Reply To: EM v P4

Members Forum Miscellaneous Coffee Lounge EM v P4 Reply To: EM v P4

Dai Davies

John Cutler said
A question I have often been asked by my non-modelling friends is why I choose to model in EM gauge rather than the more precise P4. It is quite difficult to give a single satisfactory answer, other than it should be easier!

It is a bit surprising that there is no readily available summary of the pros and cons of EM to help prospective EMGS members which direction they want to take. Maybe a Manual Sheet is needed?

So here are my thoughts for what they are worth.

Advantages of EM:
1. Tolerances are generally looser than P4, making it easier for a novice without sophisticated tooling or skills to achieve reasonable running. (Do you have the capability of accurately measuring and building to a 0.01mm tolerance?).
2. Wider tyres and greater flange-to-rail gap allows tighter track radii to be employed (36” compared to 42” practical minimum for P4; source Iain Rice. Note that successful layouts in both gauges have been built with lesser radius curves).
3. Deeper wheel flange helps prevent derailments without the need for compensation or springing of vehicles. But some P4 heretics successfully run EM wheels on P4 track.
4. Availability of ready-to-lay turnouts.
5. Narrower frames allow greater tolerances for setting up outside cylindered locomotives. RTR OO locomotives can often be simply adapted.
6. The existence of a fairly comprehensive Manual for referral.
7. Despite RP25 wheels not conforming to the EM standard, OO RTR wheels can often be used successfully if eased out on their axles. This seems to be increasingly so as RTR makers are becoming more finescale oriented.

Advantages of P4:
1. Looks better, especially the track and wheels. But still not 100% prototypical (=S4).
2. In the absence of perfectly engineered track to mainline standards, P4 locomotives require compensation or springing. Electrical pick-up is therefore better than rigid EM locomotives but EM vehicles can also be sprung or compensated.
3. Wider locomotive frames give more space for springing, compensation, gears and motors. Split axles are also easier to use because of the greater clearance between gearbox and frames. The wider frames also make it easier to incorporate representations (or even working) of inside cylinder mechanisms.
4. A better and more informative magazine (Scalefour News).
5. If you are an engineer, the EM standards allegedly contain some inconsistencies for track and wheels not found in the P4 standards.

Please agree/disagree and offer amendments.

Hopefully we will end up with something that helps the newbies out there.

Plus easier conversion of stock to EM. Indeed some locos can just have their wheels pulled on their 00 axles.”