I have had four BEEPs, by four different makers.
None of them came with two rubber tires on them. They all had just one. And, two of them would not run reliably over switches until I removed the traction tire at John's suggestion. Now they have no problems.
Do not ignore two other possible causes for your problems:
The BEEP has a really short length. Accordingly, if you have a traction tire on it, and it goes around a curve where the track is not totally level, and the traction tire is running on the outside of the curve, it is possible that the inner drive wheel with no traction tire is lifting/tilting off of the track, and getting no traction. It only takes the smallest hint of lift to do this. And, it is why my two of my BEEPS would not run across a Lionel 022 turnout without stalling dead on the turnout. Removing the traction tire removes the canting among all four wheels and keeps it level on the track. And I can pull 8 average weight cars with no problems.
Second, all BEEPs have super stiff couplers, and there is not enough room in the surrounding pilot to let them swing back and forth as much as they need to on 031 or 027 curves. Normally, this causes the first car to be forced off the track with a front truck derailment. I think it is possible, though, that if you have a heavy enough train of cars, then the result may be that the stiff coupler actually tries to force the BEEP wheels off the track. A tiny little bit of lift will stall them out.
You have to aggressively cut back the inside edges of the pilot about a little more than an eighth of an inch to get enough swing room, and maybe even a little more. I used a nylon reinforced dremel cutting wheel.
The super stiff coupler springs never softened up in any of my BEEPS, despite using them for six months with long strings of cars and always parking them on a curved section.
I finally got mad and flipped the BEEP over, slipped a small slotted screwdriver onto the top edge of the spring arm that sticks outward from each side of the couple, and aggressively bent it backwards (inwards) another 15 to 20 degrees. You have to do this on each side. That spring is so strong that you really have to put pressure on it and hold it for about 15 seconds to get it to bend backwards and stay there. ( I did one BEEP by putting my index fingers on both springs at once and pulling backwards, and my fingers started to bleed!) In my opinion, it was "criminally insane" for the makers to use such stiff springs. :-)
After this, my coupler would never return to dead center again, but it was close enough. It was softer and mushier. But I never had another problem from those terrible springs or derailments.
If you are into lots of switching, coupling and uncoupling, then do the bending in stages, maybe 5 degrees at a time, testing after each set of bends, to make sure you can still do all of that stuff.
Here is another critical thing to know about the BEEPS, the ones that were made prior to mid-2015 have poor circuit boards and really slow motors. The ones made after this were greatly improved by RMT, for good reason.
You can tell if you have an older one by looking at the railings. All of the ones with the bright "chrome painted" handrailings are the old ones. All of the ones with handrails in different painted colors are the newer ones. The Halloween BEEPs are all good once. I bought one and simply pulled the shell off of it and put a shell on that I wanted. All of the shells fit, and they are easy to find new and used on the web.
The first BEEP I bought was an old one, and I was so disappointed in its slow speed, that I immediately sent it back! The upgraded ones run significantly faster. Buying a used BEEP that looks like a new one can be tricky, because some crooked sellers take an old BEEP and just put a newer shell on it.
About a year ago, I posted on this BOARD a list published by RMT in 2015 when they made a press release of the new improved circuit boards etc. Search under BEEPs here and you should easily find it. If you can't, then e-mail me and I will send it to you. They made about 15 different colors/railnames of the new ones.
Hope this info helps. BEEPs are really cute, interesting little diesels, but you have to tinker with them to get them to run right on the tracks. And you can end up pulling your hair out. Sadly, they have no sounds, but I am buying a Lionel Railsounds Boxcar, with diesel sounds, to tow behind mine.
Mannyrock
