[Spridgets] calculating speed

David Lieb dbl at chicagolandmgclub.com
Mon Oct 20 07:22:03 MDT 2008


> Personally, I have calculated the top speed of my '76 as 62.5 MPH, for 
> that is
> the speed at which the front wheels start to hop slightly, allowing the
> steering wheel to be sawed backed and forth with absolutely no effect on
> trajectory.

Drew,
A vibration in the front tires at that speed means that the tires are not 
properly balanced. Yes, I know, you had them electronically balanced and the 
guy swears they are fine. If you look at them, I bet they each have a rather 
large weight on them somewhere. You see, modern rims are "hub-centric", 
which means that the hole in the middle of the rim is perfectly centered. 
Our rims are "lug-centric", meaning that there is a hole in the middle, but 
there is NO precision to it at all. The tapers of the lugnuts center the 
wheel in place. Few balancing machines these days are equipped for 
lug-centric, but most have optional bits to do it. Whether the operator has 
a clue or not, is another story. What we HAVE to do, is to watch when the 
balancing machine spins it up to see if there is any runout on the part of 
the rim you can see. If you can see it moving up and down, it will not end 
up balanced for your car (it will be perfectly balanced for use on the 
balancing machine, however). Explain this to the tire dude and he will 
probably understand and take the extra time to minimize runout. Back tires 
are not nearly so fussy because the rear axle bearings really limit the 
amount it can move. Any time you see a tire weight 3"or longer on a Spridget 
wheel, you KNOW they are not properly balanced.
David Lieb
1972 1960 1974 1973


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