Wheel profiles

[DaveHarris]

As a relative newby I would like a little 'practical advice' regarding wheel profiles in respect of what is suitable for running on P4 locos. I have read the sheets on wheel profiles in both the Scalefour and EMGS manuals, and given that the track for both is the same profile(I think), I am a little confused by the profile differences for wheels in both manuals in that whilst I appreciate that both scales will have different back to back dimensions and for the purist the profiles will be different ( a relatively minute amount), my question is can wheels that have been profiled for EM use be used for a P4 loco with just the obvious axle change?. My question arises from a purchase I made recently of a set of wheels for a 9f loco which came with axles for EM use. When I asked if I could just substitute the 'EM' axles with P4 axles to allow the construction of a chassis for the 9f loco I am looking to build I was informed that the wheels made with a EM profile were not suitable for running on P4 track!

A clarifying explanation would be appreciated

Dave Harris

[beachboy]

Dave,

A comment rather than advice, is that building detailed models, it kept nagging me that the finer profile of P4 finishes off the model to look akin to the real thing. Plus, I was not happy with having to move components on loco frames etc. to allow for the clearance of the EM flang depth. I have been converting some of my old EM models, and suprised how unrealistic the wheels are. Have a look at the real thing.

As for the profiles when it comes to Sharman wheels, I have a job sometimes to tell the difference. I had to return several times, EM wheels for the correct requested P4, and some still do not look right. The profile also looks different to a Gibson or Ultrascale equivalant.

There was a previous debate in the Index about using EM wheels on P4 Permanent Way, where the profiles were aired by members, and also an interesting one on altering EM's to P4.

Steve.

[Philip Hall]

P4 and EMGS wheel profiles are very different. The P4 wheel is narrower (2mm), has a smaller & thinner flange, and is very close to scale. Wheels sold by most manufacturers confirm to these published dimensions. There are two other choices. In EM there is the EMF profile, developed by Ultrascale, in conjunction with Pendon Museum; this has a narrower tyre (80 thou/2mm, same as P4, but with the EM (thicker and deeper) flange profile. In P4 there is the Exactoscale wheel, which has an exact scale width tyre (1.85mm) and flange profile the same as the P4 standard.

Some P4 modellers on here have chosen to use the EMF profile (only available from Ultrascale, by the way) on P4 track. This does work but as the flange is thicker means that track gauge variations are more critical, and also that wheels should be wobble free. It has been found that with a thicker and deeper flange roadholding on non - suspension fitted vehicles can be better.

Sharman wheels, no longer available new, had a middle width tyre (wider than P4 standard, narrower than EM standard), because Mike Sharman used the same tyre blank for both gauges. His EM flange also seemed a bit smaller than standard sometimes, so when you find these wheels on the secondhand market you have to be a little careful.

If you are starting in P4 the strongest possible advice would be to stick to the recommended standard P4 profile to start with. The vast majority of P4 modellers use the standard dimensions which have been proven to work over many years. It is merely that some experienced modellers have chosen to experiment along a different path which they have found successful. To answer your specific question about a 9F, I would say that if there was ever an engine where you should not deviate from the standard, this has got to be it! Further, unless you are familiar with constructing chassis already prior to adopting P4, I would advise starting with something a lot simpler. Merely a question of acquiring skills (say on a simple 0-6-0) before jumping in at the deep end.

Good luck, you'll find there is plenty of help on here when you need it.

Philip

[DaveHarris]

Gentlemen,

Thanks for your comments.
The purchase was for a future project, rather than a first attempt.
Given your comments it would seem the best thing to do in respect of a future '9f project' will be to resell the set of wheels and axles I have, and purchase a new 'P4' set for the model at a later date.

Many thanks for your comments

Dave

[Tim V]

This issue has been discussed many times on this forum.

Some say that EM wheels can be used through P4 pointwork.

So far, only vehicles have been fitted with EM wheels, not locos.

We await developments.

