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Why do metal wheels perform better than plastic?

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Why do metal wheels perform better than plastic?
Posted by John-NYBW on Sunday, October 31, 2021 10:17 AM

Based on experience, there's no doubt in my mind that they do. They seem to roll much more freely. I've never understood why. It seems to me the important factor would be the friction between the axle ends and the pockets in the truck. I don't know why that would be different if there are metal or plastic wheels on the axles. 

Whenever I put a new piece of rolling stock on the layout, I do two things. I put KD 148 whisker couplers on and replace the plastic wheels with metal if they don't already have them. The replacement wheels definitely make them roll better even if I don't know why. 

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Posted by tstage on Sunday, October 31, 2021 10:41 AM

John,

Here's a couple of possible reasons...

  • The overall construction of metal wheels makes them more rigid; allowing them to ride more consistently on top of the rails than flexible plastic wheels
  • Metal wheels add weight that aid in rolling inertia.

Tom

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Posted by dti406 on Sunday, October 31, 2021 11:52 AM

The major problem with derlin wheels is they pick up oil and dirt then spread it all over the layout. Nickle silver wheels usually do not do that the wheels and the layout keep clean, it is the reason our club bans plastic wheeled cars.

 

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Posted by ricktrains4824 on Sunday, October 31, 2021 12:00 PM

Scaled down, same reason the real railroads use metal wheels - Contact area. Smaller contact area means less friction. 

And as Rick J mentions, the "crud" that plastic wheelsets gather (and spread) affects that contact area. More build-up of crud on the wheels makes a bigger contact area, making more friction. (And more crud on rails makes less power transmision ability.)

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Posted by willy6 on Sunday, October 31, 2021 12:11 PM

I agree 100% about the metal wheels usage. Also, I am learning metal wheels performance can decrease or increase based on the truck in which they are installed.

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Posted by Pruitt on Sunday, October 31, 2021 12:12 PM

A lot of it is angular momentum. While total angular momentum isn't much on scale wheels, the angular momentum of metal wheels is still much greater than plastic, because of the difference in density of the materials.

That gives metal wheels more ability to roll past a brief increase in friction that might be caused by dust in the bearings, and also a bit more ability to roll over irregularities in the track that might stop or significantly slow plastic wheels.

Also, many brands of metal wheels are turned rather than just cast, making them much more consistently round than their plastic counterparts, so the car's linear momentum is dissipated much more evenly than is a car's that has plastic wheelsets.

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Posted by peahrens on Sunday, October 31, 2021 12:37 PM

My guess is that the largest part of improvement (even with clean plastic wheels) is a much lower friction factor of the metal rim to rail vs. the plastic rim to rail.  I believe that a push of a plastic wheeled truck along a straight piece of track will cause it to roll considerably less far than a similar truck with metal wheels in almost all cases.  

The frictional force against movement is a combination of the friction factor and downward weight.  If the steel wheeled truck goes farther, with the same initial push (on flat track) than the plastic wheeled truck, then the friction factor improvement is greater than the (potentially negative) effect of the additional downward weight on the wheel to rail friction force.   

There is also the difference in the amount of axle tip friction in the axle cone, but my guess is that is a secondary effect, assuming the axle lengths are appropriate (in particular, not too long and tight) in both cases.

That's my story but if missing something, I'll be glad to not stick to it.

Paul

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Posted by doctorwayne on Sunday, October 31, 2021 1:26 PM

While I have some cars that came with metal wheels, I much prefer plastic, although in most cases, I don't change-out the metal ones for plastic.


I would agree with the superior rolling qualities of many metal wheels, but not all of them.
As for plastic wheels, I have purchased pre-owned rolling stock with crud on the plastic wheels, but it's easy enough to remove.  As for crud on the wheel treads of my own rolling stock, I've yet to see any in the 30 years-or-so that my layout's been in operation.

