Alignment specs

[RRoller123]

I thought of making small spacers for the rear, so the strings could be as close to parallel to each other on each side as possible, and then with the steering centered, one can use the tire sides (PERFECTLY LEVEL GROUND, ALL VERY CLOSE EQUAL PRESSURE) to measure the gap from front of the front tire to the rear of front tire, get it to what is wanted, and make sure it is equal on both sides. It takes some fiddling, but it works pretty well. My car doesn't pull, although I must admit I go through front tires pretty quickly. I think I have too much toe in. It tracks really well too, no wandering, another sign of toe in.

[Nut124]

I used 4 jack stands to support the wires. I placed the stands far enough in front and behind the car so that I could measure the spacing between the wires forward and behind the car. The spacing was 64". About 2-3" outside the front tires.

I have too much toe-in for sure. Based on the US convention, I have 15mm toe-in at the rims. i believe this should be only 3mm per my shop manual. My toe-in angle is 2.2deg currently.

Google seems to show typical toe in angle for a similar RWD car to be about 0.5-0.6 deg total. That is about a 1/4 of what I have. 1/4 of 15mm is 3.75mm.

[18Fiatsandcounting]

I used 4 jack stands to support the wires. I placed the stands far enough in front and behind the car so that I could measure the spacing between the wires forward and behind the car. The spacing was 64". About 2-3" outside the front tires.

I have too much toe-in for sure. Based on the US convention, I have 15mm toe-in at the rims. i believe this should be only 3mm per my shop manual. My toe-in angle is 2.2deg currently.

Google seems to show typical toe in angle for a similar RWD car to be about 0.5-0.6 deg total. That is about a 1/4 of what I have. 1/4 of 15mm is 3.75mm.

That all sounds fine, but a couple questions: I believe the 3mm of toe-in is for the car fully laden. Is this how you are measuring it? Also, how are you measuring the toe-in angle, from some sort of measurement or a geometry calculation?

-Bryan

[18Fiatsandcounting]

My car doesn't pull, although I must admit I go through front tires pretty quickly.

How quickly? Just curious.

I bought a spider parts car once and drove it home (20 to 30 miles), but one front tire was so far out of alignment that the steel cords were showing by the time I got home. Squealed the whole time I drove it home. Now THAT was too much toe-in!

-Bryan

[Nut124]

That all sounds fine, but a couple questions: I believe the 3mm of toe-in is for the car fully laden. Is this how you are measuring it? Also, how are you measuring the toe-in angle, from some sort of measurement or a geometry calculation?

-Bryan

Bryan, if you look at my post with the pictures and the data sheet, the left side had a toe-in of 10mm (50-40mm) over 381mm at the rim. Using an online atan calculator, this turns into 1.5deg.

The right side had 5mm over 381mm. This is 0.75mm. 2.25 deg total. The tire based measurements were similar.

you need a atan calculator that gives the result in deg not radians. asin would be about the same at these very tiny angles.

https://www.math.net/calculators/arctan

I could draw a pic.

With my lowered suspension, stiffer springs, laden, unladen I think makes little difference. I weigh 200lbs and I'm usually the only load.

[Nut124]

Here's a pic:

[18Fiatsandcounting]

Thanks, Nut. Maybe I'm overly simplistic, but I just set my toe-in (unladen, i.e., no one in the car) to about 6mm on each wheel. In other words, toe-in is 6mm, which translates to 12mm on the difference in distance between the front and rear of the tire from the parallel string. When the car is loaded (2 svelte European passengers plus their luggage for their July vacation in the Seychelles), the toe-in should be 3mm on each wheel.

My thought: If you are relying on the 2nd differential of the cosine function in the limit when x goes to zero, you are overthinking this...

-Bryan

[RRoller123]

I can't quite say with a lot of certainty how fast I go through the front tires, as I drive so little, but I probably get just under 7 or 8000 before I move the fronts to the back with tread still on them. I am pretty sure I have too much toe-in. But it takes me about 6 or 7 years too, so I could really care less. I drive it pretty normally, but I do throw it into the corners pretty hard each chance I get. I guess that is normal..... hahahahah!

