[PRCo] Re: B2 and B3 Trucks

[Fred Schneider]

Correction:  The B3 truck frame can only bend at two corners but that is all
that is needed to allow flexibility at four corners.  (see Jim's statement that
is now in a larger font, below)  Take your thumb and forefinger of each hand
and touch them thumb to thumb, forefinger to forefinger to simulate the box
shape of the frame.   Now notice how you can move them so that you can lift any
one of the four corners independent of the other three. Lifting a wheel at the
fix corner flexes the rubber in two non-fixed corners.   Functionally it is the
same as the B2.  It allows each wheel to apply equal weight to the rail no
matter which corner is higher.   the B3 had frame equalization, i.e. the frame
was allowed to flex.    It wasn't totally common but there are other designs
out there that did the same thing, such as the St. Louis EIB series (you'll
find them on a lot of the older Johnstown cars).
Spring equalization, however, was much more common.  Meaning springs were used
to transmit equal weight on the rail at each wheel  It just takes a lot more
parts to do the same thing

I wish I had all of the comments that went back and forth between the engineers
during the ERPCC and TRC truck design phases.  I suspect that for both the B1,
B2, B2b and B3 designs, minimum weight remained a very important
consideration.  When Philly Suburban asked for a MCB type truck for their 1949
St. Louis cars, they got a PCC style body with a fabulous ride not matter how
rough the track was.  But it had solid steel wheels and a solid steel frame ...
there wasn't an ounce of rubber to keep the high frequency noises from
penetrating the car body.  Noise suppression was not as important on an
interurban railway as it was on city streets.  It was a much heavier design.

Boris's statement about the movements a truck dampened was very good.  The B2
bolster hangs on four swing links.  If centrifugal force tries to push the body
to the outside of a curve, it is lifted up on the swing links and immediately
falls back down to center.  Just picture a beam hung on rods at each end that
can rotate about an axis.   On the B3 the bolster simply moves sideways against
rubber blocks.

The B2 designs were not all alike.  The earliest cars had rubber springs
vulcanized to steel coil springs, eight to a car, two at each end of each
axle.  The were simply following on a practice done for years .. that one type
of spring has different properties than another.  For years the industry used
eliptic springs above coil springs for the same reason.  When World War II came
along, with the attendant rubber shortages, the few new cars came through with
steel coil springs.  Come to the Baltimore Streetcar Museum some day when I'm
there and I'll show you just how rought steel coils alone can be.  When I was
doing the PCC book I came across all sorts of spring drawings for a B2 truck.
I surmised that this was one of those cases where "Its your car.  You're paying
for it.  You can have whatever you want."   The same thing resulted in a
ghastly number of different control versions, mostly just differences in
resistance development.  An engineer from GE told me that there was no valid
reason for all the differences except that GE was in business to make money and
they would make whatever the customer wanted.   Westinghouse wasn't dumb
either.

Remember two that one of the most important things the ERPCC was trying to do
in 1930-1935 was to reduce noise (audible vibrations) as well as rough riding.
They were trying to copy an automobile.  The B1 and B2 trucks gave the quiet
cushioned ride they wanted.  The B3 came about because of a need for a truck
that could ride acceptablly well on Pittsburgh's rough unpaved tracks.  It
should come as no surprise that PRC was behind the B3 because they had more
miles of private right-of-way than any city of that size or larger.  And
therefore the needs were different.

For the model builders out there who question why we must equalize a truck ...
it isn't done in small models such as HO and N gauge because we solve the
problem of uneven track with gigantic flanges.   And model builders need not
worry about comfort to the little people in their cars, nor to problems with
momentary loss of traction to one axle.

I'm thinking through my fingers when I say that there might also have been
fewer problems with the B2 had American's not staggered rail joints.  Had we
put all the rail joints opposite each other like the British do, there would
have been a lot of bounce on rough track but not a lot of sway.

"James B. Holland" wrote:

