Having applied Hi-Los and some smart 165/60/12 profile tire shod 12 x 5-inch alloy 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 tire to hit the front arch?
To be more exact - why does the tire 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 tires? 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 tires…
Backing the truck up a bit here, there is basically two reasons why misalignment is causing the tires 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 tire 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 manufacturers 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 centerline 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 it's 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:
21A450 Standard tie-rod only.
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