From the Syncro list, Steve Schwenk <steve@syncro.org> wrote:

>
>Some believe that going to 15" wheels without a gear
>change involves too much of a trade off in loss of
>power, climbing ability, acceleration and crawl ability
>to possibly justify the benefits provided by bigger
>wheels, which include ground clearance, improved
>handling, off road and on.  (It's probably harder on
>the engine, too).  And if you drive in the mountains,
>the higher gearing may result in a slower van over any
>distance compared to stock.  I don't know if the
>additional power of the ticco would compensate for the
>higher gearing sufficiently to make it still feel like
>stock.  my guess is it is not, but i do not know.

After I installed my Tiico conversion, I stuck w/14" wheels but I needed
new tires anyway, and I switched from Yokohama 185/75s to Dunlop 27x8.5.
The increase in tire diameter is 1.5".

I had some experience driving my new engine on the 185/75s, and when I
switched to the 27x8.5s the difference was quite dramatic.  I need to
double-check the tuning on my ECU, since it was reset to default values
around the time of the tire-switch, but qualitatively I would say that
tire swap whacked me back to a small fraction of the torque increase I
had originally experienced from doing the conversion.  I'm still enjoying
the other benefits of the conversion (smoother and wider power band), but
I'm back to nearly the same RPM/gearing on my standard highway grades
that I had before.  (The much higher top speed offered by the larger
tires and higher redline are of no advantage to me. I'm sure with a
tailwind I could hit 120 easily.)

In the near future will be looking more carefully at the ECU tuning to
see if I'm getting optimum performance from my Tiico; I'll report back if
I find that the root cause of the power loss was really mistuning.

I may also be considering a fuel rail/injector/pressure regulator swap
depending on the consensus among the rest of the Tiiconauts as to the
efficacy of this upgrade on low-RPM performance.

-Steve Hoge