Date: Fri, 3 Mar 2006 14:27:02 -0800
Reply-To: Doug F <vanagon@ASTOUND.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Doug F <vanagon@ASTOUND.NET>
Subject: Re: Power loss with 15" wheels?
Content-Type: text/plain; charset="iso-8859-1"
Running the SA 15" wheels with 215/75/15s on my 87 syncro with a stock 2.1L
wbx have shown me that it has definitely hurt gas mileage and power.
The stock gearing with 14s allow you to run the engine at the proper RPM
for the wind load in 4th gear.
The stock water boxer develops certain amounts of torque at specific RPMs,
VW matched it pretty well to the wind loads at 60-75 to where you feel like
you have pretty good performance for the little power you have.
When you up the gearing the engine is no longer matched to the relative wind
load and you have to push down on the throttle more to maintain the same
speed.
I can tell I am burning more fuel to go the same speed.
Even travelling at higher speeds or RPMs I feel the loads are no longer
matched and the engine is no longer running in it's optimum efficiency.
Need to lower the R&P or perhaps add more torque (suby)
Doug
----- Original Message -----
From: "Anthony Egeln" <regnsuzanne@YAHOO.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, March 03, 2006 1:24 PM
Subject: Re: Power loss with 15" wheels?
> I guess it was your last point, about the lower RPMs at higher speeds that
gives me the impression of having more power. Also, we have precious few
hills here in NE Florida so I couldn't judge it that way. Thanks for the
explaination.
> Anthony
>
> Sam Walters <sam.cooks@VERIZON.NET> wrote: "My impression was that I
GAINED power going from 14 to 15...just my personal impression. Anthony
> '89 Syncro GL (Hidalgo)"
>
> It may be an impression, but it is impossible if nothing else was changed
and the tires on the 15" wheels were larger than those on the 14." If
somehow you put smaller and lighter tires and wheel into the 15" setup, you
could gain power.
>
> As Mark Drillock's post explains, if the tires that you put on the 15"
wheels are larger in radius, or diameter, than those that were on the 14"
wheels you will lose power. Basic rule of physics involved. It is like
changing the length of a lever. With the larger diameter wheel, it is as if
the ground against which you are pushing has a longer lever with which to
resist the van's force.
>
> Mark is right in what he stated - you can compare the size of the tires -
not the wheels and figure out the % of power lost. But he also omitted
something of some importance - weight. Rotating weight is more costly to
power transmission, acceleration, etc., than static weight, like the van's
body or its cargo. So the extra weight of the wheels, if any, and the
larger tires - almost certain, will also use up some additional % of your
available power.
>
> With larger tires you can go 70 mph with lower rpm from the engine. At
some point as the wind and rolling resistance increase with speed
(exponentially), the van will not have the power to push against the
resistance. So, the top end may not be any greater, or maybe even less,
with larger tires, even though you can go 50, 60, or 70, with fewer rpms
with the big tires.
>
>
> --
> Sam Walters
> Baltimore, MD
>
> 89 Syncro GL, Zetec Inside
> 85 Westy Weekender
> 85 Mercedes Benz 300D Turbodiesel - to become veggie oil powered
>
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