I have a 2.5 awd x type jaguar which is scrubbing
out the inside edge of the front tyres. I have rec'd conflicting opinions re correct wheel allignment. Can you help or recommend a good firm near orpington to solve the problem. Many thanks
If only one tire is affected, "camber" is too low on that tire. That is the inward or outward tilt of the wheel as viewed from the front of the car. On some cars, most Ford front-wheel-drive cars in particular, camber is not adjustable. You just take what you got and keep buying tires. Camber IS adjustable on most better cars. It can be too low on both wheels. In addition to inside edge wear when it's too low, each tire wants to roll in the direction it's leaning so the alignment technician will set them to equal values to offset each other's pull. He will usually make the left one a little higher to offset "road crown". That is when roads lean to the right so rain runs off. Experience tells him how much to make that offset. It's not included as part of the alignment specs.
When both tires on one axle are affected equally, "total toe" might be misadjusted. In your case, the front tires would be toed out. That means they are both steering away from the center of the car when you're driving straight ahead. The leading edge of both tires will scrub off. If you exaggerate it for clarity, suppose the left tire is toed out and steering left when you want to go straight. Imagine it turned more, ... And more, ... Until it's turned 90 degrees to the car. Now it's easy to see that the inside edge is in front and is the leading edge of the tread. Now imagine holding a pencil upright with the eraser on the table. Put a little downward pressure on it, then drag it straight across the table. You'll see the leading edge scrubs off and makes eraser crumbs, but the trailing edge lifts up off the table so no wear takes place on that part. That's what's happening to a pair of tires when the total toe is too much toed out. While camber only affects that one tire, incorrect total toe affects both tires. Total toe can be wrong when only one wheel is misadjusted. That will make the steering wheel off-center when you're driving straight ahead.
One somewhat common problem that a lot of inexperienced alignment mechanics overlook is proper ride height. Cars with front struts are a little more forgiving, but when a car has upper and lower control arms, the geometry changes as ride height changes. Without going into a lot of detail, in a broad sense, the frame, spindle, and two control arms form a square. When the frame is low due to weak springs, that square turns into a parallelogram or trapezoid. The wheel can still have camber adjusted to specs, but it will tilt in and out on top differently as the car goes up and down over bumps in the road. That can cause edge wear when everything appears to be aligned correctly, or it more commonly just causes even but rapid wear as the tire scrubs sideways back and forth as the car goes up and down. If ride height is excessively low it can reduce tire life by 50 percent. Experienced alignment mechanics shudder when they see cars and trucks with lift kits or that are lowered in the misbelief it looks cool. All manufacturers and car models have their ride height measurements and points to take those measurements listed in a small book that every alignment mechanic uses called a "ride height guide". Anything outside those published specs needs to be corrected if the alignment is to be done properly.