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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]
>     >>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.