[DaveHarris]

I have found the previous discussion thread on this subject since my last post and whilst interesting, I personally find it somewhat confusing(maybe that's just me). As a newby I must say I am somewhat confused regarding the minute differences in dimensions in both clearances through points and the apparent differences(if I understand the discussion correctly) between different wheel manufactures wheel dimensions over the years. Whilst I can understand the basic differences between EM and P4, the apparent critical minute differences in tolerances through point work and wheel dimensions does seem to be very restrictive for little apparent benefit. Also from reading various articles regarding conversion of locomotives that have appeared over the years it seems that some modellers undertake conversions utilising R2R wheels whilst others use wheels manufactured by one or other of those who have come into the wheel market, which leaves me wondering just what can be used and what critical tolerances must be strictly adhered to and which may be modified, apparently at individuals discretion?

It seems to be a case of buying 'made to gauge' wheels, so without wishing to relite the previous thread I will obtain a set of P4 wheels before I think about the project again.

[Paul Willis]

I have found the previous discussion thread on this subject since my last post and whilst interesting, I personally find it somewhat confusing(maybe that's just me). As a newby I must say I am somewhat confused regarding the minute differences in dimensions in both clearances through points and the apparent differences(if I understand the discussion correctly) between different wheel manufactures wheel dimensions over the years. Whilst I can understand the basic differences between EM and P4, the apparent critical minute differences in tolerances through point work and wheel dimensions does seem to be very restrictive for little apparent benefit. Also from reading various articles regarding conversion of locomotives that have appeared over the years it seems that some modellers undertake conversions utilising R2R wheels whilst others use wheels manufactured by one or other of those who have come into the wheel market, which leaves me wondering just what can be used and what critical tolerances must be strictly adhered to and which may be modified, apparently at individuals discretion?

It seems to be a case of buying 'made to gauge' wheels, so without wishing to relite the previous thread I will obtain a set of P4 wheels before I think about the project again.

Hi Dave,

I think that it can be summed up in two simple ways:

- P4 standards are the prototype dimensions, scaled down at 4mm to the foot. They work with the same tolerances as the fullsize ones do. The rail and wheel profile are intended to work together as a "system".

- EM or OO RTR wheels are a compromise, on either size, gauge, profile or all, leading to a different appearance to that of the fullsize prototype. They work because there are increased clearances that allow "space" for them to work together.

Neither of them are "better" in terms of enjoyment, it's just what you choose to do, and what you want to take from your modelling.

For what it's worth, I think that you're right in your decision to not try and compromise by getting EM profile wheels to go through track at P4 standards.

The truly minute differences (such as the top and bottom tolerances on P4 back to back numbers) are there to recognise manufacturing tolerances. As long as you stick to (say) one BTB gauge, rather than using two different ones alternately then you don't have to worry about this...

Hope this helps,
Flymo

[DaveHarris]

Thanks for the clarification Flymo. Having given the matter some more thought before reading your response I had decided to re read the dimensional info and having done so , decided that a 'bright idea' when purchasing the wheel set for the 9f was not such a good one after all! The wheel set will go up for sale and I will obtain the right ones at a later date, meanwhile I will concentrate, as suggested earlier, on getting a successful 0-6-0 chassis running first.

Dave H

[Philip Hall]

Dave,

I don't know where you live, but if you are able to get to the AGM on 21 June there will be many people there who can help with anything you might have to ask. There are three demonstrations dealing with locomotives, either conversions or construction. Having seen the (very comfortable) venue, it will be a very good day out even if the formal business of the AGM doesn't grab you...

Philip

[DaveHarris]

Thanks for the 'plug' about the AGM. It is my intention to attend and also listen and learn from the demonstrators. The combination of layouts demonstrations is a very good one... not sure if there will be time to attend the official AGM business! lol

[Terry Bendall]

not sure if there will be time to attend the official AGM business! lol

Some at least of the demonstrators/layout people will need to be at the official business anyway. Normally that part of the event stops whilst the meeting is on.

