<VV> More stuff on Tires

[Sethracer@aol.com]

Tires on Corvairs. A long running subject. Webre getting a lot of mileage
out of this thread. Tires are like opinions, everybodybs got one b or four
sometimes! So, here is mine. My opinion, that is. Changing tire overall
diameter
changes many things. First, speedometer readings. Corvair Speedometer
readings  were notoriously optimistic, showing faster speeds than you were
actually
going.  It was probably by design. Bad to have your new car owners getting
tickets when  they thought they had a little cushion. Larger diameter tires
mean
you are  really traveling further for each wheel revolution. So at the same
revolutions,  you are going faster. You can actually use slightly larger tires
to
correct for  the factory optimism. If you go much bigger, you stroll into
ticket land. The  Plus one and Plus two concept. These are commonly discussed
tire strategies to  use larger diameter wheels and corresponding tires, but
retain the original tire  outside diameter. Plus One for the Corvair is
replacing
the 13 wheel with a 14b  wheel and the original bstyleb tire with a
wider, but
shorter tire. To fit the  conflicting  specs, a larger wheel  and the same
outside diameter, the tire design must change to a smaller height  of
cross-section. Enough lecture. Generally speaking, the lower the
cross-section, the
stiffer the ride through the tire, since the tire is the  first
bshock-absorberb
your car has. Of course, to a point, the stiffer the  cross-section the
better the handling of the car, because the compliance of the  tire usually
affects
itbs ultimate traction. (More compliance=less traction). If  we all drove on
billiard-table smooth roads, we could all drive on 35 series  tires as well.
We donbt, so we donbt!  I think the Corvair is easily up to the challenge
of
stiffer sidewalls  and lower cross-sections. Again, to a point. I would not go
lower than 50 series  tires on a street car, and 55 series is a better fit.
There are several 55  series 15b and 16b tires that can meet the needs of
a
late model Corvair, and  still retain the same diameter as commonly available
13b
tires.  Some comparison numbers on Revs per mile  (RPM). All numbers are from
BF Goodrich literature. (PS b For the purposes of  this note, I donbt care
what the original tires were like, okay?)
185/80-13=844 RPM    205/60-15=842 RPM      205/55-16 839  RPM
225/50-16=839  RPM     245/45-16=846  RPM
There is some debate on the merits of 13b tires vs. 15b tires, based on
rotational weight. If the tire/wheel combination weighs the same, and the OD
is
the same b both reachable with the right tire/wheel choice, I see no
difference  in acceleration or braking performance. It means spending a bit
more money
on  very lightweight wheels and selecting low cross-section tires. 15b
wheels
also  bigger braking components inside the wheel. Not a big thing for street
use,  perhaps, but nice on an E/P race car.
- Seth Emerson