Because the prototype does

Simple answer: Because the prototype has different size wheels. There are also 28" wheels for some intermodal equipment. As a side note most cars pre-1965 are 33" after that larger and heavier cars have 36" wheels. I hope this helps. One some modern cars the wheel size is indicated on the data on the end of the car. On some models this data is duplicated and can be used to decided which wheels to buy.

Re: Wheel Size for freight cars

Cars of 100-ton or so capacity will tend to have 36" wheels, while 70-ton and lower capacity cars will have 33".  There are exceptions, but you can use this as a general guide.

Wheel sizes

Rob;  

Thanks for the info.  Does the 36" vs 33" have anything to do with age of equipment? Like late 1980's to mid 1990's?

David Cameron 

Wheel Sizes

 "Mountain Goat" Greg;

So cars running in the late 1980's to to Mid-1990's would have 36" wheels?

David Cameron 

Re: Wheel Sizes

"Does the 36" vs 33" have anything to do with age of equipment? Like late 1980's to mid 1990's?"

As was noted in another post above, the larger wheels started to become more common in the 60s, coinciding with the development of higher capacity cars (roughly over 70 tons).  You can realistically include them from the early-mid 60s on, maybe a bit before.

Size vs. Age

Wheel size has more to do with capacity of the equipment than its age.

As noted, trucks designed for 100-ton capacity cars will generally have 36" wheels.

70ton trucks generally have 33" wheels. This is basically your "standard", but in recent years most new cars are larger and heavier.

Modern autoracks have 28" wheels. Automobiles are relatively light, bulky cargo, plus the small wheels lowers the bottom of the car a bit.

33" and 36" wheels need to be used appropriately on specific cars, not just randomly based on their age.

Let us not forget the 38"

Let us not forget the 38" wheels on the 246K cars now in service.

If someone wants to do an article

If someone wants to do an article for MRH illustrating the different wheel sizes and how to know when to use which - with prototype photos - that would be great.

An example of things to cover would be how do you know a 70-ton car from a 100-ton car? Can you tell just by looking at the trucks what sized wheels should be included?

The more "teaching a modeler to fish" rather than just "give them a fish" type insight you can provide, the better. Then modelers will feel much more confident about what wheel size goes where.

Me me I will..

Joe,

I would be willing to write that article...I have access to car repair facilities, wheelsets, trucks, and FRA rulebooks to help supliment the article.

I look forward...

I look forward to reading such an article. I have been swapping like wheels for like when I replace N scale plastic wheels with metal wheels. It'd be nice to have more of an idea of why I am doing what I am doing.

Adam

wheel sizes

Don't forget the rib backed wheel that represent early cast iron wheels installed up through the early 1950's.  These were used in freight and passenger service.  The passenger service wheels were usually 36" diameter. A rule of thumb is that if the car was built with friction bearing trucks and was still riding on them the wheels were ribbed on the back until the wheel set was changed out when repair was needed.  Later cast iron wheels (freight cars built late 50s' and on) had smooth backed wheels. During the 1970's the cast iron wheels (particularly on 100 ton and more cars) were found to be major causes of wrecks.  All rolling stock (including the diesels) had to be inspected by a certian date and marked with a white or yellow dot inside a black square indicating whether the wheels were cast iron or not.  If they were cast iron they had to be replaced by a mandated date.  You can still see older (1960's and early 1970's built equipment) that exhibit these dots.  So depending on the era that you model the wheels may have ribb backed wheels or smooth backed wheels.  Sorry to add to your confusion!

Ben

Hey Greg, you're on

MountainGoat, go for it - love to see an article from you on this subject!

Joe, I would be willing to

I would certainly love to see that article.

So far I have on my website:

I know this is not fully correct, but it's darn near the best I could do.

Right on!

I look forward to an article that explains the how and why of different wheel sizes!

Wheels

This is the kind of article that I'd be very interested in reading.

Roy

Don't forget to include...

Hey Mountain Goat,

Please make sure to add within the article the manifactuers that produce these HO sets and recommendations based on quality and detail.

Thanks,
Burt

Burt

Will do!!

I will also include N and O Scale.

Was this article ever written

Just wondering if this article was ever followed up on?

Wheel sizes

As a newbie to this can someone tel me how the prototype wheel is measured, is it over the flange or the diameter of the wheel in contact with the rail?