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Watts Z-Link on GM Cruze

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70AARCUDA

70AARCUDA

Electrical
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...this is more of an informational question, but what 'real' beneft(s) is there to the Watts Z-Link rear suspension that GM has installed in their North American Cruze cars?

...it's an economy car, so "high-performance" road handling seems rather dubious.

...any "real-world" users have comments?
 
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Well it has a nice technical sounding ring to it in the advertising.

It may help to a virtually non-perceivable extent re fuel economy by reducing sideways movement over bumps and tracking straighter.

Regards
Pat
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Panhard rods swing in an arc and locate the axle out near the end, which can cause some asymmetrical bump response, particularly if the car is loaded in a way such that the rod is not horizontal (away from nominal ride height). With a Watts linkage, it is possible for a significant up and down motion to approximate a straight line, and the axle locating point is at the center of the axle, so it doesn't respond asymmetrically.

It's more related to controlling rear-wheel bump steering effects than anything else.
 
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I suspect the answer is marketing. For 30-40 years people have been fitting twist beam rear suspensions to that size of car, and they work fine. A couple of manufacturers have raised the bar with more complex offerings, so GM have done the cheapest defensible upgrade possible to a twistbeam to fight back. Panhard doesn't work on a twistbeam because it only works on one wheel.

In useful objective terms it should give less compliance oversteer than a basic twistbeam.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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"In useful objective terms it should give less compliance oversteer than a basic twistbeam."

Sounds like a stability control benefit.


Norm
 
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Probably due to packaging by adding a Watt's link they could improve location while improving ride by using lower rate bushings. They could also maximize track width within the body panels pushing the wheels out as far as possible adding visual appeal. Don't laugh this stuff is important to selling cars, ask Bob Lutz.

Why they mixed a torsion bar in the twist beam tube and added coil springs is beyond me though unless there was some sort of IP issue they wanted to cover themselves on.
 
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...I'm assuming by "IP" you meant Intellectual Property, correct?

...oh, by the way, we own a 2011 Cruze, but the Z-link (from what I've read) seems out of place, being more commonly used on racing and slalom & gymkhana racing cars.
 
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byte - The torsion bar in the twist beam will provide roll stiffness without adding as much ride stiffness over one-wheel bumps or any at all over two wheel bumps.


Norm
 
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Norm

But the coil springs?

I think GM had a twist beam in the J series chassis in the mid 80s, so IP should be well and truly public domain by now. I think VW had it in a Golf or Passat even before that, like maybe late 70s.

Regards
Pat
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Twistbeam for FWD was basically introduced in the VW Polo, mid seventies. That was originally an Audi design.

A twistbeam is not a brilliant suspension, but it is good enough. To my mind the major failing is that the twist beam cuts right across the car, making packaging of the exhaust and brake lines and fuel filler and tank and spare tire more difficult than they might be. It is also a bit heavy, offset by the simplicity of the body structure that can be used.

The dynamic deficiencies are real and measurable, but for a town/commuter car I doubt they really matter to many customers.




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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70AAR

Sorry yes I meant intellectual property. This is what you get when your wife of 30 years is a lawyer. For a lateral locating linkage for stick axles the Watt's link is hard to beat IMO.

I think the Z-link name is marketing hype. Watt's links have been around a long long time. Crown Vics have had them for many years and is part of why those monsters handle so surprisingly well for what they were. Heck I installed a Watt's link in my S197 Mustang GT.

Norm!

Yeah I figured that out after I posted and had a few minutes to ponder it on the throne. Thanks.



 
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Pat - I'm not sure what you're asking ("But the coil springs?"), but you still need the ride springs for load and pitch behavior reasons. Just that rear springs so chosen (and located) may not provide the desired roll stiffness or roll stiffness distribution.


byte - now you've got me curious about whether that Watts link on your Mustang happens to be "brand F", "brand S", or somebody elses.


Norm
 
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Norm.

It's a while since I saw a torsion beam rear end. I was imagining the beam acted as a torsion bar spring, but I guess it acts as the anti roll bar and you still need springs.

In that case, I guess if you want not to much ARB, you end up with a flexible torsion beam and a lot of lateral compliance, then the watts link fixes that issue.

I still think it's a snazzy sounding name for marketing spin though.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
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Pat - I'm perhaps a little more familiar with twist beam arrangements, as that's what's under the rear of one of my other cars. On a forum dedicated to that particular model in all of its "generations", there are many who aren't even aware that there is an OE rear sta-bar at least in some of the sub-models.

With a dedicated lateral locating device, you have better control over roll steer and compliance steer effects than when the only lateral axle location comes from some sort of arm or link acting in cantilever bending. The only car I can think of that used a cantilevered anything for lateral axle location is the Mk I Sprite, and that car had a reputation for being a bit "twitchy".


Norm
 
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Norm,
The only other car using cantilever springs for location I can recall is the early MkI Jaguar sedans circa 1960 / 61.

Yes the Sprigets were a little "twitchy"...downright treacherous if you really want to be honest... but a great fun drive and all at or below the legal limit in most places too.

Peter.
 
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