Steering ratio differences between models? Year specific or engine specific?

[Corellian Corvette]

Just a little piece of minutia I'm curious about.

Just replaced the tires on my 2002 4.6, and one observation that hit me is that the steering feel is much, much lighter than on my 2005 3.0 Sport.

Like, the 3.0 feels similar to my e39 530i - pretty weighty and tougher to turn than most modern cars.

The 4.6 is finger light to turn the wheels and it feels like the ratio is much faster as well. Which is even more surprising given how much wider the front tires are on the 4.6

Anyone know why this is? I know the 3.0 is a LCI model, but the engines are different as well so I'm not sure if the lighter steering is an early vs. late change, a V8 vs I6 change, or something unique to the 4.6

Any ideas?

[andrewwynn]

Look up your steering rack on real oem on both cars. I suspect one is servotronic model the other is not.

[Corellian Corvette]

Well, good thinking.

According to my vin decode the 4.6 does indeed have servotronic, and the 3.0 does not.

Now, I'm embarrassed to ask because I thought that was just a standard feature on pretty much every BMW. What exactly is the difference technically?

[aheckenast]

Originally Posted by Corellian Corvette

Just a little piece of minutia I'm curious about.



Just replaced the tires on my 2002 4.6, and one observation that hit me is that the steering feel is much, much lighter than on my 2005 3.0 Sport.



Like, the 3.0 feels similar to my e39 530i - pretty weighty and tougher to turn than most modern cars.



The 4.6 is finger light to turn the wheels and it feels like the ratio is much faster as well. Which is even more surprising given how much wider the front tires are on the 4.6



Anyone know why this is? I know the 3.0 is a LCI model, but the engines are different as well so I'm not sure if the lighter steering is an early vs. late change, a V8 vs I6 change, or something unique to the 4.6



Any ideas?

I too have noticed this between my '03 3.0i & my father's '05 4.8iS. I simply assumed it's due to different p/s pumps on different engines. I do prefer the heavier feel of the 3.0i.

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[wpoll]

Originally Posted by Corellian Corvette

Well, good thinking.

According to my vin decode the 4.6 does indeed have servotronic, and the 3.0 does not.

Now, I'm embarrassed to ask because I thought that was just a standard feature on pretty much every BMW. What exactly is the difference technically?

Servotronic is an electric steering assistance system - like hydraulic power steering but electric.

According to Mr. Steffen Koch - BMW Unit Head Steering System Development.

Power steering: This assisted steering is one of the greatest evolutionary steps in steering technology. It boosts the driver’s steering power hydraulically. Before power steering, parking a car was an involuntary workout. Only with the advent of the power steering system could larger and heavier vehicles be offered to a greater pool of customers, notes Koch.

Servotronic: The next development in hydraulic power steering was Servotronic, which makes it possible to adjust the amount of steering assistance to suit the speed of the vehicle, explains Koch. Since Servotronic assists with maneuvers, little effort is required from the driver. And it provides stability at higher speeds. In contrast to plain power steering, both are now possible. Koch adds, “So not only is it easy to park, it also delivers sharp handling when driving fast, with the focus on driving pleasure.”

[Clavurion]

Originally Posted by Corellian Corvette

Well, good thinking.

According to my vin decode the 4.6 does indeed have servotronic, and the 3.0 does not.

Now, I'm embarrassed to ask because I thought that was just a standard feature on pretty much every BMW. What exactly is the difference technically?

On this era BMW's servotronic was an optional additional equipment. On servotronic rack there is a solenoid valve (torque converter) changing the hydraulic pressure and hence the assistance force. This works speed dependent so there is more assistance when the speed is lower and assistance drops when speed is increased. This solenoid valve is controlled by body module (GM3) which gets the speed info via ABS module (rear left speed sensor) like speedo on instrument cluster.