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MG MGB Technical - toe in measurement

I want to set up my toe-in using one of the various techniques published. But I can't find out where the measurement is taken. Is it at the wheel rim or at the outside of the tyre?
Steve Church

Steve, the WSM for the A says measure at the rims, using an adjustable gauge rod. But, seeing as the spec for the A is zero, it really doesn't matter! What is important is getting a point that has no run-out, or if you can't, allowing for it. Also need to have no play in the steering joints or wheel bearings. I don't know the spec for the B.
Art Pearse

Level ground. Drive straight forward and stop using only the hand brake. Take the measurement at the rim. If you have re-bushed with Ploy bushes you can set to 1.5mm toe in to parallel, rubber bushes 1.5mm to 2.3mm toe in.
Allan Reeling

Buy a gunsons Trakrite gauge. Then you don't need to know the actual setting for your car, the gauge does it for you.
Mike Howlett

Further to Allan's instructions, do that, then push the car forward another 1/2 wheel turn and repeat the measurements. Take the average. This will correct for wheel runout.
Art Pearse

I've got the toe in about right. Enough to get me to the garage where they will set to the correct value for £20.
Steve Church

I am an ex-Michelin enginer. I can say with certainty, never use the rims for measuring toe, especially with wire wheels. The lateral runnout will definitely give you an inaccurate result.

I suggest that you use the following Procedure as it eilminate the runnout error.

Checking/Setting Front Axle Toe-in

Toe-in can be easily checked on any automobile and with a little effort corrected to the required 1-mm plus or minus 1-mm or 1/32nd plus or minus 1/32nd. To complete the task you will need masking tape, a tape measure, preferably metric, a pen and an able helper.

You start by driving the car forward and backward on near level ground for at least 5 tire revolutions in each direction while fiddling with the steering wheel to ensure that the wheels are pointed straight ahead. The last step in this part of the process is to back the car to its starting point and stop the engine. Now, take your hands off of the steering wheel and have your helper push the car forward for about two tire revolutions. If the car tends to roll use the hand brake only to stop and hold the car in place.

The measurement phase consists of placing a piece of masking tape, about 2-3 inches long, at the rear of each tire. The tape should be place vertically near the center of the tire tread. Next, using your pen, place a small horizontal tick mark at the inner edge of each piece of tape. The tick marks should be as high off the ground as possible while still being able to have a clear line of sight from tick mark to tick mark. With the aid of your assistant, CAREFULLY measure the distance between the edges of the each piece of masking tape at their respective tick mark locations. Be sure that the tape measure does not touch any part of the underside of the car. Now, push the car forward, without touching the steering wheel, while carefully observing the masking tape. Stop the car, using the hand brake only, when the tick marks are as high off the ground as possible while having a clear line of sight between the tick marks. Remeasure the distance between the tape edges at their respective tick marks. Now, subtract the two measurements to obtain the toe value. If the distance measured at the rear of the tire is greater than the front, your front axle will be toed-in. It is easier to get an accurate measurement if you use the 100-mm or the 4-inch as the starting point because we are not interested in the actual distance but rather the difference between the front and rear.

This method of checking front axle toe is very accurate because you are measuring between the same two points on each tire while the points are at both the front and rear positions. Tire and wheel run out and tread pattern irregularities are accounted for.

If you find the your toe is out of specification you can make proper adjustments. Start by changing the front distance by one half of the error. Then push the car forward (never backwards) and remeasure the rear distance. Make a small toe adjustment if necessary, and repeat the entire process until you have reached the desired toe-in value. After you think that the toe is correct take the car for a short drive and repeat the measurement process.

Although time consuming, I can assure you that this toe measurement technique is at least as accurate, and more reliable than alignment shops offer. This is a direct measurement that does not rely on equipment calibration to ensure accuracy. If you want caster and camber measured/corrected or a four-wheel alignment on a modern car you must go to an alignment shop. Use the above method to check their work. You will be surprised! Have you ever noticed tire wear after 6-months of driving after an alignment, taken the car back and told that you must of hit a curb or a chuckhole. Sure…

Frank Grimaldi
Frank Grimaldi

Frank's method sounds good.

Rather than compensate for runout I used a dial gauge to measure verticle and horizontal run out on my rims and fitted the best ones from my collection on the car.
David Witham

Thanks Frank for the comprehensive reply. But it still begs the question of where the toe in measurement should be taken. A 2mm toe-in at the rim will be different to a 2mm toe-in at the tyre circumference.
Steve Church

Steve,

You are splitting hairs. Measure at the tire's tread. Ideally, you want zero toe under dynamic conditions. When the tires are rolling the forces that they see tend to spread the tires apart at the front. That is why you generally set the toe to 1mm or 1/32 of an inch toe-in.

Frank Grimaldi
Frank Grimaldi

This thread was discussed between 02/04/2011 and 07/04/2011

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