The distance you are measuring is the difference in distance between the rims at the front of the wheel and at the back.
If you have nothing between the wheels then this is easy. However you will have loads of junk in the way.
All a tracking gauge does is to measure the distance between the rims, either the inside edges or the outside edges. Making your own tracking gauge is not too hard, basically a long U shape that can reach the wheel rim on one side, on the other you can just have a fixed upright, measure from the upright to the rim at the back, note the measurement and remeasure to the the front of the rim, the difference is the toe -in (out)
Using straightedges they need to extend beyond the front of the car to be convenient to measure between. The two measurements should be taken at the same distance apart as the points that the edges touch the wheels. Take one measurement from the other and you have your toe in (or out) Remember which is the bigger measurement so you know if it is showing in or out.
set the edges up on the floor to prove this to yourself.
I may be wrong but, on front-wheel drive, the front wheels are usually toed-OUT.
On rear-wheel drive, the front wheels are toed-IN. [At least this is how it used to be.]
On front-wheel drive, I think the rear wheels (usually independent trailing radius arm suspension) are often toed-IN. [I'm pretty sure my Mondeo's did.]
On rear-wheel drive, with a solid axle, the rear wheels are obviously parallel - but if it was independent suspension, I guess it might be toe-OUT.
Nissan 200SX multi-link rear suspension. Unladen, full tank, rad full, oil to top mark, spare tire, jack, hand tool and mats.
Toe-in 0-28min (0.46 degrees), 0-5mm.
The toe control arm is at the rear of the upright. As it comes under drive load the axle and upright will move slightly forwards and the result will be movement towards toe-out so it starts with toe-in.
Especially at the back of most front wheels (gearbox / sump etc). However, given the rims should be parallel in construction and accepting that anything other than a measurement taken across the middle of the wheel would be less accurate compared with one taken lower down over less of the full width of the rim, you could at least get such a measurement on most cars that weren't slammed on the floor.
Understood. Those I have used consist of two floor standing rails that have adjustable prongs that can be moved to match the diameter of the rim at their height and an eyepiece at the end that looks at an angle scale on the end of the other arm.
Roll the vehicle forwards with the wheels straight, offer the bars up to the wheels and read the tracking angle though the scope.
Sorry MrC, I get the goal of what we are trying to do but not that explanation of the means of doing it (if it matters etc).
Understood. So, that would give you the first (of two) measurement(s).
So, unless you have some mechanism that extends those points down to the ground (where you could take a measurement from the outside of each wheel) whilst keeping everything true, how wound one do that at home?
Yeah, I get the principal and know how to do it all with the proper gear, I can't see how you could do it with a couple of straight edges (other than when you have clear access as per a dinghy trailer etc).
Again, I can see how *if* you could get the measurements you could check for parallel (numbers the same) or a general toe in or out (numbers different +/-) but not how you could actually measure such (from the outside)?
So, take a dinghy trailer, get two people to hold a straight edge against the outside of each wheel (assuming the edges touch the rims not the tyres etc) and measure between the straight edges at the front, then rotate the wheels 180 Deg and measure the same edges at the back (repeated at different points on the rims). If these values are the same the wheels are set parallel.
Now, I'm not sure how you would set them to say 1 degree toe-in (0.5 each side) unless you did the calculations from the required mm (radius at point of measurement & distance apart at front and back etc to give toe-in/out and what angle) but the angle is easier as it can be read at any distance from the centre of the wheel. ;-)
The traditional tracking bar or gauge has no sighting, just measurement, and is basically a bar wider than the vehicle with two uprights m one of which is moved against one rim, the other is adjustable to measure the distance to the opposite rim. This is used at front and back of the wheels being measured, and a difference calculated, giving a toe in in distance rather than degrees. Most vehicles have the info for either degrees or mm easily available.
Using straightedges is a reasonably accurate method especially if you double check by moving the vehicle forward.
An example gauge, showing how easily you could knock one up:
One question. How flat does the floor need to be? (NB I do mean flat rather than level.) I ask as it seems to me that if the 2 wheels are standing on surfaces tilted with respect to one another then one wheel will tend to be tilted with respect to the other. But I'm totally lost as to the size of the effect.
Ideally the floor should be as level as possible, but I doubt that it would be a problem with inaccurate readings unless the car is significantly tilted, or one wheel is up a big bump.
I sometimes have taken my tracking slip plate out with me to a large flat car park and tweaked the adjustments there.
So that's what I have typically used when fitting Indespension units on trailers etc.
Ok.
Check.
Ah, a picture speaks 1000 words. ;-)
Yup, you could easily knock one of those up and would at least be able to give you a rough idea (depending on how rigid you made it and how carefully you applied it etc).
Another project ... thanks (as I have a quantity of 25 x 25 x 1.5mm box section tubing in the workshop)! ;-)
I wonder if you could use a digital vernier depth gauge (tyre tread depth gauge?) to do the actual reading?
You could certainly use a vernier caliper to measure, but a steel ruler would do just as well. On the one I made up, I had an adjustable height pin for the 'fixed' side, and a piece of flat steel on the measuring side (exactly at 90 degrees to the bar and to the 'fixed ' side, then just measured from the flat steel to the wheel rim. The whole job is much easier with an assistant !!
I guess the thing is you can get too accurate a reading for the job in hand. Like there might variation in the edge of an old steel rim that you would have to average out anyway (with multiple readings).
Understood.
I bet ... the trouble with assistants you need to be able to trust they are actually doing what you are asking them to do ... like 'are you sure you are holding your side on the centre of the rim ...?'
By making the 'fixed' pin variable height you can be sure the pin is at the right height on the rim. If you have steel rims then you could use a magnet out of a hard drive to locate the fixed pin, you could then dispense with the assistant. With a bit of experience you can use a gauge on your own, I added on a narrow foot to my one so that the gauge would stay upright on its own, make sure the foot is small enough to be drawn under the car (or make the foot swivelable), or only have a foot on one end, when it can be any size.
Is that so you can take the measurement at the rear? What if the 'U' was deep enough to allow you to take both measurements from the front (assuming you don't / it isn't etc)?
Presumably the bigger you make the gauge the more 'flex' it might have in it and therefore the gentler you might have to be with it for fear of distorting the measurements?
It is usual to move the gauge from front to rear of each set of tyres, probably because of flex if you had arms long enough to reach front or rear, they would have to be about 2 foot long at least, rather than below one foot long.
So, I've also got some 25 x 50 x 1.5mm box steel ... if I made a large U from that with the box 'on edge' (and wide enough to take the Connect), I'm sure that would be both rigid and light enough to be able to do all the measurements from the front? Then you could also have your 'foot' (or feet) to keep it up at somewhere near the middle of most size wheels.
It could even have small wheels on it so you could easily roll it back and forth as you take measurements and move the vehicle etc. ;-)
And with you patented single operator 'Magno-lok' probe on the other end, it would nearly do itself (well, on steel wheels anyway). ;-)
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