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Discussion Starter · #1 ·
I've read a few posts regarding this but I'm still confused !
I'm running 235/45/18 at the moment, at a Speedo reading of 60mph my sat nav says 56mph ....on 2 different satnavs . My tyres need changing soon and I noticed some are fitted with 235/40/18.....so if I fit the latter will this make the Speedo reading correct or make it even more inaccurate ? I'm pretty sure the car came with 235/45/18 according to Ford Etis......
Any help would be great
Cheers
 

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I Love Diesel
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235/40/18 would make the speedo reading more inaccurate.
 

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Discussion Starter · #4 ·
Thanks, that's all I needed to know....i'll go with the 235/45/18 then that's fitted now ...bit confusing for second owners who are not sure which tyres were fitted from new
Cheers
 

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If you want to add 8-10% the following will do (but also change the overall gear ratio, reduce acceleration due to the higher ratio and potentially make the engine struggle at low(ish) speeds and drink more fuel)

185/75-18 is 9,86 % larger
195/70-18 is 9,19 % larger
205/65-18 is 8,22 % larger
225/60-18 is 8,74 % larger
245/55-18 is 8,67 % larger
265/50-18 is 8,00 % larger
275/50-18 is 9,49 % larger
295/45-18 is 8,07 % larger
305/45-18 is 9,42 % larger

Not all of these sizes will fit your rim width
 

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Tyre size or circumference (and therefore speedo ranging) can be electronically changed, either by a dealer (£) or at home using a OBD2 device and a laptop/Smartphone
 
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