In narrow gauge recommendations - TWO FOOT
Minimum radius should be 20 times the longest
wheel base. The absolute minimum is 12 times the longest wheel
Gauge widening of 7mm for curves between the 20 times and 12 time
wheel base. Equivalent of 1.5mm in 5" gauge.
5" Gauge Example - Trojan wheel base is 254mm
minimum radius would be 5.08m
absolute minimum 3.048m (10 feet).
Any more gauge widening and the bogies can crab, leading to the
bogie turning out of the curve and increasing friction and wear on the leading
That is the theory -
In practice if going down to a six foot radius gets you a loop or
return on the line then it is worth doing.
The line above is the Wooburn Green Railway. Six foor radius and
one very proud owner. Power is provided by a Trojan and trains are short. Don't
let the theory stop you from building a railway.
The tracks in our tunnel - inside is a 10 foot radius.
For full sized railways the practice of going from one curve
straight in to another should be avoided as it can lead to buffer locking. Most
miniature railways use a bar connector so buffer lock shouldn't be a problem.
That said excessive direction change is uncomfortable for passengers which can
lead to derailments.
0-6-0 engines - Having a centre set of wheels can cause problems.
If you are intending to run an 0-6-0 on tight radius track it may be worth
removing the flange from the centre set of wheels. We have done this on our
electric Thomas and it means it can now traverse the inner loop. It is a brave
one way decision but the benefits may pay off.
It is very hard to track down figures on gradients. There are
numerous factors that make most rules and formulars a waste of time.
Factors affecting gradients
- Lead in to the gradient - standing start or run up
- Type of rail
- Weather - wet rail can see loss of adhesion by over 50%
- Dirt oil on track - as above
- Load - 1 or 20 people
- Type of engine - Hercules will take a 1 in 20 many won't
- Curved or straight?
- Rolling stock - huge variation on friction/resistance of different designs
Some of our tests
||1 in 10
Hercules on a angle iron track. Pulled 18 stone adult from standing
||1 in 20
Hercules on steel track, 6.5 feet radius. Two adults from standing start.
Could have pulled more but no volunteers.
||1 in 40
Chingford Various gradients - 9 adults after a days running. The engine was
more than comfortable pulling this load around the
A couple of things to think about
Avoid gradients in sidings and stations if at all possible.
On our railways the 10/12' radius curves and steep inclines means
most steam engines are limited to the driver + 1 passenger.
Walking up a 100mm rise is barely noticeable over a distance of 2
metres. The same can no be said for trains. Move the landscape in preference to
the line when building a line.
Next Stage - Site Survey