What's the maximum speed of a horse drawn coach or carraige?

Disconcerning safety, what is the fastest possible speed a horse drawn carraige or coach can attain if the horses are in full gallop and the only load on the vehicle is the driver? How long can the horses continue going this speed? I'm wondering about a carraige driven by two strong horses, but I'd also... show more Disconcerning safety, what is the fastest possible speed a horse drawn carraige or coach can attain if the horses are in full gallop and the only load on the vehicle is the driver? How long can the horses continue going this speed? I'm wondering about a carraige driven by two strong horses, but I'd also like to know about other numbers. Is it possible to go even faster with more horses? Also, I'm curious as to how safe it would be to go full speed. I'm not planning on attempting this myself (because it would scare me), but I'm curious.
Update: Disconcerning safety, what is the fastest possible speed a horse drawn carriage or coach can attain if the horses are in full gallop and the only load on the vehicle is the driver? How long can the horses continue going this speed? I'm wondering about a carriage driven by two strong horses, but I'd also... show more Disconcerning safety, what is the fastest possible speed a horse drawn carriage or coach can attain if the horses are in full gallop and the only load on the vehicle is the driver? How long can the horses continue going this speed? I'm wondering about a carriage driven by two strong horses, but I'd also like to know about other numbers. Is it possible to go even faster with more horses? Also, I'm curious as to how safe it would be to go full speed.

If you can't tell, I'm thinking about the typical Hollywood movie scene where the stage coach / horse drawn carriage can reach alarming speeds. I'm wondering whether it's actually possible to reach such high speeds in real life or whether they're just making it up.
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