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Re: tire pressure


On 20 Dec 97, Toby Basiliko wrote:

> 	But Chevy did the tire-pressure differential to the corvair, too, and
> their reason was that their suspension could have dangerous handling
> characteristics.  Lowering front pressures was a (criminally
> ineffectual) bandaid for a car that american drivers could get
> upside-down pretty easily.  
> 	The corvair suspension was very similar to the VW- in fact, the rear's
> tha same as our pre-67's.
> 	Did VW do the same for their swing-axle designs?
> Toby (it's gonna be trailing-arm IRS) B

I believe the reason for different tire pressures is to produce the 
same effective tire contact patch area for both front and rear tires. 
Thus it is necessary to use greater pressures on tires that support 
more weight.  This is just sound enginering practice and I believe VW 
has recommended it from the very beginning.  I have a 1957 Clymer 
VW manual that shows differential pressures recommended then.  

You should note that cars used in oval track racing usually use 
different tire pressures in the inside vs. outside tires since the 
cars are always turning the same direction and there is more 
downforce on the outside tire.  So there can be a left/right 
differential as well as a front/rear difference.

I suspect that it's true that overinflation is much less important 
now that everyone drives belted tires. Since underinflation is still 
a problem, it is just easier to recommend a single one-size-fits-all 
approach and inflate all the tires to the larger number.

Front engine cars can probably get along better with overinflating 
the rear tires than rear engine cars can do when overinflating the 
front tires because the rear wheels on a front engine car are much 
less important to handling than the front wheels on a rear engine 
car.

When I was growing up, my dad bought a Corvair on the FIRST day that 
they were available at the dealer.  I learned to drive in that car 
and very much enjoyed driving it even though it was an AT with the 
smallest Corvair engine, 88 BHP.  I have a lot of respect for Ralph 
Nader, but I think he was misguided in this particular attack.  I 
drove that car rather hard and never had any trouble; I always 
thought it handled pretty well.  Much better than the Buicks and 
Pontiacs my folks also had in that era.  I don't remember Chevy 
changing the tire pressure recommendations, but perhaps they did.

VW changed to IRS in 1969, Corvair changed in 1965, I think the BMW 
2002 changed in 1967.  I have always been surprised that VW got away 
with it as long as it did, but, then again, my swing axle VWs never 
gave me any trouble, either.  I DO like how much easier it is to 
remove and work on the IRS transmission.

Jim
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       Melissa Kepner                                    Jim Adney
                             Laura Kepner-Adney
                         jadney@vwtype3.org      
                             Madison, Wisconsin
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