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*To*: "'quattro@coimbra.ans.net'" <quattro@coimbra.ans.net>*Subject*: RE: Tires*From*: "Mike Miller (Volt) (Exchange)" <a-mikemi@Exchange.MICROSOFT.com>*Date*: Wed, 10 Jul 1996 13:31:11 -0700*Sender*: owner-quattro@coimbra.ans.net

As I recall, the typical tire has a tread depth of about 12/32 inch. At 2/32 they are considered "bald". Taking away 10/32 of the rolling diameter from a 15 inch 215/60 reduces the rolling distance from ~2007mm to ~1982mm or about 1.25%. This would be about .75 mph difference at 60mph. So the difference in a new tire and an old one is only about 3/4ths the difference of going from a 205/55 to a 215/50. >---------- >From: Peter Henriksen >Sent: Wednesday, July 10, 1996 9:44 AM >To: 'quattro@coimbra.ans.net'; 'jackr@internet.kronos.com' >Subject: RE: Tires > >From my calculations (read: YMMV :-): > >Tire size Total diameter Rollout Change from stock >205/55 631.9mm 1985.1mm N/A >215/50 621.4mm 1952.1mm 1.7% >225/45 608.9mm 1912.9mm 3.6% > >Formula being: ((2*((<profile>/100)*<width>))+(<wheel size>*25.4)) to >get a result in milimeters for the diameter and then 2*pi*r to get the >rollout (pi somewhat equal to 3.1415). > >Did I just do something stupid or is that right? It's still pretty >early, I haven't had nearly enough coffee and I haven't done anything >like this since college... > >On that note, how much of a difference is generally acceptable in >rollout before the speedometer and odometer start getting way off? Where >do you go to get the instruments recalibrated? >- peter henriksen, peterhe@microsoft.com, issaquah, wa > 91 200qw > 94 acura legend gs > 80 mazda 626 > >>---------- >>From: jackr@internet.kronos.com[SMTP:jackr@internet.kronos.com] >>[snip] >> >>One question. Has anyone put new tires on yet? I am planning on >> >>putting 225/50 R16 Dunlop D40M2's this week. They have the same >> >>circumference as the 205/55's and supposedly enough clearance. Has >> >>anyone heard differently? >> >> My understanding of tires is that a 215/50 or 225/45 would have the >> same circumference as a 205/55. > > >> >

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