

Posted
Posted

i have 18" 350z rims on my r33

im running 235/40/18s on all fours which keeps my speedo pretty darn close to being correct.

its out like 0.5% or something

that should give you something to go by, instead of just relying on the tyre guys word.

also google for wheel size calculator or something similar. there is a site that will work it out for you

thanks Trav, thats what I've mostly been reading on the internet.

much appreciated.

GoldZilla Grand Master

GoldZilla

Posted
Posted

Here's one for you, Shane.

http://kumho.com.au/tips_diameter.htm

Punch in the details of your current tyre package, and then find the dimensions of a set of 18's that have the same or similar rolling diameter.

SHANE666 Mentor

SHANE666

Posted
  • Author
Posted

Thanks Nick, ive used that to check...

the new rims are 108 and 164 mm larger in front and rear rolling diameter, respectively.

What difference will this make??

wow thats a 5 and 8% change in rolling diamtere. it says +/- 2% is a safety net. think ill need new tyres

br3ndan Mentor

br3ndan

Posted
Posted

Lower profile tyres will compestate for the larger rim as said above. No need to calibrate anything.

IT will go out by a very small percentage tho, maybe 0.5kmh. Nothing to worry about at all.

Tho from stock, the factory makes the speedometer read faster then ur actually going. Ive tested with my apexi rsm. At 100kmh you are actually going 97kmh. At 110kmh you are only going 104kmh. Something to do with safety...

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