> All the  *problems*  with B3s are lateral and that is where the B2
> excels.       And I believe a case can be made for the B2 being better
> on rail joints as well since the framing of the B2 allows flexing at All
> 4-corners of the truck, Not Just 2.       Vertical shocks have more room
> for absorption in a B2 and less is transmitted to the bolster and car body.
>
> Going to a system like Shaker is where one can experience an absolutely
> exquisite ride on B2 trucks at Break Neck Speeds.       Have done that
> often.       The Operators Did Not Like the B3-equipped IT cars because
> they bounced considerably  --  never had the opportunity to ride them on
> Shaker but I Did Try!       But I shall dismiss the problem bouncing to
> age and very low maintenance of the springs and spring pots over time
> --  the cars were only for extra usage to fill schedules.       Had they
> been brought up to standards of other Shaker equipment, the ride may
> have been much better and without bounce.
>
> Boston is also an excellent example of using B2s on prw at High
> Speeds.       From an engineering perspective the B3 may be better on
> prw but from the perspective of the rider, I think the B2 would be Just
> As Good and Possibly Better than the B3.
>
> The B3 being stiffer makes the ride harder  --  but don't get me wrong,
> I Favor the B3.
>
> The  BIG  area where B2 fails is that motor vibration is transmitted to
> the car body because the motors use the same springs for shock
> absorption that supports the body.       Riding a B2 at speed on PRCo
> was quite an experience with body panels and windows and all else
> rattling to beat a band and on prw the value of the B2 is masked by the
> motor vibration problems.       But otherwise I found the Actual Ride
> Very Acceptable on B2s on prw  --  we had quite a bit of prw on city
> lines in the Burger.
>
> I am Quite Partial to the  B2B  and  Know its Absolutely Wonderful
> Riding Qualities from experience.       What you say about the B2B being
> between a B2 and B3 may be true from an engineering standpoint, but I
> would Far Rather Ride a  B2B  than Either a B3 or B2.       The B2B
> performance on city prw was excellent  --  would liked to have
> experienced the same on Interurban prw.
>
> How this all affects maintenance may be another story altogether.
>
> Jim__Holland
>
> Boris Cefer wrote:
>
> > No no no! The B-2 is softer vertically (=> bouncing), while the B-3 is
> > in vertical direction stiffer and thus better for prw with rail joints
> > in poor condition (but relatively straight vertically).
> > The B-2 does not transmit lateral irregularities of the track to the
> > body as much as the B-3.
> > As for the B-2b, the truck bolster was laid on the truck frame
> > somewhat higher than on standard B-2, from which I deduce that the
> > riding quality on B-2bs was a transition between B-2 and B-3, but
> > closer to B-2.
> >
> > Boris
> >
> > ----- Original Message -----
> > From: "James B. Holland" <PRCoPCC at P-R-Co.com>
> > To: <pittsburgh-railways at dementia.org>
> > Sent: Thursday, January 27, 2005 7:16 PM
> > Subject: [PRCo] Re: Nosing
> >
> >
> >> You Say It So Nicely!
> >>
> >> So in theory, the B2 would provide a better ride on open prw than the
> >> B3 -- yet theoretically the B3 was designed Just For That kind of
> >> operation!!!!!!!
> >>
> >>
> >> Jim__Holland
> >>
> >>
> >>
> >> Boris Cefer wrote:
> >>
> >>> The problem of B-3 is obvious. The main (coil) springs are higher on
> >>> B-3 than on B-2, which means that the B-2 truck is laterally stiffer
> >>> than B-3. In addition to that, on B-3 trucks the car body rests on
> >>> the truck frame at higher point than on B-2s. The B-2 truck bolster
> >>> design is selfcentering and the weight of the car body drives it to
> >>> its lowest position (the result is automatical dampening). Also the
> >>> tapered tread plus inadequate gauge clearance (bad track) provides
> >>> very good excitation for lateral motions of the truck and whole the
> >>> car body.
> >>>
> >>> Boris
> >>>
> >>> ----- Original Message -----
> >>> From: "James B. Holland" <PRCoPCC at P-R-Co.com>
> >>> To: <pittsburgh-railways at dementia.org>
> >>> Sent: Thursday, January 27, 2005 6:41 AM
> >>> Subject: [PRCo] Re: Nosing
> >>>
> >>>
> >>>> Can be a variety of things.
> >>>>
> >>>> [[Snip]]
> >>>>
> >>>> It needs to be recognized that all *hunting__is__Not__hunting* --
> >>>> the differences in design between the B2 and B3 make for different
> >>>> performance on the same track. There was a portion on Church Street
> >>>> here in SF outbound between 17th and 18th downhill that was quite
> >>>> rough -- a B3 equipped car slammed back and forth sideways while a
> >>>> B2 passed through with barely a disturbance. The Swing link
> >>>> possibly saved sideways motion on the car on a B2 truck as the
> >>>> truck itself moved back and forth on the uneven track -- the bad
> >>>> track was short enough that the motion was not transferred to the
> >>>> body. But the framing of the B3 truck would even get the spring
> >>>> pots moving from side to side which then transferred this motion to
> >>>> the body. The motion ceased when the car passed this brief section
> >>>> of bad track -- that would not happen with hunting -- hunting seems
> >>>> to intensify once begun until measures like purposely slowing are
> >>>> taken to alleviate
> >>>
> > same.
> >
> >>>> This same type of situation is pointed out in the PCC books about
> >>>> Chicago B2s and B3s on rough track -- considerably sideways action
> >>>> to the B3 whereas it is hardly noticeable on the B2.
> >>>>
> >>>> Yes, the B3 was developed for open track but have said before that
> >>>> the B2 did just fine from a ride standpoint -- don't know if it was
> >>>> more problematic for maintenance. Would Dearly Like To Know what a
> >>>> ride on the interurban would be like with the *Original__B2Bs* ----
> >>>> A Truly Superb Ride And The ONLY equipment I have ever ridden that
> >>>> aptly fit the description of *Riding__On__A__Cloud!*
> >>>>
> >>>>
> >>>> Jim__Holland
> >>>