Wednesday, June 28, 2017

Fred, the Big Lug, Doesn’t Have Lug Nuts

In the 44-09-12 episode “Changing Stembottom's Tires”, Vic complains bitterly about being invited over to the Stembottom’s to help Fred work on his car.  While Vic claims to enjoy working on cars, or “tinkering” as he calls it, he considers the work Fred has lined-up to be just manual labor.  Let’s understand why…

First some definitions.  A wheel is comprised of three parts: 1.  The tire (the rubber part that wears out),  2. The rim (the center section that holds the tire and attaches to the car) and 3. The inner tube (the inflatable bladder inside the tire – note that all new cars are tubeless and do not have this part).

Rotating one’s tires refers to the practice of changing the position of the tires to equalize wear on them and to prolong their life (this would have been really important during the war when rubber was scarce).  With older rear wheel drive cars the rear tires would wear more quickly.  On newer front wheel drive cars the front tires wear more quickly.  To maximize the life of the entire set of tires, the front and rear tires can periodically be exchanged.  Newer cars, with radial tires, require that the front and rear tires be exchanged but remain on the same side of the car.  Older cars, with bias ply tires, require that the front and rear tires be exchanged by crossing sides (e.g. front passenger side tire is exchanged with the rear driver’s side tire).   On a diagram this makes an “X” and is referred to as “cross switching”

On newer cars the tire/rim assembly (the wheels) are attached to the car using several nuts or “lug nuts”.  The entire wheel assembly (rim and tire) can be removed easily by removing the lug nuts.  But on some vintage cars, particularly those prior to 1920 or so, the rim is semi-permanently attached to the car and only the tire can be removed1.  Removing just the tire (i.e. manually de-mounting a tire from the rim) is a tedious and difficult process.

Fred’s car doesn’t have lug nuts, so the tires must be de-mounted from the rims.   The rims remain attached to the car. The tires must then then be re-mounted on the rim at the tire’s new position.  And unlike the swapping a complete wheel assembly, the tires must be deflated to de-mount them and then re-inflated once they are on the new rim. 

De-mounting/re-mounting a tire is difficult, as the diameter of the rim is slightly larger than the tire’s inner diameter.  A set of pry bar like tools are required to pry the tire off-of / onto the rim.   More often than not it results in a pinched finger!  Professional garages use a tire mounting machine which makes it much easier. 

Fred’s old car requires all four tires to be deflated, manually de-mounted, re-mounted to the new location, and then re-inflated.    To make matters worse, the tires need to “cross”, so the you cannot simply jack up one side of the car at a time.  

With today’s cars, the wheels can be rotated in less than 30 minutes.  On Fred’s car, with its permanent rims and bias play tires, the job may take several hours.  It’s no wonder that Vic howled like a panther when he heard what Fred had in store for him! 

Leave it to Paul Rhymer to make something as dull as rotating tires into an interesting and humorous episode! 
-- Dave Duckert (Dave in Wisconsin)

1.        Popular Mechanics December 1970  p 113

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