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Aligner les roues (En)

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 at speed, 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.