|
14 October 2002 |
Having
applied Hi-Los and some smart 165/60/12 profile tyre shod12 x 5-inch ally rims,
discussions get around to a subject that has cropped up a zillion times in the Knowledge,
at shows, my e-mail address, etc. - just why does this combination cause the
tyre to hit the front arch?
To be
more exact - why does the tyre just rub, twang the plastic arch off, or foul
the arch to the point of bending it? Even if the genuine, original fitment
'Cooper' alloy 12-inch rims are used with the 165/60/12 tyres? Well, it's all a
question of alignment - either subframe to body or suspension to subframe.
When
trying to source/cure the problem, many folk have discovered that shim plates
have been used between the front panel to subframe teardrop mounting and the
subframe - and wonder if the car has been in an accident and been 'fudged', so
could be causing the problem. The answer is more than likely not. Those shims
are actually a Rover part, fitted at the factory - not to re-align the
subframes as some folk believe (be impossible when you consider the magnitude
of the tower mounting bolts and rubbers!) - but to push the front panel
forwards to give clearance to the tyres…
Backing
the truck up a bit here, there are basically two reasons why misalignment is
causing the tyres to foul the arch, which, incidentally, generally occurs
between three and six inches above the top edge of the bumper on the leading
edge of the front arch line. The first one to check is the tie-rods - the
components that go from the outer end of the bottom arm forwards to the front
of the front subframe. I have seen many of these bent - they're supposed to be
straight. A bent tie-rod pulls the wheel/tyre forwards, increasing the caster
angle and causing it to hit the arch. The general cause of this is the car
being jacked up on the tie-rod bracket where it bolts to the subframe. I've
seen this all too often at tyre fitting centres. As the car is raised in this
fashion, the suspension drops, the tie-rod rests on the outer edge of the jacks
'cup' and the powerful rubber spring combined with the suspension weight causes
the tie-rod to bend. They're only made of basic steel. They can be straightened
- but they cost little, so fit new ones along with new bushes.
Having
assessed and sorted any problems with the tie-rods get the suspension geometry
checked. The manufacturer’s tolerances are quite wide, but shouldn't cause the
fouling problem. I have, however, come across a few cars where the geometry is
outside the standard tolerances. Again it's the caster angle causing the
problem. Somehow those cars ended up with an extra degree of caster on one
wheel. Unfortunately I didn't have sufficient time to source the cause, but
fixed it by using one of the aftermarket harder tie-rod bushes fitted to the
wheel side of the tie-rod where it fits to the front subframe. This pushes the
wheel back, getting the caster angle back within the specified limits, and
stopping the fouling problem.
Happy
the tie-rods and caster angles are sorted, it's time to consider the panel
work. Now, the reason why Rover had to start using these spacer-shims between
the front panel teardrop mounting and the subframe on the 12-inch wheeled
Coopers is because the bodyshells were a bit misaligned, and the subframes were
not always totally square fitted into the shell. Consequently these
spacer-shims were used to push the front panel forwards, away from the tyres.
So this is another avenue of attack - except there is a point of no return
here. The arch reaches a point where it is being pushed so far forwards by
over-use of the spacer-shims it starts deforming in towards the centreline of
the car, thus causing the arch line to bend backwards slightly. Back to square
one with the fouling thing.
Some
folk have tried fitting wheel spacers to the front wheels. This is not at all
recommended for safety reasons and it is very unlikely to solve the problem
since moving the wheel/tyre further out increases its peak turning arc, making
the tyre more likely to foul.
So if
you suffer from this affliction, check your tie-rods and caster angles first,
then cogitate the issue of the panel work. If it's neither of these - it could
be serious…
Useful
part numbers:
|
8G4249 |
Standard tie-rod assembly complete with
all new bushings and washers, nuts and bolts. |
|
21A450 |
Standard tie-rod only. |
|
21A1091 |
Heavy-duty adjustable tie-rods, pair. |
|
31G1155 |
Standard rubber tie-rod bush, 2 needed per
side |
|
C-STR628 |
Up-graded tie-rod bushings for fast
road use, set of 4 |
|
C-STR629 |
Very hard competition use only tie-rod
bushings, set of 4 |