The problem with the roller wheels is that because they are not aligned properly, they tend to face different angles. This causes the bike to roll erratically and wobble when pushing the bike. Sometimes the bike tends to go to one side, which is quite irritating as you have to use quite a bit of strength to control the direction and move it back to the direction you want
Luckily, the rear roller wheels which are mounted on the rear rack can have its angle modified. This is done by bending the tabs on the rear rack slightly to the angle you want.
As seen from the picture above, all 4 of the roller wheels seem to be misaligned!
For the rear roller wheels as seen above, the wheels are attached to this small tab protruding from the rear end of the rear rack. To align the rear roller wheels, just remove the wheel and bend the steel tab.
Front roller wheel in original position. Misaligned!
As for the front roller wheels, these wheels are attached to the rear triangle via beefy supports. I have tried screwing in an M6 bolt and bending the support, but only the bolt bent. Not possible to adjust the angle of the front roller wheel mount.
I came up with this method of using a bent bolt for the roller wheel axle instead. As shown below, the bolt is bent a few degrees.
Using a bent bolt as the axle for the front roller wheel
By bending the bolt, when you screw in the bolt it will tend to rotate off centre. This actually makes the angle of the roller wheel vary as you screw in the bolt! The trick here is to fix the bolt at the angle you want.
Bent axle as the axle of the roller wheel! 2 nuts are there to help position the bolt and wheel. One of it will be tightened against the wheel, the other will be tightened against the rear triangle mount.
Front roller wheel with better angle alignment! Compare it with the original angle shown above
It is quite hard to describe exactly how the wheel is being fixed, if you are interested I can show you the bike instead.
This mod makes the right side front roller wheel stick out slightly more, due to the longer axle and the 2 nuts on the bolt. But luckily it does not interfere with my pedalling.
Basically what I did was to use this bent axle technique on one of the front roller wheels, and bent the tabs for the rear roller wheels. By doing so, the wheels are more or less aligned. The bike still does not roll perfectly straight, but it is much better than before.
In fact, the rear roller wheels are aligned so that they point slightly outwards. The effect of this is that I can make the bike roll towards the left or right just by leaning the bike slightly more on the left or right roller wheel.
Quite pleased with the modification, not pretty but it works!