DIY Toe-In tool w/pics

When the front tires have straight channels like yours, I just use a tape measure front to rear. When by myself, I use duct tape to hold it on the other side. The main problem is you can't go up too high on the back side without bumping into things. I try to measure at the same height up on both sides. You are shooting for a very slight toe-in, plus try to get the steering wheel centered. I set a 1/16" difference since my front ends have new parts. Toe-in is just to compensate for slight play, so the wheels are perfectly straight when driving. For FWD cars, set a very slight toe-out. A 1/16" adjustment barely moves the tie-rod couplers (<1/8" turn), so I doubt an alighment shop could or would do any better. The sad fact is that as the height changes over time, it affects the toe-in, so it needs regular adjustment to stay perfect.