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Power steering on a car is a form of torque amplifier: the driver applies X Nm (or ftLb) of torque, and the power steering adds Y torque - but maintaining the same angle of turn. But what's the approximate ratio of Y:X for the power steering on a typical domestic car? Is it e.g 10:1 ?

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  • $\begingroup$ Too broad, some add more, some less, depends on the tire sizes and ratios so many answers possible. I have driven vehicles where a finger is all that is necessary others where it has minimal effect. $\endgroup$ – Solar Mike Jan 23 '20 at 9:42
  • $\begingroup$ I'm just looking for an example number, or even a range of numbers. For a domestic car that range can't be too broad. $\endgroup$ – Richard Pawson Jan 23 '20 at 10:36
  • $\begingroup$ I am writing something about historical use of torque amplifiers (not in automotive use) that multiplied the torque by 10,000:1. I want to compare this to the power steering on a car, which I am guessing is maybe between 10:1 and 100:1? I am just seeking some confirmation that I'm in the right ballpark. $\endgroup$ – Richard Pawson Jan 23 '20 at 10:50
  • $\begingroup$ You should just be able to measure this with your car and a protractor. Start with your tires straight, turn the steering wheel 180 or 360 degrees, see how much your tires have turned. Figure out how many turns of your steering wheel it would take to rotate your tires 360 degrees, this angular displacement reduction ratio is the same as your torque increase ratio (power in = power out = torque x displacement / time). $\endgroup$ – jko Jan 23 '20 at 13:16
  • $\begingroup$ Older Chrysler products required about zero effort ; I believe they have changed as many did not like "no" road feel. $\endgroup$ – blacksmith37 Jan 23 '20 at 15:15
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I had a go at measuring it - on my Toyota Auris. I used a handheld digital device (for weighing luggage), which conveniently records the maximum weight sensed in a measurement. I strapped it around the spoke of the steering wheel in a fixed location, just inside the rim, and made sure that I was always applying the force tangentially.

My measurements were all taken with the vehicle stationary (not while driving!) and with the car parked on gravel.

With the power steering on, turning the wheel seemed to take a force of anywhere between 5 and 20 N (so maybe 1-4 Nm torque). With the power steering off I got readings of between 15 and 25 N. Not great data, but it seems to suggest that the amplification from the power steering is of the order of 10:1. Though, I am not very confident in this result, and I have to say that my subjective impression was that it was greater than this

If anyone can provide a more specific figure based on manufacturer's design specs- for any domestic car - I would still appreciate it.

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  • $\begingroup$ Well done! That is right in line with what I was thinking, but you went and measured it! $\endgroup$ – Tiger Guy Jan 24 '20 at 14:03

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