1)I dont have radials, they are the originial 9.50-14 type Silvertown bias
ply tires.
2)I always have my GPS running which is accurate to 15 feet and .1 mph
anywhere in the world. My odometer is correct.
3)I think the biggest deviation is from driver habit.
>From: "D. Dardalis" <dardal@xxxxxxxxxxxxxxx>
>Reply-To: mailing-list@xxxxxxxxxxxxxxxx
>To: mailing-list@xxxxxxxxxxxxxxxx
>Subject: Re: IML: 18 MPG in an Imperial?: deviations
>Date: Tue, 22 Jan 2002 10:53:27 -0600
>
>At 08:30 PM 1/21/2002 +0000, you wrote:
>>Hi hugh, I get almost exactly the figures posted in your PM article with
>>my 1958. Maybe a little better (13.4) at a sustained 70mph. Perhaps my
>>electronic ignotion helped a bit!
>More likely its your radial tires vs the original cross ply. The rolling
>resistance is much lower. Also, keep in mind that the gas mileage people
>report is based on the odometer readings. These are not always as accurate
>as we would hope. Part of the reason is the tire sizes and rolling
>diameters are now a bit different. In the 66-69+ model years, the
>235/75/15 used is very close to the original 9.15-15, although not all
>agree as to what the exact difference is. On my 68 sedan, the odometer
>under-reads by about 3% which is a very small difference (indicating my
>235/75 are just only slightly larger than the original 9.15) while my 68
>Lebaron under-reads by over 10% (this is more likely instrument error which
>is very strange as the speedometer is more accurate than the sedan in the
>usual speed range!). The point is, the "absolute" reported values can
>deviate some, and odometer errors could be the cause as much as engine
>tune. As said by somebody else, its more important for your mileage to be
>consistent with what you "used to get" in the past, rather than how it
>compares with other reported values. Of course, if you estimate 8mpg on
>the highway at 70, there is something wrong! D^2
>
>
>
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