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MG MGA - Tyre wear

On checking my front tyres they both show approx 1 mm more wear on the outside of the tread compared with the inside and I wondered why this should be so. Does the suspension set up give any bias to the flat of the tyre? Alternatively would toe in produce this wear pattern -I run with a small amount of toe in , about 0.25 degree?
J H Cole

More rapid wear on the outside of the tyre would normally indicate an excess of toe-in. You do not give the tread depths as I would accept 1mm difference at the end of life (around 3mm remaining tread depth) but not if the tread depth is still 7mm.
Best is to take the car for an alignment check along with the workshop manual and check it is all in tolerance (castor & camber should be fixed but any damage could change it).
Let me know if you have any further questions.

Neil
engineering Mgr
Bridgestone
Neil Purves

As far as I can tell there is no toe-in or toe-out on the mga. The book says both front wheels should be parallel. Correct me if I'm wrong.

Frank
F Camilleri

I agree that toe-in is the logical cause, but I had excess wear on the outside of the right front wheel only on my MGB, and the reason turned out to be a defective shock absorber. I changed it and put on new tyres, and tyre wear has been absolutely even since.

Tore
Tore

I'm with Neil on this one. I was wearing on one tire on the inside edge after not being careful enough on reassembly after replacing torn steering boots. Checking the alignment revealed 1/8 toe-out. I corrected the toe-out to nil and the wear stopped.

warmly,
dave
Dave Braun

Agreed Frank but I've played around with toe in/toe out over the years and found that the most responsive arrangement for my car is with a very small amount of toe in. The present depth of tread is about 4 mm measured at centre so the tyres are going into old age but still with some useful life. Barney has a discourse on tyres that I don't think applies to this situation but if I remember correctly he suggests the painting of the tread to see where the wear pattern is. This might be worthwhile as an insitu test. Neil for track adjustments I measure between the front and rear outside rims using a trammel arrangement I made with vernier threaded stud. Not as accurate as a laser but I hope not too bad.
J H Cole

Hi JH. At 4mm remaining tread depth the 1mm worn additionally on the outside is to be expected with this level of toe-in.
I am also of the opinion that a small amount of toe-in improves handling (at least at higher speeds) so I have around 0.15 of toe. This seems to give no undue wear affect.
As with any suspension adjustment that makes the tyre point in a direction other that straight ahead there will be some additional wear. Balancing what feels the best with what wears the best can be tricky and usually involves changing a number of parameters such as camber and castor angles as well as toe.
If you like the handling where you have it I would leave it alone and live with the additional wear. If you want to try to improve the wear then drop the difference in the rim front/rear to 1mm. This should give you around 0.15 degrees of toe.

Neil
Neil Purves

Toe out causes "nervous" handling and tire wear. IMHO 1/16" toe in is ideal. Yes the book says to set them parallel but any looseness in the tie rod ends allows the tires to go toe out once moving. I use just enough toe in so I know there is NO toe out. Too much toe in can also cause tire wear. Toe wear leaves a "feathered" pattern. Sliding your hand over the tread it will "catch" in one way but not the other.
R J Brown

RJ how is your 1/16" measured? Is this for each wheel at the rims or overall between rims?
J H Cole

Here is an accurate method to measure and adjust front axle toe.

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

This thread was discussed between 08/08/2010 and 25/08/2010

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