Originally Posted By: rubberchicken
Look up the Hunter GSP 9700 machine- they have some good notes on this problem, and how a "road force measurement" tire balance can solve them.
Ah ...... Mmmmmm ...... not exactly. That machine can only tell you where to place the tire, so you can't feel the pull - BUT - the tires have to stay in that positon and can't be rotated!
Where the machine is helpful is pairing tires on an axle.
First, it is conicity (root word: cone) that is the issue here. Conicity is the sideways force that a tire generates, and it can be pushing in or pushing out (or not be there at all!) (IF I remember correctly positive is pushing out and negative is pushing in.) Every tire has conicity to some extent - and it is the vector sum of BOTH front tires that is important.
Example: If you have a vehicle that is sensitive to 6, then a -4 and a +1 (vector difference = 5) does not produce a pull. But a -3 and a +3 do! (vector difference 6!) So it isn't a single tire - although changing a single tire might change the vector sum.
- BUT -
Conicity can be worn into a tire due to alignment. What commonly happens is that a rear tire will develop uneven wear (and conicity) and when it is rotated to the front, it causes a pull.