Lynn
Chip seal pavement has unique characteristics and sensitivities when
compared with asphalt.  In this part of the world chip seal is used
sparingly.  Where it is used, it seems to stand up well as long as the
sub-grade is sound (it does not do well in freeze thaw if the subgrade is
poor).

Tire scuffing was an issue raised here in Canada in the mid 80's as a major
concern governing axle spread and the number of axles in a group.  Some
jurisdictions that use chip seal were reluctant to accept tridems because of
this concern.  It turned out that the concerns were not well founded.  It
seems that in the conflict between rubber and road, the road does rather
well.  It is also important to appreciate that when the number of axles in a
group increase, weight and dimension regulations see to it that the
individual axle loads are reduced therefore reducing to some degree, the
shear force between the tire and road.

You are correct that scuffing will increase as axle spread increases.   I am
not sure about the "shorter forward distance" on the trailer though.
However shorter forward distances on the trailer will result higher tractive
forces at the drive axles to turn the trailer.

I think this would be a perfect test scenario for CAPTIF provided the test
facility would have the power to overcome the frictional forces.  You might
want to check with Kieran Sharp at ARRB to see if he has any insight into
this.

John



-----Original Message-----
From: The list is for the use of academics and others interested in
technical, op [mailto:[log in to unmask]]On Behalf
Of David Cebon
Sent: Thursday, November 01, 2001 6:46 PM
To: [log in to unmask]
Subject: Fwd: Tyre scuffing and quad axles


Message from Lynn Sleath
Commercial Vehicle Policy Manager
Transit New Zealand

Question

What do you know about the mechanics of tyre scuffing of chip seal surfaces
by multi axle groups on truck trailers/semi-trailers. What factors increase
it?

I have determined that it can be measured by the lateral force transmitted
to the surfacing when the tyre is dragged sideways during tight cornering.

So I figure that scuffing increases on tighter turns, with shorter forward
distance on the trailer, and with wider wheelbase on the axle group. So it
is likely to be worse on a quad axle that on a triaxle because the tyres
are further away from the centre of the rear axle group's axis of rotation.

But I wonder whether it would also be worse on twin tyred axles cf single
large tyred axles because of the greater contact area and the doubling of
the tyre edge that is doing the "brushing".

The latest work in Australia on vehicle performance standards doesn't
adequately document the phenomenon or what steps to take to avoid it.
Can anyone offer me any help please.

Lynn Sleath
Commercial Vehicle Policy Manager
Transit New Zealand
PO Box 5084
Wellington
New Zealand
Tel +64 4 496 6684
Fax +64 4 496 6666
Email [log in to unmask]
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