Rolling qualities aren't much of a concern for me, as all of my locomotives have "tonnage ratings", which allows me to assign the proper loco(s) to each train with consideration to the many grades they're likely to encounter.

I generally don't clean track, either, unless it's just been ballasted, as excess glue does need to be removed from the rails. 

I attribute the low maintenance to good housekeeping in the layout room.

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Posted by JDawg on Sunday, October 31, 2021 4:11 PM

Confused

I'm torn on plastic vs metal. Metal wheels oftentimes do perform better, but they make a lot of noise. Plastic wheels don't make the noise, but they can and do warp, leading to poor performance. So the debate continues.

I guess for me, I don't swap metal for that plastic, and I don't swap plastic for metal. I will sometimes replace stock plastic wheelsets with a higher grade plastic version if they are warped. Accurail had a problem with warped wheelsets for a while. 3/4 sets would be fine, but the 4th was really nasty. Huh?

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Posted by tstage on Sunday, October 31, 2021 4:23 PM

JDawg
Metal wheels oftentimes do perform better, but they make a lot of noise.

So do the 1:1 wheels. Smile, Wink & Grin  I actually like the sound - especially the clickity-clack, as the metal wheel sets ride over the track joints.  Makes it more real for me.

So, yea - I switch out all my plastic wheel sets for metal ones.

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Posted by JDawg on Sunday, October 31, 2021 5:55 PM

tstage

 

 
JDawg
Metal wheels oftentimes do perform better, but they make a lot of noise.

 

So do the 1:1 wheels. Smile, Wink & Grin  I actually like the sound - especially the clickity-clack, as the metal wheel sets ride over the track joints.  Makes it more real for me.

So, yea - I switch out all my plastic wheel sets for metal ones.

Tom

 

I agree that the metal wheels make a pleasing noise at low to mid speeds, but once you crank it up a bit the racket becomes unbearable for me, personally. I guess that point is when I can't hear the loco sounds anymore.Dots - SignLaugh

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Posted by PM Railfan on Monday, November 1, 2021 4:05 AM

I havent had a layout since before this era of metal wheels came about in the hobby. Most of my rolling stock is all original. I do recognize the superior performance of the metal wheel sets over plastic and am still interested in reading the posts relaying experience with said wheelsets vs plastic. 

What got me about this thread was Tom mentioning the 'clickety-clack'. Now that i do remember and did like. Hadnt really thought about it when thinking of changing out to metal wheels, but now im looking forward to a louder than before rolling sound.

Put me down as a wheel changer - I will be going from plastic to metal. More for performance and look than sound. Thats the icing.

 

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Posted by doctorwayne on Monday, November 1, 2021 9:40 AM

PM Railfan
...What got me about this thread was Tom mentioning the 'clickety-clack'. Now that i do remember and did like. Hadnt really thought about it when thinking of changing out to metal wheels, but now im looking forward to a louder than before rolling sound...

The din of HO scale metal wheels is nowhere near similar to that of the wheels on a real train, and I'm not speaking of volume, but rather of the type of sounds generated. 
If you don't believe that, it's time you got out for a little railfanning.

If you want the clickety-clack of wheels going over the rail joints (not all that common on the real ones nowadays), use a razor saw to make a slight cut every 39' (HO), staggered, in the top of the rails.

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Posted by richhotrain on Monday, November 1, 2021 9:48 AM

doctorwayne

If you want the clickety-clack of wheels going over the rail joints (not all that common on the real ones nowadays), use a razor saw to make a slight cut every 39' (HO), staggered, in the top of the rails. 

LOL. You beat me to it. My late brother-in-law did that on his DC layout.

Rich

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Posted by Doughless on Tuesday, November 2, 2021 8:03 AM

As someone who is an outlier in this forum, I run 8 car trains slowly and switch the cars, free rolling cars hinder performance.

Also, locomotive pulling power is nearly irrelevant.

As long as the cars roll, the layout works.  It works best when the cars do not roll well.  

I'm concerned about free stopping, not free rolling.

