wheel axle length ?

[gregc]

I only recently noticed that ReBoxx wheels come in different lengths.   I didn't realize that wheels come in different lengths and wondered if replacing plastic wheels with metal wheels (Intermountain) all of one length is best.

I ended up replacing plastic Accurail wheels (0.978" and 0.988") with Intermountain wheels (1.0").   But I noticed that even the Intermountain wheels fit loosely (~0.03" = 1/32") in the trucks.

Since ReBoxx sells wheels from 0.95" to 1.07", in most cases in steps of 0.005", they obviously think it matters.

I realize that the conical axle ends self-center themselves.   Would using wheels that fit more snugly length-wise be better?  better in what way?  how snugly?

[peahrens]

I went through the same curiosity earlier.  I like building kit freight cars and decided to go with metal (33" on my non-modern cars) wheelsets also.  Lots of folks seemed to like, in general, the Intermountain and/or Proto 2000, so i got some of each.  I wanted the ribbed back P2Ks for some older cars (though I never take time to notice).  Also got a digital caliper from MicroMart (Harbor freight has a similar one).  And encountered the Reboxx site with the various specific axle length offerings and original axle specs.  

I then just experimented.  I always reamed the trucks with the MicroMark truck tuner first.  Then ran the original axles down my 2.4% grade and observed the rollout.  Measured the original axles, of course, Accurails around 0.095", Athearn blue box around 1.025", Bowser around 1.024".  The Intermountains I measured around 1.002", the P2K ribbed back around 1.018" and flat back around 1.015".

While the performance (rollout) of the originals varied, the replacements always rolled much better.  Like you, I expected that on the Athearn and Bowser, the IM's, not as close a fit to the original (i.e., looser), would not give the better performance.  But in most cases even for the Accurails the IMs did a bit better, though the P2Ks were technically a bit long vs. the originals.  But I don't know how much "play" the originals had which would help accommodate the longer P2Ks.  So I in general developed the approach of using IMs as my standard.  On the older cars, I used the P2K ribbed backs if they rolled nearly as well as the IMs, otherwise just used the IMs.

Two other points (I believe people have commented on these issues before but I don't recall the specifics):

a) I believe the IM and P2Ks wheel treads are different in terms of metal and/or machining.   That also affects rolling resistance and, I would think, potential for dirt accumulation.  Not sure which has any advantages there, if enough to matter.

b) I did also wonder whether relatively loose (shorter) axle length would be a negative.  That is, if the original and/or replacement fit with just a tad of looseness in the end of the truck cone, is that really better that a shorter axle point riding further down from the end of the cone.  It occurs to me that if the cone angle and axle end angle match perfectly, it doesn't matter very much if the shorter axle end is riding down a bit from the center of the cone, though there would be a slight change of contact area.  Haven't quite figured out (I think there's a theoretical effect) whether that's enough to make a noticeable performance difference, nor whether the axle point riding further down on the cone causes an undesireable wear pattern (a vertical slot) that eventually results in measureable performance deterioration (I doubt it). 

Anyhow, that's where I came down.  I didn't conclude I needed precisely "matched" axle lengths, and my testing would toss out any too long substitutions that resulted in poor initial performance.

[gregc]

Paul

thanks for the comprehensive response.   I think you addressed some issues that hadn't occurred to me.  but is rolling friction the only real issue?

As I read your response it occured to me that the play it not only laterally but longitudinally (parallel to the track) as well.   When the wheel slides sideways it is firmly planted into the code of the truck on the one side and very loose on the opposite side, allowing that wheel to move forward or rearward and sit at an angle on the track.   I wonder if this angled wheel is more likely to pick a turnout point resulting in a derailment.

again, why does Reboxx sell a product we presumably don't need?

[rrinker]

 Some make of trucks are so much narrower that the standard length IM or P2K wheels just won't fit. I have a couple of cabooses that are actually the Life Like train set versions with added detail and correct paint and lettering (I think if you keep going back these were the Varney Northeast cabooses). They have very narrow truck spacing and the only thing that fits are some of the smaller length Reboxx wheels. The P2K version of this caboose is the same way, although since they have metal wheels already I don't bother changing them out.

 If the axle is so long in puts tension on the sideframes, the truck is not going to roll worth anything. The more out of spec it gets, you hit a point like the LL caboose where you can;t bend the sideframe enough to even get the wheelset in. So as you get too long in axle length, it's just a friction issue up to a point when it becomes a mechanical fit issue.

 If the axle is short, it won't ride in the middle of the conical section of the bearing surface. Sitting still, this will tend to lower the car slightly. Running, since the fit is loose, the truck can wander side to side, or maybe it will catch slightly and rock side to side, rocking the car. Or just run skewed - which is just asking for derailments. Obviously taken to extremes, the wheelset would just fall out when you picked up the car.

 That said, the majority of my rolling stock is Athearn and Accurail, and the standrd P2K axle length fits them just fine. Plenty of my cars have racked up lots of mileage with no evidence of abnormal wear in the trucks. Outside of the LL caboose, everything else I have came with metal wheels (a few Kadee cars, my stack of P2K tank car kits, Branchline kits, etc) and as long as they are in proper gauge and not damaged I generally see no reason to replace one metal wheelset with another. I suspect some other older stuff like Tyco and AHM will have different requirements like the LL cars.

                    --Randy