21mm gauge wheel sets for IRM Park Royals and Mark IIs

[lucas]

A couple of weeks ago, while browsing the forums well after my bedtime, I half jokingly asked how difficult it would be to have some aftermarket wheel sets made to regauge the upcoming IRM Park Royals.

On 29/4/2026 at 1:22 AM, lucas said:

Looking at the pictures shared earlier it does look like much the same setup as the Mk2s. Makes me wonder how difficult it would be to get a factory to run off a small batch of 21mm split axle wheelsets

The Park Royals use split-axle wheel sets similar to the Mark 2s for electrical pickups for the interior lighting. This has the side effect of making them a bit of a pain to regauge.

To answer my own question, I did a little digging and found a guy who's happy to run off a small batch of wheels for a half decent price.

So would there actually be enough interest to justify producing some wheels?

They would 12mm diameter EM profile wheels set to 19.3mm back-to-back on a 28mm long 2mm diameter split-axle. I know this is not ideal for those using P4, but I guess it's better than nothing? From what I can tell 21mm EM seems to be more popular (and it's also selfishly what I'm using).

These will be designed to fit the Park Royals when mine arrive. They should also fit the Mark 2s, I don't see why they wouldn't, but I don't personally own any to test with. If someone can send me a few measurements of theirs to double check it would be much appreciated!

The cost should work out to around €9-€10 per coach (set of 4 axles), depending a little bit on how many I order and what I end up getting charged for import tax.

So, I'm trying to gauge interest to see if anyone else would want a set. I'm happy to take on the risk of ordering the wheel sets, but only if I can be somewhat sure I will sell them.

Please reply below or send me a PM letting me know how many sets you would want for either the Park Royals or Mark 2s. This is purely to get an idea of numbers, I'm not accepting pre-orders. I don't want to take anyone's money until I have the wheels in hand. But on the off chance I run out, anyone who expresses interest now would get priority.

[Mol_PMB]

This sounds like an excellent plan - thank you for taking the initiative!

Somewhere I think I have a spare pair of IRM B4 bogies from the first batch of Mk2s that I could measure up, if that would help? No guarantee the wheelset interface is the same as the Park Royals of course.

Potentially I would be interested in enough for 20 coaches. 
I’m in GB so if there was a way to avoid getting taxed twice that would be advantageous!

Cheers,

Mol

[murphaph]

Is it not possible to just push the wheels out like other IRM bogie stock? I never really looked closely at the Mk2 bogies. Just assumed they could be pushed out like the 42' flats etc.

[Brendan8056]

The IRM (and the latest batch of Murphys AC stock) are easy coaches to regauge to 21mm. See the pic, which shows the difference. I did not worry about removing the brakes on my IRM ones, they were only for show anyway!

I feel sure the same design would be used on the Park Royals, why change something when it works well.

A supplier of 28mm length axles could be useful for rebuilding the older Murphys AC stock and the Craven bogies. I make my own 28mm axles but some may not wish to do this.

[Horsetan]

7 hours ago, lucas said:

.... did a little digging and found a guy who's happy to run off a small batch of wheels for a half decent price.

So would there actually be enough interest to justify producing some wheels?

They would 12mm diameter EM profile wheels set to 19.3mm back-to-back on a 28mm long 2mm diameter split-axle. I know this is not ideal for those using P4, but I guess it's better than nothing? From what I can tell 21mm EM seems to be more popular (and it's also selfishly what I'm using)....

I only work to P4 standards, so I wouldn't be in the market for these.

Bear in mind that both the Mk2 and the Park Royal bogie wheels are based on a 1mm/1.5mm dia stub axle, and the "live" pinpoint bearings are matched to this. A 2mm diameter pinpoint does not work properly in the IRM bearings as the angle of coning is different - this was the first thing I tried, using Scalefour Society 28mm axles, and found that a 2mm pinpoint results in significant rolling resistance / dragging.

P4-profile coach wheels commonly come on a 2mm axle, so that means finding a suitable converter bush to press into the wheel centre to reduce it to 1mm/1.5mm. Bushes of that kind are very hard to find. Most 1.5mm i/d bushes on the market have an outer diameter of 2.4mm so cannot be pressed into a standard P4 coach wheel.

IRM list their pinpoint stub axles as spares in the coach instruction leaflets but whether they are actually available is another thing altogether.