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.

[lucas]

On 15/5/2026 at 3:29 PM, Mol_PMB said:

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.

If you could get some measurements of the wheelset and the bogie that should be great! Just to double check; wheel diameter should be 12mm, axle length should be 28mm, and there would need to be >~24.5mm space between the frames. And you wouldn't be able to get an accurate measure of the cone angle on the axle pinpoint?

I'll get the measurements for the Park Royals when they arrive here, and take it from there.

On 15/5/2026 at 3:29 PM, Mol_PMB said:

I’m in GB so if there was a way to avoid getting taxed twice that would be advantageous!

I don't think there is an easy way to avoid that unfortunately. As far as I know I can't deduct VAT the way a business can. I had thought about splitting the shipment (sending half to Ireland and half to the UK) but we'd end up paying shipping twice in that case and for a small order it's actually a good chunk of the overall price. So that really wouldn't end up being any cheaper in the end.

 

19 hours ago, Brendan8056 said:

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'd read quite the opposite in a few places. Something about the sleeve being what maintains the proper gauge in OO. Also the difficulty in moving metal wheel on metal axle, unless you have the proper tools to do that.

 

17 hours ago, Horsetan said:

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.

I wonder if it's the 2mm axle or the pinpoint angle that causes issues? or both? I know some axles are made to 55° angle while others are 60°. Could it be that the bearing expects a 55° angle while the axle is 60°? It would be ideal if a 2mm axle could work with the correct cone angle.

[Horsetan]

22 hours ago, Brendan8056 said:

The IRM (and the latest batch of Murphys AC stock) are easy coaches to regauge to 21mm. See the pic, which shows the difference. ....

Pushing the IRM stub axles out on the insulating muff results in quite a wobbly wheelset, as there's little grip left.

[Mol_PMB]

7 minutes ago, Horsetan said:

Pushing the IRM stub axles out on the insulating muff results in quite a wobbly wheelset, as there's little grip left.

Presumably the length over the pinpoints is then also too long?

is it possible to shift the wheels on the stub axles? 

[Horsetan]

10 minutes ago, Mol_PMB said:

...is it possible to shift the wheels on the stub axles? 

The wheels are force-fitted on the stub axles, so the only way of shifting them is with a proper press tool. If you take the expedient route and try to hammer it from the pinpoint end, you may well end up blunting the pinpoint, which will result in detrimental running.

A new IRM stub axle, and a new wheel is the best solution, but I don't know if IRM's Chinese contracting factory keeps stocks of 1mm pinpoint axles for spares purposes. They are certainly listed as spares and even have parts references, but that's not the same as actually being available to purchase. 

[Mol_PMB]

Just now, Horsetan said:

The wheels are force-fitted on the stub axles, so the only way of shifting them is with a proper press tool. If you take the expedient route and try to hammer it from the pinpoint end, you may well end up blunting the pinpoint, which will result in detrimental running.

A new IRM stub axle, and a new wheel is the best solution, but I don't know if IRM's Chinese contracting factory keeps stocks of 1mm pinpoint axles for spares purposes. They are certainly listed as spares and even have parts references, but that's not the same as actually being available to purchase. 

Thanks. And since almost all replacement wheels will suit 2mm axles, it's not an easy fix.

I'll try and find my pack of B4 bogies tomorrow and have a closer look and a measure.

[Horsetan]

10 minutes ago, Mol_PMB said:

Thanks. And since almost all replacement wheels will suit 2mm axles, it's not an easy fix...

The ideal solution would be a 2mm o/d bush pressed into the new wheel and bored 1mm/1.5mm for the stub axle. That's the only way of retaining the original "live" function for lighting and other things.

It's not meant to be easy. When Rapido started doing RTR OO, it was quite clear that it had been designed to prevent people from tampering with the model, so rewheeling to a wider gauge was very difficult indeed or virtually impossible.

Edited 10 hours ago by Horsetan

[DJ Dangerous]

3 hours ago, lucas said:

I'd read quite the opposite in a few places. Something about the sleeve being what maintains the proper gauge in OO. Also the difficulty in moving metal wheel on metal axle, unless you have the proper tools to do that.

I’ve been following this thread with a mix of curiosity and fear.

Would you mind posting some of those links, please?

 

19 minutes ago, Horsetan said:

The wheels are force-fitted on the stub axles, so the only way of shifting them is with a proper press tool.

So with one of THESE, a cheap wheel puller, the IRM wheelsets are easy to re-gauge to 21mm?

[Mol_PMB]

I have a wheel puller and I have made some extra tools for it including a hollow-tipped one so that I can push on a pinpoint without blunting it. 

However, the non-insulated IRM wheels on 2mm axles are very hard to shift. I can do it, but if the ones on 1mm axles are as tight a fit then I'd be wary of bending the thinner axle. 

I tend to discard the IRM wheels and replace them with EM profile wheels as the IRM wheels have a surprisingly coarse profile. I guess that's to suit a wide range of OO track standards, but it's not ideal for EM. I put the EM wheels on the IRM 28mm axle once I've pushed the old wheels off. That's OK when the axles are 2mm diameter but doesn't work for 1mm axles. The EM profile wheels I use are insulated so would not be ideal for lighting pickups either. All these problems can be solved but it's a faff, hence the attraction of getting a batch made up of exactly what we're after.

[Brendan8056]

If it helps I use this for doing my 21mm gauge wheelsets now. It is superb, and costs the same as in Germany, as the manufacturer deducts the VAT for export to the UK. He responds very quickly to enquiries in perfect English. Until I purchased this I was using the hammer method.

https://www.fohrmann.com/en/wheel-spacer-h0.html

As for wobbly wheelsets, I have had a few go like that with the IRM bogie wagons,, and a couple wrecked and replaced by spare axles from IRM bogies purchased on their own. The non insulated wheelset is a very tight fit.

But the IRM B4/B4 bogies have caused no such problem, I have done 6 coaches worth to date, the axle length on the insulated sleeve remains the same, as the wheels are moved out on the axles. Hopefully this is clear in the picture I uploaded.

 

Edited 10 hours ago by Brendan8056

[Horsetan]

1 hour ago, DJ Dangerous said:

So with one of THESE, a cheap wheel puller, the IRM wheelsets are easy to re-gauge to 21mm?

Might do. Want to give it a go?