E46Fanatics - View Single Post - Yet another alignment thread. [Pics of steering rack]
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Old 01-18-2020, 11:55 AM   #3
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Join Date: Jan 2012
Location: car-nation
Posts: 1,614
My Ride: 2004xit, 2001ci
If you've read my posts on other threads, you know I'm going to say-

the improvement in handling was due to the increase in front toe in.

Below is all predicated that we're talking about an E46.

Camber has very little effect on straight- line handling, especially on smooth roads.
As it goes up, the car's tendency to follow pavement grooves increases, and its ultimate
cornering grip goes up, but it is otherwise pretty transparent.
And tire wear is affected only slightly. In fact, if you like some toe- in for stability
then a little negative camber can actually balance that out.

Toe has a big effect, especially when your tires are all almost at zero toe.
Increasing toe- in in the range of 0 to .25 degrees you'll feel as increasing stability,
resistance to side winds, and predictiability.
The trade off will be that you start to lose responsiveness- it'll take an increasing amount of
wheel movement to get the car to turn 'right now'.
Depending on your tires, toe over about .25 degrees will increase wear at an exponential rate, AND
the car will feel 'numb'

Caster also has a big role in feel, and also in cornering grip, but with fewer tire costs.
The more caster, the more stable the car feels, the higher steering effort there is, and often,
the more cornering grip the front has, from the camber gain that you ... gain.
It is also very hard to adjust on the front of a stock BMW without plates, bending things, or moving suspension points.

Most of this is based on tires being compliant- 'rubbery', if you will. They distort significantly in outside diameter
with the car's weight, and also laterally when you corner. Since they are really very dynamic springs as you are driving,
a small amount of 'non parallel' movement from toe- in is absorbed by 'springing' the sidewall of the tire.
So wear, at first, doesn't go up, as the tire deflects slightly. It also pre- loads against the other tire, so that as weight
transfers from side to side, the car tends to 'self correct' against outside loads.
Heat DOES go up, as does rolling resistance, but not enough to matter for our purposes.

The other upshot of all this is, that since the tire's a conforming spring, precise alignment becomes less and less important
as you approach exact accuracy- that last tenth of a degree of camber might only be felt on a racetrack at full cornering load,
and then ONLY as a 'the front goes away first' sensation.
So since toe is such a powerful tuning tool, if everything else is within the BMW spec, it's quick and easy to adjust the car
with it.
In fact, I keep less toe on for commuting, and will toe the car in a little bit more when I know we'll be on long freeway trips, when there's very little
actual driving to be done, just so it's easier to be lazy....

way more words than you needed,

"I'm sorry. I actually had to poop and ended up breaking the car."
- Hot Tub

Last edited by TobyB; 01-18-2020 at 11:59 AM.
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