Checking toe-n and other DIY alignment issues

A proper wheel alignment on a modern vehicle involves all 4 wheels, which pretty much requires a 4 wheel alignment machine. An alignment machine finds the centerline of the vehicle by having a sensor head attached to each wheel. You've probably seen the results of a DIY alignment when you see a vehicle dog-walking down the road, where it looks like it is going down the road at an angle.

The difficulty in performing an alignment with a toe gauge or a tape measure is that making an adjustment on one axis can change another axis at the same time. For example, adjusting camber will affect toe and vice versa, and it is possible to have proper toe while at the same time having improper caster. The Cressida has quite a bit of positive caster, and as you turn the steering, you will notice that the camber on the front wheels changes noticeably.

The other tricky part is due to wheel offset, where the physical centerline of the wheel is not the same as the pivot point of the wheel when turned left-right so you have to calculate the centerline of the wheel and the centerline of the movement.

Finding the centerline of the car entails measuring diagonally in an "X" from wheel centerline to wheel centerline and then measuring left-right and front-rear.

I do most of the work on our vehicles myself, but I take them to a shop with a 4 wheel alignment machine when it is time for an alignment.

Ray O wrote in article ...

Oval-track and road racers have been doing four-wheel alignments with string lines for decades before the introduction of computerized, four-wheel alignment machines.

Many - including me - still do!

We used to sometimes back IRS cars such as the Corvette onto two-wheel projector-style alignment machines to do camber and toe. It was unnecessary with magnetic guages and mechanical toe measurement.

More likely to be an alignment done by the $7.00-per-hour "Alignment Expert" at the local discount parts store who used to be an "Expert Latte Maker" at Starbucks last week - but was given a quickie course in how to set up and read the machine.

The people working at PepBoys-type parts-and-service or discount tire operations often don't have the understanding of complicated suspension geometries, and simply move things around until the computer tells them they are "close enough."

Computerized alignment equipment is sold to the shops NOT on its accuracy, but on its ease of use, and the ability to train "....virtually anybody..." to be taking alignment readings within an hour or so. They won't have a clue as to what they're doing, but they WILL be taking readings, and the computer WILL be telling them what to change, and they WILL move things around until the computer says it's okay........

........sorta' like the cashiers who give you $18.75 in change from a $10 bill for a $9.37 purchase because that's what the computerized register said to give back for change.

Adjusting camber CAN - most likely WILL - affect toe AND, possibly, caster, but adjusting toe affects toe ONLY.

That's why it is done last.

It is possible to have virtually ANY combination of correct and/or incorrect alignment settings......What's your point?

The wheels tip when turning about the caster axis, but you are NOT actually changing camber when you turn the wheels.

You are simply seeing the caster illustrated.

Why?

Scrub radius is built into the suspension.

Changing the wheel offset changes the scrub radius.

You cannot correct scrub radius that has been altered by different wheel offset except by going back to the original wheel offset.

You really don't want a "zero scrub" setup, because it would take away a lot of the "road feel" from the steering.

You have described how to find the centerPOINT of the car's suspension - NOT the centerLINE.

The centerpoint "X" as described above also does NOT give you the thrust line - off which various left/right angles are measured.

You need both centerline and thrust line data to determine various angles - and to make sure the car doesn't "dog-walk" (your term) down the road.

Centerline is taken from front and rear tire track centerpoints - NOT an "X" measurement - and thrust line is taken from the orientation of the rear wheels.

Smart man!

Very true, but the folks doing alignments with string lines are much more knowledgeable about alignments than your average DIY-er.

No argument from me there!

The point is that one should know the cause and effect of each change in setting to avoid unsatisfactory results.

Yup, poor choice of words on my part.

I know what I don't know...

Ray O wrote in article ...

If only some of the others who post here could be as aware......

Didn't mean to sound argumentive - just correcting what I saw as technical errors in your original post.

Your response suggests you understood that.

Thank you!

I think Ray was only suggesting that its not an area you want to get into in a DIY fashion without deep knowledge of the subject, not that it wasnt possible to do any other way.

Its the only thing I trust someone else to do on my car, and even then i watch them like a hawk to learn and check they have more knowledge of what they are doing than me! If they know no more than me I'd worry!

As coyoteboy mentioned, my point was that doing an alignment with a measuring tape and strings is not something that a do-it-yourselfer is likely to have success with and was not meant to be instructional on how to do an alignment.

I have no problem when people catch my errors and correct them because that is one of the ways I learn or am reminded of stuff I've learned in the past and have forgotten.

OTOH, I do have a problem when people who don't know what they're talking about argue with the facts!

Thanks,