I just recently upgraded all my old Athearn Blue Box cars and several various other manufactures to 33" Intermountain brass wheels. Great improvement. Now I need to do my passenger cars and non powered "B unit" locomotives. If I have this right, I need 36" wheels for the cars and 38" wheels for the locos. On the Intermountain site they list "38 inch wheels" and "38 inch semi scale wheels". Ummm, what's the difference? They are the same price. Please give this old relatively newbie a little help here.
Thanks!
Joe,
You are correct using 36" wheels for your passenger cars. However, the prototype F Units(including the boosters) have 40" wheels. Athearn 'BB' locomotives have 42" wheels. I am not sure what 'BB' dummies you have, but some have trucks with plastic wheels, and others have basically the metal 'sintered iron' wheels that are in the powered units.
If you are bound and determined to replace the booster wheels, you might want to send a note to NWSL - They are sort of replacement specialists and should be able to assist you. On my old 'BB' engines, I replaced the original wheels with either Jaybee or NWSL n/s metal wheels - Much better electrical pickup...
BTW, the 38" wheels are used in high capacity freight cars(like 125 ton covered hoppers) and on some articulated intermodal cars. They usually have thicker axle bearings and the 'contact' patch on the rail is larger(less deformed rail).
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
This is covered in a recent Trains of Thought column by Tony Koester in MR. Normal NMRA wheels (code 110) are wider than scale due to track standards and other compromises.
A few modelers attempt to use exact scale wheels. But more and more modelers are using semi scale (Code 88) meaning narrower wheel treads than NMRA standard but not quite as narrow as exact scale. Those who use the narrower wheels report surprising success in situations where the engineers who created NMRA standards predicted problems. But track which is at the outlying edges of NMRA standards could give problems to the semi scale wheels.
So the "standard issue" wheels are just billed as 33" or 38" wheels, while the Code 88 wheel widths that some guys use are billed as semi scale.
It can be confusing because "semi scale" sounds like a decrease in scale fidelity -- in the sense that some Lionel trains are described as semi scale -- but in actuality it is an increase.
Edited post: as Jim points out, 38" wheels are not meant for EMD F units but for the heavier duty freight trucks. The day of 33" being the normal or standard freight car wheel is disappearing fast.
Dave Nelson
Semi-scale wheels are another term for code 88 wheels. These usually have the same RP25 flanges as the normal wheels, but have a narrower width. Code 88 wheels are 0.088 inches wide, "normal" NMRA HO wheels are code 110, or 0.110" wide.
Turnouts built to NMRA standards and practices work best with code 110 wheels. The code 88 wheels present a better appearance, particularly on older-prototype rolling stock where the wheel width is more visible. The code 88 wheels will generally work with NMRA spec turnouts, but there may/will be some wheel drop in the frogs, especially larger number frogs.
With the move away from sprung trucks, wheel drop isn't as much of an issue as it used to be. In rigid trucks, the wheel is actually suspended by the sideframe when it would otherwise drop. OTOH, rigid trucks are less tolerant of vertical imperfections in the track work, as the wheels cannot move as easily.
just my experiences, your choices
Fred W
All good info, thanks for the info on the Athearn BB dummy units. Mine have the plastic wheels. Sounds like time to retire them if I can't find those 42" wheels. They aren't all that "pretty" anymore. A lot of time in refurbishing would be required.
Not sure what NWSL is, but I'll try to figure that out.
Thanks to others that replied also as that cleared up the "semi scale" issue.
Joe HO FanNot sure what NWSL is,
Gidday, North West Short Line.
http://www.nwsl.com/
Cheers, the Bear.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
For those that are interested here is the NMRA wheel standards.
S4.2(Standard .110)
http://nmra.org/standards/sandrp/pdf/S-4.2%202010.02.24.pdf
S4.1(Proto 87).
http://nmra.org/standards/sandrp/S-4_1ProtoWheels.html
Unless I'm blind in one eye and can't see out the other I couldn't find any mention of C88 wheels in the P87 standards but,did in RP (Recommend Practice)24.2.
