I'm not sure if this is the correct site to ask, because I could not find other site that suit better.
Consider this picture
The top-state is the car when wheels are straight. I found on the Why is chosen for steering option b, instead of a?
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4$\begingroup$ This may receive better answers on engineering SE. $\endgroup$– user191954Jul 1, 2018 at 16:47
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$\begingroup$ @Chair i don't know how this question can be moved to engineering SE $\endgroup$– Faceb FacebJul 1, 2018 at 18:33
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$\begingroup$ It's fine, if a lot of people suggest that it belongs over there, one of the moderators'll arrange for it to be migrated. $\endgroup$– user191954Jul 2, 2018 at 0:41
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2 Answers
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the straight-axle steering is called "wagon steer" and it is not used in cars because if one of the wheels hits a rut in the road, the wheel gets caught, the whole axle pivots into a full-deflection turn, and you crash.
answered Jul 1, 2018 at 20:43
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$\begingroup$ Wagon steering is meant for vehicles that are being pulled, as with horses or oxen, or with your toy wagon. Then the design works OK, and is the simplest. You need something more sophisticated when the wagon is being pushed by an internal engine. The answer by niels nielsen is what happens if you use the wrong design. $\endgroup$ Jul 2, 2018 at 18:19
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$\begingroup$ Agree with @peterdiehr. the pulling action tends to straighten out the axle and counter the effect of a caught wheel. I built a recumbent trike with wagon steer as a proof-of-principle for my rear-wheel-drive propulsion system. It served its purpose but if I scuffed a curb at speed I was in big trouble. $\endgroup$ Jul 2, 2018 at 22:59
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If the entire wheel rotates like that, then where does the suspension go? Do you just pull the whole spring assembly out of the car when the wheels turn?
Also, consider how big the wheel well is in your car. Either this wheel well must extend into the car or you have to severely limit the turning radius. Do you know where the wheel well would need to go? Driver and front passenger's leg space, pedals, and the front door hinges.
There's also a lot more equipment to move, so the steering hydraulics need to be bigger, and the shafting needs to be bigger, and you can't have front wheel drive unless you have an elaborate differential or the transmission rotates, too, but then you need the engine to rotate.
So, practicality. That's the reason cars don't steer that way. It's not practical. Definitely an engineering question.
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1$\begingroup$ While these are significant issues, they were not so pressing when the first cars were modeled on carriages, wagons, and railcars (which did have turn-as-a-unit wheel assemblies when they have any capacity to turn the wheels at all). $\endgroup$ Jul 1, 2018 at 17:27
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$\begingroup$ @dmckee I understand. It's the way rail cars still work. Carriages, wagons, and rail cars are all towed, though. Ackerman steering wins nearly every active steering application I can think of, except maybe a snowmobile. $\endgroup$– ChuckJul 1, 2018 at 17:37