Tapered vs. cylindrical wheel tread on real trains

The "cylindrical" wheel profile, which was sort of "discovered" by a mechanical manager on the Santa Fe railroad, sometime in the early to mid 1940s, when he was riding the Chicago, North Shore & Milwaukee Railroad once. H was amazed at how smooth the North Shore electric cars rode at speeds of 90 MPH or above. He asked the folks in the North Shore Mechanical Dept. about how they were able to maintain such a smooth ride, without all the side-to-side lateral motion. It seems the North Shore had been machining their wheels to a cylindrical tread profile for many, many, many years.

The Santa Fe quickly purchased tooling for turning the wheels on their new EMD passenger "F Units" to the cylindrical tread profile. This quickly eliminated the side-to-side lateral  of the wheel, axle & traction motors, which not only provided an unpleasant ride for the cab crew at speeds above 80 MPH, but also stopped the "pumping action" of the axle end within the oil lubricated roller bearing journal boxes. The "pumping action" was so severe that the oil from the journal boxes would be almost complete "pumped out" on just one from Chicago to Los Angeles.

Thus, the Santa Fe specified all future passenger units be delivered with cylindrical profile wheels, right up and through the Amtrak era. EMD also provided cylindrical profile wheels  to any other railroads which ordered passenger units, such as SDP40 and FP45 units.

Forgot to add:

The Cylindrical profile wheels staid in use on the Santa Fe assigned Amtrak SDP40F units for many many years. As most of the "older/experienced" mechanical managers retired and were replaced by "newer" folks, eventually some cost  cutter wondered why Amtrak was paying Santa Fe "extra fees" for maintaining two different locomotive wheel profile cutting tool sets. Since nobody left working at either Amtrak nor Santa Fe actually knew, the answer of "because that's the way we've always done it." was not acceptable, so the cylindrical cuttes were done away with. Guess what happened next?

The EMD Engineering Dept. had to get involved, again, concerning the "rough riding" complaints, even on the F40PH units. After much research into why the cylindrical wheel tread profile was actually developed and used, a "compromised" wheel profile was developed, between the long standing 1 in 20 taper "freight" profile and the pure cylindrical profile. Thus, the 1 in 40 taper tread profile with a wide flange "uni-point contour"  was developed for all diesel locomotive wheels. Plus, those four axle locomotives assigned to either higher speed freight or passenger service, also have hydraulic dampeners on the bolster to under frame as well as certain journal box to truck frame locations.

Thank you Hot Water, that is most interesting. I'm wondering if tapered wheels wouldn't have been so useful for North Shore because they also had to negotiate very sharp curves in places, including the Chicago Loop. Perhaps tapered tread profiles wear out too fast on sharp curves? And transit systems might not have had canted rails.

Also very interesting that Santa Fe used cylindrical tread for high-speed passenger service. Santa Fe managed to get good service out of the problematic SDP40F units that Amtrak gave up on and I've wondered if tread profiles were a factor. (apparently there were multiple factors with the SDP40F derailment problems although it was never completely explained?)

In theory tapered wheels should track better in most conditions but it also depends on maintaining the wheel profile, and also depends on track conditions. Cylindrical treads would have had more flange wear, I expect. I'm interested to discuss this further ...

Ace posted:

Thank you Hot Water, that is most interesting. I'm wondering if tapered wheels wouldn't have been so useful for North Shore because they also had to negotiate very sharp curves in places, including the Chicago Loop. Perhaps tapered tread profiles wear out too fast on sharp curves? And transit systems might not have had canted rails.

Also very interesting that Santa Fe used cylindrical tread for high-speed passenger service. Santa Fe managed to get good service out of the problematic SDP40F units that Amtrak gave up on and I've wondered if tread profiles were a factor. (apparently there were multiple factors with the SDP40F derailment problems although it was never completely explained?)

