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Comment by giobox | Hacker News Reader

Allows you to vary the steering ratio dynamically (how many "turns" lock to lock). Means a lot less arm twiddling during lower speed maneuvers, and can gradually increase the ratio as speed increases. Traditional mechanically linked steering racks (electric or hydraulic) don't do this and are the same number of turns lock to lock regardless of speed - they can only dynamically vary the amount of power assist, not the ratio. It's been something car manufacturers have wanted to do for a while.

Another benefit in theory is packaging - you can free up more space for cabin, front trunk or motors etc when you don't have to route a physical steering column.

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You also don't need a collapsible steering column, as there is no steering column.

BMW had this on mechanically linked system for 20 years. It's called "Active Steering" in their marketing speak.

It's not really the same at all in practice though. With steer by wire you can get the lock to lock literally as little as you like - 150 degrees at low speed lock to lock in the Lexus system for example. In theory it could go from one extreme to the other in a single degree, its just software, although obviously no one sane would implement this. Active Steering on BMWs doesn't get remotely close to 150 degree low speed lock to lock.

It's a system that changes the ratio of the steering wheel rotation to the wheel angle dynamically while still mechanically linking the wheels to the steering wheel. It does not have the same parameters as Lexus system but many other things differ between BMWs and Lexuses too.

I’ve been driving a BMW with the variable ratio steering rack for over 10 years. It’s great. But it’s only variable ratio, not a dynamic ratio. Don’t confuse the two.

A variable ratio is just a regular rack and pinion setup, except the teeth on the rack are more narrowly spaced at the centre. It’s pre-defined, fixed and static. 30 degrees of steering input will always result in the same movement of the front wheels. It’s mechanically fixed.

The Cybertruck is a truly dynamic steering ratio. 30 degrees of steering input will result in a different outcome depending on othe variables such as road speed.

Active Steering is dynamic. It's not in every BMW though, you can test if your car has it by turning the steering wheel when stopped: it should only require 2 turns between locks with AS.

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