Re: [T3] Wheels and tyres, etc.

["Jim Adney" <jadney@vwtype3.org>]

On 20 May 99, at 17:42, Per Lindgren wrote:

> Jim Adney wrote:
> 
> > This is true, but the stresses on the bearingsÜ'¼Š changed
> > because of the cantilevered load. On a unloaded car this is no
> > problem, but a loaded car will be a different story, and if you do
> > much of it you may start to have bearing failures.
> 
> Yes, the stress is bigger on the bearings when you use wider wheels, but if you
> change the 46 wheels for the 40 wheels, the stress is not big enough to cause
> any premature wear of the bearings. Only if you exceed an offset of 20 less
> than the original, you can get this effect. The bearings should not have too
> much problem, the bearings are the same as those in the Beetle, aren't they?

The Bentley manual warns against using Beetle wheels because of the 
extra stress on the bearings. I think that is still sound advice. Of 
course it is true that the stress goes up as the offset goes down, 
but there is no reason to expect there to be a sudden failure 
threshold. 

You are correct that the Beetles use exactly the same bearings (in 
the same year), but the beetle is lighter and the bearing stress is a 
function of both offset and weight (as well as driving habits, and 
road conditions.) If you NEVER plan to carry anything close to the 
rated load in your car then there can be no doubt that you will be 
just fine, but who can say that with assurance.

I'd like to point out that the main place where this is a problem is 
for the rear bearings on an IRS car. I think the load on the fronts 
is still somewhere between the bearings and the load on the outer 
swing axle bearing changes only very slowly with offset.

With the IRS rears, the outer bearing is already a roller bearing 
because a ball bearing can't take the stress, even on a Beetle. The 
geometry of this bearing arrangement is such that a small change in 
offset makes a large change in the bearing stress. These are the 
wheels that carry most of the weight anyway, and  this is also the 
place that gets extra load when you carry any cargo. They are also 
expensive and a royal pain to replace.

That said, I'll have to admit that I have never seG1r IRS 
bearing fail, but that outer front bearings fail commonly. The outer 
fronts will see more stress with less offset, so this problem should 
worsten.

Jim
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Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
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