Measuring toe

[Rich_G_SC]

Hi, new guy question related to measuring toe. I attempted to do this using a trammel bar but I must be doing something wrong. I loaded the car with driver/fuel weight, bounced the car & rolled it back and forth about 6' three times between measurement (final roll is forward). Measured using tread blocks (using DriverZ cup tires, not slicks) and calipers. I could simply not get reproduce-able measurements. I would be off by as much as .1 -.2" in total toe pretty much every time (rear was a little better).

It was so frustrating that I decided to measure front/rear 3x between each roll (to remove variance due to tread and/or settling of the chassis) and averaging the results. I also measured the tilt of the bar from floor to tires each time to make sure I wasn't measuring at different heights on the tire. This cannot be the best way. I'm no mechanic but this seems like it should be easier - maybe a technique I don't know about?

Good news is the car drove great after I set both front & rear to about .08 - a little more than 1/16" toe in. This is a Citation 90v.

Appreciate your suggestions!

[Bobsy SR 6]

I use the straight strings set up. The kit is a little pricey but once you get it set up and use its definitely worth the price. Measure to the edge of the wheel (assuming the wheels aren’t bent) and you will get repeatable results. Due to the brackets being attached to the car you can roll and bounce the chassis and not affect the set up of the strings. I use mine on both my race car and my miata track toy.

[10rmotor]

If you disconnect one shock eye (usually the top) on each corner, and support the lower chassis rails on ride height blocks, you no longer need to roll the car or bounce the suspension. If you want, you can cycle the suspension just by lifting the tire but that's not really necessary.

I do my alignments on a platform but its not necessary, you can just use shims under the tires (and blocks) to get four in-plane and level surfaces.

I setup a centerline string based on plumb bobs hanging from the lower pickup points, and then a second string outside of the wheels parallel to the CL string and half the tire diameter up from the floor. I scribe the tires and measure toe from the scribed line to the string with a scale. Some people just measure to the outside of the wheel rim, or sidewall of tire as well.

When I'm done setting the toe I usually do a sanity check and use the trammel bar against my scribed tire lines. They always repeat.

[BLS]

"Measured using tread blocks..."

I'm guessing this is part of your problem. Try scribing a line around the circumference of the tires and then set them.

[GregSmith]

I would also be sure that one or more wheels aren’t bent and wheel bearings tight and/or adjusted. Also helpful to measure the wheelbase side to side to insure that the car will track straight without “dog tracking”. And bump steer can always be an issue with a Vee, although the Citation steering seems to minimize that characteristic. Toe comes last on the list.

[Lotus7]

"Measured using tread blocks..."

Tires with treads are purposely molded asymmetrically to avoid droning sounds at steady speeds due to resonance.
You are unlikely to ever repeat measurements using this method.
Better to adopt a simple parallel strings method.

[veeten]

Most Vee folks
use scribed line on slicks. On some street tread tires it is possible to find continuous tread
to scribe a line on after coating them with chalk.
Most Challenge Cup drivers use Toe Plates and 2 tape measure when at the track
If you're looking for less than a 1/16 it is hard to get a repeatable measurement with
the toe plates.