Why do passenger cars have 6 wheels per track? Are they heaver than a boxcar?
Sleeper
Passengers are more delicate and prone to complaining about rough rides than freight.
For the last 60 years or so, passenger cars have been built with four-wheel trucks. They are known as “lightweight” cars. In the earlier part of the 20th century, “heavyweight” all-steell cars were built. They normally had six-wheel trucks to reduce the per-axle load. Some of the smaller heavyweight cars (say 60-feet long) were converted from four to six-wheel trucks to compensate for the weight involved with the later addition of air conditioning.
Mark
When I eventually get my 12" to the foot passenger car, if it doesn’t already have 6 wheel trucks, I am going to re-equip just for that purpose.
I recently saw a Trains and Locomotives episode that showed a bunch of what looked like older, long heavy weight cars with 4 wheel trucks. 6 wheel Pullman type cars, but with 4 wheel trucks. Did the lines ever redo these cars and change them to 4 wheel trucks? Anyone ever do this to their models?
Passanger cars have six wheels so they can roll on the track.
Well somebody had to say it
Mark has expressed my own notion of this. The term “heavyweight” must have had some meaning in the context of passenger cars at the onset of WWII and earlier. It was that they were truly heavy cars, and when loaded, even heavier. The three axled trucks made for a safer ride in terms of accidents caused by derailments and other problems associated with overloaded rails below them. This was afforded by the weight being distributed over two additional axles per car.
For example, the SP lightweight (4-axle) baggage/coach class 77-CB-1 weighed 114,000 lbs., while the shorter, non-airconditioned heavyweight (6-axle) baggage/coach class 72-CB-2 originally weighed 136,500 lbs.
Mark
A lot of it has to do with weight. Heavyweight cars were called so because…well they were heavy. They traditionally rode on the 6 wheeled trucks because the weight was better distributed over 6 wheels versus 4.
An oddity in the “modern” era of lightweight passenger cars is the Santa Fe Hi-Level diner. Due to the immense weight, this car rode on 6 wheel trucks instead of the normal 4 wheel trucks the other Hi-Levels rode on. Interestingly all Superliners ride on 4 wheel trucks.
The older, ‘heavyweight’ cars were an attempt at making the ride smoother for passengers by increasing the mass of the cars making them less bouncy over the occaisional piece of rotten track.
In fact, in addition to the steel construction these cars had concrete poor into their floor pans to increase the weight.
The 3-axle trucks were needed to distribute the weight over more rail. Beacuse of this it would be very unlikely that a heavyweight car would have its 3-axle trucks replaced with 2-axle trucks (not to say that this never happened though).
Eventually they figured out that tuning spring rates to body mass could result in a good ride but without the need for all that extra weight. Since the extra weight put more wear and tear on the track and required more fuel to hoist it up a grade, and also wore down the brakes more when slowing down (plus was slower to accelerate to speed) light weight cars became popular amoung the railroads whose marketing departments portrayed them as more ‘modern’ to the railroad traveling public so the heavyweights, when not scrapped got relegated to secondary (or tertiary) service.
At least that’s my story (and I’m stickin’ to it - for the moment anyway).
Regards,
Charlie Comstock
As far as the Santa Fe goes, they had some stainless cars (some would call lightweight) with 3 axle trucks. The first that comes to mind was the hi level diner, which was the largest and heaviest dining car built (I am pretty sure it was the heaviest). Then there were the Budd “Big Domes”, which is quite a large car itself. The last ones that come to mind were the Budd built business cars, such as the “Topeka”. They were quite heavy due to all the equipment that made them a self sustaining car (generators and what not).
Hi,
The older cars are often termed “heavyweights” today, as that is exactly what they were, in comparison to the Modern cars of the 50s and forward. Being heavier, they needed that extra axle on each end to spread the weight, and to give a smoother ride.
ENJOY,
Mobilman44
BCSJ:
You’re right about weight distribution and unsprung weight ratio, but I doubt the heavyweight cars were ballasted simple to make them heavy. I don’t recall the concrete floors being that thick, and I think they were more “how to make a quiet, durable floor” than “how to make a car heavier”. I’m pretty sure streamliners had concrete floors, too. (could be wrong, lost my Cyc a while back) I think the extra weight was just an artifact of having all the strength in the underframe, as these cars did, and was something not considered a problem (since it improved the ride) rather than a thing actively sought.
There were some lighter cars made, where the sides did some work. The Erie’s Stillwell cars were this type, and had four wheel trucks.
The principal reason for the development of “heavyweight” cars was to replace wooden cars with all-metal cars to provide more protection of passengers from the danger of collision, fire, and derailment. For example, there were incidents where one car would “telescope” into another car, sort of like a syringe. It took about 40 years to develop and accept the use of lighter metals and improved design for what became “lightweight” metal cars.
Mark
Because wheels work better on steel rail than skids.
RETAININGLY yours
R. T. POTEET