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Comment by seanflyon | Hacker News Reader

I think that there are a lot of options for reducing friction wear. My first thought would be to put wheels between the tube an its supports (attached to the supports, not the tube).

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You're increasing the cost a lot there because the wheels need to be on bearings because you've going to have to hold the tube with some amount of preload. You can't just let it rest on the wheels, the wheels have to be pressed onto the tube at all times because the vehicle is moving very fast and any kind of minute deviation up or down will result in substantial forces between the tube and the vehicle which have to be transmitted through the wheels and into the foundation and eventually into the ground.

So now you have wheels, bearings, preload springs, hinges, travel arms, etc. Instead of a big piece of plate that is welded to the tube and bolted to the foundation you're talking about a big apparatus with moving parts and precision bearings. The plate and welding might cost $500 per. The other might cost $20k apiece. A person can buy a lot of rebar and concrete and forms and whatnot for $20k.

I don't imagine any sort of suspension would be needed. The system is always loaded (with only a slight increase when the vehicle is over a given support because the tube is most of the weight). It needs bearings, but they don't have to move quickly or be particularly low friction. Even if the bearings failed the tube would just slide; you would want to replace them before too much wear, but it would not be urgent.

If that is too complicated, just put in replaceable slide plates. More regular maintenance, but fewer moving parts.

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