Passive Rear Steering

[Remonster]

I was chatting with a Tesla engineer the other day and he noted that the 5 link suspension on the Model 3 allows for passive rear steering which helps handling in quick turns. I think it helps it feel more nimble compared to my old Mazda 3. It also has very little body roll.

 

[spectrum]

This is absolutely not true.

 

[JulienW]

...passive rear steering.....

Oxymoron: Steering is an activity. If there was such a thing you could say a differential was passive steering.

 

[focher]

Whenever I let my mother ride in the back seat, I've personally experienced passive rear steering. My 12 and 7 year old daughters also provide this functionality at times.

 

[Msjulie]

3 ways in which suspension affects understeer and oversteer

Suspension design does have pretty much everything (well a lot anyway) to do with handling, so maybe broad use of a term but I'm guessing they're proud of their complex suspension and the positive effects it has on handling of such a heavy car.

They didn't say active..

I think a Honda Prelude or something had that as well as a couple other Japanese cars of later 80s? vintage..

Also Steering - Wikipedia

"Passive rear wheel steering
Many modern vehicles have passive rear steering. On many vehicles, when cornering, the rear wheels tend to steer slightly to the outside of a turn, which can reduce stability. The passive steering system uses the lateral forces generated in a turn (through suspension geometry) and the bushings to correct this tendency and steer the wheels slightly to the inside of the corner. This improves the stability of the car through the turn. This effect is called compliance understeer and it, or its opposite, is present on all suspensions. Typical methods of achieving compliance understeer are to use a Watt's link on a live rear axle, or the use of toe control bushings on a twist beam suspension. On an independent rear suspension it is normally achieved by changing the rates of the rubber bushings in the suspension. Some suspensions typically have compliance oversteer due to geometry, such as Hotchkiss live axles, semi-trailing arm IRS, and rear twist beams, but may be mitigated by revisions to the pivot points of the leaf spring or trailing arm, or additional suspension links, or complex internal geometry of the bushings.

Passive rear wheel steering is not a new concept, as it has been in use for many years, although not always recognised as such."

 

[focher]

It was the Prelude that had it - which is really that the rear wheel also "turn" as part of the handling / turning process. The cost that it adds versus the benefit in everyday driving has meant that manufacturers have never really seen it as a viable feature to add to vehicles.

 

[WarpedOne]

My 2009 Renault Laguna Coupe GT has active rear wheel steering.
I love it and miss it from new Model 3.

 

[67King]

It was the Prelude that had it - which is really that the rear wheel also "turn" as part of the handling / turning process. The cost that it adds versus the benefit in everyday driving has meant that manufacturers have never really seen it as a viable feature to add to vehicles.

I'm going off of memory, but the unique thing about the Prelude was that the wheels turned in the same direction as the front at small angles, so that the car remained pointing forwards while doing lane changes. But at larger input, they turned in opposite directions, to decrease the turn radius, and reduce scrub and all of that.

GMC Trucks had it as a really spendy option a few years ago. Porsche has it on some of the nicer 911's, I think the track oriented ones such as the GT3 and GTS. Not positive, but I think that is the case. I do not believe either of these used the same strategy as the Prelude, but rather just steered opposite.

 

[DopeGhoti]

Whenever I let my mother ride in the back seat, I've personally experienced passive rear steering. My 12 and 7 year old daughters also provide this functionality at times.

I think that's passive-aggressive steering.

 

[brkaus]

I'm going off of memory, but the unique thing about the Prelude was that the wheels turned in the same direction as the front at small angles, so that the car remained pointing forwards while doing lane changes. But at larger input, they turned in opposite directions, to decrease the turn radius, and reduce scrub and all of that.

This is also how I remember it. I don’t think made much difference, but no way to turn it off so hard to compare.

It was tied to the steering wheel angle, so I would consider the Prelude implementation “active” steering.

 

[jyalpert]

I'd assume this just means they built in some amount of toe-in under compression in the rear? You see that now on lots of cars with rear multi-link suspensions (including the Mazda3). One famous example of this design is the first-gen Honda S2000, which had so much toe gain under compression that the car would be prone to spinning as the suspension unloaded (and toe-out happened quickly).

 

[Daniel in SD]

I'd assume this just means they built in some amount of toe-in under compression in the rear? You see that now on lots of cars with rear multi-link suspensions (including the Mazda3). One famous example of this design is the first-gen Honda S2000, which had so much toe gain under compression that the car would be prone to spinning as the suspension unloaded (and toe-out happened quickly).

Ha. I’ve always wondered why I see S2000’s spin out so frequently at autocross.