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Daninplymouth

Speedo reading 18s

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Hi I have just fitted new wheels and tyres. 225/40 18, I think these should under read by about 2% so can I just confirm where I normally set my cruise control at 75 I will now be going a little slower and not the other way.

i will double check my Speedo against a sat nav but I won’t have that for a few days so just wanted make sure I had it the right way around as it’s full of speed cameras here on my little commute

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47 minutes ago, vanko25 said:

With that tyre setup the speedo will be reading higher than reality i.e. at 60 mph real speed will be 58.88 mph 

image.png.587899de4b589ce9103e97dbb5475693.png

Thank you thought that was the right way. Another benefit of the wheels then it should be harder to get a speeding ticket 😁

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On 4/7/2019 at 6:56 PM, vanko25 said:

With that tyre setup the speedo will be reading higher than reality i.e. at 60 mph real speed will be 58.88 mph 

image.png.587899de4b589ce9103e97dbb5475693.png

Ah think I have this wrong and the Speedo under reads so if my Speedo says 70 I would now be doing 72

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1 hour ago, 86guns said:

Mine has factory 18” wheels.

Do you think Toyota will have reprogrammed the speedo? 😂 

No! 😂 The speedo over reads anyway. Only way to work out your true speed is via GPS. I have a GPS speed read out from my TEIN EDFC, so have used that to get used to what speed I'm actually doing compared to the speedo reading. 

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When I compare my dash readout to GPS and OBD app, it seems to read high by about 4%. That's my excuse to drive at indicated 73 anyway!

From this tyre size comparison site, it suggests when changing from 17" to 18" wheels the circumferance is 3% more - which should almost negate the over reading. Although maybe everyones car is different.

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38 minutes ago, Tarnish3 said:

From this tyre size comparison site, it suggests when changing from 17" to 18" wheels the circumferance is 3% more - which should almost negate the over reading. Although maybe everyones car is different.

I expect they're all the same. ;) 

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