Setup Fixture

[Rick Iverson]

Gents;

I have a floating alignment upright system reasonably close to this (although mine has roller balls on all corners that will accommodate any directional change), but it is missing the toe plate.



My conundrum: Do I understand correctly the zero point on the toe plate rulers must be the centerline of the tire, and the width between the inside distances of the two (2) rulers should equal the OD of the tire?

I would just as soon measure from my fishline parallelogram to the wheels flanges, but EVERYONE on Apexspeed knows I suck at math. So therefore, as you would explain to a child, is there a method to do so? Also consider the front and rear tracks are different.

[Rick Iverson]

Gents;

I did not do a very good job in relating my understanding of toe measurements. Allow me to try again.

In the past, car jacked up a bit:

• I took a can of silver spray paint, spun the wheels while spraying a stripe at the mid-point working surface of the tire
• I then scribed a line at the best estimate of the tire centerline using a large sponge (on the ground) to act as a spring, and a piece 90 degree thin wall aluminum channel as the scribe. One end of the scribe was anchored on the ground, the other was wedged at the bottom mid-point of the tire with “sprung pressure” applied by the sponge.
• Spinning the tire, uniform centerlines were etched.
• Measurements were taken from that scribed centerline to line parallelogram, both fore and aft.

So here is this: presumably the fish-line runs through the notional centerline on the tire.



Then there is this. The measurements are taken less than the OD on the tire, say close to the rim flange, maybe center rim flange.

So here is the deal: toe measurements ANGLES from the axle CL to the OD of the tire (say 11”), as opposed to, say three (3) inches from that axle CL are identical. Same angle, done deal.

But the distances from the string parallelogram to the scribed tire etching as opposed to the three (3) inches from the axle CL (or say, wheel flange centerline) are different.

So, is there a formula to eliminate the OD tire stuff, and just deal with the rim flanges, or is this so minuscule that it is irrelevant? As you all know, I suck at math.

[steve zemke]

The rim is more likley to be repeatable than the sidewall of the tire, if you are sure the rim is not bent. Easy to determine with a fixed point gage and spinning the rim.

[alangbaker]

When you see a toe measurement like 1/16", what is actually being represented is the sine of the angle between the fore and after direction on the car and the direction the wheel is actually pointing. (Some folks will tell you it's the tangent, but it's not. The tire diameter you're measuring on is the hypotenuse and you're measuring perpendicular to the car's centreline, so opposite over hypotenuse is sine, but it's moot anyway, because at angles this small the difference between the two isn't noticeable

So if you're measuring (say) 1/16" of difference between the front measurement to the tires OD centreline and the rear measurement to the tires OD centreline, and the tire is 22" in diameter (say), then what you've got is the sine value 1/16 / 22, or 1/352, and if you convert that to degrees, asin°(1/16 / 22) = 0.163° (which is precisely what using the inverse tangent function gives you to the 5th decimal place)

Now, if you suddenly have a different fixture, and it's measuring to the centre of the rim flanges, your diameter has gone from 22" to something like 14" (maybe a little less, but let's keep the numbers round.

To keep the same toe angle (which is what you actually want), you just reduce the measured difference between front and rear edge in the same proportion. 1/16" toe becomes (1/16" * 14/22)... ...about 2.5/64" on a ruler with very fine markings.

Does that help?

(Oh! Your first picture is of my buddy Alan's car when Marty came down to showcase his goodies )

[tlracer]

Toe settings are either a distance (eg. 1/16") and are usually stated as 'at the rim' or and angle, in which case it doesn't matter where they're measured so long as the measurement points can be relied upon:

Distance - set up strings at wheel centre height and measure the distance from the string to the wheel rim at both the front edge and rear edge of the wheel. Subtract the one measurement from the other to get the toe distance;

Angle - measure across two horizontal points. Wheel rim is usually easiest as it's a hard point, where tyres can create errors due to flex, sidewall curvature, etc.

At the front end it is vital to have the steering set dead straight ahead. The easiest way I've found to do this is measure the distance between the end faces of the rack body and the steering end-stops. Set so that left and right distances are exactly equal and the rack must be dead centre since this gives equal amounts of lock to both left and right.

