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Speedo Reeding
Posted: Mon Aug 10, 2009 10:10 am
by MICALEE
Can anyone advise the difference in speedo reading when upgrading from 235/40/18 to 235/35/19?
I see a few threads stating %'s slower or faster - how is this worked out or is there a website which does it for you?
RE: Speedo Reeding
Posted: Mon Aug 10, 2009 2:26 pm
by s4marsh
by rights it shouldnt make a difference to the speedo your increasing the wheel size but reducing tyre size so in effect the rolling radius or diameter i cant remember which it is now is the same, the easiest way is to record what speed you get per 1000rpm eg: 30mph or whatever you get and compare with the new wheels before buying if possible.
RE: Speedo Reeding
Posted: Mon Aug 10, 2009 3:03 pm
by MICALEE
Well, the wheel diameter is increasing slightly - Standard=18" with 45 series tyre, upgrade is 19" with 35 series tyre. If Im right, to retain the exact size, a 19 would have to have a 30 series tyre.
RE: Speedo Reeding
Posted: Mon Aug 10, 2009 7:28 pm
by davs4
RE: Speedo Reeding
Posted: Mon Aug 10, 2009 7:31 pm
by s4marsh
good link dav,
Re: RE: Speedo Reeding
Posted: Mon Aug 10, 2009 7:38 pm
by MICALEE
Many thanks there Dav, just what I was after.
For ref for others who may wish to know, as its a popular upgrade, these were the findings:
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
235/40-18 3.7in 12.7in 25.4in 79.8in 794 0.0%
235/35-19 3.2in 12.7in 25.5in 80.0in 792 0.3%