liamstears Posted February 12, 2019 Share Posted February 12, 2019 Bit confused here Old wheels: 195/50 R16 New sheels: 205/40 R17 In forscan change Tire dimension from old to new but what about tire circumference? Its currently set at 1835mm but that doesn't make sense to me when using circumference calculators, what should it be set to for 17" alloys? What do you guys have it set to? Quote Link to comment Share on other sites More sharing options...
TomsFocus Posted February 12, 2019 Share Posted February 12, 2019 Doesn't it change automatically when you change tyre size? You can work it with some maths...I make it 1874mm. There will be some tolerance because tyres aren't as exact as you'd think, plus sidewall flex etc. Quote Link to comment Share on other sites More sharing options...
WES180 Posted February 12, 2019 Share Posted February 12, 2019 I got 1872mm. To be fair though I'm useless at maths!😂 Wheel 17 inches - 431.8mm Tyre profile 40% of 205mm x 2 = 164mm Total 595.8 x pie (3.14159) = 1,871.759322mm Quote Link to comment Share on other sites More sharing options...
isetta Posted February 12, 2019 Share Posted February 12, 2019 depends how exact you want to be with PI. A lot of people use 3.14 and hardly anyone goes beyond 3.142 in terms of decimal places I reckon. 3.14159265358979323846264338327950288419716939937510...[ As Tom's Focus says There will be some tolerance because tyres aren't as exact as you'd think, plus sidewall flex etc . Also the difference between new and barely legal tyre with be about 35mm difference in circumference. 1 Quote Link to comment Share on other sites More sharing options...
WES180 Posted February 12, 2019 Share Posted February 12, 2019 I just googled 'Maths Pie' lol, my school days are well behind me, the fact I put 'Pie' rather than 'PI' says it all really.😂 Quote Link to comment Share on other sites More sharing options...
liamstears Posted February 12, 2019 Author Share Posted February 12, 2019 Thanks for the informative replys guys but you have all missed the kicker on this one Work out my original wheel size and you will get somewhere around 1887 but my car was set to 1835 This was the reasoning for my question and really want to know what people have theirs set to out the factory with 17" wheels... Quote Link to comment Share on other sites More sharing options...
WES180 Posted February 12, 2019 Share Posted February 12, 2019 41 minutes ago, liamstears said: Thanks for the informative replys guys but you have all missed the kicker on this one Work out my original wheel size and you will get somewhere around 1887 but my car was set to 1835 This was the reasoning for my question and really want to know what people have theirs set to out the factory with 17" wheels... You're right, well, I got 1889mm for your originals. So (16") 1889mm - 1835mm (factory set) = 54mm (17") 1872 - 54mm = 1818mm Problem solved!🤔 Only joking mate, I'm sure someone will be able to check exactly what they have it set to with 17's from the factory soon. That's more maths than I've done in the last 25yrs!😂 Quote Link to comment Share on other sites More sharing options...
Paulkp Posted February 12, 2019 Share Posted February 12, 2019 Is the factory setting for a half worn tyre or down to the TWIs ? Quote Link to comment Share on other sites More sharing options...
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