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Wheel alignment, TR4A IRS


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Manual figure is 0 to 1/16" toe in front and rear. I have no idea where the 1/16" is measured so cannot translate to a degree and minutes figure as measured by, e.g., Hunter laser equipment. Can anyone enlighten please?

 

Tim

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Hi Tim,

it gets more vague.

The toe in is measured at the 3 or 9-o-clock position on the wheel.

The value is 0 - 1/16" (or as Ian states 20 minutes of arc).

 

The dimension suggests 1/16" in total :) (1/32" per wheel) but 20 minutes of arc suggests 20 minutes per side = 40 minutes or 1/8 in total.

 

I would go for 1/16 or 20 minutes in total.

 

My local tyre fitter does it in mm and I ended up with 2mm per side - which is a bit over the top. I will need to get them sorted again.

 

Most garages with the Hunter system (very good system) don;t have the figures for the TR4/4A but may have TR6 data - but maybe not

 

Can any body give an absolute clarification on the toe in dimension.

 

Roger

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No problem if you do it parallel (0 value)."

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Thanks everyone for the input. I also received the following reply from "Ask the Experts". Looks like an old school guy who should know his onions.

 

"Hi Tim,

 

I was a line mechanic in dealerships from 1960 to the early 70's and in several of the dealerships the mechanics did the alignments. We set everything by the factory specs and they always quote Castor and Camber in degrees and toe-in in inches. I never used Hunter equipment and I never seen toe-in quoted in degrees.

 

The standard method to set toe-in is to jack the car up and hand spin the wheel while holding a scribe or pencil up against the center of the tire so as to scribe a line in the center of the tire. (the tread can not be used as it is not true enough)

 

If you have turn tables set the car down on the turn tables and turn the steering wheel right and left and set it straight ahead. (if you don't have a pair of turn tables you can use a couple of plastic garbage bags that you spray the inside with silicone spray or some other spray lube.) Be sure to turn the steering wheel right and left a few times to seat the suspension.

 

Then set your toe-in gauge to line to line at the front or rear of the tires. If you don't have a toe-in gauge, you can use a long stick or anything long enough and that you can accurately mark on. When you use a stick or such you will need to rest it on two blocks to keep it parallel with the floor. When you set it at the front of the tire on the scribe line the front measurement should be 1/16 in shorter then the measurement of the "line to line" of the rear measurement.

 

If the specs quote "0" to "1/16 in" I would opt for 1/16 in toe-in because I have tried "0" or straight toe-in and due to the small free play in the steering and suspension on most cars it makes the car wander all over the road. So I like a little toe-in on any car except front wheel drive cars which require "toe-out".

 

Howard"

 

This indicates that the quoted 1/16" is a total figure for both wheels so we are looking for 0 to 1/32" toe in on each wheel. the nominal rolling radius of my tyres is 323mm so as a close approximation I calculate that an arc of 1/32" (0.8mm) on a circle of 323mm radius would subtend an angle of 0.14 degrees at the centre of the wheel. 0.14 degrees is 8 minutes of arc so I reckon the alignment should be 0 to 8' toe in each wheel or 0 to 16' total toe in.

 

Tim

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I hadn't considered the wobbly-wheel rear end TRs, where one has to set each wheel on its own. I'm glad that I don't have to worry about such complexity!

 

At the front, one needs toe-in for stability (see Howard's advice in post #8), and I find it difficult to imagine how one would set each wheel independently - they should be measured as a pair and set to toe-in of 20 minutes or 16 minutes of arc - choose either my figure or Tim's, as you wish!

 

Ian Cornish

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