One thing to remember is that the wiper blade requires a certain amount of
pressure to maintain contact, and wipe successfully, with the windshield at
speed.  When increasing the length of the blade, the pressure is divided
over the additional length, so it may not clear the windshield during a
heavy rain at speed.

I've used the snap-on vanes to take care of that, since they use wind
pressure to put more pressure on the blades at speed.

Greg McKinney
CKCS Cavalier Rescue USA
AR, Northern MS, and TN
www.cavalierrescueusa.com
gmac999@gmail.com

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David Beierl
Sent: Wednesday, October 31, 2012 10:46 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Wiper blade recommendation? Now Length?

At 11:15 AM 10/30/2012, Alistair Bell wrote:
>some food for thought... a switch from 19" to 21" blades results in an
>(rough estimate) 22% increase in swept area. If one assumes same swept
>area increase on pass. side wiper, it would be a 44% swept area
>increase overall (from stock)l. Boy that seems like a lot doesn't it?

It does seem like a lot.  If you assume that the 19" blades sweep out an arc
with a 5" radius hole in the middle, giving r=24", then shifting to 21"
blades (r=25" with 4" hole) gives a difference of ~ten per cent.  If this
happens twice (driver and passenger side) the difference will still be ten
per cent because your initial swept area is also increasing.

Does this not fit better with intuition?

Yrs,
d