Larry
Conductor.
Summerset Ry.
"Stay Alert, Don't get hurt Safety First!"
jrbernier Joe, You are correct using 36" wheels for your passenger cars. However, the prototype F Units(including the boosters) have 40" wheels. Athearn 'BB' locomotives have 42" wheels. I am not sure what 'BB' dummies you have, but some have trucks with plastic wheels, and others have basically the metal 'sintered iron' wheels that are in the powered units. If you are bound and determined to replace the booster wheels, you might want to send a note to NWSL - They are sort of replacement specialists and should be able to assist you. On my old 'BB' engines, I replaced the original wheels with either Jaybee or NWSL n/s metal wheels - Much better electrical pickup...
JIm,
I'm a little confused now. I have replaced all my sintered steel wheels on my Athearn BB locomotives (SD40's, GP30's, GP38's and GP35's) with replacement Athearn 40' wheels. Was that wrong? Should I have used 42" wheels? They seem to operate OK and the electrical pickup is better. I'm learning new stuff every day after being out of the hobby for 25+ years, so I can add this to my list of 'experiences'. Thanks.
Len S.
Thanks for the link! They have stock numbers for exactly what I need.
BRAKIE For those that are interested here is the NMRA wheel standards. S4.2(Standard .110) http://nmra.org/standards/sandrp/pdf/S-4.2%202010.02.24.pdf S4.1(Proto 87). http://nmra.org/standards/sandrp/S-4_1ProtoWheels.html Unless I'm blind in one eye and can't see out the other I couldn't find any mention of C88 wheels in the P87 standards but,did in RP (Recommend Practice)24.2.
Proto87 is a completely separate and operationally incompatible standard for both track and wheels, based on scaled prototype practice. The wheel width is the equivalent of code 64 to code 69. More importantly, the flange width is only 0.012in instead of the 0.025in of code 88 and code 110 wheels. This means that P87 flangeways are too tight to pass an NMRA wheel, and the tolerances are way too big on an NMRA turnout to let a P87 wheelset through without dropping in the frog and/or derailing.
Code 88 wheels were developed as pretty much the narrowest wheel that would still work with NMRA-spec track. The full NMRA flange was retained with these wheels. Unfortunately, track and wheels have to work together to a common standard. Code 88 wheels only work as well as they should when track is kept to minimum gauge and minimum flangeways in turnouts - the 2 numbers work hand-in-hand to maintain the same critical span and check gauges.
The specs for code 88 wheels are listed under the Fine Scale Options (bottom of page) in S-4.1 Wheels, Proto and Fine Scales. There is no separate standard for HO track using code 88 wheels. However, code 88 is the standard NMRA wheel for HOn3 (and Sn2), and a peek at the flangeway dimensions shows what happens when one uses the narrowest dimension listed for HO instead of the target. The HO track targets are built around optimum performance with code 110 wheels.
There is a full blown 28 page discussion of wheel and track standards, including the development of the Proto standards at:
http://nmra.org/standards/sandrp/pdf/TN_1_1_2.pdf
Personally, I use code 88 wheels in both HO and HOn3 where possible because the era I model places trucks a lot closer to the end of cars, and cars are not as low slung as their modern counterparts. This allows me to use commercial components while getting closer to accurate scaling. My commercial HO turnouts suffer some wheel drop of the code 88 wheels - especially on sprung trucks (I prefer sprung trucks). My handlaid turnouts are adjusted to code 88 wheels and are very smooth, without any wheel drop under any conditions.
FWIW, there are more than a couple of model railroaders that believe in keeping the track gauge a lot closer to minimum NMRA spec than most commercial track or the NMRA "targets" do. The tighter track gauge helps prevent "wallowing", as well as better supporting code 88 wheels. The downside is that minimum radius isn't as "minimum" as when track gauge is wider, especially for 6 wheel trucks and longer steam driver wheel bases.
Hope this clears up any misconceptions - probably a lot more than most of us want to know.
....modeling foggy coastal Oregon, where it's always 1900....