[VAC] Re: Anti-sway

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx>]

Bob: Mixing bias ply and radial tires is a ticket able violation in
Iowa. Legality aside, its a truly BAD idea. Often punished by the
vehicle leaving the road going sideways, then rolling umpteen times. The
problem is that a radial tire flexes to fit the road better, and so puts
more rubber in contact with the road. That along with more grippy tread
compounds causes the radial to grip the road better and in a rapid stop,
the end (or side) with radial tires stops better than the other end. If
the radials are in front, the back end of the vehicle will nearly always
pass the front because the bias ply tires will lock up (and then slide)
easier. This means it takes up two lanes or more as the vehicle spins
violently.

Because the tread of a radial tire rolls smoothly, doesn't squirm when
flexed the way a bias ply tire does, the tread compound can be softer
and so grip the road better and still wear like iron. That increases the
difference in grip between bias and radial tires.

The sidewall of the radial being much more flexible does allow more side
sway. That's why some people don't like radials on a trailer. But the
radial rolls more easily and so is energy efficient on all wheels.

Since you didn't even notice by observation that you had mixed tires,
how are you going to keep the radials on the back and bias on the front?
What's the spare? Mixing bias and radial on the same axle is worse than
bias on the rear and radial on the front because the tires mixed on the
axle adds a twist to start the spin quicker. I believe this is the cause
of those rapidly curved skid marks I see leaving the pavement on many
roads.

Radial tires won't look lower until they are down to under 15 psi, but
that will cost at least a couple miles per gallon fuel. At rated
pressure or maximum pressure radials still flex the sidewalls. Its part
of their design.

Except when needing a different front to rear pressure for control (VW
Beatle, where 6 to 10 psi more in the rear than the front made for best
stability), I found that running the maximum rated pressure on tires
gets the best gas mileage. Running the factory suggested pressure tends
to cost at least 1 mpg. Running high pressure does make the road surface
be more noticed in the ride, though I've found that to depend on the
individual tire design.

Gerald J.