Actually it was very definitely "explained", after a number of years of testing on railroads other than the Santa Fe, i.e. those railroads with crap track! The eventual root cause of the Amtrak SDP40F derailments was proven to be that darned lightweight baggage car when coupled directly behind the units. The action of that lightweight car caused the lateral forces to exceed the downward forces, thus the car derailed pulling the rear end of the SDP40F with it, on very slight curves (2 degree). Thus, the mechanical forces term "L over V" became a watch term formula for the american railroad industry. Per obvious "political reasons" Amtrak was in no real position to be telling the management of U.S. railroads that; 1) their track structure wasn't good enough to support big 398,000+ pound passenger units, and 2) those poorly maintained lightweight baggage cars were a MAJOR problem.

Amtrak took the easy way out, and "traded-in" SDP40F units on short, lighter weight F40PH units.

In theory tapered wheels should track better in most conditions but it also depends on maintaining the wheel profile,

Actually no, because with the 1 in 20 tapered profile, even when perfectly new, the wheels are constantly trying to "center" them selves, at train speeds above 65 MPH. As you pointed out earlier, the rails are "canted" inwards so as to match that original 1 in 20 wheel tread taper, thus allowing trouble free operation on any and all curved track. However, at high speeds the wheels constantly hunt backhand fourth, trying to center themselves. The "old fashioned" cylindrical tread profile eliminated that wheel hunting action back and fourth.

and also depends on track conditions. Cylindrical treads would have had more flange wear, I expect. I'm interested to discuss this further ...

Really interesting thread!  Jack, do you know if the GN SDP40 and SDP45 passenger units had the cylindrical tread profile?  I don't believe GN trains ever exceeded 79 MPH (legally) but I could be mistaken about that... 

The GN Man posted:

Really interesting thread!  Jack, do you know if the GN SDP40 and SDP45 passenger units had the cylindrical tread profile?  I don't believe GN trains ever exceeded 79 MPH (legally) but I could be mistaken about that... 

I'm pretty sure that the GN did NOT request, nor receive< the cylindrical profile wheels, as they would have no way to maintain a different tread profile whiteout purchasing/owning different wheel truing machine cutters. I remember delivering new SDP45 units to the GN, in 1967 and nothing was said about the wheels from the guys in the Mechanical Dept. there in Minneapolis.

Now, where there different track and rail profiles (other than rail weight) as well as the wheels of locomotives?  There was an article in TRAINS about the T&P 2-10-4's.  In it there was mention that engines reacted on the SP trackage rights in west Texas differently because the SP track profile was different.  Am I remembering the theme of the article correctly?  

This article has some interesting discussion of tapered wheel treads and tracking stability:

https://en.wikipedia.org/wiki/Adhesion_railway

... It should be noted that some railway systems employ a flat wheel and track profile, relying on cant [curve superelevation] alone to reduce/eliminate flange contact...

Now I'm trying to figure out if steam locomotives used tapered wheel treads - or not?

Ace posted:

This article has some interesting discussion of tapered wheel treads and tracking stability:

https://en.wikipedia.org/wiki/Adhesion_railway

... It should be noted that some railway systems employ a flat wheel and track profile, relying on cant [curve superelevation] alone to reduce/eliminate flange contact...

Now I'm trying to figure out if steam locomotives used tapered wheel treads - or not?

 

Steam locomotives have used the standard 1 in 20 taper since the early 1900s.

Tapered wheel thread on cast and forged wheels, freight cars, locomotives and passenger car mu's and trailers. Type in tapered railroad wheel thread do a search click on images on the web and this taper of the wheel cross section will be seen. This taper has an affect the truck dynamic performance, wheel set tracking and hunting, there are other factors that also have an influence on hunting.

In the early 1970's, did Amtrak ever consider the GP40P-2?  The GP40P worked on commuter work on CNJ, and SP also had good service with the Dash 2 product?

Dominic Mazoch posted:

In the early 1970's, did Amtrak ever consider the GP40P-2?  

No. A full width carbody design was required for the service needs on the Santa Fe.

The GP40P worked on commuter work on CNJ, and SP also had good service with the Dash 2 product?

Commuter train service is a LOT different than Chicago to Los Angeles!