Can you use 1:64 vehicles with HO scale trains? It’s a common question. The answer is you can do whatever you want.
The next question is whether you’ll be happy with it. And under some circumstances, you might be.
This is as good of a time as any to explain scale. Scale is the size of a model relative to the real thing. In HO scale (1:87), 3.5 mm (.138 inches) represents one real-world foot. In 1:64, 3/16 of an inch (.1875 inches) represents a foot.
So a true 1:64 model is more than 25% oversize for HO, though it’s perfect for S scale American Flyer.
But a lot of stuff in the stores that’s labeled 1:64 isn’t actually 1:64.
Estimating scale in the wild
A lot of “1:64 scale” stuff would be better labeled “whatever fits in the package” scale. In particular, this is true of a lot of Hot Wheels and Matchbox cars and their off-brand equivalents. That doesn’t really bother the target audience, though some people argue it should. But my three-year-old son doesn’t care if his miniature Dodge Challenger is the same length as his miniature VW Beetle.
The typical passenger car (automobile) is about 6 feet wide. Knowing this, you can estimate the actual scale of a miniature vehicle while it’s in the package in the store, using your pocket change.
6 feet in HO scale is about .8275 inches. A U.S. nickel, conveniently, is about .8268 inches, and a Canadian nickel is approximately the same size. (I’ve rounded off the numbers.) So if a vehicle is close to the width of a nickel, it’s going to be close enough to 1:87 scale that you’re not going to know the difference.
The width of a quarter is pushing it. And if it’s much wider than a quarter, it’s probably too big.
So that gives you an idea of your margin of error.
A purist probably wouldn’t look in the toy aisle, but I can understand the pull. The 1:87 vehicles sold by train makers cost about $3-$4 apiece, usually come in packs of 3 or 4, and are usually sold in specialty shops. That compares to $1 in toy aisles, one of which you can find in any discount store or drug store, among other places. And the selection there will be wider, or at least have choices not available in a Walthers catalog.
So what do you do if you find a vehicle you must have, but the scale is too big?
O scale guys face this problem all the time.
Generally speaking, the further you place it from the viewer, the more difficult it will be to perceive the difference. Close up, someone with a sharp eye could perceive a difference of 1/8 inch, but probably not at 8 feet. So you can use more “proper” vehicles around the edges, where a viewer will be up close, and use your more marginal stuff where it’s not possible to get a really close look.
You can also get away with more if you’re careful about placement. Don’t put an oversized vehicle right next to a garage that it visibly will have difficulty getting into, and don’t put it in a narrow alley. Put it in the middle of the street instead, where there’s less to compare it to. And don’t park a true 1:87 right next to it. If you have a street scene that’s partially obscured by buildings, trees, and other details and all the vehicles are slightly off, most viewers won’t notice. Objects like trees, light posts, and commercial buildings vary in size enough to make it more difficult to judge size.