Greetings FWDLKR's! - Just a note on the radial-tire "harshness" thing -
there are TREMENDOUS differences in low speed ride quality between brands of
tires produced today. If you are suffereing from such "harshness" with your
radials, - don't necessarily blame your "non-radial" suspension. Virtually
all cars produced lately have a "radial-tuned" suspension, and many of these
cars suffer from the same low speed harshness that can be found in
non-radial-tuned vehicles, and it is due to the tire itself. Now I am not a
tire "expert", but my butt is *not* numb, and my ears work, and there are a
*lot* of cars out there with this problem.
Best way to avoid this "problem" is to use Michelin tires. There are many
other brands available that are just fine, but not knowing *which* brands to
use can lead to expensive R & D. Don't bother asking the tire dealer - if
he knew, he probably wouldn't tell you anyway. The only one I know for sure
that won't have this problem is the Michelin. NOTE - Here are two brands to
avoid - Big O "Legacy" (this tire will turn almost any car into a dump
truck), and "Mastercraft" - about the same results. The "legacy" is
manufactured by a company that makes truck tires (it shows), I have no idea
where the "Mastercraft" originates, but it is sold by Michel Tire - not a
"slam" against Michel Tire - they have many fine brands available (I do not
however, know for sure which ones are "good" - just that the Mastercraft is
not). I recently installed a set of Firestone "SS 010"s on my daughter's
car - very nice ride qualities. Her car is not an "old car", but the tires
I removed (with *lots* of tread still on them BTW) were horrible. - oh yeah,
they were the "Radial GTS" - sold by NTB (National Tire & Battery) - add
them to your list of "don'ts". Wish I could offer more info, but that's
about it. Next time you ride in someone's car with a particularly nice ride
at low speeds, make a note of the brand of tire on it - and add it to your
list of "do's". (and vice-versa!)
Regards,
DaveG.
----- Original Message -----
From: <LARSPAINTR@xxxxxxx>
To: <L-FORWARDLOOK@xxxxxxxxxxxxx>
Sent: Tuesday, May 16, 2000 12:18 PM
Subject: [FWDLK] Radial tire harshness
> Well I hope for the last time, I have FOUND the quintissential (whatever
> that means) reason for radial tire harshness at in-town speeds, when
putting
> same on older cars. The entire article is over 5 pages but an exerpt:
>
> Car Life June 1967 article RADIALS
>
> Why have the worlds carmakers been so slow to even experiment seriously
with
> radial tires? The answer can be summed up in a few words--- slow speed
ride
> harshness. Radial tires deliver a rough ride, especially at low speeds.
> When a set of radials is put on a standard car (not originally designed
for
> radial tires), a harsh, thumpy ride that can be heard as well as felt, is
the
> result. Its as if the stiff belt between the tread and carcass can be
felt.
> Small bumps, such as tar strips and railroad tracks, are especially
> noticeable. and the ride over such minor irregularities seems much worse
at
> low speeds up to 35 or 40 mph. At highway speeds the tires smooth out and
> provide, if anything, a better than bias ply ride.
> Bajer says its not primarily the stiff that causes ride harshness.
"What
> happens is that the radial cords are acting something like a separate set
of
> spokes of the wheel," he explains. "when the belt runs over a bump it
tries
> to shift backward a little, or actually rotate around the tire bead. The
> radial ply 'spokes' resist this backward shift and give an actual
> circumferential springing effect. But every spring has its natural
vibration
> frequency. In this case (of radials) its between 40-50 cps. When the
> frequency 0f road bumps synchronizes with this natural frequency of the
> carcass, the ride harshness and thumpy sound is encountered. This happens
at
> speeds up to 40 mph."
> "But at higher speeds, the radial tire tends to give a smoother ride
> than the bias ply type. This is because centrifigal force pulls outward
on
> the belt and tends to stiffen it up substanatially. It literally glides
> right up over the bumps. Its as if you're riding on hoops that are
connected
> to the wheel by springs (the belts)- but without the synchronous problem
> because youre above the natural frequency of the (pseudo) springs. This
is
> better than bias plys becasue you're always working against rubbing
friction
> between the plies, and a continual tread and carcass distortion at the
> contact patch". END of quote from article
>
> I must add that the last sentence has to do with the inherent tread
> distortion of bias plys at higher speed, there is an extreme distortion of
> the contact patch AND the tire itself, causing vibration and
'squirrelyness'
> of the entire tire. Some of you readers may recall seeing test photos of
a
> bias ply tire running at 80 mph and the tread looks abysmally distorted.
The
> radials will not get this distortion, thanks to the stabilizing design of
the
> plies.
>
> Many of us have radials on our old wheels but the above is the most
detailed
> and factual coverage of WHY there is an decrease of low speed ride comfort
if
> we retrofit our cars. Interestingly there is no commentary on rim widths.
> And the impact problem is such that it will transmit into the old rims,
that
> will often allow a full wheel cover to be thrown off in spite of its
> apparently adequate fit. My 51 Merc lost 2 fine Lincoln turbine covers,
> thanx to this secondary problem. And I know of others that have similarly
> lost rims. No its not to back fit, its to to wheel (rim) flex which is
> caused by the road irregularities transmitted into the older style rim,
then
> the slight distortion plus centrifigal force causing the wheel cover to
> loosen and eventually get thrown off.
>
> Modern design has long solved the low speed ride harshness problem due to
> suspension tuning, again some of us recall optional RTS (Radial Tuned
> Suspensions) on some cars, mostly GM in the late 70's. At that time both
> bias belted and radial tires were available, and this option tuned out
that
> harshness. Since radials are universal now, all suspensions are designed
for
> them. In fact so well designed we can have 50 and 55 profile tires on
cars
> and still have an extremely plush ride with the bonus of quick steering
> response and mega traction.
>
> All FYI
>
> Lars
>
> Lars
|
|
Back to the Home of the Forward Look Network