[DieselSpider]

The most common issue people will have with aligning the cars unladen using the laden specs should be that the front wheels will end up severely toed out when fully laden causing the inner tread on the tires to feather and wear out in short time. You may even hear the wheels chirp very loudly after going over a bump in the road when they align them this way. Gives motorcycle riders, bicyclists and pedestrians a good scare too.

The extra stress for some reason tends to also wear out the passenger side joint on the center link that attaches to the idler arm more quickly as would having a idler that's too stiff and in need of lubrication.

[Nut124]

How do you guys assess how much toe-in changes when loading? Have you tested this or some have source?

My car has lowered suspension and stiffer springs. I doubt that me sitting down in the car changes toe-in. I supposed I could put 5 salt bags on the seat and check.

Bryan, lost me on your math joke(?). The formula I used is just the inverse Tan function in degrees.

I think I'm going to set mine for 2mm at each wheel for a total of 4mm. My book says 3mm.

[18Fiatsandcounting]

I'm hoping someone will correct me if I'm wrong, but here's my understanding.

Due to the geometry of the double wishbone suspension, there are slight changes in the toe angle when the car is laden or goes over bumps. I believe the tires "toe out" slightly under these conditions. This is because the steering linkages are mechanically fixed, so as the suspension moves up or down, there is a slight change in the direction of the tires (toe angle) without you turning the steering wheel. This is known as "bump steer". It doesn't take much in terms of change in toe angle.

If the suspension is aligned when the car is unloaded, there will be too much toe-out when you put passengers in the car or go over a bump. This causes the chirping of the front tires that Dieselspider noted and, if excessive, can cause abnormal wear on the inside of the tires.

So, the solution is to set up the alignment so that you never get into a situation where the tires are toed-out. To do this, you align the car with a slight toe-in, and the amount depends on whether you are doing this with the car laden or unladen.

Honestly, though, I don't think you'll run into a problem unless your toe (and camber) are way out of spec. Set the toe-in for a few mm on each tire with the car loaded, and maybe double that amount if the car is unloaded. I use the spec of 3mm laden and 6mm unladen, on each tire.

Also note that there is no "alignment" of the rear, as the tire geometry is fixed by the solid rear axle. But, that's OK, since the rear tires don't participate much in steering. All the rear tires need to deal with is the different rotation speeds of the two rear tires as you go around corners, but that's taken care of with the differential.

-Bryan
PS: Yes, my comment about the 2nd differential of the cosine was purely a joke!

[18Fiatsandcounting]

Here's a quick experiment. Using some tape, attach a string from one side to the other, across the front of the tires and with the string not quite tight. Then have 2 people get in the car. See if the string tightens (increased toe out) or slackens (increased toe in). That would be your answer.

-Bryan

[18Fiatsandcounting]

Another fun experiment that we can all do at home!

Attach a long straight rod, like a yardstick, across one of the front tires, parallel to the ground. Sit on the front fender for that tire and observe whether the front (or rear) of of the yardstick moves, indicating a change in toe angle. 200 pounds (or whatever you weigh) ought to be enough to simulate what the car would do if it were fully loaded with 2 passengers plus luggage.

Spoiler alert: I just did this on my car, with a yardstick extending a couple feet in front of the tire. The tire toes out when I sit on the fender, perhaps several mm. When I bounce on the front fender, the tire toes out as much as a centimeter. This is more than the front of the tire moves, but the bottom line is that the tires toe out when the suspension is compressed (either through a bump or the car being loaded).

-Bryan

[Nut124]

Last nite I set the toe-in to 4.5mm. It was 15mm previously and there was some evidence of unusual tire wear.

This 4.5mm is per the US convention: difference between left to right spacing as measured from forward edge to forward edge vs the same measurement at the trailing edges of the rims.

[18Fiatsandcounting]

Last nite I set the toe-in to 4.5mm.

Was the car loaded up or unloaded? I'm thinking for loaded, your adjustment is probably very close, but for unloaded, it may be on the low side.

-Bryan