Wheel alignment.
There's
a whole lot to know about suspended multi-track vehicle dynamics. I'll
sum up a few of the parameters involving wheel alignment, with some
brief and simple definitions. Some will be expanded later on in this
article, all of them are extensively explained on the www.
- Camber
is the tilting of the wheels from the vertical plane when viewed
from the front of the vehicle. The WAW has a negative camber to increase
stability and reduce frontal area. A disadvantage of this is a tiny
drag caused by the variable diameter of the wheel over the tyre contact
patch (camber thrust).
- Caster is the tilting of the
steering axis, viewed from the side. This is what makes any vehicle
track straight. No settings are to be made, it's taken care of by the
WAW's McPherson strut suspension.
- Center point steering AKA
zero scrub radius AKA kingpin offset is basically what makes the
vehicle go straight on when braking on one wheel. Some deviation from
this optimum is a good thing according to some and is then called brake
steer: the ability to ease the vehicle through a corner by braking the
inside wheel.
- Toe is the convergence (toe-in) or
divergence (toe-out) of the front wheels. With a small toe-in at
standstill, the deflections of the suspension system during the ride
ensure that the wheels become parellel.
Allow me to
elaborate on toe-in, this is the setting we have to finetune every now
and then, and especially during the first weeks of WAW riding.
Too
much toe-in makes one of the front tyres scrub sideways. This causes
more tyre wear and, more importantly, increases rolling resistance. Too
much toe-out generally does the same, with the added problem that the
vehicle becomes
wobbly as the weight is shifted constantly from
one wheel to the other.
Good quality tyres can last 5000 to
20000 km, according to type and purpose. If the tyres wear too fast
and/or unevenly, you can conclude it's time for some finetuning.
Although
the deviation is small, all measuring should be done
under load.
This means that either the usual rider sits in the vehicle and the
static measuring is done by a friendly neighbour, either a comparable
weight is positioned on the seat. The center of gravity of the rider -
or substituting weight - is approximately the position of the belly
button.
Different methods each have their followers.
1.
Visual alignment. Bottom line: if it looks parallel, it is. Rectangular
pavement is a great help. Round off to the smallest toe-in.
2.
Measuring front and rear distance from wheel to wheel. You may increase
precision by turning the wheels or tying longish objects to them.
3.
A time consuming but very rewarding method is the coastdown method.
While varying the toe-in setting, roll-out from a hill is measured
(distance or time) and set out on a little graph. Top of the parabola
determines the best real-world setting.
Factory settings are
obviously limited to method 1. and 2. as rider weight is relatively
important compared to the tiny weight of a WAW.
Therefore we
recommend that every rider performs the roll-out test to fine tune the
wheel alignment in real world conditions.