Terry Bendall

[Andy W]

I think the KISS theory kicks in here. Keep it simple. I know some people mix standards - like Martin with his EM
wheels, but to start with I think it's advisable to stay wth one set. Otherwise it could be like having a toolset comprising of both imperial and metric items. I understood P4 values when building stock, but it was only when I started building turnouts and track that the whole thing came together. Then I appreciated that not having too much slop in the common crossings/check rail clearances etc. actually made for better running.

[martin goodall]

I think the KISS theory kicks in here. Keep it simple. I know some people mix standards - like Martin with his EM
wheels, but to start with I think it's advisable to stay wth one set. Otherwise it could be like having a toolset comprising of both imperial and metric items. I understood P4 values when building stock, but it was only when I started building turnouts and track that the whole thing came together. Then I appreciated that not having too much slop in the common crossings/check rail clearances etc. actually made for better running.

Actually, mixing them up doesn't seem to make any difference.

I have a tender loco which still has P4 wheels under the loco, but EM wheels under the tender.

I also have at least one wagon with a P4 wheelest at one end and an EM wheelset at the other.

They run perfectly happily on my P4 layout (with no adjustment to the track, other than to ensure that the track gauge is nowhere less than 18.83 mm)

And, contrary to assumptions that are sometimes expressed, you can't detect the difference in the depths of the flanges when the rolling stock is on the track.

[Colin Parks]

Hi Martin,

Reading your post re. using EM wheels on P4 track, is there a particular make of wheel that you use? As a beginner in P4, I am sorely tempted to use EM profile wheels on at least my wagons if it means less/no derailments!

All the best,

Colin

[Ian Everett]

Hi Martin,

Reading your post re. using EM wheels on P4 track, is there a particular make of wheel that you use? As a beginner in P4, I am sorely tempted to use EM profile wheels on at least my wagons if it means less/no derailments!

All the best,

Colin

I too would be interested to know what make. I once had a loco on Gibson's wheels which ran dreadfully, in fits and starts. There seemed to be mechanically and electrically o.k. Eventually I realised I had been wrongly supplied with EM wheels and the flanges were hitting the chairs, making the wheels lose contact with the rails. I was amazed I did not notice the larger flanges and wider treads when I fitted the wheels!

Incidentally Colin Seymour replaced them free of charge without demur. Excellent service, as always (apart from the packing error but everyone - even I - makes mistakes.

Ian

[grovenor-2685]

As a beginner in P4, I am sorely tempted to use EM profile wheels on at least my wagons if it means less/no derailments!

As a beginner I strongly recommend you stick to the P4 standards that have been fully proven and demonstrated to work over the past 47 years on hundreds of layouts, one member going off on a tangent for reasons of his own is, at best, a reason to experiment when you have gained some experience.
Regards

[Philip Hall]

I have seen Martin's Burford Branch and can confirm that his use of EMF wheels does work. It works for him, on his railway, in the way that he does it.

But I must sound a note of caution here. I had an engine through my workshop recently, a conversion of a Bachmann Hall, and once it was running, I thought the wheels were very tight in the four foot, and the wheelset correspondingly was quite stiff, if you understand me, as it rolled along. After a lot of searching, I found that my customer had inadvertently been supplied with one EM wheelset and I hadn't noticed it! What is not appreciated is that if you are to use wheels with thicker and deeper flanges than the P4 standard, ie EMF, then those wheels MUST be absolutely wobble free or the wheelset could have a tendency to hunt. The tolerance that is built into the P4 standards (which essentially means slop in the gauge) gives this degree of leeway. Thicker flanges will remove some of this tolerance. However much you may think that your wheels are completely true and free of wobble, there will always (unless you are very skilled, lucky or both) be a little bit of it. Even if they are absolutely bang on when you put them on, they WILL move, maybe only a tiny bit, over a period of time. This is what the tolerances built into P4 are there for. I believe Martin uses Ultrascale wheels which satisfy those demanding criteria at the outset. But they can still move over time.

