String wheel alignment. Question about measuring toe

[Gunnytron]

I am.going to have another go at string aligning my RX7.

One thing I am unsure about is measuring toe. Last time I tried it I used a ruler and measured from the outer edges of my rims and adjusted from there. It has just dawned in me that if I was aiming for, say -1.5mm, then a 17" wheel would have more toe than if you used an 18" wheel as you are measuring further out from the wheel centre.

So, when you are given a toe figure in inches or mm, then how do you know if that's for a 16,17 or 18" wheel.

[Cobranut]

Take the toe spec for the stock size wheels and calculate it in degrees.
Then recalculate for 18 or whatever size you have installed.

Personally, I wouldn't worry too much about it.
I adjust according to how the car responds.

[Gunnytron]

Well, Howard Coleman shoots for upto 3mm on 18" and stock is 1mm on 16" so i will aim for 1.5 o. 17". Should be somewhere decent.

At this point I just want the steering wheel straight and for it to be less sketchy to drive.

[blacksi]

I put a bit more on the passenger side to adjust for the crown of the road to keep the car straight. I want to say the last one I did I put like .040driver and .065"passenger on 18s. That may be hard to do with a tape though.   Is it just me or is 3mm on 18 different then 1mm on 16?

[Gunnytron]

No, you will probably be right. Thre measurements for 16" is stock, the 18" measurement is more aggressive than stock.

[blacksi]

I never really thought about it on the RX7 just cause I have a lifetime alignment with firestone.  But to my understanding the reason to add toe is because during forward movement the suspension flexes and the front tires drag rearward causing more outward toe.  If you have upgraded stiffer bushings I would expect you would actually need less toe in but like cobranut said you can adjust it based on how the car handles.  I believe the spec is at least up to 1* toe in on the FD.

I have a laser system(not for aligning cars but I use it for that) and the first car I used it on was a GEO tracker with a lift kit.  I set everything exactly parallel and took it out on the streets and it drove like complete ass pulling with every surface change of the road.  That is when I researched and realized toe is needed.

[jwvand02]

You can covert between wheel sizes by converting the original spec to degrees and then back. That said, street alignments are not very sensitive and I have yet to find a car that doesn't react well to zero toe in front and ~3mm total toe rear.