And well you should ask, Bill.
For-tune-ately, I have the later AKM2092
Official Midget Workshop Manual and so:
for the stock radial 145-13 "slim" tire....
22F/24R for "normal" weight
22F/26R for "max" weight
"It is recommended that for sustained
speeds at near the maximum the above
tyre pressures are increased by 4lbs."
While I find only dry weights for the earlier
cars (1400-1490lbs), I find the following
are specified for later Sprite Mk.IV and
Midget Mk.III:
Kebside Full fuel, all optional
extras/accessories 1,701lbs
(cats not mentioned!)
Normal +driver/pax&50lb bag. 2,001
Max + towbar hitch load 2,151
(though max towbar hitch load is defined
as 100lbs. Makes sense, eh? Yeah, right!)
When the footprint is enlarged beyond
the factory stock tire, than for equal ride
comfort (to you and the suspension built
with the stock "smaller" footprint in mind)
pressures would be less BUT, in reality,
handling would suffer and tire wear increased due to underinflation.
Thus, when going to a larger footprint than factory stock, you might as
well make up your mind that for like handling
qualities, the vehicle inclusive of suspension is going to take more of
a
beating to one extent of the other, all
else being equal.
The weight each tire will support will be
less per larger footprint than with the
stock footprint as well. So as far as keeping the tire "on" the road
over anything but the smoothest of surfaces,
more than stock pressures on the stock
"smaller" factory tire footprint will be required, all other things
being equal.
You will definitely notice this in the rain
on smooth surfaces (tendency to aquaplane) and most definitely on a less
than smooth surface, especially going
around corners. Here again, all other
things being equal.
And of course, "they" never are. Tread
design, compound and design differences
between bias and radial enter into all of
this along with rim width, etc. We would need an engineer to figure it
all out...at least, I would.
But assuming the stock rims or even slightly wider ones, I would start
with the
stock 22F/24R on a stock Spridget and go
from there.
Based on my personal experience,
you'll probably end up with 24/26 as
a compromise for decent handling/ride.
or even 24/24 in the "oversprung" stock
factory BE 1/4 ell. set-up.
A lot of guys go well beyond these pressures for "better" handling in
terms
of both "turn in" and "adhesion" at the
expense of ride comfort, right up to the max pressure as shown on the
tire.....
a matter of different tastes, priorities and as in all cases...different
strokes
for different folks. No right or wrong, here.
Remember, if you change factory rec.
fore/aft pressure ratios, you will get a
little more or a little less oversteer or
understeer. No big deal unless you get
"way out" on the ratio. This is something
you can easily feel and compensate for
to your taste. More in the front or less
in the back = oversteer. When it's the
other way, it's the other way! :)
The thing to remember is that factory
recommended is a place to "start".
Nothing is written in stone except the
max tire inflation pressure as given
on the side of the tire.
Vehicle tire pressures are given "cold"
by the vehicle manufacturer. I am not
sure about those given by the tire
manufacturer. I assume cold?
Cap'n. Bob
'60 :{)
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