I do actually believe that slightly deeper flanges will help with road holding on rigid vehicles on less than perfect track. So I think that a 'deeper' P4 flange is not a bad idea, and I have heard of instances where this has been done and it works. It is important, though, that the thickness of the flange and the root radius must be the same as the P4 standard. Whatever the purists may say, the important bit is the profile of the flange, and a little bit of extra depth will do no harm. As if to prove this point, I recently saw a set of 'Golden Age' Pullmans running, and these had their version of the P4 profile (which seemed to me to be nothing like it, but the flange was approximately the same thickness, with a different root radius and a deeper flange). And they ran very well.

The danger in all these discussions is that the newcomer to P4 might think that the standards are not proven and that people are constantly experimenting to produce a slightly different standard that works better. That is emphatically not the case. As Keith says, P4 standards have been around for nearly 50 years and do work, and work very well indeed; as well if not better than the other 4mm standards. What we are discussing here is further work, by those keen and skilled enough to do it (and who feel the need) to try, possibly, to improve the behaviour of certain types of vehicle (ie generally with no suspension). There is absolutely no case, nor desirability, for the newcomer to try and mix the standards.

So to all of you out there who are just starting in P4 or who are confused, can I earnestly implore you to stick to the established standard. If you do this you will have success. If you want to experiment, that's fine but there is no need, as you start out, to tinker with a system that assuredly works and has done for many years. There are many old hands on here (sorry lads) who have been at this game for more years than they care to mention, so I would go so far as to say that this advice comes with a lot of weight behind it.

Philip

[Terry Bendall]

As a beginner in P4, I am sorely tempted to use EM profile wheels on at least my wagons if it means less/no derailments!

As a beginner I strongly recommend you stick to the P4 standards that have been fully proven and demonstrated to work over the past 47 years on hundreds of layouts,

I would fully support the comments make by Keith and supported by Philip. It is by no means a given that using EM wheels on P4 track will not prevent derailments. One person, out of the hundreds of people who have successfully built layouts using P4 standards throughout, has made it work. Well done him. There is always a reason why things fall off and all that is needed is to find the reason. Soimetimes finding that reason takes a lot of time and effort but it can be done.

Anyone who does decide to use EM wheels on track built to P4 standards will not be modelling in P4 since they would be using a mish mash of different standards. If that is what someone wants to do, then fine, but it won't be P4 modelling.

Terry Bendall

[Noel]

Anyone who does decide to use EM wheels on track built to P4 standards will not be modelling in P4 since they would be using a mish mash of different standards. If that is what someone wants to do, then fine, but it won't be P4 modelling.

Without any wish to provoke contention, Terry, I would suggest that most people would classify by the track gauge of 18.83mm, by which criterion Martin is a P4 modeller, even if he has chosen to diverge from the accepted standards in some respects. So long as what he is doing is clear to others, does it really matter? Don't forget that we are trying, hopefully, "to get it all right", which is about much more than just the wheels. The downside of Martin's variation may appear if he wants to run his stock on someone else's layout. His wheels may not respond as well on track made by someone else, thus losing the theoretical interoperability of the full P4 standards. If his stock stays on his layout then this is not an issue.

Noel

[Paul Townsend]

The downside of Martin's variation may appear if he wants to run his stock on someone else's layout. His wheels may not respond as well on track made by someone else, thus losing the theoretical interoperability of the full P4 standards. If his stock stays on his layout then this is not an issue.

Noel

Some of Martin's EMfd rolling stock visited Highbridge last year and ran OK.

[martin goodall]

Hi Martin,

Reading your post re. using EM wheels on P4 track, is there a particular make of wheel that you use? As a beginner in P4, I am sorely tempted to use EM profile wheels on at least my wagons if it means less/no derailments!

All the best,

Colin

For loco wheels I use Ultrascale EMF profile (with P4 axles). If you give Ultrascale a precise specification of what you want they will supply any required variation. In fairness to them, though, you do need to be precise and accurate in what you order.

For coach and wagon wheels, my favourites are Kean Maygib, but nowadays they only do the all steel disc coach wheels (14mm) and all-steel disc wagon wheels (12mm). These wheels roll superbly. For spoked wagon wheels, it is either Ultrascale or Alan Gibson (the former for preference, but I have found the Gibson wagon wheels satisfactory if carefullly checked for concentricity, etc.). These EM wheels all run very happily on P4 track, so long as it really is P4 (i.e. not less than 18.83mm gauge).

