This is born out by the way the 15 inch wheels "fixed" my speedometer.  With the 14" wheels my speedometer always read 5 mph higher than my actual speed.  With the 15" wheels the speedo is dead on accurate.
Anthony

mark drillock <drillock@EARTHLINK.NET> wrote: The difficult thing for some people to grasp is the effect if you change
all 4 wheels to the same larger size. The rpms will be lower at the same
road speed but that means TRUE road speed. NOT what the speedometer
says. If you change from 14" wheels of the same tire size to 15" wheels
all 4 of the same size, the speedo will still read the same speed at
4000 rpm as it did before but you will actually be traveling faster than
before.

This can also add to the perception of power loss since going from 0-60
on the speedometer is now actually going from 0-64 in "real" speed.
Naturally it takes longer to go from 0-64 than 0-60 but the instruments
are still reading the same as far as the driver can see so he thinks it
is slower than before by more than it really is. In reality the van is
going 4 mph faster than it used to when the speedo reads 60.

My words above refer to the 7% tire size increase with the 15" tires
that I use.

Mark

Anthony Egeln wrote:

>I guess it was your last point, about the lower RPMs at higher speeds that gives me the impression of having more power.  Also, we have precious few hills here in NE Florida so I couldn't judge it that way.  Thanks for the explaination.
>Anthony
>
>
...........

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