Rear Toe - Caution Math content

[HealeyBN7]

I recently rechecked my alignment.  I found that the rear toe-in on my Zetec/S2 was a bit more then I needed.

I measured .230 total toe at the rim edge .   The workshop manual calls for higher toe-in for the Twincam cars, so maybe that is where I was setting it originally, but I am targeting .125  (1/8 of an inch) which is in line with Colin Ham's Jensen tuning guide.

Before just adding shims to move the trailing arms out, I tried to figure out the calculated impact of adding some measured amount of (washers) but my trig skills were a bit too rusty - I tied.

So instead I installed one washer or .068 of thickness on each side and measured the resulting impact.  I found that my overall rear toe was reduced by .117, to yield .113 (.230 - .117 = .113) which is close to where I wanted to end up.

So, it looks like moving the front trailing arms out .136 yields .117 of toe change.  In other words, for every .010 of desired toe change you need to add or subtract .016 in shims. 

Did I miss anything here?  I would like to jot some notes in my "manual" but I would hate to repeat mistakes when I refer to it years from now:)

Dean

[BDA]

I think that's basically right (I'm assuming you measured and did your math correctly). There will be a small error because the bolt at the frame is not perpendicular to the trailing arm (if memory serves), but that is not worth discussing.

That's a great addition to a manual and something I've wondered about. Thanks!

[EuropaTC]

Hi Dean,

When I was struggling with the same problem last year I did quite a lot of searching around the knowledgebase, the result of which was......    complete confusion     There seemed to be many variables in terms of camber, lower links, etc so in the end I just went with what I had.  My last notes were "1mm shim added, 0.8mm toe movement" which isn't identical to your ratios, but not too far off given I'm measuring with string and old eyesight !

A guy called Neil Petersen did a lot of work and apparently created a spreadsheet of shim/toe relationships which was to be posted in the Yahoo group files. I looked at the time but couldn't find it so maybe it never got there ?  If anyone has a copy, or if in fact Neil is still around, a re-post would be very useful.

Brian