Bigger tyres , by how much does it effect speedo accuracy ?

Hi Guys

I got 33s on my car . I know the speedo isn't as accurate. What are average kmph it is out by ?

I'm in the middle of resetting my dawes and needle valve

thanks

Gday mate. With a GQ going to 33" inch tyres, you will be travelling at 100km/h when your Speedo says 95. But as all Speedos are slightly different you may want to double check with a GPS.
Also there are lots of websites with tyre size calculators, just Google away

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Originally Posted by taslucas

Gday mate. With a GQ going to 33" inch tyres, you will be travelling at 100km/h when your Speedo says 95. But as all Speedos are slightly different you may want to double check with a GPS.
Also there are lots of websites with tyre size calculators, just Google away

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It varies so much... my old patrol was 100% accurate with 33"s according to GPS. Same GPS on my new one and with the same 33"s on when my speedo says 100km/h I am actually travelling 110km/h

My Speedo is currently 8k above actual road speed, so 33's will bring mine up smack on..

As mentioned above speedo readings vary from car to car, as a rule (ADRs) a speedo on a standard vehicle should under read, i.e. when speedo says 100 kph you are actually doing say 97.

Use a GPS to check your actual to speedo reading. On my GU IV I replaced the speedo cable cog at the gearbox from a 16 tooth to a 15 tooth, the speedo now reads spot on with the three different GPS units I have checked it against.

This thread is worth a read

What I posted was the ratio change as stated on tyre size calculators.

But yeah if you do 100 on the Speedo in ten different standard vehicles you'll get ten different actual road speeds

would it be safe to just drive under 5kmph ?

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Originally Posted by Limmy

would it be safe to just drive under 5kmph ?

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Perfect. That's at a hundred k's.

thanks all for advice! just another thought.
how much off would it be with 35inch ?

I went from 31's to 33's on the GU and now the speedo is spot on against at least 2 gps'

used to read slower before....