• At what speeds does truck hunting begin?

  • General discussion about railroad operations, related facilities, maps, and other resources.
General discussion about railroad operations, related facilities, maps, and other resources.

Moderator: Robert Paniagua

  by slashmaster
I was watching a pentrex video that showed a unloaded TTX car at the end of a train which was hunting pretty badly. Makes me wonder what speeds wheel hunt starts to become a problem and what kind of cars are more likely to hunt. I get the feeling it's faster than 40 mph and unloaded cars are more likely to hunt?
  by Finch
Hehehh...umm, so in all seriousness what is "truck hunting?"
  by slashmaster
Finch wrote:Hehehh...umm, so in all seriousness what is "truck hunting?"
It is when the flanges of a truck bounce between the rails from side to side, sometimes hard enough to go over the rail.
  by DutchRailnut
truck hunting can occure at any speed, depending on mech condition of truck.
One reason for truck hunting is hollow tread on wheels, the wheels will then kind of like a gutter ball at bowling alley find their tracking.
other reason is if one wheel gets a very small bit smaller than other on same axle, it makes the wheel set veer over to one side.
there are probably at least 4 more reasons for truck hunting.
  by Cowford
There's a great two-part article in Trains Mag that goes into trucks and motion-related issues like hunting: the remarkable three-piece truck by JH Armstrong, July-August 1983. The author also touches on it in his book, The Railroad, What It Is, What It Does.
  by ex Budd man
Hollow tread is probably the #1 cause of hunting trucks, with worn pedistal liners on cast truck frames and poor track as #2 & #3. Defered maintenance on track and trucks are the culprits.
  by BobLI
Is truck hunting related to the harmonic rocking action? Will truck hunting start that?
Or is that just related to the nature of the track sections being 30 something feet on jointed rail?
  by ex Budd man
Harmonic rocking is caused by poor track, unless the right of way is reballasted and the track relaid it will only get worse. Hollow tread will cause hunting even on the best track.
  by DutchRailnut
Harmonic rocking is caused by certain lenght freight cars, rocking on stick(jointed) rail.
The centerpoint of both trucks goes over the two rail joints at same time.
at certain speeds the train gets in harmonics and could actually roll of the tracks or derail.
Believe speed is between 15 and 25 mph, trains with multiple box cars of certain lenght had to accelerate as fast as they could from 10 to 25 mph and not operate at speeds in between 15 and 25 mph.
  by roadster
Harmonic Rock is a condition that can occure in certain cars depending on weight(particularly large covered hoppers loaded with grain). It's not the condition of the rail, it will accure on CWR(although a rough rail section doesn't help.) Accures between 14 mph and 21 mph. Fed. testing in Colorado discovered the condition and found that the weight of these cars, the speed between 14 and 21, combined with the earths rotation(NO BULL) caused "Harmonic" rocking action. It's simular to the natural actions of whirl pools and cyclones which always have a counterclockwise rotation. As engineers, we were trained to avoid operating between these speeds whenever possible. Either get it above 21mph, as soon as safely possible or stay below 14mph.