Wheel alignment terminology and signage vs NCT?

CiniO

So - I've came across this video few days ago, which explains it quite well about wheel alignment terminology.

Now - I always though same as with the video, that "toe in" is when wheels point towards each other (front of a tyres are closer together than the rear of a tyres - like that looking from above the vehicle / \). This would cause excessive wear on the outside of the tyres. And is marked with "+" on tests.
"Toe out" would be opposite so marked with "-" and wheels pointing like that \ /. Excessive wear on the inside of the tyres.

I double checked my car, and looks like rear wheels are a bit toe in (+) and front wheels are a bit toe out (-).
However on NCT test a while ago, on side slip test it was exactly opposite. Rear axle -4 m/km and front axle is +2 m/km.

Does anyone know if NCT is just using this signage opposite, or there is something more wrong?

Special Circumstances

Different units different measurement afaik. Toe in/out is measured in degrees.
Side slip is a distance of "drift" left or right. Not sure whether left or right is positive.

That's my understanding at least.

5W30

The slip test results just refer to how much meters the car will slip to one side for every kilometre.

If the number is positive it means the axle is making the car go towards the centre of the road (offside). If it's negative the car is going towards the kerb (nearside).

It does not matter if the wheels are toe in or out. What matters is amount of toe between each wheel. If both wheels on the front are toe out by the exact amount the car will go straight. The same can be said if they are toe in.

CiniO

5W30 wrote: »

The slip test results just refer to how much meters the car will slip to one side for every kilometre.

If the number is positive it means the axle is making the car go towards the centre of the road (offside). If it's negative the car is going towards the kerb (nearside).

Allright then.
I get it now.
So pretty much side slip test has nothing to do with wheel alignment really. It just measures how straight the car goes if you release the steering wheel loose.

I found this here:

The Side Slip Test:
This test simulates driving on a straight, flat road without touching the steering wheel.
This measurement indicates how many metres a vehicle would deviate to the left (-) or to the right (+)
hand side over a distance of 1km.

It does not matter if the wheels are toe in or out. What matters is amount of toe between each wheel. If both wheels on the front are toe out by the exact amount the car will go straight. The same can be said if they are toe in.

Well in that case I wouldn't agree with the above.
It doesn't matter completely what toe wheels are set to.
If left wheel it toe out by say 2 degrees, and right wheel is straight, then together they will be toe out by 1degrees each, when steering wheel is turned slightly right.
And considering for the test steering wheel is let loose, then it doesn't matter which wheel's toe is set what. Toe setting itself is not going to affect if car is pulling to the right or left.
Cambar or caster setting on each individual wheel might.

5W30

CiniO wrote: »

Allright then.
I get it now.
So pretty much side slip test has nothing to do with wheel alignment really. It just measures how straight the car goes if you release the steering wheel loose.

Well it kind of does because if the toe on the left wheel differs to the toe on the right wheel the car will naturally pull to one side, regardless if the steering wheel is held or not.

This means side slip exists and the car needs an alignment.

The reason the steering wheel is released for the NCT is so the tester doesn't correct the pulling with his hands from my understanding.

CiniO

5W30 wrote: »

Well it kind of does because if the toe on the left wheel differs to the toe on the right wheel the car will naturally pull to one side, regardless if the steering wheel is held or not.

Well, I can't agree with that.

By toe setting, we are just talking about relative setting between steering column and front wheel.
Car naturally goes straight, no matter how toe is set.

F.e. if you set "toe out" on left front wheel (f.e. by 2 degrees), and leave toe straight on right front wheel, by your logic car will be pulling to the left.
Indeed it will - but only assuming someone will actually hold the steering wheel at centre position.
But considering the setting, centre position won't be natural for steering wheel then. If you release steering wheel free while driving with such setup, steering wheel will automatically move right, and car will go straight.
There's no force to keep steering wheel straight and let car turning the the left.

Going further with that example - if you set "toe in" on right wheel now (again by 2 degrees), wheels will be perfectly straight and total toe between them will be 0. Car will go perfectly straight. Only thing is that steering wheel won't be straight when car is going straight.

hi5

The NCT measures sideslip, this is a combination of both toe and camber.
So your toe in could be perfect according to specs but you could have too much camber (top of the wheel leaning in,or out) this gives you sideslip.
Think of a motorbike leaning into a bend, the more angle the wheel leans the more the bike wants to go in a circle same with the wheel on your car.
Left and right specs often differ to allow for camber on the road.
So the more negative camber you have the more toe out you will need to compensate.