Romford/Markits wheels won't do (too wide), nor will any wheels turned to the RP25 flange profile (the flange is too fat). (This is a pity in both cases, because these wheels are of high quality - it's just that you can't get them to run on P4 track, unlike the wheels listed earlier. Both, of course, will run perfectly well on EM Gauge track.)

Oh, and by the way, I am not trying to "get it all right". I don't give a damn about scale accuracy. My models (both individual models and the layout as a whole) are intended to be no more than 'an artist's impression'. I like my rolling stock to run smoothly, which is why I decided to change over to EM wheels, but if I were starting again, I might well adopt 'finescale' 00 standards (with Code 75 rail). My reason for continuing to work to P4 track standards is that I had already built the layout to these standards, and I can't see any point in trying to emulate the GWR and convert it all to Narrow Gauge.

[Will L]

Without any wish to provoke contention

Think you are doomed to fail there Noel

I would suggest that most people would classify (P4?) by the track gauge of 18.83mm

No sorry, that may be a common misapprehension but all that means is we should seek to gently correct the misunderstandee. P4 is a set of standard that includes 18.83 track but also implies modelling in 4mm scale and using a given set of track and wheel dimension standard that work together. There is another set set called S4 which shares the same gauge track gauge but user an even closer to scale wheel and track standards.

by which criterion Martin is a P4 modeller

Not in my book. There is of course no reason at all why you shouldn't build models to 4mm (or some other) scale on 18.83 gauge tack and fit wheels that don't correspond the the P4 standards. You may do what you wish on your railway, but like the S4 boys it would only be polite to give it a different name.

The problem with Martin's little heresy is that it runs against the grain. In an understandable attempt to persuade the the great under gauged majority that P4 modellers are really nice people, not elitist xenophobes, we have tried to seem welcoming and helpful to all comers and not indulge in criticism of those who approach to life doesn't match what we expect from ourselves. As our politician are currently discovering, you can only take this approach so far. We should not willingly throw out both bathwater and baby and accept as "P4" a compromise that would prevent, among other things, the modelling of a 9F with a correct to scale wheelbase. Which is, I think, where we came in.

[martin goodall]

[........a compromise that would prevent, among other things, the modelling of a 9F with a correct to scale wheelbase.

Hmmm. An interesting point, which I cannot answer from personal experience, as it is very unlikely that a 9F would ever run on the Burford Branch. Previous experience has shown, though, that a number of larger P4 locos built by other people have not succeeded in running on my layout without falling off. This, I suspect, is mainly due to lack of sideplay. (Which rather gives the lie to the idea that P4 rolling stock is or should be capable of running on any P4 layout. I have always believed strongly in 'horses for courses' - rolling stock really needs to be built and/or adjusted to run on a particular layout.)

I would be prepared to hazard a guess, though, that any engine equipped with P4 wheels that can successfully negotiate the track on my layout (minimum radius 3-feet), mostly 6-wheel engines, and certainly nothing larger than a 2-6-0 at the very most, would be equally capable of doing the same if equipped with EMF wheels. The key in both cases (i.e. either P4 or EM) is that there must be plenty of sideplay on the middle axle.

[andrew jukes]

I generally agree with the points made earlier by Keith and Philip, but would like to add some comments about the way the standards have evolved.

If you are a P4 newbie, work to the P4 standards, preferably using a back-to-back gauge measuring 17.75mm. This dimension is at the upper end of the range provided by the P4 standards, as set out by the MRSG in the 1960s. These standards specify a nominal back-to-back of 17.67mm: experience showed that the 'slop' provided by the 17.67mm back-to-back is unnecessarily large and can be a nuisance.

So the basic advice is straightforward - work to the P4 standards, using a Society back-to-back gauge (or an Exactoscale 17.75mm gauge). If you have a back-to-back gauge from another source, best to get it checked. If it's 17.67mm, then it will be OK, but it would be better to use a 17.75mm gauge. This is the position described in Scalefour Digest 1.2 (see page 2), which is essential reading if you want a deeper understanding of the standards and the consequences of deviating from them.

