Hi Ed,
I think you are guilty of "over thinking" this tire thing. I used to
do that a lot and usually found that I either missed some factor or I
simply had false information about the tires in question. I found
that Michelin thinks these things through better than I could and I've
never been unhappy with their tires. I don't use them on my Amphicars
though since they don't make a wide white wall version and I like the
original look.
On a convertible, I would be much more concerned about tread noise
from my tires than I would about slipping on the boat ramps. I've
never had any slippage whatsoever on the ramps and I'm not using all
weather type of tires. I've had some horribly noisy all weather tires
in the past however and I couldn't wait for them to wear out. (Five
of my six cars are convertibles.)
The problem with not using inner tubes on these cars is that if you
are wrong about them holding on to the rim, the car could flip when
the tire suddenly collapses in a sharp turn. Now that could be a
serious problem. Without tubes you also aren't able to reduce the
pressure in your front tires very much without really getting into
dangerous territory and low front tire pressure may be a requirement
to get these cars to track well. I run the specified 14 lbs. on the
fronts of my White car, with bias ply Coker Classics, and it tracks
perfectly. Another thing is that when I restored my cars I noted rust
on the insides of some of the wheel rims and if water can get in, air
can get out.
Good Luck, (we need all the So. Cal Amphi people we can muster)
John Friese
Santa Barbara
67 White
67 Red
--- In amphicar-lovers@yahoogroups.com, "Ed Price" <wb6wsn@c...> wrote:
> After a lot of net research, I finally settled on the tires that I
wanted to put on my Amphi. I selected the Cooper Dominator All-season
P175/70R-13 82S black-wall models, which cost me a total (mounting on
loose rims, valve stems, dynamic balance and 50k miles warranty) of
$241 at Discount Tire.
>
>
http://www.discounttire.com
>
> I chose this tire for its ratings on wet traction, and I liked the
design of the tread. I had been leaning toward the Yokohama Avid
All-season touring tires, but ultimately rejected those since they
have a pair of continuous center circumfrential ribs on the tread, and
I find that tires with these ribs are very sensitive to the grooving
used on our local freeways (CalTrans cuts slits into the concrete
surface to help shed rainwater; when the ribbed tires catch the groove
pattern just wrong, they give you a lateral "squiggly" feel). True,
I'm not expecting to drive my Amphi at 80 MPH, but it was enough to
tip the balance toward the Dominators.
>
> The Dominator tread pattern is nicely open (I think the term for
this is "wide sipes"), and has gotten great reviews for snow traction.
OK, so what does snow traction have to do with Amphi tire selection?
Well, the official ratings for wet traction are really a measure of
how well a tire avoids hydroplaning at speed. While this is important,
I was really thinking about traction at very low speed. I wanted a
tire tread that got a good grip on a moss-covered concrete ramp and on
loose gravel. Needless to say, this isn't one of the official tire
rating tests. I felt that a tire that gets a good grip in snow and
slush would be the best choice for ramp traction too.
>
> The ideal is a tractor-style tread, but this would yield far too
much vibration at any speed on a surfaced road. The next best is the
military-style tread pattern; this can be used on a road, but will
yield a lot of noise (tire noise is the least of your concerns if
you're driving a 2-ton 6x6). When you finally get to winter or
all-season tires, your choices are pretty limited in a 13" wheel size.
>
> According to calculations, the 175/70-13 tire should be slightly
(about 3.2%) smaller in OD then the original 6.40-13. OTOH, the
"standard rim width" for a 13" wheel is 5", but our Amphis have a 4.5"
rim width. Since the 4.5" width holds the tire beads closer together,
this will make the tire stand a bit taller than calculated, so I think
the errors pretty well cancel out.
>
> I also decided to not use any tubes. I based my decision on the fact
that the Amphi rim flanges seem quite deep, and the fact that a 13"
wheel will take more side-loading that a larger rim before the tire
bead deflects away from the rim. I think it's a safe call, as Amphis
don't really ever experience slalom racing. However, only some time
and road miles will tell if this was a dumb idea.
>
> Anyway, the new tires fit and look great mounted on the Amphi rims.
>
> Ed
> El Cajon
> 67 Rust Guppy
>
>
>
> [Non-text portions of this message have been removed]
