New Sound Dampening System at Ashmont

One of the few places that got rid of resilient wheels for the noisier all steel wheels.

The noise difference between resilient wheels apposed to solid wheels is quite minor (hang out at Boylston St. for a while and listen to how quiet those resilient wheels aren't). The problem is the two wheels on an axle are solidly attached, while the distance each wheel travels through a curve differs. This means that one wheel is not spinning at the same speed that the rail is passing under it. The conical shape of the wheels does assist with this issue, but not enough to eliminate the sound. Another reason, is that the wheels aren't moving absolutely forward, they are bound to be in line with the truck's other axle, meaning they cannot remain parallel to the rail when turning. The point of all this is that there is no way to avoid friction between the rail and the wheel in a curve or loop, which is what causes the noise. A wheel's resiliency may give the flexibility to cut down on some of the friction, but not enough to eliminate the noise.

The difference between noise level of solid steel and resilient wheels for squeal reduction varies from 0 db up to 30 db(depending on the make of wheel), according to Transit Cooperative Research Program Report 23. A 10 db reduction appears to the ear to be half as loud.

When (and why) did the MBTA change from resilient wheels to all-steel wheels? Also, what is a resilient wheel?

Resilient wheels have rubber pads sandwiched between the center and the outer rim. They produce less noise than solid steel wheels.

I think the T ditched them on the PCCs for maintenance reasons (the T was incredibly cheap back in the '60s). It's unknown why they haven't switched back, since all newer Green Line equipment has had resilient wheels and the PCCs have probably been due for wheelset replacements at some point anyway.

obienick wrote:When (and why) did the MBTA change from resilient wheels to all-steel wheels? Also, what is a resilient wheel?

The MBTA started replacement of resilient wheel sets in 1964 and completed the process by 1974, the main reasoning was cost. A resilient wheel can be thought of as a automobile wheel/tire. You have the metal center wheel and a metal tire between them is a rubber gasket. The wear & tear items being the metal tire and the rubber gasket, which if I am not mistaken you needed a special machine/process for replacing those items. With the solid wheel set the special machine/process is eliminated. The problem is that noise level is increased and the ride is harder. Also remember by 1964 streetcar service is just about what we see today, less Watertown and Arborway, and not the multitude of streetcars lines of the 40s so people living by the tracks were diminished so who cares about noise. Plus the switch to a government agency.

Several posts back by jwhite07 has a link to Penn Machine and shows pictures and cross sections of resilient wheels.

JoeD

One reason is that the T has stated in a past news article that they have plenty of spare steel wheels for the PCCs and therefore don't want to go back to resilient, and the maintenance issues cited.
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http://www.metro.us/boston/local/articl ... g-trolleys

Boston Metro mini article on wheel noise.

So how does this sprinkler system work when the temperature drops below freezing? Assuming the water has enough pressure to keep it liquid until it hits the rail, will it end up as a slippery glaze of ice, or is there some kind of antifreeze added?

typesix wrote:http://www.metro.us/boston/local/articl ... g-trolleys

Boston Metro mini article on wheel noise.

Does that mean they're going back to resilient wheels?

No, it means the wheels will have sound dampers added to them, like the new Blue cars. There will be no cushioning of bumps or jolts from the rail.

If you have noticed, there were numerous PCC accidents whereby the car not only left the rails, but left the upright as well- the cars are on their sides. I have a sneaking suspicion that engineers realized that the original PCC design of the resilient wheel brought a new dynamic to lateral and possibly vertical movement in the cars. I recall the difference vividly in cars with resilient and super-resilient wheels compared to the solid steel varieties. The wafered wheels caused a rythmic side to side sway in the cars that would build up as the speed increased. I believe that it is very possible that this new movement increased the centripetal and centrifugal forces (inward and outward circular forces) that the cars were not designed for, causing them to be unstable, particularly if broadsided by another force acting in the same direction as one of these extra forces. I also think that it is very possible that the streetcar industry, already keenly aware that GM and friends would have loved such a safety issue to arise, kept this "top secret #1", and quietly reverted to solid wheels throughout almost the entire U.S. PCC network. As evidence as to what I suspect, I point to the fact that maintenance on the wheels was a very simple procedure using a hydraulic pump, that such maintenance could be handled routinely at lighter car shops, that the resilient wheels produced a very comfortable ride, yet most of the U.S. companies with PCC's converted (at some expense) to solid wheels.

Here's a cross-sectional diagram of a super-resilient wheel assembly.

Not to say that you're wrong, but most of the images of other systems' PCC streetcars seem to show them with the resilient wheels, even in later years. For example, there are Pittsburgh cars with the resilients and they had some fairly rough track. NJT also still had resilients on their cars according to this report on wheel noise reduction: http://onlinepubs.trb.org/onlinepubs/tc ... rpt_67.pdf. The T got rid of most of the resilient wheels in the 1960s, with a few cars riding around on one truck with resilients till the late 1970s. I read that it was rumored that the nuts on the wheels tended to work loose because of Riverside's rough track and that was one reason for replacing the wheels, also, the rubber may have worn out much faster because of the track and the rubber being in shear instead of the compression of modern resilients . It may have been a maintenance issue for the T, officially disguised as a way to improve ride quality. Supposedly, some transit agencies maintenance workers have also stated that they think the resilient wheels also reduce truck wear because of the rubber isolation, but don't have any proof.

Yup- Just like I don't have any proof, all theories accepted and deemed possible, it's just as I state, a "suspicion" of mine, but one which I believe has a high chance of being "on target". San Francisco kept their resilient wheels, Chicago and Boston changed them over to the solid variety. Most European PCC's kept the resilient design. I think that it may have to do with the dynamic of the tracks also, with flat, even track not causing the undulations in the wheels that irregular track does. Not to beat this to death as it really has nothing to do with this thread topic, but while having seen many pictures of PCC accidents pre-change-over that have the car on it's side, I can't recall seeing one post-change-over that way. (??)