Wheel Alignment Using a Laser 1. Introduction Correct
wheel alignment makes a huge difference to the handling if it's accurate.
You shouldn’t necessarily rely on a new rear tyre being correctly
aligned when fitted and maker's graduations on the swing arm are not to be
trusted either. In addition, each time the chain is adjusted, you
run the risk of shifting the alignment.
The time-honoured method of using string lines works just fine, but
is time-consuming to set up and care is required to take the actual
measurements. I set out to build a laser rig to make the set-up and measurement faster from materials which I already had at home. There are multiple permutations on the design shown, and also variations in the way it can be used. The following method is just one way of approaching laser alignment.
2.
Rig Construction ![]()
The
laser target is constructed from a piece of straight dressed
timber painted white, with Perspex end-pieces. The overall length is 500
mm, the height above datum of the timber surface is 80 mm and the height
of the Perspex end-pieces is 130mm. The timber is 58mm wide with a centre
line marked on it. The centre line of 29mm equates to half the difference
between the widths of the front and rear tyres.
If this is different for other tyre combinations, it doesn’t
really matter as a steel rule can be used to measure how far away the
laser beam is from the edge of the front tyre. Illustration 2 shows the end-pieces being struck by the beam.
Illustrations 2 & 3 – Laser light striking the Perspex end-pieces Section 3 shows how the alignment rig is positioned and used. Illustration 4 shows the general arrangement. ![]() Prior to commencing the alignment process, spin the front and rear tyres to look for any significant oscillation on the widest part of the tyre wall. The laser beam can be helpful for this purpose. If the rims are in good order and the tyre has been fitted properly, it will be negligible. If any movement is >1-2mm, then position the wheel so that the laser is roughly at mid-point of the oscillation. Align
the front wheel as close as possible to the centre line of the bike by
eye. The
target part of the rig is then pushed up against the front tyre.
It can be held in place with light elastic if there is any concern
over possible movement.
The laser emitter and support assembly are placed at the back of
the rear tyre so that the beam just kisses the widest part of the tyre
front and aft.
Illustration 5 shows
the beam touching front and aft rear at maximum tyre width.
Turn the forks until the laser beam lines up with the lines on the
Perspex end plates, or runs parallel with it.
This is shown in
Illustration 6.
In
the latter case, measure the distance from the beam to the widest part of
the tyre. ![]() ![]() ![]() ![]() Re-check the alignment when tightening the rear axle to ensure that nothing has moved. A suggestion to increase the interval between full alignments is to scratch some small alignment marks on the swing arm and adjusters if the stock ones are inaccurate. Eccentric adjusters require a slightly different approach. |