Alignment : Toe

[Superman]

It has been my understanding that all four wheels should be square when the car is going down the road. Further, it has been my understanding that road forces cause the front wheels to move outward and engine/transmission forces cause the rear wheels to pull inward.....and that therefore there should be front toe-in and rear toe-out.

And yet, the Porsche chassis guys I trust the most suggest toe-in for both axles. Often more in the rear the front!

'Splain this to me.

Also....what alignment specs do you recommend for a mostly street driven 911 with 22/29 torsion bars and Carrera sways? I'm thinking 1 degree front camber and 1.5 back.

[Bill Verburg]

Originally Posted by Superman

It has been my understanding that all four wheels should be square when the car is going down the road. Further, it has been my understanding that road forces cause the front wheels to move outward and engine/transmission forces cause the rear wheels to pull inward.....and that therefore there should be front toe-in and rear toe-out.

And yet, the Porsche chassis guys I trust the most suggest toe-in for both axles. Often more in the rear the front!

'Splain this to me.

Also....what alignment specs do you recommend for a mostly street driven 911 with 22/29 torsion bars and Carrera sways? I'm thinking 1 degree front camber and 1.5 back.

Front: road forces push the tire to toe out, directional stability goes down w/ toe out, spec is 0° pressed, a bar is used to simulate road force so that there is 0 static toe, I prefer this, but some will want a small amount of toe in for increased straight line stability at the expense of turning

camber spec is 0°+/-10', I like more for better cornering, -1° to -1°30' works well, the more camber the more toe chage w/ suspension travel, bump steer is a concern w/o compensation



In back spec is 10'+/-10' of toe in, you need toe in here because as at the front road forces try to sply the wheels, toe in provides braking stability, less toe in imparts less braking stability, too much is a drag, so use 0 to 10' of toe in depending on what you like for braking.
camber spec is -1°+/-10' as w/ the front more helps cornering up to -2°30' works well

[Quicksilver]

An easy way to visualize the reason for rear tow in is to just imagine how the rear tire is steering the car when the weight is transferred onto it. Tow out will cause the car to rotate farther into the corner and when you realize that the tire's slip angle will add a LOT more "rear steer".

So , yeah, rear tow in is important.

[KTL]

Superman,

Remember this? Maybe not, since it was FIFTEEN YEARS ago. Holy carp I can't believe it's been that long.........

Toe Adjust Techniquest

[Superman]

Originally Posted by Quicksilver

Tow out will cause the car to rotate farther into the corner .....

Do the tires 'toe out' when the rear suspension is compressed? This would certainly help explain the importance of toe-in at static alignment. Plus, as you say, the skid steer thing.

Originally Posted by KTL

Superman,

Remember this? Maybe not, since it was FIFTEEN YEARS ago. Holy carp I can't believe it's been that long.........

Toe Adjust Techniquest

Ugghh.... Visiting that thread....I miss Ron. He came by to see me on one of this driveabouts (he lived in NY, I am in Puget Sound) I imagine he stayed the night, I know for a fact he showered at my house. He reminded me of a wet, hairy ape. God bless you, Ron.

This is the third time someone has responded with one of my old threads. I'm missing a step it seems, now that I am becoming more weathered. 60 now. I'm just glad to be back here, caring for my car finally. I apologize to you guys for the stuff I've forgotten, and glad you are here to remind me.

[Bill Verburg]

Originally Posted by Superman

Do the tires 'toe out' when the rear suspension is compressed? This would certainly help explain the importance of toe-in at static alignment. Plus, as you say, the skid steer thing.



......

both end react the same way dynamically, but differently at the same time
acceleration - fronts rises(extends) & rear drops(compresses), front toes out and rear toes in
deceleration - front drops(compresses) & rear rises(extends), front tires toe in & rear tires toe out

statically the same - drop toes out & rise toes in at either end

in cornering one side compresses the other extends, the compressed side toes in the extended side toes out. The difference in toe side to side is bump steer aka roll steer