Timm's Fairy Tales - The Wobbly Tire Theory
A month or two ago, listening in to a conversation at Irwindale, the
consensus was that it's best to buy your tires from a big
distributor like Summit or Jegs. I learned that those numbers,
scribbled on the tire in yellow pencil, are the measured tire
circumference. When you order from a vendor with ample stock, you're
more likely to get a matched set. Joe's Speed Emporium may have two
on the shelf and those are the two your gonna get.
The numbers on my new tires, from Summit, differed by 5/8 inch so I
measured them right after they were mounted. They were within 1/4
inch. That seemed good to me.
This rolls into my theory about why the RPM data on my recent graphs
are so raggedy. See -->
HERE
When you have a spool, as I do, different tire diameters will cause
one to drag and the car will pull to the side of the smaller tire.
My car has a two finger pull to the left - it did not do that with
the Hoosiers. It's not bad. If I take away my two fingers it drifts
to the left slowly - but surely.
If the tires are hard, like mine are on the highway, the small tire
will scrub along smoothly. But what about when the tires are soft -
like at the track? My theory is that the tire will drag and twist up
the side wall for a short time, till the force required to twist it
further is greater than the traction at the tire patch, and it will
slip and pop back to a neutral position. And do that over and over
and over - kind of like the oscillation I see on my graphs.
So I measured my tire diameters today with 20 PSI. The difference is
one inch. That sucks. As the smaller tire scrubs along, it keeps
getting smaller. That sucks too.
I put 40 PSI of air in the smaller tire - now they are the same
diameter. Can I drive like that? How about 60 PSI and I scrub the
other side till they're even again?
Tomorrow at Irwindale I'll run my tires harder and test my theory.
Oh - and I solved the mystery of the converter unlocking with the
left turn signal but not the right.
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