Watch: Model railway items keep derailing? Check your back-to-backs!
Wagons derailing through points? Learn how checking model railway wheel back-to-back measurements can identify poor running and improve reliability.
If a wagon repeatedly derails through points, don’t automatically assume the track is at fault. The problem could be the wheelset.
Incorrect wheel back-to-back measurements are a common cause of unreliable model railway running. Fortunately, they’re also relatively straightforward to check.
In our latest Layout Concepts workshop video, we demonstrate how a simple back-to-back gauge can help identify wheelsets that may be contributing to derailments and poor running.
What is a wheel back-to-back measurement?
The back-to-back measurement is the distance between the inside faces of the two wheels on an axle. For a wheelset to travel reliably through trackwork, this spacing needs to fall within the appropriate tolerance for the track and wheel standards being used. If the wheels are positioned too close together or too far apart, problems can become particularly noticeable around:
Points and turnouts
Crossings
Check rails
Complex junctions
Tighter sections of track
A wagon might run perfectly well along plain track before suddenly derailing every time it encounters a particular point. That can make the track look like the obvious culprit when the wheelset itself deserves checking.
Shop the Layout Concepts back-to-back range here, or visit your favourite stockist.
Check the wheels before changing the track
When one particular wagon or coach continually derails in the same place, there's a useful first question to ask:
Do other models pass through the same section without a problem? If several different models derail at exactly the same location, the track may well need closer inspection. However, if most of your rolling stock passes through reliably and one vehicle repeatedly causes trouble, inspect its wheels before altering track that may already be correctly installed.
A back-to-back gauge makes this quick to check.
How to check wheel back-to-back
A dedicated gauge is designed to show whether the wheel spacing is suitable for the modelling standard you're using. Place the gauge between the inside faces of the wheels as demonstrated in our video. The fit will indicate whether the spacing needs further attention.
Make sure you use a back-to-back gauge appropriate for your scale and track standard, as the required dimensions are not universal across every model railway system. Also check every axle on the troublesome vehicle. One incorrectly set wheelset can be enough to cause intermittent derailments.
Shop the Layout Concepts back-to-back range here, or visit your favourite stockist.
What else should you inspect?
Back-to-back measurement isn't the only possible cause of poor running.
While you have the model on the workbench, check that:
Wheels rotate freely
Axles are correctly seated
Wheels aren't visibly damaged or distorted
Nothing is fouling the wheelset
Couplings aren't restricting movement
Bogies or chassis components move freely where required
If the wheelsets check out correctly, you can then turn your attention back to the track with greater confidence.
Small differences can have a big effect
Model railway wheel and track geometry works to relatively fine tolerances. A difference that is difficult to spot by eye can sometimes be enough to affect how a wheel passes through pointwork.
That's why a gauge is so useful. Instead of guessing whether the wheels “look right”, you have a simple tool designed specifically to check the spacing. It's a particularly worthwhile test when dealing with second-hand rolling stock, older models, replacement wheelsets or a vehicle that has developed unexplained running problems.
Watch the Layout Concepts guide
In our video, we take a troublesome wheelset to the workbench and demonstrate how the back-to-back measurement can be checked with a dedicated gauge.
So, the next time a wagon decides it doesn't like your points, resist the temptation to start adjusting the track straight away.
Check the wheels first.
A few seconds with a back-to-back gauge could identify the problem — and help get your rolling stock running smoothly again.
Shop the Layout Concepts back-to-back range here, or visit your favourite stockist.
