rear wheel toe in?

[flyinlow]

My front end rebuild is done . All new Moog parts on a '73.

Set caster to 3.5 * pos. 
Camber  0.2 neg
Toe in 1/16

Car tighter and drives well.

Alignment guy got a kick out of working on an antique. 

Spec sheet showed 1/16 toe on the rear axle. Is there toe in on the rear?

[tan top]

  most modern  cars have adjustable real wheel alignment ,  prolly just the read out , of being on a 4 wheel alignment machine ,  was it the same both sides ??  .. 

hypothetically  a  nother reason could be bent axle shaft or wheel , but you would be noticing that

[flyinlow]

yes it was a 4 wheel Hunter  rack. Lasers , LCD readouts ,smoke and mirrors. I was impressed.

Just wondered if they built the rear axle with some toe built in. Can't change it anyway.

[John_Kunkel]

There is no designed in toe in the solid rear end but a slight deflection near the center of the axle will produce noticeable toe at the front of the tire. Deflection can be due to bent wheel, bent axle flange, bent axle housing (most likely).

Every rigid rear axle car I've had aligned on the newer machines shows some toe.

[HPP]

Is it toe or thrust? Thrust angles can easily be off and can be adjusted by shimming the front spring hangers.

FWIW, when I was oval track racing, we used to put the rear end housing in a  press and bend them until we had a .5-1 degree of negative camber on the right side. Never noticeable by tech, but sure made the cars stick. Did wear out splines on the axle kinda funny.

[John_Kunkel]

Thrust angle would show a difference in wheelbase from one side to the other which would appear as toe-out on one side and toe-in on the opposite side, not the same as the toe measurement.

[flyinlow]

rear spec sheet said :   


cross camber  0.2*

total toe -2/16 in

thrust angle  0.11*

Original rubber isolated 8 1/4 axle was replaced with a '71 8 3/4 Roadrunner axle two years ago before I installed the 440.

I know last 35 years of the cars history.  Right 1/4 panel  and passenger door replaced before that.

I noticed they rotated the front wheels durring the alignment ,but not the rears.

Car drives well and the tire wear rate is acceptable. 


Does the thrust angle mean the back wheels are 1/10 of a degree out of track with the front?

[John_Kunkel]

Yep, the thrust can be corrected with a shim plate under one spring hanger, toe can't be corrected without some bending (or unbending)

[flyinlow]

Yep, the thrust can be corrected with a shim plate under one spring hanger, toe can't be corrected without some bending (or unbending)

Any idea how thick of a shim for 1/10 of a degree?

Does a positive thrust angle mean the rear wheels are steering the back of the car to the right?

[John_Kunkel]

Personally, I wouldn't even worry about it, I imagine there are cars with more thrust angle than that and nobody ever notices.

It's one of those cases where "a little knowledge can be a dangerous thing".   

[flyinlow]

Personally, I wouldn't even worry about it, I imagine there are cars with more thrust angle than that and nobody ever notices.

It's one of those cases where "a little knowledge can be a dangerous thing".   

Probably good advice.   

Drove for decades without knowing those numbers.

[HPP]

i agree. 1/10 of a degree is pretty darn minor to start messing with.

[flyinlow]

Last question: why dos a small amount of negative camber increase corning ?

[elacruze]

Simply put, when you're cornering there are a lot of forces at work trying to push the tire sideways. The tire resists at the bottom, the push comes at the bearings near the center so the wheel tends to trip and increase negative camber.
So, having some positive camber built in sets the tire straighter to the road when these forces are acting on it.

[HPP]

Negative camber allows the tire to remain verticle to the road as the body rolls in the corner. The amount needed is a function of how much body roll against how much cornering do you do. -2 degrees will stick better than -.5, but will also wear the inner edge of the tire faster during straight driving.  So drag racers want no camber, oval rqacers want more. Street cars are the compromise. On an oval track car, you would want negative camber on the tire on the outside of the turn and postive camber on the tire on the inside of the turn. Road cars would want a small amount of negative on both sides.