Understanding toe-in

[phillpot]

Referring to the diagram below if the car had zero toe-in or out, wheels are dead parallel Bt and At will be equal, lets say 5 feet exactly.

Would 1/16" toe-in make Bt 4 feet 11 and 15/16"? or is it 1/16" per side so 4 feet 11 and 7/8"?


Or.... is 1/16" toe-in the total difference front to rear so Bt will be 1/32" less than 5 feet and At 5 feet and 1/32"?



I don't do degrees

[frodo_monkey]

I've always understood toe to be measured as a total so 1/16" would equal 1/32" each side (making Bt in your example 4ft 11 and 15/16", and At 5ft 1/16")...

Edited by frodo_monkey on Tuesday 1st August 20:26

[GreenV8S]

phillpot said:

I don't do degrees

Do it in degrees. It's so much clearer, and avoids worrying about whether you, or the person you're telling or listening to, is making the same assumptions.

[Mignon]

phillpot said:

Or.... is 1/16" toe-in the total difference front to rear so Bt will be 1/32" less than 5 feet and At 5 feet and 1/32"?

This.

FWD cars pull the front wheels toe in under power so static they usually have a little bit of toe out and RWD cars push the front wheels toe out so they have a little bit of toe in static. 2mm total is a good average figure for most cars if specs are not available.

[phillpot]

GreenV8S said:

Do it in degrees.

Don't have a tape measure with degrees, only inches or millimetres

[GreenV8S]

phillpot said:

Don't have a tape measure with degrees, only inches or millimetres

It's trivial to convert to degrees using the 1/60 rule. Measure distances, talk angles.

[finishing touch]

I find it easy to visualise 3mm or 1/8th but find it more difficult to visualise a degree.

I have always taken it as the difference between the wheel rim at the rear edge and the front edge, so not for each wheel but for the axle.


These figures do rely on the wheel rim being true. I took some tyres off the other day and the rims had been distorted by tyre changer clamps.
As the wheels sat on a spraying turntable you could see the run out.


I made this to check track. A simple box section frame with a stop one side and a vernier the other. (sorry but no degrees )

Paul G

[227bhp]

finishing touch said:

I find it easy to visualise 3mm or 1/8th but find it more difficult to visualise a degree.

I have always taken it as the difference between the wheel rim at the rear edge and the front edge, so not for each wheel but for the axle.


These figures do rely on the wheel rim being true. I took some tyres off the other day and the rims had been distorted by tyre changer clamps.
As the wheels sat on a spraying turntable you could see the run out.


I made this to check track. A simple box section frame with a stop one side and a vernier the other. (sorry but no degrees )

Paul G

That's a good post, I like the tracking bar too, but it doesn't take into account the centreline of the car.
Then what happens when you change wheel size? If you went up a size (say from 15" to 16") I guess you could drop your measuring point down below the centreline until you reach the 15" point.
I wonder how many people realise that when they're tracking cars with lasers and non original wheel sizes...

Edited by 227bhp on Friday 4th August 10:04

[GreenV8S]

finishing touch said:

I have always taken it as the difference between the wheel rim at the rear edge and the front edge, so not for each wheel but for the axle.

That's how you'd measure it, regardless of whether you specify it in terms of distances or angles. Your picture and description makes it clear what you're talking about, but there are other ways to describe these which can affect the readings by a factor of two or four, as we've seen in this thread. And no doubt there are people trying to measure at the tyre instead of the rim. Presumably you only compare readings from the same size rims, but if you discuss geometry in terms of distances like this then inevitable people are going to try to apply your figures to different vehicles with different size wheels and get the wrong result.

Describing this geometry in terms of angles avoids a lot of these problems. I'd expect you to be using angles for other measurements anyway. You don't define camber and caster distances, do you?

[finishing touch]

227bhp said:

finishing touch said:

I find it easy to visualise 3mm or 1/8th but find it more difficult to visualise a degree.

I have always taken it as the difference between the wheel rim at the rear edge and the front edge, so not for each wheel but for the axle.


These figures do rely on the wheel rim being true. I took some tyres off the other day and the rims had been distorted by tyre changer clamps.
As the wheels sat on a spraying turntable you could see the run out.


I made this to check track. A simple box section frame with a stop one side and a vernier the other. (sorry but no degrees )

Paul G

That's a good post, I like the tracking bar too, but it doesn't take into account the centreline of the car.
Then what happens when you change wheel size? If you went up a size (say from 15" to 16") I guess you could drop your measuring point down below the centreline until you reach the 15" point.
I wonder how many people realise that when they're tracking cars with lasers and non original wheel sizes...

Edited by 227bhp on Friday 4th August 10:04

One of my "sporty" cars has 15 x 50 profile while the other has 16 x 45, although I intend to upgrade to a wider 15 soon anyway.

That is however complicating matters as since there's only 1/2" difference to centre, less with the lower profile, there's a couple of
far simpler solutions. Let 5psi out of the slightly larger wheels, or, pop a spacer under bottom bar to lift it off the floor.


Paul G

[finishing touch]

GreenV8S said:

finishing touch said:

I have always taken it as the difference between the wheel rim at the rear edge and the front edge, so not for each wheel but for the axle.

That's how you'd measure it, regardless of whether you specify it in terms of distances or angles. Your picture and description makes it clear what you're talking about, but there are other ways to describe these which can affect the readings by a factor of two or four, as we've seen in this thread. And no doubt there are people trying to measure at the tyre instead of the rim. Presumably you only compare readings from the same size rims, but if you discuss geometry in terms of distances like this then inevitable people are going to try to apply your figures to different vehicles with different size wheels and get the wrong result.

Describing this geometry in terms of angles avoids a lot of these problems. I'd expect you to be using angles for other measurements anyway. You don't define camber and caster distances, do you?

In the case of my Seven I made the wishbones and the castor was incorporated into the jig as a distance in mm.

I set camber with a "Wixey" digital protractor, so yes indeed this is an angular measurement.


Paul G