From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Regrooveable Tires
Date: Tue, 23 Jan 2001 20:17:02 -0500

Dick Lucas wrote:

Geez, I hate to post anything on tires lest I incite the bozo
brigades but here goes.  This is a summary of some of what I learned
from the Goodyear racing engineers from back in my racing days.  I'm
not much of a chassis man but I did pay attention :-)

> The tires on my diesel pusher are marked "Regrooveable."  I have been able
> to ascertain that this means that there is enough rubber on the tire that
> new grooves can be made after the tread has worn off.  These regrooveable
> tires are common on 18 wheelers.
>
> I have a couple of observations and several questions.
>
> First, is that I have seen information that shows that the rolling
> resistance of a tire decreases as the tread wears down.  I assume that the
> distortion of the tread blocks contributes to the rolling resistance. Is
> that correct?

Yes.  The hysteresis of the rubber is carefully controlled as a
balance between rolling resistance (indicates low hysteresis) and
control and ride quality(indicates high hysteresis).  If the rubber
is too "bouncy" (low hysteresis), it will tend to bounce off the
pavement as it makes contact, reducing traction and contribute to a
harsher ride.  The desirable situation is where the rubber contacts
the pavement, deforms to conform to the pavement texture and the
energy of deformation is dissipated as heat by internal friction.
The problem is, this is energy that is provided by the engine and
detracts from gas mileage.  Thus the compromise.  In a situation
where mileage is not a consideration, such as with a motocross
racing tire, the rubber can be made extremely soft and with
extremely high hysteresis.  In about '72 Goodyear developed a rubber
that was both tough and tear resistant and soft and ultra-high in
hysteresis.  This tire was revolutionary and was almost unfair until
others caught up :-0


> Is the maximum height of the tread blocks determined by  a desire to reduce
> rolling friction, or is there some other factor such as grip, stability or
> wear involved?   Otherwise, why not simply make the tread deeper and
> eliminate the need for regrooving?

It is that and the tradeoff between tread life and tread rigidity.
If the tread is too tall for the stiffness of the rubber, the tread
blocks will squirm and cause poor and vague handling, particularly
while cornering.  Taller tread also tends to contribute to tire
noise.


> Has anybody in this group ever had tires regrooved, or do the tires simply
> disintegrate because of age?

That's the issue for RVers.  Regrooving works very well if the
carcass has not dry rotted from age.

John