As far as metal or plastic, it really doesn't matter.  

The noise I hear from metal wheels is not a clicky clack, more like a steady drone like ball bearings rolling on glass.  Not realistic at all.  I prefer the silence of plastic.

Most of my rolling stock is newer product that come with metal wheels.  I'll probably take the trucks off and treat the axle cone tips with somehting to make the cars more free stopping and enhance their sit-tightedness when being coupled.

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Posted by John-NYBW on Tuesday, November 2, 2021 8:15 AM

Doughless

The noise I hear from metal wheels is not a clicky clack, more like a steady drone like ball bearings rolling on glass.  Not realistic at all.  I prefer the silence of plastic.

 

 
Maybe it is due to my mild hearing loss but I have never noticed a clickety-clack or any other noise coming from the wheels of my rolling stock. Now that I have been made aware of it, it'll probably drive me crazy. 
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Posted by John-NYBW on Tuesday, November 2, 2021 8:26 AM

There's one other factor that has nothing to do with the wheels. I said earlier I put KD 148 couplers and metal wheels on all my rolling stock. If the trucks are plastic, I also use a reaming tool I bought from Micro-Mark that fits in the truck and ream out the pockets that the axle tips set in. This also helps improve the free rolling of the wheelsets. My layout has a 1.5% grade about 20 ft. long between two of my towns. To test the cars out, I give a gentle nudge from the top of the grade and the car should reach the depot in the next town which is on the flat. If the cars are really free rolling, they will go a yard or two past the depot but they need to at least reach the depot for me to be satisfied. 

As another poster just pointed out, free rolling isn't for everybody but I prefer it for my rolling stock. 

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Posted by deckroid on Tuesday, November 2, 2021 8:55 AM

I have both good and bad wheel sets be they metal or plastic. Not to throw anyone under the bus... Bachmann... but when I first had Annie and Clarabel running, I had to play with the wheels on both of them to get them free spinning. Likewise, some Athern plastic wheels needed some help.

As for crud, I am with Wayne. I think the dust, hair extra bit of ballast or foam can be attributed to Maintenance-Of-Way cleaning.

And who DOESN'T like clickity-clack? I think that is one of the top 5 reasons I want a layout again... the "local" club only meets on Wednesdays and, like coffee, my addiction needs feeding. Smile

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Posted by Doughless on Tuesday, November 2, 2021 12:57 PM

John-NYBW

 

 
Doughless

The noise I hear from metal wheels is not a clicky clack, more like a steady drone like ball bearings rolling on glass.  Not realistic at all.  I prefer the silence of plastic.

 

 

 
Maybe it is due to my mild hearing loss but I have never noticed a clickety-clack or any other noise coming from the wheels of my rolling stock. Now that I have been made aware of it, it'll probably drive me crazy. 
 

Yeah, its not a big deal. When I turn up the speed I can hear the metal wheels hit against the rail joints, but outside of that noise, I hear the wheels glide on the steel rails like ball bearings rolling on glass.  Pleasant, but not very realistic, IMO.

I keep the speed low so noise isn't really an issue for me either. 

 

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Posted by MisterBeasley on Tuesday, November 2, 2021 1:43 PM

I've replaced all my plastic wheelsets with metal.  I find I don't need as much motive power and I can run longer trains.  For some older rolling stock I needed to replace the trucks, too.  I have a dozen or so Tyco operating hoppers that had metal trucks which could not be taken apart, so they went into the trash.

I am pretty fussy about keeping my track level, so I don't have much trouble with rolling stock that won't stay put.

It takes an iron man to play with a toy iron horse. 

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Posted by Doughless on Tuesday, November 2, 2021 5:11 PM

Industrial spurs that transistion from roadbed to none have grades.  A three car spot sometimes has the last car on a slight slope and that's enough to push the other cars off their mark if they are too free rolling.  

