I have a Bachmann Spectrum K-4 Pacific steam loco that came in a set with 22" radius EZ Track curves. However, the set contained no turnouts so I have just been using the turnouts that came in another track set.
The tender of my K-4 always derails when trying to negotiate the standard sized LH and RH EZ Track turnouts. 
Which of Bachmann’s turnouts would serve best for this particular loco? The no. 5 or no. 6 turnouts? According to Bachmann, both are listed as accommodating larger locos and rolling stock with longer wheel bases. In either case, I don’t want to wind up too short or too long in the fix. Thanks.
We have no problem running our Northerns(w/ centipede tender) or Berkshires on the 5s.
Richard
All the turnoutsni have ever bought except one have been junk. I had one bachmann snap switch that was awesome. I have sold all my switches and have 2 crossovers left but feel bad about selling those because they are so loose and one raiil fell apart. Never again!
I have a pair of Backmann K4s, and I run them on a temporary layout made from Bachmann EZ-track. Though neither are in service currently (one is having decoder difficulties and the other is missing a bell) I have been able to run them through 18" rad turnouts at slow speeds without a problem.
Bachmann’s stock K4 tender is quite a bit light, so add a couple ounces or lead weight to the inside of the tender. In addition, you should use an NMRA gauge and check the wheel gauges on the tender - it sounds like a wheelset may be out of gauge. Further, you should probably file the points on the turnouts that you are using so that they are sharp to prevent the wheel flanges from “picking” the point. While you’re at it, use the standards gauge to check the turnout, too.
The Spectrum K4 can run just fine around 18" radius curves. I’d recommend being careful which turnouts you use, since their geometry may not match that of Bachmann’s track.
P.S. I have the Specturm K4 passenger set, and it still runs fine after being used for ~5 years with no maintenence. Very durable loco! Have fun.
Even though I use Bachmann’s EZ-Track exclusively including the turnouts I DO NOT recommend you use the EZ-Track turnouts. They’re notorious for causing derailments and unless you know how to tweak them they’ll cause you nothing but trouble and heartburn. You can use Atlas turnouts with the EZ-Track without modifications to the turnouts other than putting roadbed beneath them. The EZ-Track rail joiners will connect to the Atlas track with no problem. The joiners are identical.
Yeah, I have been hearing bad things. Thanks for all the tips, guys.