[Rick Iverson]

This is good stuff. Thank all

[problemchild]

This thread is making the most simple task appear like rocket science technology. Why does anyone need $1000s of dollars worth of tools to set toe? There is not even math involved. Two trammel bars approximately 4' feet long that bolt to the chassis close to axle centerline, that position fishing line down each side of the car. Use a fine ruler to measure toe to the inner wheel (inner of wheel usually truer than outside). It can be done in the trailer. Tire pressure and level ground do not matter. The most important part is putting your glasses on and having decent light (probably not LEDs in a row), so you can read your values.

If we are going to encourage people to race more and work on their own cars, we need to simplify tasks like this. Checking toe should be a 10 minute job. Setting toe may stretch it out to a 1/2 hour job.

[aims20]

... My conundrum: Do I understand correctly the zero point on the toe plate rulers must be the centerline of the tire ...? ...

.

1) No, it does not have to be the centerline of the tire - The requirement is that zero point for the rulers be the same along the same line or parallel plane to the surface you are measuring to. The rulers must also be parallel to each other.

... and the width between the inside distances of the two (2) rulers should equal the OD of the tire? ...

.

2) Not necessarily.
The points just have to be equidistant from the axle centerline if you want to use the diameter of the rim in the math.

Most prefer using the OD of the rim because the greater the distance, the more accurate, provided the rim has a flat, consistent, non-damaged surface.

If you use good measurement practices, you end up in the same place as all the other practical advice in this thread.

[J Leonard]

Dunlop dial toe computer

[Rick Iverson]

This thread is making the most simple task appear like rocket science technology. Why does anyone need $1000s of dollars worth of tools to set toe? There is not even math involved. Two trammel bars approximately 4' feet long that bolt to the chassis close to axle centerline, that position fishing line down each side of the car. Use a fine ruler to measure toe to the inner wheel (inner of wheel usually truer than outside). It can be done in the trailer. Tire pressure and level ground do not matter. The most important part is putting your glasses on and having decent light (probably not LEDs in a row), so you can read your values.

If we are going to encourage people to race more and work on their own cars, we need to simplify tasks like this. Checking toe should be a 10 minute job. Setting toe may stretch it out to a 1/2 hour job.

Sir;

I simply asked a question, nothing more. I have been doing the scribed tire method since 1972, and was only considering an easier method. I had a thought, then asked the question. Not necessarily for the procedure mind you, but for my general fund of knowledge.

Firstly, high school level math IS involved. But as I stated, I am math challenged, which prompted me to ask the question. And from this thread, I learned toe measurements are generally made at the rim flanges. That, I did not know.

But most importantly, several chimed in with their thoughts, knowledge, and ideas with the assumption they would not be ridiculed or humiliated for their contribution.

I do not have $1000s of dollars worth of tools to set toe. But one tool I have is tact. I hope I used it wisely today.

[Farrout48]

At the front end it is vital to have the steering set dead straight ahead. The easiest way I've found to do this is measure the distance between the end faces of the rack body and the steering end-stops. Set so that left and right distances are exactly equal and the rack must be dead centre since this gives equal amounts of lock to both left and right.

On my WF1, the steering has a tendency to move whenever the adjusting rods are twisted. It does not take a lot to blow up a 1/16" or 1mm toe setting. My solution was to determine the dead centre distances between the end faces of the rack body and vertical portion of the U fixture on the ends of the steering shaft. Then I made a couple of shims out of Aluminum angle to that distance. Pressing them into the end gaps keeps the steering locked into position.

[alangbaker]

On my WF1, the steering has a tendency to move whenever the adjusting rods are twisted. It does not take a lot to blow up a 1/16" or 1mm toe setting. My solution was to determine the dead centre distances between the end faces of the rack body and vertical portion of the U fixture on the ends of the steering shaft. Then I made a couple of shims out of Aluminum angle to that distance. Pressing them into the end gaps keeps the steering locked into position.

I did precisely the same on my previous car and still need to make a set for my current car.

Measure carefully the total travel of the rack (including checking that the rack is actually mounted in the centre).

Divide by two and cut two spacers so they're just a tiny bit longer than half.

The sand them together until they fit with no slop.

Then you can just lock out the rack when you're doing setup.