The P4 newbie should stop reading this here as what follows has great potential for adding confusion, but needs to be said partly as a response to Martin's insistent encouragement of the use of EM wheels (for which an official tyre profile is hard to find) on P4 track. What more experienced P4 modellers have often done is move in exactly the opposite direction to that suggested by Martin.

The 'slop' referred to earlier results from the MRSG choosing a 17.67mm back-to-back, compared with the prototype equivalent dimension of 17.87mm. Quite early on, Ray Hammond asked the obvious question - what happens if instead one uses exact scale dimensions throughout? He demonstrated their practicability and christened the resulting standards 'Scalefour' (or S4), which of course made the Society's subsequent adoption of this as the name of the society promoting the use of P4 standards slightly awkward!

The use of the 17.87mm back-to-back dimension has consequences, of course. It makes gauge widening on curves more important, it will show up any under-gauge track (should always be avoided anyway), it is likely to make true running wheels more essential and it requires check and crossing flangeway dimensions that will rule out interworking with stock to P4 standards - but nevertheless, the use of these or at least 'finer than P4' standards is not unusual.

Turning to wheels, for wheels sold as 'to P4 standards', compliance is not universal but at least it is clear what the standard is. The Exactoscale wheels are an example of non-compliance in that they are narrower than the P4 standard of 2.0mm (the flange profile is to the standard but the tread width is reduced). Coach and wagon wheels are 1.67mm wide and loco wheels are 1.83mm wide, both being scaled down prototype measurements. Wheels as narrow as 1.67mm, particularly used with a 17.67mm back-to-back, may risk a slightly bumpier ride at crossings, as continuous support of the wheel is less certain.

The Golden Age Pullmans had wheels that were clearly too deep in the flange and I took this up with Golden Age, providing them with the Digest 1.2 profile drawing and an Exactoscale coach wheel drawing. The Coronation train was duly delivered with wheels that look like P4 wheels (though I haven't done a proper dimensional check). An interesting sequel has been that the train as delivered was very prone to derailment, especially on transition curves. Close inspection revealed bogie attachments that are not only heavily loaded (between 150 and 200gm/bogie) but have a spring underneath the attachment screw, resulting in a bogie very stiff in yaw. The spring was probably there to reduce body wobble but removing them all has resulted in a train that is remarkably derailment-free. As there are other ways of controlling body wobble, the conclusion to draw from this is not that the standards need amending to incorporate deeper flanges but that reliable running comes from adopting an appropriate solution for each aspect of a vehicle's suspension. The same comment could apply to rigid long-wheelbase vehicles where the solution is not deeper flanges to allow wheels to work with a gap between tread and railhead but to have sufficient compliance in the vehicle's suspension to ensure all the wheels are always loaded.

So, in summary, use the P4 standards, preferably using a 17.75mm back-to-back gauge. If you want to deviate from them, understanding Digest 1.2 is the place to start. Experienced modellers (e.g. CLAG) do work to finer standards, but there is no reason to feel any pressure to follow them. Using EM wheels obviously does not fit with a desire to continue to refine the standards and seems likely to introduce additional restrictions or complications whilst any problems their use might be imagined to solve invariably have other, better, solutions. That said, feel free to follow Martin if you wish - the P4 standards are there to provide a consistent framework but their use is not obligatory.

Sorry to have gone on a bit!

Regards

Andrew Jukes

[grovenor-2685]

The Exactoscale wheels are an example of non-compliance in that they are narrower than the P4 standard of 2.0mm

The P4 wheel width has never been specified as 2mm. but as 2.0 mm MAX and 1.85 mm MIN, the max being intended to allow3 for certain wide tyred prototype locos.
So the Exactoscale non-compliance is not quite as much!
The tendency of wheel makers to go with the MAX rather than the MIN is regrettable IMHO.
Keith
PS Pity we don't have US style self checking frogs, would force more consistent wheel widths.