Explanation of 2000 tire diameter adjustability in the PCM (and my problem).

From: Steven T. Ekstrand (cyberlaw@earthlink.net)
Date: Fri Oct 06 2000 - 12:02:37 EDT


| If the tire size is not adjustable in the PCM, does this mean each PCM is
| preconfigured at the factory for a specific tire size or are we all using
a
| single setting regardless of tire size.
|
| Ken

No, the tire size is adjustable. They are quite proud of the fact that you
no longer have to replace a part! Just a setting in the PCM. However, the
range is so small there's not much point to it. They allow you to go from
a 28 inch tire to a 29 inch tire. That's it. Well at least using the revs
per mile method. I seem to remember a 30 inch tire available using the
tire size method. Let me explain.

There are two ways to adjust.

First there is a list of available tire sizes for your vehicle in the
computer. You choose the size. There aren't very many choices and they
are for the most part the same diameter.

For example:

255-65-15---28.05"
255-55-17---28.04"
215-75-15---27.70"
235-75-15---28.88"

There are a couple of more choices in the LT non-metric sizes. I seem to
remember one of these being a 30x10.5-15 but I'm not sure. I wrote it down
and can't find it now. I'm not sure if a size 30x10.5-15 is actually 30"
in diameter.

The second way you can adjust is to enter the revs per mile for the tire in
use. The range is approximately 723-755 revs/mile.

That is a similar range. Basically 27.7" to 29.2" diameters.

I'm need a short sidewall tire, but don't want to spend $2K-$4K to go to 19
inch rims and matching exotic tires. A 295-50-15 is 26.6" so I just have
to eat 5% extra miles. I have a lease, so that gets a little expensive.
But I really want 50 series rubber. The best fix for me would probably be
R/T rims and 275-50-17 rubber. That would nearly match the stock tire
diameter. But that's a rare size tire. And I really don't want to spend
the money. I have five more sets of tires to buy in the next year (I have
a lot of vehicles and they all need tires right now). And foretunately or
unforetunately depending on how you look at it.... All these cars require
very expensive tires.



This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:55:51 EDT