On Tue, 6 Jun 95 13:39:12 CDT Cetin Seren said:
>Now I'm worried...  Maybe Joel or someone else can help...
>My '87 weekender says it's doing 73 mph at 4200 rpm (in fourth, to be sure
>It's got 205 / 14 pirellis.  Joel, how about your Vanagon?

my bus with 185/14's is doing right at 71 rpm at 4200 rpm.

now, the bentley book says that with our gearing in the later model vanagons,
that we should be getting 18 mph per 1000 rpm ... which is  75.6 mph for 4200
rpm. my "testin" with the calibrated trip computer and a stop watch yielded
a figure of 16.75 mph per 1000 rpm. i guess because of drag and friction in
the drivetrain and slipshod low-quality labor and such.

but that's 70.4 mph at 4200, and my trip computer shows 71, but the speedo
shows about 75 mph.

now ... since you have the larger tires, which my 91 bus had, you are likely
doing actually closer to 75 mph when your speedo shows 71 ... the larger
tires mean you travel farther in one revolution than you are supposed to,
and so you are going faster at a given rpm than your speed is showing.

the only way i know to get a more accurate idea of how much off you are,
is to get a fairly flat and level stretch of interstate, and time yourself
on cruise control (when there is very light traffic, so you don't have to
speed up or slow down or change lanes) for about five or ten miles. now,
the mile markers are NOT that accurate, but for an average of ten miles,
they are probably pretty close. i hope.

joel