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MG MGA - Front end alignment

I've had to do a front end alignment on the car.

In order to do that I've make straight edge jig to set the front wheels parallel to the rear wheels.

This is the point at which I get a little confused.

Barney's page suggests 1 degree of toe in, which is equivalent to 3/8" in from parallel.

Other pages suggest toe be based only relative to the front tires i.e. decrease the distance between the front of the front tires by the amount of toe in.

So if you did Barney's method, both tires would move in 3/8' or a total reduction in the distance between the front of the tires of 3/4".

If you did the other method it would only be 3/8"

Which is it?
T McCarthy

I haven't looked at Barney's site but the factory manual advises 0 to 1/8" toe in. 3/8" or 3/4" is going to eat your front tires fast. Unless you have access to decient measuring equipment, take it to an alignment shop, it will be more accruate and they can also tell you how straight the rear tracks to the front.
J Heisenfeldt

Stick with the 1/8" toe in setting. If you read through the thread linked here http://www.mgexperience.net/phorum/read.php?1,709638,710174#msg-710174
you will get a lot of information on how to check the alignment at home and save some bucks. If you're careful you can be very accurate with this "string" method as described by Hap. Can't check caster or camber this way, but these aren't adjustable on the MG anyway.
Bill Young

Bill,

Thanks. That is more or less what I did. Instead of a string, I got a 10 foot long piece of 1" conduit. That become the straigh line. I then stuck spring steel "whiskers" through to touch the wheel rim at even distances. That allowed me to set the wheels at parallel.

So my question worded another way would be "is toe in measured from the parallel straight line?" So that would be 1/8" for each side OR is the 1/8" the total decrease in centerline distance between the fronts of both tires?
T McCarthy

It is easy to set toe without any special tools. First jack up the front end. Paint the center of the tire with a light colored paint. Spin both tires against a nail held securly in a fixture (a 2x4 will work). Now you have a line around both tires. Drop the car to the ground and roll it back and forth until it drops to its normal ride height. A pair of carpenter squares and a tape measure will work. When the measurment from the front center of the tires is 1/8" less than the measurement to the rear center of the tires you have 1/8" toe in. This can actually be much more accurate than all the fancy equiptment in the world for this measuring equiptment can never get out of calibration.
R J Brown

1) The toe angle of a wheel is the angle the wheel makes with respect to the longitudinal axis of the car.

2) The factory Series MGA specification for the toe-in on the MGA is listed as "wheels parallel," i.e. zero (0) degree tow-in.

3) Barney Gaylord qualitatively mentions the possible effects of +- 1/4 degree tow-in on the steering alignment on his website (http://mgaguru.com/mgtech/suspensn/sr106.htm).

4) Regarding measuring the tow-in using basic techniques, note that if the front wheels both have zero toe angles, then the distance between the outer edges of the two tires measured at the front facing portion of the tires will be equal to the distance between the outer edges of the tires measured at the rear facing portion of the tires. Now, if each front tire has one quarter degree of toe-in then the distance between the outer edges of the two tires measured at the front facing portion of the tires will be reduced relative to the case of zero toe-in (tires parallel) by the amount of 2 x tire_radius x sin (1/4 deg.), which is approximately 2 x 12 1/2" x sin (pi/180/4) = 2 x 12.5" x 0.0044 = 0.111 in. or about 1/8" meaning each wheel has a tow-in of about 1/16". The distance between the outer edges of the two front tires measured at the rear facing portion of the tires will be similarly reduced by 1/8". Thus, for one quarter degree of toe-in the difference between the outer edges of the two tires measured at the front facing portion will be about 2 x 1/8" = 1/4" less than the difference between the outer edges of the tires measured at the rear facing portion. A full one degree of tow-in, which is an enormous amount of tow-in for an MGA, increases this differenece by roughly four times to a total of about 7/8". Note, the tow-in specification for the MGB is 1/16" to 3/32".

5) In his technical note on steering alignment Barney mentioned using a straight edge to project the small tow-in from the front wheel back to the rear wheel. In this case a tow-in of one-quarter degree corresponds to a displacement of about 3/8" over the wheel base of the MGA, which is about 94", viz. sin(1/4 deg) x 94" = 0.0044 x 94" = 0.410" ~ 3/8".

6) Recommendation: Adjust the tow-in to the factory specification of "wheels parallel" (0 degrees), and not more than 1/4 degree.

Steve K

Thank you Steve. That is exactly what I was looking for.


T McCarthy

As I understand it, the toe-in is to ensure that when the car is in motion, the wheels run parallel, so the toe-in is presumably to take account of the free play in the steering and suspension. If this is so, then the true adjustment would really depend on how much wear there is in the steering/suspension. I don't know how you would measure this, so I always go with the factory figure. I set the toe-in using a narrow and thin length of board, just longer than the width between the front wheels. This has a sheet of paper taped on each end, and with the car on level ground and with the steering set dead ahead with no loading (roll the car a couple of feet for this), I place the board behind the front tyres, just touching them. Then, using a small plumbline held against the exact centre of the tread half way up the tyre, place an alignment mark on the sheet of paper. Repeat for the other wheel, placing a measuring mark on the paper. Then place the board against the front of the tyres, and repeat the process (aligning one wheel with the alignment mark you made, using the plumb) and mark the plumb for the second wheel on the paper. Then measuring the distance between the two marks will give the toe-in, and you can adjust accordingly. I find this to be pretty accurate. AB
A Bennett

Don't know if you can still find one, but an old alignment shop I use at one time had a spring loaded telescoping rod that had a graduated scale on it. You would stand in a pit under the alingment rack and place the rod beteen the inside edge of the wheels at the front, you then rolled the car forward until the same point on the wheels was to the back and then take the measurment at the same point on the wheels. This was quick, easy, and accurate. They also used to do a great job of truing wire wheels and they still had the old Stewart Warner on the car wheel balancing machine. Now all this has been replaced by "modern equipment", somtimes progress sucks.
J Heisenfeldt

After I noticed odd tyre wear I took my car in to a tyre fitters to have the toe-in reset. I forget the exact cost but it wasn't worth, in my mind at least, the effort of making a special tool.

For anyone taking this route, a tip. Take the manual in with you. The MGA will almost certainly not appear in the data they hold and they were unwilling to set it up purely on my say.

The toe-in (it was actually toe-out) was off their gauge when they first measured it and I had to reset the steering wheel afterwards. We set the centre point by counting steering wheel turns. The tyre wear stopped but I can't say I noticed any difference to the way the car handled.
Malcolm Asquith

Toe in normally won't affect handling but is hard on tires, castor and camber on the otherhand can result in some strange handling.
J Heisenfeldt

I'll second J Heisenfeldt's anecdote. Based on similar advice, I made my own "alignment" tool using two pieces of aluminum angle iron and duct tape. Duct tape "sticky side out" at a couple of places, and you have a sliding scale. Couple of scratches on the side and you're good to go !

-Chuck
Chuck Mosher

If you want to get real creative McMaster Carr sells steel telescopic tubing where one just slides into another. You can scribe your own graduations on the inner tube and add a setscrew to lock it in place. Would be very accurate for a home tool.
J Heisenfeldt

This thread was discussed between 02/06/2008 and 06/06/2008

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