I have a couple of 1x1 square tubes I bungee to the outside of the tire, then you can hang a tape on one side and measure to the other. this is all I have ever done for my jeep. for the mercedes I would space it to the wheel lip, but I usually get that one done at the shop. they didnt do a great job last time so I may be trying soon just as a check. the last time when I got it home the tie rods were not lock nutted

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)