Date:         Fri, 18 Aug 2006 00:25:00 -0400
Reply-To:     Kim Brennan <kimbrennan@MAC.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Kim Brennan <kimbrennan@MAC.COM>
Subject:      Tires and fuel economy
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

When I first got the GoldBrick (86 Syncro passenger Vanagon) I got
about 18mpg with the stock engine rolling on 205/70R14 BFG tires.
Later I changed to 15" wheels and went with 215/75R15 BFG A/T T/A
tires. I still got about 18mpg. Then I did the Tiico conversion on it
(well, I'd blown one waterboxer and transmission, so it was time to
replace the 2nd waterboxer with something else.) Afterwards I got
about 16mpg. All fuel economy was based on real mileage figures
correcting for odometer distortion due to tire sizes.

Today I just did my first full tank on a new set of tires. Vredestein
Comtracs in the 205/65R15 tire size. These are substantially smaller
in diameter than the 215/75R15 tires. More like the stock 205/70R14.

And waddya know, my fuel economy is substantially improved. 19.4 mpg
(corrected...odometer now reads 4% more mileage than actually
travelled). The Tiico engine is noticably affected by the rolling
diameter of the tires.

Oh, I should mention that 19.4mpg figure was driving from Washington
DC to Pittsburgh, PA at speeds of 65-75mph across the Applachians
(I-70, I-68, I-79). Very steep grades, with the AC running.

These Comtracs are pretty stout tires (C Rated, with 65 psi max, I'm
running 40 psi front, 48 rear). They are SUMMER tires, not all season.

I've also been running Winter Comtracs on my Westy Syncro, and while
much quieter than the BFG's they don't give me the same feeling of
invicibility the BFG's do. They also didn't perform as well in the
mud at SdM Este, but that's a different tale. On my Westy, I am
running 225/70R15 (which is a slightly smaller in diameter than the
215/75R15 I was previously running). I've noticed a minor improvement
in gas mileage, but I have done many other things in the drive train
on it, so it was much more difficult to judge the affect of the tires.

On the GoldBrick, I have no such problem. The only change on it was
the tires.

I dearly love those BFG AT tires, but the size is killing the fuel
economy of my engine.