# Re: Tires

```Hairy green toads from Mars made Peter Henriksen say:

> >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
> >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.
>

The original question was correct, as is Peter. Jack is not quite right:

# tire_size 205/55/16 215/50/16 225/50/16 225/45/16
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
205/55-16         4.4in  12.4in    24.9in         78.2in        811        0.0%
215/50-16         4.2in  12.2in    24.5in         76.9in        824       -1.7%
225/50-16         4.4in  12.4in    24.9in         78.1in        811       -0.1%
225/45-16         4.0in  12.0in    24.0in         75.3in        841       -3.6%
#

--

Andrew L. Duane (JOT-7)			duane@zk3.dec.com
Digital Equipment Corporation		(603)-881-1294