Date: Sat, 6 Mar 2004 09:18:24 -0500 From: "Fred W." <Fred.Willsnospampam myrealbox.com> Subject: Re: wheels on 900s
"Jody Burke" <jodyburkenospamsouth.net> wrote in message news:tuc2c.61004$Tn.21108nospamews5.bellsouth.net... > I was interested in putting a larger wheel on my 95 900s convertible. I did > some calculations with info from the tire rack site and the wheels and tires > I am considering would give me an extra inch in diameter. Does anyone have > any experience as to how much this increase would affect my speedometer and > final drive ratio? Thanks in advance for any assistance! The answer to your question is a simple equation: Indicated Speed Change as a % = Change in size / Present size * 100 Tire Rack indicates your car was originally equiped with Michelin MXV4 in 195/60VR15 size. These tires have a diameter of 24.2", so (1 / 24.2) *100 = 4.13% Also, in case you didn't realize, the indicated speed on the speedo will *decrease* with an increase in tire diameter, as will the overall final drive ratio, resulting in the calculated decrease in engine rpm at any particular speed. -Fred W