But an overall point given the type of layout, for a switching layout that has shortish trains and slow speeds, there is no reason to put a lot of effort into making cars free rolling, or see a difference in metal vs plastic performance, IMO.

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Posted by 1arfarf3 on Wednesday, November 3, 2021 11:07 AM

I use the truck tuner from Micro Mark to clean the pockets. But don't be to aggressive. Its very sharp and you will take plastic out also thus risk enlarging the pockets.

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Posted by John-NYBW on Wednesday, November 3, 2021 11:30 AM

1arfarf3

I use the truck tuner from Micro Mark to clean the pockets. But don't be to aggressive. Its very sharp and you will take plastic out also thus risk enlarging the pockets.

 

I thought taking out the plastic was the idea behind the tool. According to the listing on the Micro-Mark website, the tool is intended to reshape the bearings and clean out grime. I don't know how it could reshape the bearing without removing some plastic. Whenever I use it I always take some plastic shavings out.  

HO Truck Tuner (micromark.com)

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Posted by doctorwayne on Wednesday, November 3, 2021 5:53 PM

Doughless
But an overall point given the type of layout, for a switching layout that has shortish trains and slow speeds, there is no reason to put a lot of effort into making cars free rolling, or see a difference in metal vs plastic performance

I agree, Douglas.  Even though my layout's more than just a switching layout, there's not much in the way of high speeds, and most trains are less than 20 cars, due to the abundance of grades.  If a train needs an additional locomotive, there are lots available.

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Posted by CGW103 on Wednesday, November 3, 2021 7:47 PM

Nope not a reamer. I used reamers daily for 40 years. I know reamers. It is closest to a center drill that one uses on a lathe.

 

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Posted by SeeYou190 on Wednesday, November 3, 2021 10:00 PM

Asolutely NOT a reamer.

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Posted by CGW103 on Thursday, November 4, 2021 8:43 AM

Rolls his eyes.

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Posted by SeeYou190 on Thursday, November 4, 2021 6:50 PM

I guess being a factory certified Field & Alternative Repair machinist for three different engine manufacters, and then being qualified to certify new machinists by one of the largest engine manufacturers in the world makes me a "Self Proclaimed Machinist!"

Laugh

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Posted by John-NYBW on Friday, November 5, 2021 10:11 AM

Rather than argue about the defintion of the verb ream, why don't we turn to the dictionary defintion:

ream

 verb
reamedreamingreams

Definition of ream (Entry 2 of 2)

transitive verb

1ato widen the opening of (a hole) COUNTERSINK
b(1)to enlarge, shape, or smooth out (a hole) with a reamer
(2)to enlarge the bore of (something, such as a gun) in this way
cto remove by reaming

Strictly speaking, the Micro-Mark truck tuner is not enlarging or shaping a hole although what it is doing with the bearing is very similar so it doesn't seem like much of a stretch to call it reaming.

 
 
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Posted by Overmod on Friday, November 5, 2021 11:44 AM

The Scientific Models truck tuner isn't a 'reamer' in the usual machining sense.  This is what a 0-14mm reamer looks like:

 Note the angle involved, and how the blades are intended to act.

The truck tool is described as a 'cutter' and I think the point to remember is that it is used the same as a reamer, with a light touch to dress the final form and surface finish of the 60-degree recess right up close to its apex.  The edge here performs the same slight removal and surface-finish improvement as a reamer when 'operated' correctly; this is also why the opposite locating rnd of the tool is machined as a point and not another cutter -- it would be difficult to control the action of two edges simultaneously, particularly in relatively soft material.

As noted by at least one excellent 'article' discussion here, the 'point' of the 50-degree axle cone does not seat in the apex of the 60-degree bearing, and indeed you will note that the very tip of the truck tuner is slightly rounded (very slightly, but visibly so) so a different tool would be needed for truly-accurate point bearing finishing... incidentally that would obviate most if not all actual need to dress the face of the 60-degree-recess.  Assuming anyone in model railroading would have a need for point-bearing in practice.

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